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in 1962 , a cave explorer named michel siffre started a series of experiments where he isolated himself underground for months without light or clocks . he attached himself to electrodes that monitored his vital signs and kept track of when he slept and ate . when siffre finally emerged , the results of his pioneering experiments revealed that his body had kept to a regular sleeping-waking cycle . despite having no external cues , he fell asleep , woke up , and ate at fixed intervals . this became known as a circadian rhythm from the latin for `` about a day . '' scientists later found these rhythms affect our hormone secretion , how our bodies process food , and even the effects of drugs on our bodies . the field of sciences studying these changes is called chronobiology . being able to sense time helps us do everything from waking and sleeping to knowing precisely when to catch a ball that 's hurtling towards us . we owe all these abilities to an interconnected system of timekeepers in our brains . it contains the equivalent of a stopwatch telling us how many seconds elapsed , a clock counting the hours of the day , and a calendar notifying us of the seasons . each one is located in a different brain region . siffre , stuck in his dark cave , relied on the most primitive clock in the suprachiasmatic nucleus , or scn of the hypothalamus . here 's the basics of how we think it works based on fruitfly and mouse studies . proteins known as clk , or clock , accumulate in the scn throughout the day . in addition to activating genes that tell us to stay awake , they make another protein called per . when enough per accumulates , it deactivates the gene that makes clk , eventually making us fall asleep . then , clock falls low , so per concentrations also drop again , allowing clk to rise , starting the cycle over . there are other proteins involved , but our day and night cycle may be driven in part by this seesaw effect between clk by day and per by night . for more precision , our scns also rely on external cues like light , food , noise , and temperature . we called these zeitgebers , german for `` givers of time . '' siffre lacked many of these cues underground , but in normal life , they fine tune our daily behavior . for instance , as natural morning light filters into our eyes , it helps wake us up . traveling through the optic nerve to the scn , it communicates what 's happening in the outside world . the hypothalamus then halts the production of melatonin , a hormone that triggers sleep . at the same time , it increases the production of vasopressin and noradrenaline throughout the brain , which help control our sleep cycles . at about 10 am , the body 's rising temperature drives up our energy and alertness , and later in the afternoon , it also improves our muscle activity and coordination . bright screens at night can confuse these signals , which is why binging on tv before bed makes it harder to sleep . but sometimes we need to be even more precise when telling the time , which is where the brain 's internal stopwatch chimes in . one theory for how this works involves the fact that communication between a given pair of neurons always takes roughly the same amount of time . so neurons in our cortex and other brain areas may communicate in scheduled , predictable loops that the cortex uses to judge with precision how much time has passed . that creates our perception of time . in his cave , siffre made a fascinating additional discovery about this . every day , he challenged himself to count up to 120 at the rate of one digit per second . over time , instead of taking two minutes , it began taking him as long as five . life in the lonely , dark cave had warped siffre 's own perception of time despite his brain 's best efforts to keep him on track . this makes us wonder what else influences our sense of time . and if time is n't objective , what does that mean ? could each of us be experiencing it differently ? only time will tell .

that creates our perception of time . in his cave , siffre made a fascinating additional discovery about this . every day , he challenged himself to count up to 120 at the rate of one digit per second . over time , instead of taking two minutes , it began taking him as long as five .

why do you think siffre took longer and longer to perceive 120 elapsed seconds as he got older ?

translator : ido dekkers reviewer : ariana bleau lugo so what is gravity ? i bet most of you think it 's : `` what goes up , must come down ! '' is that right ? well , sorta , but not really . technically , the law of gravity is an equation . it is : f = g x m1 x m2 / r^2 , where g is the universal gravitational constant , m1 and m2 are the masses of the two objects , and r is the distance between them squared . that was easy , right ? probably not . what does this actually mean ? well it means that - well , everything is attracted to everything else . what i mean by that is if you have two objects , any two objects , they are attracted to each other . ok. let 's try and wrap our minds around this . what happens when you drop a rock off a cliff ? it falls to the earth . right ? well , yes , but something else happens . you see , the law of gravity says that both objects , the rock and the earth , are attracted to each other . this means that the rock falls towards the earth , and the earth falls towards the rock . wait a second - you mean to tell me that if - the earth falls up to meet the rock ? yes , that 's exactly what i 'm saying . and the reason you do n't see the earth fall up to meet the rock is because the objects move towards each other proportionate to their respective masses . the earth is much much much more massive than the rock , so it moves a very very small distance , and the rock is much less massive , so it moves farther with respect to the earth . maybe a better way to understand gravity is to take two teenagers in spacesuits , and place them far out in space - away from all the planets and the stars . it turns out they will be attracted to each other . i 'm not talking about that kind of attraction . see , they have mass , and since they have mass , they will move towards each other . they are attracted to each other . maybe one more thing might help . have you ever played with two magnets ? you know , the magnets with the north and the south poles ? when you take the magnets and put them closer to each other , they move together . they are attracted to each other . and the closer they are , the stronger the attraction . think of the mass of the object like the strength of a magnet and the distance between the objects like the distance between the two magnets . now understand , i 'm not saying that gravity and magnetism are the same , they just behave in a similar way . let 's think of one other thing - astronauts . you know , astronauts , they weigh less on the moon than on the earth . why is that ? well you see , the moon is less massive than the earth . therefore it has a smaller gravitational pull on the astronaut . it 's like the moon is a weaker magnet . they are n't as attracted to each other . distance also plays a role . think back to playing with a magnet . the pull of the magnets towards each other are stronger when they are closer together . the same is true of gravity . for example , the sun is the most massive object near the earth . it dictates most of the gravitational forces in our solar system . it is very very massive . but it is relatively far away , so even though the sun is a much stronger magnet , so to speak , it is a long ways away . therefore the attraction is n't as strong . so let 's look back at that law of gravity . the equation : f = g x m1 x m2 / r ^2 . you see the force of gravity is equal to a number . that 's that universal gravitational constant g times the mass of object one , times the mass of object two . think of m1 being the mass of the sun and m2 being the mass of the earth . and then we divide by the distance between them squared . this determines the force of attraction between the sun and earth . you could just as easily plug in your mass and the earth 's mass and the distance between you and the center of the earth , and find out how much you are attracted to the earth , and the earth attracted to you . so , what 's gravity ? everything is attracted to everything else . everything . oh , one last thing , just to make you wonder . what causes gravity ? why are two objects with mass attracted to each other ? well , the answer is - we do n't know . the cause of gravity remains a mystery to scientists . we do n't really know conclusively what causes gravity . it is one of the great mysteries of science .

ok. let 's try and wrap our minds around this . what happens when you drop a rock off a cliff ? it falls to the earth .

when you drop a rock from a cliff , which of the following happens ?

imagine the brain could reboot , updating its withered and damaged cells with new , improved units . that may sound like science fiction , but it 's a potential reality scientists are investigating right now . will our brains one day be able to self-repair ? it 's well known that embryonic cells in our young developing brains produce new neurons , the microscopic units that make up the brain 's tissue . those newly generated neurons migrate to various parts of the developing brain , making it self-organize into different structures . but until recently , scientists thought cell production came to an abrupt halt soon after this initial growth , leading them to conclude that neurological diseases , like alzheimer 's and parkinson 's , and damaging events , like strokes , are irreversible . but a series of recent discoveries has revealed that adult brains actually do continue to produce new cells in at least three specialized locations . this process , known as neurogenesis , involves dedicated brain cells , called neural stem cells and progenitor cells , which manufacture new neurons or replace the old ones . the three regions where neurogenesis has been discovered are the dentate gyrus , associated with learning and memory , the subventricular zone , which may supply neurons to the olfactory bulb for communication between the nose and brain , and the striatum , which helps manage movement . scientists do n't yet have a good grasp on exactly what role neurogenesis plays in any of these regions , or why they have this ability that 's absent from the rest of the brain , but the mere presence of a mechanism to grown new neurons in the adult brain opens up an amazing possibility . could we harness that mechanism to get the brain to heal its scars similar to how new skin grows to patch up a wound , or a broken bone stitches itself back together ? so here 's where we stand . certain proteins and other small molecules that mimick those proteins can be administered to the brain to make neural stem cells and progenitor cells produce more neurons in those three locations . this technique still needs improvement so that the cells reproduce more efficiently and more cells survive . but research shows that progenitor cells from these areas can actually migrate to places where injury has occurred and give rise to new neurons there . and another promising possible approach is to transplant healthy human neural stem cells , which are cultured in a laboratory , to injured tissue , like we can do with skin . scientists are currently experimenting to determine whether transplanted donor cells can divide , differentiate and successfully give rise to new neurons in a damaged brain . they 've also discovered that we might be able to teach other kinds of brain cells , such as astrocytes or oligodendrocytes to behave like neural stem cells and start generating neurons , too . so , a couple of decades from now will our brains be able to self-repair ? we ca n't say for sure , but that has become one of the major goals of regenerative medicine . the human brain has 100 billion neurons and we 're still figuring out the wiring behind this huge biological motherboard . but everyday , research on neurogenesis brings us closer to that reboot switch .

but a series of recent discoveries has revealed that adult brains actually do continue to produce new cells in at least three specialized locations . this process , known as neurogenesis , involves dedicated brain cells , called neural stem cells and progenitor cells , which manufacture new neurons or replace the old ones . the three regions where neurogenesis has been discovered are the dentate gyrus , associated with learning and memory , the subventricular zone , which may supply neurons to the olfactory bulb for communication between the nose and brain , and the striatum , which helps manage movement .

what factors have been shown to possibly stimulate the neurogenic process ?

`` all men are created equal and they are endowed with the rights to life , liberty and the pursuit of happiness . '' not so fast , mr. jefferson ! these words from the declaration of independence , and the facts behind them , are well known . in june of 1776 , a little more than a year after the war against england began with the shots fired at lexington and concord , the continental congress was meeting in philadelphia to discuss american independence . after long debates , a resolution of independence was approved on july 2 , 1776 . america was free ! and men like john adams thought we would celebrate that date forever . but it was two days later that the gentlemen in congress voted to adopt the declaration of independence , largely written by thomas jefferson , offering all the reasons why the country should be free . more than 235 years later , we celebrate that day as america 's birthday . but there are some pieces of the story you may not know . first of all , thomas jefferson gets the credit for writing the declaration , but five men had been given the job to come up with a document explaining why america should be independent : robert livingston , roger sherman , benjamin franklin and john adams were all named first . and it was adams who suggested that the young , and little known , thomas jefferson join them because they needed a man from the influential virginia delegation , and adams thought jefferson was a much better writer than he was . second , though jefferson never used footnotes , or credited his sources , some of his memorable words and phrases were borrowed from other writers and slightly tweaked . then , franklin and adams offered a few suggestions . but the most important change came after the declaration was turned over to the full congress . for two days , a very unhappy thomas jefferson sat and fumed while his words were picked over . in the end , the congress made a few , minor word changes , and one big deletion . in the long list of charges that jefferson made against the king of england , the author of the declaration had included the idea that george the third was responsible for the slave trade , and was preventing america from ending slavery . that was not only untrue , but congress wanted no mention of slavery in the nation 's founding document . the reference was cut out before the declaration was approved and sent to the printer . but it leaves open the hard question : how could the men , who were about to sign a document , celebrating liberty and equality , accept a system in which some people owned others ? it is a question that would eventually bring the nation to civil war and one we can still ask today .

`` all men are created equal and they are endowed with the rights to life , liberty and the pursuit of happiness . '' not so fast , mr. jefferson !

how could the men who pledged their lives and fortunes to “ life , liberty and the pursuit of happiness ” accept slavery ?

baked or fried , boiled or roasted , as chips or fries . at some point in your life , you 've probably eaten a potato . delicious , for sure , but the fact is potatoes have played a much more significant role in our history than just that of the dietary staple we have come to know and love today . without the potato , our modern civilization might not exist at all . 8,000 years ago in south america , high atop the andes , ancient peruvians were the first to cultivate the potato . containing high levels of proteins and carbohydrates , as well as essential fats , vitamins and minerals , potatoes were the perfect food source to fuel a large incan working class as they built and farmed their terraced fields , mined the rocky mountains , and created the sophisticated civilization of the great incan empire . but considering how vital they were to the incan people , when spanish sailors returning from the andes first brought potatoes to europe , the spuds were duds . europeans simply did n't want to eat what they considered dull and tasteless oddities from a strange new land , too closely related to the deadly nightshade plant belladonna for comfort . so instead of consuming them , they used potatoes as decorative garden plants . more than 200 years would pass before the potato caught on as a major food source throughout europe , though even then , it was predominantly eaten by the lower classes . however , beginning around 1750 , and thanks at least in part to the wide availability of inexpensive and nutritious potatoes , european peasants with greater food security no longer found themselves at the mercy of the regularly occurring grain famines of the time , and so their populations steadily grew . as a result , the british , dutch and german empires rose on the backs of the growing groups of farmers , laborers , and soldiers , thus lifting the west to its place of world dominion . however , not all european countries sprouted empires . after the irish adopted the potato , their population dramatically increased , as did their dependence on the tuber as a major food staple . but then disaster struck . from 1845 to 1852 , potato blight disease ravaged the majority of ireland 's potato crop , leading to the irish potato famine , one of the deadliest famines in world history . over a million irish citizens starved to death , and 2 million more left their homes behind . but of course , this was n't the end for the potato . the crop eventually recovered , and europe 's population , especially the working classes , continued to increase . aided by the influx of irish migrants , europe now had a large , sustainable , and well-fed population who were capable of manning the emerging factories that would bring about our modern world via the industrial revolution . so it 's almost impossible to imagine a world without the potato . would the industrial revolution ever have happened ? would world war ii have been lost by the allies without this easy-to-grow crop that fed the allied troops ? would it even have started ? when you think about it like this , many major milestones in world history can all be at least partially attributed to the simple spud from the peruvian hilltops .

but then disaster struck . from 1845 to 1852 , potato blight disease ravaged the majority of ireland 's potato crop , leading to the irish potato famine , one of the deadliest famines in world history . over a million irish citizens starved to death , and 2 million more left their homes behind .

the irish potato famine occurred between _______ .

trillions of bacteria , viruses , and fungi live on or inside of us , and maintaining a good , balanced relationship with them is to our advantage . together , they form the gut microbiome , a rich ecosystem that performs a variety of functions in our bodies . the bacteria in our guts can break down food the body ca n't digest , produce important nutrients , regulate the immune system , and protect against harmful germs . we do n't yet have the blueprint for exactly which good bacteria a robust gut needs , but we do know that it 's important for a healthy microbiome to have a variety of bacterial species . many factors affect our microbiomes , including our environment , medications like antibiotics , and even whether we were delivered by c-section or not . diet , too , is emerging as one of the leading influences on the health of our guts . and while we ca n't control all these factors , we can manipulate the balance of our microbes by paying attention to what we eat . dietary fiber from foods like fruits , vegetables , nuts , legumes , and whole grains is the best fuel for gut bacteria . when bacteria digest fiber , they produce short chain fatty acids that nourish the gut barrier , improve immune function , and can help prevent inflammation , which reduces the risk of cancer . and the more fiber you ingest , the more fiber-digesting bacteria colonize your gut . in a recent study , scientists exchanged the regular high-fiber diets of a group of rural south africans with the high-fat , meat-heavy diets of a group of african-americans . after just two weeks on the high-fat , low-fiber , western-style diet , the rural african group showed increased inflammation of the colon , as well as a decrease of butyrate . that 's a short chain fatty acid thought to lower risk of colon cancer . meanwhile , the group that switched to a high-fiber , low-fat diet had the opposite result . so what goes wrong with our gut bacteria when we eat low-fiber processed foods ? lower fiber means less fuel for the gut bacteria , essentially starving them until they die off . this results in less diversity and hungry bacteria . in fact , some can even start to feed on the mucus lining . we also know that specific foods can affect gut bacteria . in one recent microbiome study , scientists found that fruits , vegetables , tea , coffee , red wine , and dark chocolate were correlated with increased bacterial diversity . these foods contain polyphenols , which are naturally occurring antioxidant compounds . on the other hand , foods high in dairy fat , like whole milk , and sugar-sweetened sodas were correlated with decreased diversity . how food is prepared also matters . minimally processed , fresh foods generally have more fiber and provide better fuel . so lightly steamed , sautéed , or raw vegetables are typically more beneficial than fried dishes . there are also ways of preparing food that can actually introduce good bacteria , also known as probiotics , into your gut . fermented foods are teeming with helpful probiotic bacteria , like lactobacillus and bifidobacteria . originally used as a way of preserving foods before the invention of refrigeration , fermentation remains a traditional practice all over the world . foods like kimchi , sauerkraut , tempeh , and kombucha provide variety and vitality to our diets . yogurt is another fermented food that can introduce helpful bacteria into our guts . that does n't necessarily mean that all yogurt is good for us , though . brands with too much sugar and not enough bacteria may not actually help . these are just general guidelines . more research is needed before we fully understand exactly how any of these foods interact with our microbiomes . we see positive correlations , but the insides of our guts are difficult places to make direct observations . for instance , we do n't currently know whether these foods are directly responsible for the changes in diversity , or if something more complicated is happening . while we 're only beginning to explore the vast wilderness inside our guts , we already have a glimpse of how crucial our microbiomes are for digestive health . the great news is we have the power to fire up the bacteria in our bellies . fill up on fibers , fresh and fermented foods , and you can trust your gut to keep you going strong .

we also know that specific foods can affect gut bacteria . in one recent microbiome study , scientists found that fruits , vegetables , tea , coffee , red wine , and dark chocolate were correlated with increased bacterial diversity . these foods contain polyphenols , which are naturally occurring antioxidant compounds .

in recent studies , all of the following foods were correlated with increased bacterial diversity except :

it can strike without warning , at any moment . you may be walking across a soft carpet and reaching for the door knob when suddenly ... zap ! to understand static electricity , we first need to know a bit about the nature of matter . all matter is made up of atoms that consist of three types of smaller particles : negatively charged electrons , positively charged protons , and neutral neutrons . normally , the electrons and protons in an atom balance out , which is why most matter you come across is electrically neutral . but electrons are tiny and almost insignificant in mass , and rubbing or friction can give loosely bound electrons enough energy to leave their atoms and attach to others , migrating between different surfaces . when this happens , the first object is left with more protons than electrons and becomes positively charged , while the one with more electrons accumulates a negative charge . this situation is called a charge imbalance , or net charge separation . but nature tends towards balance , so when one of these newly charged bodies comes into contact with another material , the mobile electrons will take the first chance they get to go where they 're most needed , either jumping off the negatively charged object , or jumping onto the positively charged one in an attempt to restore the neutral charge equilibrium . and this quick movement of electrons , called static discharge , is what we recognize as that sudden spark . this process does n't happen with just any objects . otherwise you 'd be getting zapped all the time . conductors like metals and salt water tend to have loosely bound outer electrons , which can easily flow between molecules . on the other hand , insulators like plastics , rubber and glass have tightly bound electrons that wo n't readily jump to other atoms . static build-up is most likely to occur when one of the materials involved is an insulator . when you walk across a rug , electrons from your body will rub off onto it , while the rug 's insulating wool will resist losing its own electrons . although your body and the rug together are still electrically neutral , there is now a charge polarization between the two . and when you reach to touch the door knob , zap ! the metal door knob 's loosely bound electrons hop to your hand to replace the electrons your body has lost . when it happens in your bedroom , it 's a minor nuisance . but in the great outdoors , static electricity can be a terrifying , destructive force of nature . in certain conditions , charge separation will occur in clouds . we do n't know exactly how this happens . it may have to do with the circulation of water droplets and ice particles within them . regardless , the charge imbalance is neutralized by being released towards another body , such as a building , the earth , or another cloud in a giant spark that we know as lightning . and just as your fingers can be zapped over and over in the same spot , you better believe that lightning can strike the same place more than once .

normally , the electrons and protons in an atom balance out , which is why most matter you come across is electrically neutral . but electrons are tiny and almost insignificant in mass , and rubbing or friction can give loosely bound electrons enough energy to leave their atoms and attach to others , migrating between different surfaces . when this happens , the first object is left with more protons than electrons and becomes positively charged , while the one with more electrons accumulates a negative charge . this situation is called a charge imbalance , or net charge separation .

what happens to a material that collects electrons on its surface ?

translator : andrea mcdonough reviewer : jessica ruby there are all sorts of things that happen every day that might make you ask , `` why ? why do we drive on a parkway and park on a driveway ? why does my hair get frizzy when it 's humid ? and why do my fingers get all pruney when they 're wet ? '' often we simply ca n't know the answers to these questions . but progress can often be made , and , when it comes to your pruney fingers , scientists have a few interesting ideas . the story here begins with an observation made in the 1930s in the emergency room . doctors noticed that patients with nerve damage to their hands did not get pruney fingertips like most of us do in a bath , which might make you wonder , `` why would primates want wrinkly fingers , presumably when it 's rainy or dewy ? '' what could this trait be for ? what if these wrinkles functioned like rain treads ? think about car tires . when the ground is dry , it 's generally best to have smooth tires , and race cars do . smooth tires means more rubber or surface area in contact with the road , which gives them better grip . but in rainy and muddy conditions , it 's a different story , and here 's where treads come into play . treads reduce the amount of rubber on the road , but they help channel out water when it rains , lowering the risk of hydroplaning . well , if your fingers really are like rain treads , you should be able to predict the optimal shape for them , right ? so , what would the predicted wrinkle shapes be ? that is , are our prunes actually the right shape to be rain treads ? let 's take a detour into rivers . when we think of river networks , we usually imagine lots of smaller river channels joining to make larger river channels downstream , which is what happens in concave basins . in these cases , the divides , the regions between the river segments , are disconnected from one another and diverge away from one another uphill . but river networks look fundamentally different on convex promontories or protrusions . here , the river channels are disconnected from one another and diverge away from one another downstream , not very river-like . in these cases , it 's the divides that link together to form a tree , with its trunk uphill at the top of the promontory . here , it 's the divides that look more traditionally river-like . if our pruney fingers are drainage networks , designed to channel out water when they grip , then we expect to find similar shapes on our fingers as we find out there among rivers . there should be a tree network of divides , or ridges , with their trunk near the top of the fingertip and with their more leaky parts reaching out downhill , away from the tip . the channels themselves , through which the water is channeled during a grip , should not connect to one another , and instead should diverge away from one another downhill . if pruney fingers are rain treads , then they should look like the river networks on convex promontories . in fact , that 's exactly the morphology we find among pruney fingers ! when we grip , then , our pruney wrinkles really do channel out the water . but does it actually help us grip ? new behavioral experiments have shown that they do . in a task where subjects had to grasp wet marbles and move them through a hole and out the other side , those with pruney fingers finished the task significantly faster than those with smooth fingers . pruney fingers not only ought to enhance grip in wet conditions but do . so , pruney fingers may be a crucial part of the primate repertoire . maybe , once primates lost their claws in favor of fingernails , rain treads were needed to deal with the especially challenging , often wet , grip-heavy forest habitats . by looking closely at the mysteries in our world and trying to find things that look similar , like our wet fingers and rain treads , we can come up with ideas about what 's happening . and that 's a good way to think about all sorts of questions in life , too .

what could this trait be for ? what if these wrinkles functioned like rain treads ? think about car tires .

although the “ rain tread ” hypothesis predicts both ( i ) the shapes of the wrinkles and ( ii ) the results of the behavioral experiment , which of these successful predictions provides greater support for the hypothesis ?

what do fans of atmospheric post-punk music have in common with ancient barbarians ? not much . so why are both known as goths ? is it a weird coincidence or a deeper connection stretching across the centuries ? the story begins in ancient rome . as the roman empire expanded , it faced raids and invasions from the semi-nomadic populations along its borders . among the most powerful were a germanic people known as goths who were composed of two tribal groups , the visigoths and ostrogoths . while some of the germanic tribes remained rome 's enemies , the empire incorporated others into the imperial army . as the roman empire split in two , these tribal armies played larger roles in its defense and internal power struggles . in the 5th century , a mercenary revolt lead by a soldier named odoacer captured rome and deposed the western emperor . odoacer and his ostrogoth successor theoderic technically remained under the eastern emperor 's authority and maintained roman traditions . but the western empire would never be united again . its dominions fragmented into kingdoms ruled by goths and other germanic tribes who assimilated into local cultures , though many of their names still mark the map . this was the end of the classical period and the beginning of what many call the dark ages . although roman culture was never fully lost , its influence declined and new art styles arose focused on religious symbolism and allegory rather than proportion and realism . this shift extended to architecture with the construction of the abbey of saint denis in france in 1137 . pointed arches , flying buttresses , and large windows made the structure more skeletal and ornate . that emphasized its open , luminous interior rather than the sturdy walls and columns of classical buildings . over the next few centuries , this became a model for cathedrals throughout europe . but fashions change . with the italian renaissance 's renewed admiration for ancient greece and rome , the more recent style began to seem crude and inferior in comparison . writing in his 1550 book , `` lives of the artists , '' giorgio vasari was the first to describe it as gothic , a derogatory reference to the barbarians thought to have destroyed classical civilization . the name stuck , and soon came to describe the medieval period overall , with its associations of darkness , superstition , and simplicity . but time marched on , as did what was considered fashionable . in the 1700s , a period called the enlightenment came about , which valued scientific reason above all else . reacting against that , romantic authors like goethe and byron sought idealized visions of a past of natural landscapes and mysterious spiritual forces . here , the word gothic was repurposed again to describe a literary genre that emerged as a darker strain of romanticism . the term was first applied by horace walpole to his own 1764 novel , `` the castle of otranto '' as a reference to the plot and general atmosphere . many of the novel 's elements became genre staples inspiring classics and the countless movies they spawned . the gothic label belonged to literature and film until the 1970s when a new musical scene emerged . taking cues from artists like the doors and the velvet underground , british post-punk groups , like joy division , bauhaus , and the cure , combined gloomy lyrics and punk dissonance with imagery inspired by the victorian era , classic horror , and androgynous glam fashion . by the early 1980s , similar bands were consistently described as gothic rock by the music press , and the stye 's popularity brought it out of dimly lit clubs to major labels and mtv . and today , despite occasional negative media attention and stereotypes , gothic music and fashion continue as a strong underground phenomenon . they 've also branched into sub-genres , such as cybergoth , gothabilly , gothic metal , and even steampunk . the history of the word gothic is embedded in thousands of years worth of countercultural movements , from invading outsiders becoming kings to towering spires replacing solid columns to artists finding beauty in darkness . each step has seen a revolution of sorts and a tendency for civilization to reach into its past to reshape its present .

many of the novel 's elements became genre staples inspiring classics and the countless movies they spawned . the gothic label belonged to literature and film until the 1970s when a new musical scene emerged . taking cues from artists like the doors and the velvet underground , british post-punk groups , like joy division , bauhaus , and the cure , combined gloomy lyrics and punk dissonance with imagery inspired by the victorian era , classic horror , and androgynous glam fashion .

contrast the spiritual imagery of gothic cathedrals with that of gothic literature .

translator : andrea mcdonough reviewer : bedirhan cinar hello , my name is christian rudder , and i was one of the founders of okcupid . it 's now one of the biggest dating sites in the united states . like most everyone at the site , i was a math major , as you may expect , we 're known for the analytic approach we take to love . we call it our matching algorithm . basically , okcupid 's matching algorithm helps us decide whether two people should go on a date . we built our entire business around it . now , algorithm is a fancy word , and people like to drop it like it 's this big thing . but really , an algorithm is just a systematic , step-by-step way to solve a problem . it does n't have to be fancy at all . here in this lesson , i 'm going to explain how we arrived at our particular algorithm , so you can see how it 's done . now , why are algorithms even important ? why does this lesson even exist ? well , notice one very significant phrase i used above : they are a step-by-step way to solve a problem , and as you probably know , computers excel at step-by-step processes . a computer without an algorithm is basically an expensive paperweight . and since computers are such a pervasive part of everyday life , algorithms are everywhere . the math behind okcupid 's matching algorithm is surprisingly simple . it 's just some addition , multiplication , a little bit of square roots . the tricky part in designing it was figuring out how to take something mysterious , human attraction , and break it into components that a computer can work with . the first thing we needed to match people up was data , something for the algorithm to work with . the best way to get data quickly from people is to just ask for it . so we decided that okcupid should ask users questions , stuff like , `` do you want to have kids one day ? '' `` how often do you brush your teeth ? '' `` do you like scary movies ? '' and big stuff like , `` do you believe in god ? '' now , a lot of the questions are good for matching like with like , that is , when both people answer the same way . for example , two people who are both into scary movies are probably a better match than one person who is and one who is n't . but what about a question like , `` do you like to be the center of attention ? '' if both people in a relationship are saying yes to this , they 're going to have massive problems . we realized this early on , and so we decided we needed a bit more data from each question . we had to ask people to specify not only their own answer , but the answer they wanted from someone else . that worked really well . but we needed one more dimension . some questions tell you more about a person than others . for example , a question about politics , something like , `` which is worse : book burning or flag burning ? '' might reveal more about someone than their taste in movies . and it does n't make sense to weigh all things equally , so we added one final data point . for everything that okcupid asks you , you have a chance to tell us the role it plays in your life . and this ranges from irrelevant to mandatory . so now , for every question , we have three things for our algorithm : first , your answer ; second , how you want someone else -- your potential match -- to answer ; and third , how important the question is to you at all . with all this information , okcupid can figure out how well two people will get along . the algorithm crunches the numbers and gives us a result . as a practical example , let 's look at how we 'd match you with another person . let 's call him `` b . '' your match percentage with b is based on questions you 've both answered . let 's call that set of common questions `` s. '' as a very simple example , we use a small set `` s '' with just two questions in common , and compute a match from that . here are our two example questions . the first one , let 's say , is , `` how messy are you ? '' and the answer possibilities are : very messy , average and very organized . and let 's say you answered `` very organized , '' and you 'd like someone else to answer `` very organized , '' and the question is very important to you . basically , you 're a neat freak . you 're neat , you want someone else to be neat , and that 's it . and let 's say b is a little bit different . he answered `` very organized '' for himself , but `` average '' is ok with him as an answer from someone else , and the question is only a little important to him . let 's look at the second question , from our previous example : `` do you like to be the center of attention ? '' the answers are `` yes '' and `` no . '' you 've answered `` no , '' you want someone else to answer `` no , '' and the question is only a little important to you . now b , he 's answered `` yes . '' he wants someone else to answer `` no , '' because he wants the spotlight on him , and the question is somewhat important to him . so , let 's try to compute all of this . our first step is , since we use computers to do this , we need to assign numerical values to ideas like `` somewhat important '' and `` very important , '' because computers need everything in numbers . we at okcupid decided on the following scale : `` irrelevant '' is worth 0 . `` a little important '' is worth 1 . `` somewhat important '' is worth 10 . `` very important '' is 50 . and `` absolutely mandatory '' is 250 . next , the algorithm makes two simple calculations . the first is : how much did b 's answers satisfy you ? that is , how many possible points did b score on your scale ? well , you indicated that b 's answer to the first question , about messiness , was very important to you . it 's worth 50 points and b got that right . the second question is worth only 1 , because you said it was only a little important . b got that wrong , so b 's answers were 50 out of 51 possible points . that 's 98 % satisfactory . pretty good . the second question the algorithm looks at is : how much did you satisfy b ? well , b placed 1 point on your answer to the messiness question and 10 on your answer to the second . of those 11 , that 's 1 plus 10 , you earned 10 -- you guys satisfied each other on the second question . so your answers were 10 out of 11 equals 91 percent satisfactory to b . that 's not bad . the final step is to take these two match percentages and get one number for the both of you . to do this , the algorithm multiplies your scores , then takes the nth root , where `` n '' is the number of questions . because s , which is the number of questions in this sample , is only 2 , we have : match percentage equals the square root of 98 percent times 91 percent . that equals 94 percent . that 94 percent is your match percentage with b . it 's a mathematical expression of how happy you 'd be with each other , based on what we know . now , why does the algorithm multiply , as opposed to , say , average the two match scores together , and do the square-root business ? in general , this formula is called the geometric mean . it 's a great way to combine values that have wide ranges and represent very different properties . in other words , it 's perfect for romantic matching . you 've got wide ranges and you 've got tons of different data points , like i said , about movies , politics , religion -- everything . intuitively , too , this makes sense . two people satisfying each other 50 percent should be a better match than two others who satisfy 0 and 100 , because affection needs to be mutual . after adding a little correction for margin of error , in the case where we have a small number of questions , like we do in this example , we 're good to go . any time okcupid matches two people , it goes through the steps we just outlined . first it collects data about your answers , then it compares your choices and preferences to other people 's in simple , mathematical ways . this , the ability to take real-world phenomena and make them something a microchip can understand , is , i think , the most important skill anyone can have these days . like you use sentences to tell a story to a person , you use algorithms to tell a story to a computer . if you learn the language , you can go out and tell your stories . i hope this will help you do that .

like most everyone at the site , i was a math major , as you may expect , we 're known for the analytic approach we take to love . we call it our matching algorithm . basically , okcupid 's matching algorithm helps us decide whether two people should go on a date .

what is an algorithm ?

so our reaction ’ s ready . now all we need again is a little bit of water just to start it off . so we ’ re here today and we ’ ve come back after hours because we need to use this room for a long period of time because we ’ re going to do something quite exciting . because brady ’ s bought another camera which you can see he ’ s setup over there and we ’ re going to use that second camera to capture one second of film every minute for maybe two or three hours and we ’ re going to do some time lapse . something i ’ ve seen on tv with like flowers opening or plants growing but never with chemistry developing . silver is one of the few metallic elements that occurs naturally as the metal in nature . so that if you ’ re lucky you can wander around and find lumps of silver lying around on the ground . and this is how , in ancient times , silver was discovered so it has been known for thousands if not tens of thousands of years . gold is somewhat similar and also copper . but most other metals combine too easily with oxygen or other elements so you don ’ t find them naturally . so i thought what we ’ d do today is through a competition reaction and that competition reaction is based on something called the reactivity series of metals . so we ’ re going to compare the reactivity of two metals . it ’ s a bit like a game of football . we ’ re going to give one of those metals the football and in this case it ’ s another component or another salt component , nitrate . so the two metals that are going to be competing for the nitrate are silver and copper . and really these are related by something called the reactivity series . one of these metals is going to win , i know that and i hope we ’ ll find it during this video . silver had a particular use in photography and in the old days when people used photographic film the black colour that you saw on developed negatives is in fact silver . a photographic film consists of a layer of silver bromide or sometimes silver iodide and when the light shines on it the light just starts a tiny amount of reaction making silver and then when you put it in the developing solution the catalytic amount of silver that you ’ ve produced causes a big reaction and you make a large amount of silver . and so you get this black colour which then you can print as pictures . so on the bench i ’ ve got a small beaker or an erlenmeyer flask , as we chemists call it , which is full of deionised water . so we ’ ve passed the water through a machine which has taken out all of the other ions so that they can ’ t play around with the competition reaction that we want to start today . firstly , i ’ m going to start off by giving the prize of the competition to silver . so here i ’ ve got a sample of silver nitrate . it ’ s sensitive to light so i can ’ t leave it out on the bench very often . so now what i want to do , i ’ m going to put some into the water to make a silver nitrate solution . so i want to make sure that there ’ s plenty in there so that it ’ s saturated . now we ’ ve got to put in the competitor . so what we ’ re going to do , we ’ re going to take some copper , copper metal . and this is just a sample of wire which i ’ ve rubbed with some wire wool just to make it sort of nice and shiny . and now all i ’ m going to do is dangle it into the silver nitrate . then it ’ s going to start to compete for the nitrate and we ’ ll see what happens . so brady ’ s started the recording and i think the best thing for us to do is to go away and do something a little bit more exciting and come back and have a look in an hour . silver has become quite popular recently as a potential new way of making things anti-bacterial : killing bacteria . so now we ’ re going to make some flash powder and the flash powder we ’ re going to make today is a two component mixture . it ’ s very finely ground magnesium and the second component is ground silver nitrate , solid ok . so we take these two components and we mix the two together very intimately and neil ’ s just weighing the materials out right now . so we ’ re going to put the magnesium and the silver nitrate , the two powders , together into a small plastic container here . we ’ re going to mix them very , very carefully and then we ’ re going to see what happens when we initiate a chemical reaction . for hundreds of years people have used silver spoons . partly , i think , because silver is quite easy to make but also because the silver does have properties that kill bacteria so a silver spoon is less likely to get harmful bacteria on it than if you have one that ’ s made out of wood or horn of a cow or something like that . so we ’ re mixing these very carefully , in the fume hood , just in case the chemistry starts before we want it to . and in recent times people have started making very , very fine particles of silver , so called nanoparticles , which can exist in solutions . so here i ’ ve got a solution of silver nanoparticles . you can see it doesn ’ t look silver it looks a bit yellow actually and you can tell that it ’ s got particles in it because , if i can find a torch… so here we ’ ve got particles and you can see the particles better if we shine a light through it and if you look at the light you can see that there is a cone of light that looks rather like the headlights of a car in fog . and this is an effect that ’ s called the tyndall cone which indicates that there are very , very tiny particles suspended in the solution . so this is not silver dissolved in the water but actually very tiny particles . so let ’ s start the reaction , just with a little bit of water . wow ! i think we should do it again though . yeah ! laughter people are now using the silver nanoparticles for all sorts of purposes . here you can see that they ’ ve been put onto some sort of plastic and you can now buy socks which have silver nanoparticles on them which are claimed to kill the bacteria that make your feet smell . so we ’ re going to repeat the reaction . b-b-b-b… squawcks that ’ s going to come out somewhere isn ’ t it ? silver will conduct electricity , it will also conduct heat . if you ’ ve ever tried stirring tea with a silver spoon it gets very hot , you tend to drop it . it also conducts electricity well . so we ’ re going to repeat the reaction so that you can see it again , because that was really fast . this time we ’ re going to do it on a glass dish so you can see it a bit better . we ’ ll pour out a small amount . laughter so our reaction ’ s ready . now all we need again is a little bit of water just to start it off . did you catch that ? i managed to close my eyes this time ( ! ) during the second world war , when the us government was involved in enriching uranium as part of the manhattan project they needed an enormous amount of wire to make magnets . and so a huge amount of silver was taken from the us treasury where it was stored as silver to give value to the us dollar and was turned into wires to make magnets . and i believe that the silver was never returned or at least it wasn ’ t returned at the end of the war as was promised . well , i ’ ve managed to fill maybe one minute ’ s worth of time by now maybe two because we ’ ve been away about two hours . so we ’ re going to go back and have a look at the flask to see if there are any changes . if you remember when we left it was a nice clear solution of silver nitrate with some copper wire which was just immersed inside . so let ’ s go and have a look . there ’ s been big changes in our flask ! so if you look carefully you can see now that the copper wire itself is covered in very , very sharp crystals of silver which have basically become deposited on the surface . copper has now won this chemical reaction . it ’ s now going into the solution ; it ’ s taking the salt element and precipitating solid silver crystals . so if you look carefully , you can see that the colour of the solution has changed . it was colourless , now it ’ s blue which tells me there is another ion , copper , in the solution .

i managed to close my eyes this time ( ! ) during the second world war , when the us government was involved in enriching uranium as part of the manhattan project they needed an enormous amount of wire to make magnets . and so a huge amount of silver was taken from the us treasury where it was stored as silver to give value to the us dollar and was turned into wires to make magnets . and i believe that the silver was never returned or at least it wasn ’ t returned at the end of the war as was promised .

during the second world war , a huge amount of silver was taken from the us treasury . how was it used ?

created by logician raymond smullyan and popularized by his colleague george boolos , this riddle has been called the hardest logic puzzle ever . you and your team have crash-landed on an ancient planet . the only way off is to appease its three alien overlords , tee , eff , and arr , by giving them the correct artifacts . unfortunately , you do n't know who is who . from an inscription , you learn that you may ask three yes or no questions , each addressed to any one lord . tee 's answers are always true , eff 's are always false , and arr 's answer is random each time . but there 's a problem . you 've deciphered the language enough to ask any question , but you do n't know which of the two words 'ozo ' and 'ulu ' means yes and which means no . how can you still figure out which alien is which ? pause here if you want to figure it out for yourself ! answer in : 3 2 1 at first , this puzzle seems not just hard , but downright impossible . what good is asking a question if you can neither understand the answer nor know if it 's true ? but it can be done . the key is to carefully formulate our questions so that any answer yields useful information . first of all , we can get around to not knowing what 'ozo ' and 'ulu ' mean by including the words themselves in the questions , and secondly , if we load each question with a hypothetical condition , whether an alien is lying or not wo n't actually matter . to see how that could work , imagine our question is whether two plus two is four . instead of posing it directly , we say , `` if i asked you whether two plus two is four , would you answer 'ozo ' ? '' if 'ozo ' means yes and the overlord is tee , it truthfully replies , `` ozo . '' but what if we ask eff ? well , it would answer `` ulu , '' or no to the embedded question , so it lies and replies 'ozo ' instead . and if 'ozo ' actually means no , then the answer to our embedded question is 'ulu , ' and both tee and eff still reply 'ozo , ' each for their own reasons . if you 're confused about why this works , the reason involves logical structure . a double positive and a double negative both result in a positive . now , we can be sure that asking either tee or eff a question put this way will yield 'ozo ' if the hypothetical question is true and 'ulu ' if it 's false regardless of what each word actually means . unfortunately , this does n't help us with arr . but do n't worry , we can use our first question to identify one alien lord that definitely is n't arr . then we can use the second to find out whether its tee or eff . and once we know that , we can ask it to identify one of the others . so let 's begin . ask the alien in the middle , `` if i asked you whether the overlord on my left is arr , would you answer 'ozo ' ? '' if the reply is 'ozo , ' there are two possibilities . you could already be talking to arr , in which case the answer is meaningless . but otherwise , you 're talking to either tee or eff , and as we know , getting 'ozo ' from either one means your hypothetical question was correct , and the left overlord is indeed arr . either way , you can be sure the alien on the right is not arr . similarly , if the answer is 'ulu , ' then you know the alien on the left ca n't be arr . now go to the overlord you 've determined is n't arr and ask , `` if i asked 'are you eff ? ' would you answer 'ozo ' ? '' since you do n't have to worry about the random possibility , either answer will establish its identity . now that you know whether its answers are true or false , ask the same alien whether the center overlord is arr . the process of elimination will identify the remaining one . the satisfied overlords help you repair your ship and you prepare for takeoff . allowed one final question , you ask tee if it 's a long way to earth , and he answers `` ozo . '' too bad you still do n't know what that means .

instead of posing it directly , we say , `` if i asked you whether two plus two is four , would you answer 'ozo ' ? '' if 'ozo ' means yes and the overlord is tee , it truthfully replies , `` ozo . '' but what if we ask eff ?

how do we get around the problem of not knowing whether ‘ ozo ’ means yes or no ?

85 % of the matter in our universe is a mystery . we do n't know what it 's made of , which is why we call it dark matter . but we know it 's out there because we can observe its gravitational attraction on galaxies and other celestial objects . we 've yet to directly observe dark matter , but scientists theorize that we may actually be able to create it in the most powerful particle collider in the world . that 's the 27 kilometer-long large hadron collider , or lhc , in geneva , switzerland . so how would that work ? in the lhc , two proton beams move in opposite directions and are accelerated to near the speed of light . at four collision points , the beams cross and protons smash into each other . protons are made of much smaller components called quarks and gluons in most ordinary collisions , the two protons pass through each other without any significant outcome . however , in about one in a million collisions , two components hit each other so violently , that most of the collision energy is set free producing thousands of new particles . it 's only in these collisions that very massive particles , like the theorized dark matter , can be produced . the collision points are surrounded by detectors containing about 100 million sensors . like huge three-dimensional cameras , they gather information on those new particles , including their trajectory , electrical charge , and energy . once processed , the computers can depict a collision as an image . each line is the path of a different particle , and different types of particles are color-coded . data from the detectors allows scientists to determine what each of these particles is , things like photons and electrons . now , the detectors take snapshots of about a billion of these collisions per second to find signs of extremely rare massive particles . to add to the difficulty , the particles we 're looking for may be unstable and decay into more familiar particles before reaching the sensors . take , for example , the higgs boson , a long-theorized particle that was n't observed until 2012 . the odds of a given collision producing a higgs boson are about one in 10 billion , and it only lasts for a tiny fraction of a second before decaying . but scientists developed theoretical models to tell them what to look for . for the higgs , they thought it would sometimes decay into two photons . so they first examined only the high-energy events that included two photons . but there 's a problem here . there are innumerable particle interactions that can produce two random photons . so how do you separate out the higgs from everything else ? the answer is mass . the information gathered by the detectors allows the scientists to go a step back and determine the mass of whatever it was that produced two photons . they put that mass value into a graph and then repeat the process for all events with two photons . the vast majority of these events are just random photon observations , what scientists call background events . but when a higgs boson is produced and decays into two photons , the mass always comes out to be the same . therefore , the tell-tale sign of the higgs boson would be a little bump sitting on top of the background . it takes billions of observations before a bump like this can appear , and it 's only considered a meaningful result if that bump becomes significantly higher than the background . in the case of the higgs boson , the scientists at the lhc announced their groundbreaking result when there was only a one in 3 million chance this bump could have appeared by a statistical fluke . so back to the dark matter . if the lhc 's proton beams have enough energy to produce it , that 's probably an even rarer occurrence than the higgs boson . so it takes quadrillions of collisions combined with theoretical models to even start to look . that 's what the lhc is currently doing . by generating a mountain of data , we 're hoping to find more tiny bumps in graphs that will provide evidence for yet unknown particles , like dark matter . or maybe what we 'll find wo n't be dark matter , but something else that would reshape our understanding of how the universe works entirely . that 's part of the fun at this point . we have no idea what we 're going to find .

so back to the dark matter . if the lhc 's proton beams have enough energy to produce it , that 's probably an even rarer occurrence than the higgs boson . so it takes quadrillions of collisions combined with theoretical models to even start to look .

in 2012 , a higgs boson was produced in one out of ... .. proton-proton collisions at the lhc

one of the most remarkable aspects of the human brain is its ability to recognize patterns and describe them . among the hardest patterns we 've tried to understand is the concept of turbulent flow in fluid dynamics . the german physicist werner heisenberg said , `` when i meet god , i 'm going to ask him two questions : why relativity and why turbulence ? i really believe he will have an answer for the first . '' as difficult as turbulence is to understand mathematically , we can use art to depict the way it looks . in june 1889 , vincent van gogh painted the view just before sunrise from the window of his room at the saint-paul-de-mausole asylum in saint-rémy-de-provence , where he 'd admitted himself after mutilating his own ear in a psychotic episode . in `` the starry night , '' his circular brushstrokes create a night sky filled with swirling clouds and eddies of stars . van gogh and other impressionists represented light in a different way than their predecessors , seeming to capture its motion , for instance , across sun-dappled waters , or here in star light that twinkles and melts through milky waves of blue night sky . the effect is caused by luminance , the intensity of the light in the colors on the canvas . the more primitive part of our visual cortex , which sees light contrast and motion , but not color , will blend two differently colored areas together if they have the same luminance . but our brains ' primate subdivision will see the contrasting colors without blending . with these two interpretations happening at once , the light in many impressionist works seems to pulse , flicker and radiate oddly . that 's how this and other impressionist works use quickly executed prominent brushstrokes to capture something strikingly real about how light moves . 60 years later , russian mathematician andrey kolmogorov furthered our mathematical understanding of turbulence when he proposed that energy in a turbulent fluid at length r varies in proportion to the 5/3rds power of r. experimental measurements show kolmogorov was remarkably close to the way turbulent flow works , although a complete description of turbulence remains one of the unsolved problems in physics . a turbulent flow is self-similar if there is an energy cascade . in other words , big eddies transfer their energy to smaller eddies , which do likewise at other scales . examples of this include jupiter 's great red spot , cloud formations and interstellar dust particles . in 2004 , using the hubble space telescope , scientists saw the eddies of a distant cloud of dust and gas around a star , and it reminded them of van gogh 's `` starry night . '' this motivated scientists from mexico , spain and england to study the luminance in van gogh 's paintings in detail . they discovered that there is a distinct pattern of turbulent fluid structures close to kolmogorov 's equation hidden in many of van gogh 's paintings . the researchers digitized the paintings , and measured how brightness varies between any two pixels . from the curves measured for pixel separations , they concluded that paintings from van gogh 's period of psychotic agitation behave remarkably similar to fluid turbulence . his self-portrait with a pipe , from a calmer period in van gogh 's life , showed no sign of this correspondence . and neither did other artists ' work that seemed equally turbulent at first glance , like munch 's `` the scream . '' while it 's too easy to say van gogh 's turbulent genius enabled him to depict turbulence , it 's also far too difficult to accurately express the rousing beauty of the fact that in a period of intense suffering , van gogh was somehow able to perceive and represent one of the most supremely difficult concepts nature has ever brought before mankind , and to unite his unique mind 's eye with the deepest mysteries of movement , fluid and light .

in 2004 , using the hubble space telescope , scientists saw the eddies of a distant cloud of dust and gas around a star , and it reminded them of van gogh 's `` starry night . '' this motivated scientists from mexico , spain and england to study the luminance in van gogh 's paintings in detail . they discovered that there is a distinct pattern of turbulent fluid structures close to kolmogorov 's equation hidden in many of van gogh 's paintings . the researchers digitized the paintings , and measured how brightness varies between any two pixels .

write a short paragraph ( 3-5 sentences ) that summarizes the history of vincent van gogh . what challenges did he encounter as a painter ?

if you think of culture as an iceberg , only a small fraction of it is visible . food , flags , and festivals , which are often talked about in schools , are the visible parts that we rightly celebrate . however , only when we look deeper , under the water , are we able to focus on the common values that connect us . in what seems to be an increasingly troubled world , where social and political systems are being stretched , conflict within and between countries is at times heightened , while human rights are being ignored , this desire for peace grows ever stronger . sometimes we see this common value emerging above the surface and becoming visible . for example , it is part of everyday language used when people greet one another and welcome the new day . in many parts of the arab world and parts of south asia , such as bangladesh for example , the greeting of `` as-salamu alaykum '' can be translated to `` peace be with you . '' the same is true as you walk through markets or into schools each morning in india , or nepal , or bhutan , where greetings of `` namaste , '' which has not only a strong message of peace - `` the spirit in me greets the spirit in you '' - but also its physical gesture , the palms brought together slowly at the heart , to honor a special place in each of us . in myanmar , greetings of `` mingalarbar '' are met by bowing monks as they internalize a message where others add blessing to enhance the auspiciousness of the moment , or by giggling children as they scurry off to school . after many hours of hiking through the mountains of lesotho , surrounded by the tranquility and rugged terrain , you are likely to meet a herdboy who has slept the night in a vacant rondoval and bellows out greetings of `` lumela '' or `` khotso '' , which means `` peace be with you . '' if you took a moment to research further the meanings behind `` shalom , '' or the korean greeting , you would find that they too have deeply-seated connections to peace . however , they have become quick comments made to welcome , greet , and say hello , and in this overuse , have likely lost the focus that was originally intended when put into practice hundreds or thousands of years ago . in highlighting this simple evidence of ingrained behavior , we can create the necessary shift in thinking needed to incorporate flexibility and open-mindedness in us all when looking at the globalization of the world .

after many hours of hiking through the mountains of lesotho , surrounded by the tranquility and rugged terrain , you are likely to meet a herdboy who has slept the night in a vacant rondoval and bellows out greetings of `` lumela '' or `` khotso '' , which means `` peace be with you . '' if you took a moment to research further the meanings behind `` shalom , '' or the korean greeting , you would find that they too have deeply-seated connections to peace . however , they have become quick comments made to welcome , greet , and say hello , and in this overuse , have likely lost the focus that was originally intended when put into practice hundreds or thousands of years ago .

if you took a moment to research further the meanings behind shalom or the korean greeting , you would find that they too have deeply seated connections to peace . what does jenkins suggest has happened because of their use as quick phrases meant to welcome , greet , and say hello ?

what does it mean to be one in a million ? not in the greeting card sense , in the scientific sense , where one part per million is a unit of measurement . parts per million counts the number of units of one substance per one million units of another . it can measure concentrations when a small amount makes a big difference . for example , a concentration of just 35 ppm of carbon monoxide in the air is poisonous to us . we encounter measurements like this pretty often , but because it 's hard to conceptualize really large numbers , it 's difficult to wrap our brain around what one part per million really means . so here are nine helpful ways to visualize it . if you had 11,363 pianos-worth of piano keys , one of those keys would be about one part per million . so would a single granule of sugar among 273 sugar cubes , one second in eleven and a half days , or four dots in the painting , `` a sunday afternoon on the island of la grande jatte . '' your bath tub 's capacity is about 60 gallons , so seven drops of ink would be one part per million . the english version of the harry potter series has 1,084,170 words , which makes `` hippogriff '' on page 221 of `` the prisoner of azkaban '' a little less than one part per million . a million kernels of corn is about 1,250 ears , so one kernel in that truckload would be one part per million . there are 10 million bricks in the empire state building , so one part per million would be a pile of just ten . and finally , 100 people worked together to animate this video . collectively , they have about 10 million hairs on their heads . pluck ten of those hairs , and you have one in a million .

not in the greeting card sense , in the scientific sense , where one part per million is a unit of measurement . parts per million counts the number of units of one substance per one million units of another . it can measure concentrations when a small amount makes a big difference .

parts per million , or ppm , is used to measure :

in 1796 , thomas jefferson received a box of bones he could n't identify . a long , sharp claw reminded him of a lion , but the arm bones suggested a larger animal , one about three meters long . thinking it might be huge unknown species of north american lion , jefferson warned explorers lewis and clark to keep an eye out for this mysterious predator . but jefferson 's box of bones did n't come from a lion . they came from an extinct giant sloth . prehistoric ground sloths first appeared around 35 million years ago . dozens of species lived across north , central and south america , alongside other ancient creatures like mastodons and giant armadillos . some ground sloths , like the megalonychid , were cat-sized , but many were massive . jefferson 's sloth , megalonyx , weighed about a ton , and that was small compared to megatherium , which could reach six metric tons , as much as an elephant . they ambled through the forests and savannas using their strong arms and sharp claws to uproot plants and climb trees , grazing on grasses , leaves , and prehistoric avocados . in fact , we might not have avocados today if not for the giant sloths . smaller animals could n't swallow the avocado 's huge seed , but the sloths could , and they spread avocado trees far and wide . ground sloths flourished for millions of years , but around 10,000 years ago , they started disappearing along with the western hemisphere 's other giant mammals . researchers think that ground sloths could have been pushed out by an oncoming ice age , or competition with other species , maybe humans , who arrived in the region around the time most of the sloths went extinct . some of the smaller sloths did survive and migrated to the treetops . today , there are six species left living in the rainforest canopies of central and south america . hanging out in the trees is a good way to avoid predators , and there are plenty of leaves to eat . but this diet has its drawbacks . animals extract energy from food and use that energy to move around , maintain their body temperature , keep their organs working , and all the other activities necessary for survival . but leaves do n't contain much energy , and that which they do have is tough to extract . most herbivores supplement a leafy diet with higher energy foods like fruit and seeds . but sloths , especially three-toed sloths , rely on leaves almost exclusively . they 've evolved finely tuned strategies for coping with this restricted diet . first , they extract as much energy from their food as possible . sloths have a multi-chambered stomach that takes up a third of their body , and depending on the species , they can spend five to seven days , or even weeks , processing a meal . the other piece of the puzzle is to use as little energy as possible . one way sloths do this is , of course , by not moving very much . they spend most of their time eating , resting , or sleeping . they descend from the canopy just once a week for a bathroom break . when sloths do move , it 's not very fast . it would take a sloth about five minutes to cross an average neighborhood street . this unhurried approach to life means that sloths do n't need very much muscle . in fact , they have about 30 % less muscle mass than other animals their size . sloths also use less energy to keep themselves warm because their body temperature can fluctuate by about five degrees celsius , less than a cold-blooded reptile , but more than most mammals . these physical and behavioral adaptations minimize the sloth 's energy expenditure , or metabolic rate . three-toed sloths have the slowest metabolism of any mammal . the giant panda is second slowest , and two-toed sloths come in third . moving slowly has allowed sloths to thrive in their treetop habitat . but it 's also made the sloths themselves a great habitat for other organisms , including algae , which provides a little extra camouflage , and maybe even a snack . sloths may not be giant anymore , but that does n't make them any less remarkable .

they 've evolved finely tuned strategies for coping with this restricted diet . first , they extract as much energy from their food as possible . sloths have a multi-chambered stomach that takes up a third of their body , and depending on the species , they can spend five to seven days , or even weeks , processing a meal .

how have sloths evolved to extract as much energy from their food as possible ?

what if william shakespeare had a sister who matched his imagination , his wit , and his way with words ? would she have gone to school and set the stage alight ? in her essay `` a room of one 's own , '' virginia woolf argues that this would have been impossible . she concocts a fictional sister who 's stuck at home , snatching time to scribble a few pages before she finds herself betrothed and runs away . while her brother finds fame and fortune , she remains abandoned and anonymous . in this thought experiment , woolf demonstrates the tragedy of genius restricted , and looks back through time for hints of these hidden histories . she wrote , `` when one reads of a witch being ducked , of a woman possessed by devils , of a wise woman selling herbs , or even a very remarkable man who had a mother , then i think we 're on the track of a lost novelist , a suppressed poet , of some mute and inglorious jane austen . '' `` a room of one 's own '' considers a world denied great works of art due to exclusion and inequality . how best can we understand the internal experience of alienation ? in both her essays and fiction , virginia woolf shapes the slippery nature of subjective experience into words . her characters frequently lead inner lives that are deeply at odds with their external existence . to help make sense of these disparities , the next time you read woolf , here are some aspects of her life and work to consider . she was born adeline virginia stephen in 1882 to a large and wealthy family , which enabled her to pursue a life in the arts . the death of her mother in 1895 was followed by that of her half-sister , father , and brother within the next ten years . these losses led to woolf 's first depressive episode and subsequent institutionalization . as a young woman , she purchased a house in the bloomsbury area of london with her siblings . this brought her into contact with a circle of creatives , including e.m. forster , clive bell , roger fry , and leonard woolf . these friends became known as the bloomsbury group , and virginia and leonard married in 1912 . the members of this group were prominent figures in modernism , a cultural movement that sought to push the boundaries of how reality is represented . key features of modernist writing include the use of stream of consciousness , interior monologue , distortions in time , and multiple or shifting perspectives . these appear in the work of ezra pound , gertrude stein , james joyce , and woolf herself . while reading joyce 's `` ulysses , '' woolf began writing `` mrs . dalloway . '' like `` ulysses , '' the text takes place over the course of a single day and opens under seemingly mundane circumstances . `` mrs. dalloway said she would buy the flowers herself . '' but the novel dives deeply into the characters ' traumatic pasts , weaving the inner world of numbed socialite clarissa dalloway , with that of the shell-shocked veteran septimus warren smith . woolf uses interior monologue to contrast the rich world of the mind against her characters ' external existences . in her novel `` to the lighthouse , '' mundane moments , like a dinner party , or losing a necklace trigger psychological revelations in the lives of the ramsay 's , a fictionalized version of woolf 's family growing up . `` to the lighthouse '' also contains one of the most famous examples of woolf 's radical representation of time . in the time passes section , ten years are distilled into about 20 pages . here , the lack of human presence in the ramsays ' beach house allows woolf to reimagine time in flashes and fragments of prose . `` the house was left . the house was deserted . it was left like a shell on a sand hill to fill with dry salt grains now that life had left it . '' in her novel `` the waves , '' there is little distinction between the narratives of the six main characters . woolf experiments with collective consciousness , at times collapsing the six voices into one . `` it is not one life that i look back upon : i am not one person : i am many people : i do not altogether know who i am , jinny , susan , neville , rhoda or louis , or how to distinguish my life from their 's . '' in `` the waves , '' six become one , but in the gender-bending `` orlando , '' a single character inhabits multiple identities . the protagonist is a poet who switches between genders and lives for 300 years . with its fluid language and approach to identity , `` orlando '' is considered a key text in gender studies . the mind can only fly so far from the body before it returns to the constraints of life . like many of her characters , woolf 's life ended in tragedy when she drowned herself at the age of 59 . yet , she expressed hope beyond suffering . through deep thought , woolf 's characters are shown to temporarily transcend their material reality , and in its careful consideration of the complexity of the mind , her work charts the importance of making our inner lives known to each other .

while her brother finds fame and fortune , she remains abandoned and anonymous . in this thought experiment , woolf demonstrates the tragedy of genius restricted , and looks back through time for hints of these hidden histories . she wrote , `` when one reads of a witch being ducked , of a woman possessed by devils , of a wise woman selling herbs , or even a very remarkable man who had a mother , then i think we 're on the track of a lost novelist , a suppressed poet , of some mute and inglorious jane austen . ''

can you think of different ways time has been represented in literature ? how are they similar or different to woolf ’ s approach ?

how do schools of fish swim in harmony ? and how do the tiny cells in your brain give rise to the complex thoughts , memories , and consciousness that are you ? oddly enough , those questions have the same general answer : emergence , or the spontaneous creation of sophisticated behaviors and functions from large groups of simple elements . like many animals , fish stick together in groups , but that 's not just because they enjoy each other 's company . it 's a matter of survival . schools of fish exhibit complex swarming behaviors that help them evade hungry predators , while a lone fish is quickly singled out as easy prey . so which brilliant fish leader is the one in charge ? actually , no one is , and everyone is . so what does that mean ? while the school of fish is elegantly twisting , turning , and dodging sharks in what looks like deliberate coordination , each individual fish is actually just following two basic rules that have nothing to do with the shark : one , stay close , but not too close to your neighbor , and two , keep swimmming . as individuals , the fish are focused on the minutiae of these local interactions , but if enough fish join the group , something remarkable happens . the movement of individual fish is eclipsed by an entirely new entity : the school , which has its own unique set of behaviors . the school is n't controlled by any single fish . it simply emerges if you have enough fish following the right set of local rules . it 's like an accident that happens over and over again , allowing fish all across the ocean to reliably avoid predation . and it 's not just fish . emergence is a basic property of many complex systems of interacting elements . for example , the specific way in which millions of grains of sand collide and tumble over each other almost always produces the same basic pattern of ripples . and when moisture freezes in the atmosphere , the specific binding properties of water molecules reliably produce radiating lattices that form into beautiful snowflakes . what makes emergence so complex is that you ca n't understand it by simply taking it apart , like the engine of a car . taking things apart is a good first step to understanding a complex system . but if you reduce a school of fish to individuals , it loses the ability to evade predators , and there 's nothing left to study . and if you reduce the brain to individual neurons , you 're left with something that is notoriously unreliable , and nothing like how we think and behave , at least most of the time . regardless , whatever you 're thinking about right now is n't reliant on a single neuron lodged in the corner of your brain . rather , the mind emerges from the collective activities of many , many neurons . there are billions of neurons in the human brain , and trillions of connections between all those neurons . when you turn such a complicated system like that on , it could behave in all sorts of weird ways , but it does n't . the neurons in our brain follow simple rules , just like the fish , so that as a group , their activity self-organizes into reliable patterns that let you do things like recognize faces , successfully repeat the same task over and over again , and keep all those silly little habits that everyone likes about you . so , what are the simple rules when it comes to the brain ? the basic function of each neuron in the brain is to either excite or inhibit other neurons . if you connect a few neurons together into a simple circuit , you can generate rhythmic patterns of activity , feedback loops that ramp up or shut down a signal , coincidence detectors , and disinhibition , where two inhibitory neurons can actually activate another neuron by removing inhibitory brakes . as more and more neurons are connected , increasingly complex patterns of activity emerge from the network . soon , so many neurons are interacting in so many different ways at once that the system becomes chaotic . the trajectory of the network 's activity can not be easily explained by the simple local circuits described earlier . and yet , from this chaos , patterns can emerge , and then emerge again and again in a reproducible manner . at some point , these emergent patterns of activity become sufficiently complex , and curious to begin studying their own biological origins , not to mention emergence . and what we found in emergent phenomena at vastly different scales is that same remarkable characteristic as the fish displayed : that emergence does n't require someone or something to be in charge . if the right rules are in place , and some basic conditions are met , a complex system will fall into the same habits over and over again , turning chaos into order . that 's true in the molecular pandemonium that lets your cells function , the tangled thicket of neurons that produces your thoughts and identity , your network of friends and family , all the way up to the structures and economies of our cities across the planet .

and it 's not just fish . emergence is a basic property of many complex systems of interacting elements . for example , the specific way in which millions of grains of sand collide and tumble over each other almost always produces the same basic pattern of ripples . and when moisture freezes in the atmosphere , the specific binding properties of water molecules reliably produce radiating lattices that form into beautiful snowflakes .

one of the simplest cases of emergence is the formation of sand dunes . what are the individual parts of this system ? what types of interactions do these parts have ? what other factors contribute to how sand dunes will form ?

over 100,000 metric tons of caffeine are consumed around the world every year . that 's equivalent to the weight of 14 eiffel towers . most of this caffeine is consumed in coffee and tea , but it 's also ingested in some sodas , chocolate , caffeine pills , and even beverages labeled decaf . caffeine helps us feel alert , focused , happy , and energetic , even if we have n't had enough sleep . but it can also raise our blood pressure , and make us feel anxious . it 's the world most widely used drug . so how does it keep us awake ? caffeine evolved in plants where it serves a few purposes . in high doses , as it 's found in the leaves and seeds of certain species , it 's toxic to insects . but when they consume it in lower doses , as it 's found in nectar , it can actually help them remember and revisit flowers . in the human body , caffeine acts as a stimulant for the central nervous system . it keeps us awake by blocking one of the body 's key sleep-inducing molecules , a substance called adenosine . your body needs a constant supply of energy , which it gets by breaking down a high-energy molecule called atp . in the process , it liberates adenosine , atp 's chemical backbone . neurons in your brain have receptors perfectly tailored to this molecule . when adenosine docks to these receptors , it activates a cascade of biochemical reactions that cause neurons to fire more sluggishly and slow the release of important brain-signaling molecules . in other words , you get sleepy . caffeine is what 's called an adenosine receptor antagonist . that means it derails this process of slowing your neurons down by blocking adenosine receptors . caffeine and adenosine have a similar molecular structure , close enough that caffeine can wedge into the adenosine receptors , but not close enough to activate them . to summarize , adenosine inhibits your neurons . caffeine inhibits the inhibitor , so it stimulates you . caffeine can also boost positive feelings . in some neurons , the adenosine receptors are linked to receptors for another molecule called dopamine . one of dopamine 's roles in the brain is to promote feelings of pleasure . when adenosine docks in one of these paired receptors , that can make it harder for dopamine to fit in its own spot , interrupting its mood-lifting work . but when caffeine takes adenosine 's place , it does n't have the same effect , and dopamine can slide in . there 's evidence that caffeine 's effects on adenosine and dopamine receptors can have long-term benefits , too , reducing the risk of diseases like parkinson 's , alzheimer 's , and some types of cancer . caffeine can also ramp up the body 's ability to burn fat . in fact , some sports organizations think that caffeine gives athletes an unfair advantage and have placed limits on its consumption . from 1972 until 2004 , olympic athletes had to stay below a certain blood-caffeine concentration to compete . of course , not all of caffeine 's effects are so helpful . it might make you feel better and more alert , but it can also raise your heart rate and blood pressure , cause increased urination or diarrhea , and contribute to insomnia and anxiety . plus , the foods and beverages caffeine is found in have their own impacts on your body that have to be taken into account . your brain can adapt to regular consumption of caffeine . if your adenosine receptors are perpetually clogged , your body will manufacture extra ones . that way , even with caffeine around , adenosine can still do its job of signaling the brain to power down . that 's why you may find you need to consume more and more caffeine to feel as alert . there are more and more adenosine receptors to block . it 's also why if you suddenly quit caffeine , you may experience an unpleasant withdrawal . with plenty of receptors and no competition , adenosine can work overtime , causing symptoms like headaches , tiredness , and depressed moods . but in a few days , the extra adenosine receptors will disappear , your body will readjust , and you 'll feel just as alert as ever , even without an infusion of the world 's most popular stimulant .

to summarize , adenosine inhibits your neurons . caffeine inhibits the inhibitor , so it stimulates you . caffeine can also boost positive feelings . in some neurons , the adenosine receptors are linked to receptors for another molecule called dopamine .

which of the following isn ’ t a caffeine source ?

the five fingers of evolution . a thorough understanding of biology requires a thorough understanding of the process of evolution . most people are familiar with the process of natural selection . however , this is just one of five processes that can result in evolution . before we discuss all five of these processes , we should define evolution . evolution is simply change in the gene pool over time . but what is a gene pool ? and for that matter , what is a gene ? before spending any more time on genetics , let us begin with a story . imagine that a boat capsizes , and 10 survivors swim to shore on a deserted island . they are never rescued , and they form a new population that exists for thousands of years . strangely enough , five of the survivors have red hair . red hair is created when a person inherits two copies of the red gene from their parents . if you only have one copy of the gene , you wo n't have red hair . to make this easier , we will assume that the five non-redheads are not carriers of the gene . the initial frequency of the red-hair gene is therefore 50 percent , or 10 of 20 total genes . these genes are the gene pool . the 20 different genes are like cards in a deck that keep getting reshuffled with each new generation . sex is simply a reshuffling of the genetic deck . the cards are reshuffled and passed to the next generation ; the deck remains the same , 50 percent red . the genes are reshuffled and passed to the next generation ; the gene pool remains the same , 50 percent red . even though the population may grow in size over time , the frequency should stay at about 50 percent . if this frequency ever varies , then evolution has occurred . evolution is simply change in the gene pool over time . think about it in terms of the cards . if the frequency of the cards in the deck ever changes , evolution has occurred . there are five processes that can cause the frequency to change . to remember these processes , we will use the fingers on your hands , starting from the little finger and moving to the thumb . the little finger should remind you that the population can shrink . if the population shrinks , then chance can take over . for example , if only four individuals survive an epidemic , then their genes will represent the new gene pool . the next finger is the ring finger . this finger should remind you of mating , because a ring represents a couple . if individuals choose a mate based on their appearance or location , the frequency may change . if redheaded individuals only mate with redheaded individuals , they could eventually form a new population . if no one ever mates with redheaded individuals , these genes could decrease . the next finger is the middle finger . the m in the middle finger should remind you of the m in the word `` mutation . '' if a new gene is added through mutation , it can affect the frequency . imagine a gene mutation creates a new color of hair . this would obviously change the frequency in the gene pool . the pointer finger should remind you of movement . if new individuals flow into an area , or immigrate , the frequency will change . if individuals flow out of an area , or emigrate , then the frequency will change . in science , we refer to this movement as gene flow . all four of the processes represented by our fingers can cause evolution . small population size , non-random mating , mutations and gene flow . however , none of them lead to adaptation . natural selection is the only process that creates organisms better adapted to their local environment . i use the thumb to remember this process . nature votes thumbs up for adaptations that will do well in their environment , and thumbs down to adaptations that will do poorly . the genes for individuals that are not adapted for their environment will gradually be replaced by those that are better adapted . red hair is an example of one of these adaptations . red hair is an advantage in the northern climates , because the fair skin allowed ancestors to absorb more light and synthesize more vitamin d. thumbs up ! however , this was a disadvantage in the more southern climates , where increased uv radiation led to cancer and decreased fertility . thumbs down ! even the thumb itself is an adaptation formed through the process of natural selection . the evolution that we have described is referred to as microevolution , because it refers to a small change . however , this form of evolution may eventually lead to macroevolution , or speciation . every organism on the planet shares ancestry with a single common ancestor . all living organisms on the planet are connected back in time through the process of evolution . take a look at your own hand . it 's an engineering masterpiece that was created by the five processes i just described , over millions and millions of years . can you recall the five main causes of evolution from memory ? if you ca n't , hit rewind and watch that part again . but if you can , give yourself or your neighbor a big five-fingered high five .

small population size , non-random mating , mutations and gene flow . however , none of them lead to adaptation . natural selection is the only process that creates organisms better adapted to their local environment .

which of the following is the only cause of microevolution that can lead to adaptations ?

translator : andrea mcdonough reviewer : bedirhan cinar normally astronaut training takes about one full year , and it includes such subjects as astronomy , astrophysics , flight physiology , orbital trajectories , or orbital management . another part of the astronaut basic training is survival training . in the days of gemini , you never knew for sure where a spacecraft might land if there was an emergency , deorbit . so , we had to take desert training , water training , and jungle survival training . so , we had to learn how to cook and eat snake and all other , such other good things as that , and how to make water in a desert . after that year and a half of astronaut basic training , our names were all put on a list and that list was quite a bit longer at that time then there were seats available . and so , we were all given other duties to keep us occupied and to help continue our training . five of us were assigned to the lunar module , and our job was to be with these lunar modules as they were being built . so , we spent a lot of time there . i must admit that probably i had more time sleeping on the floor of lunar module # 6 than the crew who flew it on the moon . well , my next job was to be on the support crew of apollo 8 , and apollo 8 was the spacecraft that flew to the moon and came back but did not land . when they went behind the moon , they were supposed to do a thrusting maneuver to slow them down so they would be captured into lunar orbit . so we just had to sit and cool our heels when they went behind the moon , and we knew if they came out a little early on the other side , that they had not burned enough , not slowed down enough , and were going to skip out into space , they would n't be captured in orbit . if they came out a little bit late , it meant they had over-done it , and they were n't going to be in orbit , but were going to begin a spiral down to the lunar surface . and , of course , without a lunar module , that kind of ruins your whole day . you can imagine how relieved we were at the instant that they were supposed to appear on the other side of the moon that they appeared ! my next assignment was again a support crew assignment on apollo 12 , and apollo 12 was struck by lightning on its way off the pad . a nearby thunderstorm , there was a lightning bolt that went over and hit the very tip of the spacecraft . the charge went down through the spacecraft , through the booster , down the exhaust gases , and grounded out on the launching pad . it killed the electrical power system and the computers all died . you can imagine what it must have been like for them inside because suddenly the lights all went out and then they came back on when the batteries picked up the load . and , every single warning light and caution light in the spacecraft was on and flashing , and all the necessary bells , whistles , and buzzards and things that are in there , all were going off at the same time . the crew was totally confused as to what was going on . when we were settled in orbit , we tested all the various systems and everything looked good . so , that , now i figured this is it , and sure enough , i did get an assignment , a flight assignment . i was assigned to the back-up crew of apollo 16 , which meant that i was to be on the param crew of apollo 19 . and , several weeks into the training , nasa made the surprise announcment that they were going to cancel apollos 18 , 19 , and 20 . we were in the middle of the vietnam war , the budget was in bad shape , so you can imagine there were three very , very sad hangdog guys moping around the office because we lost our flight to the moon . but , several weeks later , i got a call from tom stafford , the senior astronaut at that time , and he wanted me in his office , and i went in , and he told me that he was sorry that i had missed my opportunity for the moon , but he said , `` i 've got another assignment for you . '' he said , `` i want you to be the commander of the third and final skylab mission . '' and , he said , `` do you think you could do the job ? '' and i said , `` of course , yes ! '' and , i 'll have to admit , a certain lump in my chest and in my stomach , because i was a rookie , and they normally do n't assign a rookie to be a commander , usually you have to have at least one flight under your belt , but they assigned me to that , which was really kind of a shock because the last rookie commander was neil armstrong on gemini 8 .

i must admit that probably i had more time sleeping on the floor of lunar module # 6 than the crew who flew it on the moon . well , my next job was to be on the support crew of apollo 8 , and apollo 8 was the spacecraft that flew to the moon and came back but did not land . when they went behind the moon , they were supposed to do a thrusting maneuver to slow them down so they would be captured into lunar orbit .

apollo 8 flew to ________ , but it ________ .

space : it 's where things happen . time : it 's when things happen . we can measure where things are and when things take place , but in modern physics , we realize when and where are actually part of the same question . because when it comes to understanding the universe , we need to replace three-dimensional space plus time with a single concept : four-dimensional space-time . we 'll explore and explain space-time in this series of animations . animations ? yeah . well , we 're not very animated are we ? sure we are ! look , i can go from here to here . whoa ! how 'd you get from here to there ? how fast did you go ? did you run ? walk ? did you even go in a straight line ? ah ! to answer that , you 'll need to make our cartoon physics look more like physics physics . you 'll need more panels . more panels , please ! okay , in each panel , andrew 's in a slightly different place . so i can see each one records where andrew is at a different time . that 's great . but it would be easier to see what 's going on if we could cut out all the hundreds of panels and stack them up like a flip book . right , now let 's flip through the book so that we can see one panel after another getting through 24 in every second . see ! i told you it was an animation . now you can see me walking along . drawing all those panels and putting them into a flip book is just one way of recording the way i 'm moving . it 's how animation , or even movies , work . as it turns out , at my walking speed , it takes two seconds to get past each fence post , and they 're spaced four meters apart . so we can calculate my velocity -- how fast i 'm moving through space - - is two meters per second . but i could 've worked that out from the panels without flipping through them . from the edge of the flip book , you can see all of the copies of the fence posts and all of the copies of andrew and he 's in a slightly different place in each one . now we can predict everything that will happen to andrew when we flip through 24 pages every second , including his speed of motion , just by looking . no need to flip through at all . the edge of this flip book is known as a space-time diagram of andrew 's journey through , you guessed it , space and time . we call the line that represents andrew 's journey his world line . if i jog instead of walking , i might be able to get past a fence post every second . he 's not very athletic . anyway , when we look at this new flip book from the edge , we can do the same analysis as before . the world line for andrew jogging is more tilted over than the world line for andrew walking . we can tell he 's going twice as fast as before without flipping the panels . but here 's the clever bit . in physics , it 's always good to view things from other perspectives . after all , the laws of physics should be the same for everyone or no one will obey them . so let 's rethink our cartoon and have the camera follow andrew jogging along as the fence posts approach and pass behind him . still viewing it as a flip book of panels , we do n't need to redraw anything . we simply move all of the cutout frames slightly until andrew 's tilted world line becomes completely vertical . to see why , let 's flip it . yes , now i 'm stationery , just jogging on the spot , in the center of the panel . on the edge of the flip book , my world line was going straight upwards . the fence posts are coming past me . it 's now their world lines that are tilted . this rearrangement of the panels is known as a galilean transformation , and it lets us analyze physics from someeone else 's perspective . in this case , mine . after all , it 's always good to see things from other points of view , especially when the viewers are moving at different speeds . so long as the speeds are n't too high . if you 're a cosmic ray moving at the speed of light , our flip book of your point of view falls apart . to stop that from happening , we 'll have to glue panels together . instead of a stack of separate panels , we 'll need a solid block of space-time , which we 'll come to in the next animation .

as it turns out , at my walking speed , it takes two seconds to get past each fence post , and they 're spaced four meters apart . so we can calculate my velocity -- how fast i 'm moving through space - - is two meters per second . but i could 've worked that out from the panels without flipping through them .

when drawn a spacetime diagram , something that is not moving looks like

sometimes when a fish is reeled up to the surface it will appear inflated , with its eyes bulging out of their sockets and its stomach projecting out of its mouth , as if its been blown up like a balloon . this type of bodily damage , caused by rapid changes in pressure , is called barotrauma . under the sea , pressure increases by 14.7 pounds per square inch for every 33 foot increase in depth . so , take the yelloweye rockfish , which can live as deep as 1800 feet , where there 's over 800 pounds of pressure on every square inch . that 's equivalent to the weight of a polar bear balancing on a quarter . now , boyle 's gas law states that the volume of a gas is inversely related to pressure . so , any air-filled spaces , like a rockfish 's swim bladder , or human lungs , will compress as they descend deeper and expand as they ascend . after a fish bites a fisherman 's hook and is quickly reeled up to the surface , the air in its swim bladder begins to expand . its rapid expansion actually forces the fish 's stomach out of its mouth , while the increased internal pressure pushes its eyes out of their sockets , a condition called exophthalmia . sometimes rockfish eyes will even have a crystallized appearance from corneal emphysemas , little gas bubbles that build up inside the cornea . thankfully , a scuba diver does n't have a closed swim bladder to worry about . a diver can regulate pressure in her lungs by breathing out as she ascends , but must be wary of other laws of physics that are at play under the sea . henry 's law states that the amount of a gas that dissolves in a liquid is proportional to its partial pressure . the air a diver breathes is 78 % nitrogen . at a higher pressure under the sea , the nitrogen from the air in a scuba tank diffuses into a diver 's tissues in greater concentrations than it would on land . if the diver ascends too quickly , this built up nitrogen can come out of solution and form microbubbles in her tissues , blood and joints , causing decompression sickness , aka the bends . this is similar to the fizz of carbon dioxide coming out of your soda . gas comes out of solution when the pressure 's released . but for a diver , the bubbles cause severe pain and sometimes even death . divers avoid falling victim to the bends by rising slowly and taking breaks along the way , called decompression stops , so the gas has time to diffuse back out of their tissues and to be released through their breath . just as a diver needs decompression , for a fish to recover , it needs recompression , which can be accomplished by putting it back in the sea . but that does n't mean that fish should just be tossed overboard . an inflated body will float and get scooped up by a hungry sea lion or pecked at by seagulls . there 's a common myth that piercing its stomach with a needle will let air escape , allowing the fish to swim back down on its own . but that is one balloon that should n't be popped . to return a fish properly to its habitat , fisherman can use a descending device instead to lower it on a fishing line and release it at the right depth . as it heads home and recompression reduces gas volume , its eyes can return to their sockets and heal , and its stomach can move back into place . this fish will live to see another day , once more free to swim , eat , reproduce and replenish the population .

so , any air-filled spaces , like a rockfish 's swim bladder , or human lungs , will compress as they descend deeper and expand as they ascend . after a fish bites a fisherman 's hook and is quickly reeled up to the surface , the air in its swim bladder begins to expand . its rapid expansion actually forces the fish 's stomach out of its mouth , while the increased internal pressure pushes its eyes out of their sockets , a condition called exophthalmia .

describe what happens to the rockfish ’ s body when it is quickly reeled to the surface .

what do these animals have in common ? more than you might think . along with over 5,000 other species , they 're mammals , or members of class mammalia . all mammals are vertebrates , meaning they have backbones . but mammals are distinguished from other vertebrates by a number of shared features . that includes warm blood , body hair or fur , the ability to breathe using lungs , and nourishing their young with milk . but despite these similarities , these creatures also have many biological differences , and one of the most remarkable is how they give birth . let 's start with the most familiar , placental mammals . this group includes humans , cats , dogs , giraffes , and even the blue whale , the biggest animal on earth . its placenta , a solid disk of blood-rich tissue , attaches to the wall of the uterus to support the developing embryo . the placenta is what keeps the calf alive during pregnancy . directly connected to the mother 's blood supply , it funnels nutrients and oxygen straight into the calf 's body via the umbilical cord , and also exports its waste . placental mammals can spend far longer inside the womb than other mammals . baby blue whales , for instance , spend almost a full year inside their mother . the placenta keeps the calf alive right up until its birth , when the umbilical cord breaks and the newborn 's own respiratory , circulatory , and waste disposal systems take over . measuring about 23 feet , a newborn calf is already able to swim . it will spend the next six months drinking 225 liters of its mothers thick , fatty milk per day . meanwhile , in australia , you can find a second type of mammal - marsupials . marsupial babies are so tiny and delicate when they 're born that they must continue developing in the mother 's pouch . take the quoll , one of the world 's smallest marsupials , which weighs only 18 milligrams at birth , the equivalent of about 30 sugar grains . the kangaroo , another marsupial , gives birth to a single jelly bean-sized baby at a time . the baby crawls down the middle of the mother 's three vaginas , then must climb up to the pouch , where she spends the next 6-11 months suckling . even after the baby kangaroo leaves this warm haven , she 'll return to suckle milk . sometimes , she 's just one of three babies her mother is caring for . a female kangaroo can often simultaneously support one inside her uterus and another in her pouch . in unfavorable conditions , female kangaroos can pause their pregnancies . when that happens , she 's able to produce two different kinds of milk , one for her newborn , and one for her older joey . the word mammalia means of the breast , which is a bit of a misnomer because while kangaroos do produce milk from nipples in their pouches , they do n't actually have breasts . nor do monotremes , the third and arguably strangest example of mammalian birth . there were once hundreds of monotreme species , but there are only five left : four species of echidnas and the duck-billed platypus . the name monotreme means one hole referring to the single orifice they use for reproduction , excretion , and egg-laying . like birds , reptiles , fish , dinosaurs , and others , these species lay eggs instead of giving birth to live young . their eggs are soft-shelled , and when their babies hatch , they suckle milk from pores on their mother 's body until they 're large enough to feed themselves . despite laying eggs and other adaptations that we associate more with non-mammals , like the duck-bill platypus 's webbed feet , bill , and the venomous spur males have on their feet , they are , in fact , mammals . that 's because they share the defining characteristics of mammalia and are evolutionarily linked to the rest of the class . whether placental , marsupial , or monotreme , each of these creatures and its unique birthing methods , however bizarre , have succeeded for many millennia in bringing new life and diversity into the mammal kingdom .

directly connected to the mother 's blood supply , it funnels nutrients and oxygen straight into the calf 's body via the umbilical cord , and also exports its waste . placental mammals can spend far longer inside the womb than other mammals . baby blue whales , for instance , spend almost a full year inside their mother .

compare and contrast placental mammals and monotremes . what do they have in common ? how do they differ ?

muscles . we have over 600 of them . they make up between 1/3 and 1/2 of our body weight , and along with connective tissue , they bind us together , hold us up , and help us move . and whether or not body building is your hobby , muscles need your constant attention because the way you treat them on a daily basis determines whether they will wither or grow . say you 're standing in front of a door , ready to pull it open . your brain and muscles are perfectly poised to help you achieve this goal . first , your brain sends a signal to motor neurons inside your arm . when they receive this message , they fire , causing muscles to contract and relax , which pull on the bones in your arm and generate the needed movement . the bigger the challenge becomes , the bigger the brain 's signal grows , and the more motor units it rallies to help you achieve your task . but what if the door is made of solid iron ? at this point , your arm muscles alone wo n't be able to generate enough tension to pull it open , so your brain appeals to other muscles for help . you plant your feet , tighten your belly , and tense your back , generating enough force to yank it open . your nervous system has just leveraged the resources you already have , other muscles , to meet the demand . while all this is happening , your muscle fibers undergo another kind of cellular change . as you expose them to stress , they experience microscopic damage , which , in this context , is a good thing . in response , the injured cells release inflammatory molecules called cytokines that activate the immune system to repair the injury . this is when the muscle-building magic happens . the greater the damage to the muscle tissue , the more your body will need to repair itself . the resulting cycle of damage and repair eventually makes muscles bigger and stronger as they adapt to progressively greater demands . since our bodies have already adapted to most everyday activities , those generally do n't produce enough stress to stimulate new muscle growth . so , to build new muscle , a process called hypertrophy , our cells need to be exposed to higher workloads than they are used to . in fact , if you do n't continuously expose your muscles to some resistance , they will shrink , a process known as muscular atrophy . in contrast , exposing the muscle to a high-degree of tension , especially while the muscle is lengthening , also called an eccentric contraction , generates effective conditions for new growth . however , muscles rely on more than just activity to grow . without proper nutrition , hormones , and rest , your body would never be able to repair damaged muscle fibers . protein in our diet preserves muscle mass by providing the building blocks for new tissue in the form of amino acids . adequate protein intake , along with naturally occurring hormones , like insulin-like growth factor and testosterone , help shift the body into a state where tissue is repaired and grown . this vital repair process mainly occurs when we 're resting , especially at night while sleeping . gender and age affect this repair mechanism , which is why young men with more testosterone have a leg up in the muscle building game . genetic factors also play a role in one 's ability to grow muscle . some people have more robust immune reactions to muscle damage , and are better able to repair and replace damaged muscle fibers , increasing their muscle-building potential . the body responds to the demands you place on it . if you tear your muscles up , eat right , rest and repeat , you 'll create the conditions to make your muscles as big and strong as possible . it is with muscles as it is with life : meaningful growth requires challenge and stress .

gender and age affect this repair mechanism , which is why young men with more testosterone have a leg up in the muscle building game . genetic factors also play a role in one 's ability to grow muscle . some people have more robust immune reactions to muscle damage , and are better able to repair and replace damaged muscle fibers , increasing their muscle-building potential . the body responds to the demands you place on it .

the most commonly accepted theory of muscle growth states that _____ within a muscle activate a ( n ) ______ process that causes dormant stem cells to build and regenerate muscle tissue

when you hear the word art , what comes to mind ? a painting , like the mona lisa , or a famous sculpture or a building ? what about a vase or a quilt or a violin ? are those things art , too , or are they craft ? and what 's the difference anyway ? it turns out that the answer is not so simple . a spoon or a saddle may be finely wrought , while a monument may be , well , uninspired . just as not every musical instrument is utilitarian , not every painting or statue is made for its own sake . but if it 's so tricky to separate art from craft , then why do we distinguish objects in this way ? you could say it 's the result of a dramatic historical turn of events . it might seem obvious to us today to view people , such as da vinci or michelangelo , as legendary artists , and , of course , they possessed extraordinary talents , but they also happened to live in the right place at the right time , because shortly before their lifetimes the concept of artists hardly existed . if you had chanced to step into a medieval european workshop , you would have witnessed a similar scene , no matter whether the place belonged to a stonemason , a goldsmith , a hatmaker , or a fresco painter . the master , following a strict set of guild statutes , insured that apprentices and journeymen worked their way up the ranks over many years of practice and well-defined stages of accomplishment , passing established traditions to the next generation . patrons regarded these makers collectively rather than individually , and their works from murano glass goblets , to flemish lace , were valued as symbols of social status , not only for their beauty , but their adherence to a particular tradition . and the customer who commissioned and paid for the work , whether it was a fine chair , a stone sculpture , a gold necklace , or an entire building , was more likely to get credit than those who designed or constructed it . it was n't until around 1400 that people began to draw a line between art and craft . in florence , italy , a new cultural ideal that would later be called renaissance humanism was beginning to take form . florentine intellectuals began to spread the idea of reformulating classical greek and roman works , while placing greater value on individual creativity than collective production . a few brave painters , who for many centuries , had been paid by the square foot , successfully petitioned their patrons to pay them on the basis of merit instead . within a single generation , people 's attitudes about objects and their makers would shift dramatically , such that in 1550 , giorgio vasari , not incidentally a friend of michelangelo , published an influential book called , `` lives of the most excellent painters , sculptors and architects , '' elevating these types of creators to rock star status by sharing juicy biographical details . in the mind of the public , painting , sculpture and architecture were now considered art , and their makers creative masterminds : artists . meanwhile , those who maintained guild traditions and faithfully produced candelsticks , ceramic vessels , gold jewelery or wrought iron gates , would be known communally as artisans , and their works considered minor or decorative arts , connoting an inferior status and solidifying the distinction between art and craft that still persists in the western world . so , if we consider a painting by rembrandt or picasso art , then where does that leave an african mask ? a chinese porclein vase ? a navajo rug ? it turns out that in the history of art , the value placed on innovation is the exception rather than the rule . in many cultures of the world , the distinction between art and craft has never existed . in fact , some works that might be considered craft , a peruvian rug , a ming dynasty vase , a totem pole , are considered the cultures ' preeminent visual forms . when art historians of the 19th century saw that the art of some non-western cultures did not change for thousands of years , they classified the works as primitive , suggesting that their makers were incapable of innovating and therefore were not really artists . what they did n't realize was that these makers were not seeking to innovate at all . the value of their works lay precisely in preserving visual traditions , rather than in changing them . in the last few decades , works such as quilts , ceramics and wood carvings have become more prominently included in art history textbooks and displayed in museums alongside paintings and sculpture . so maybe it 's time to dispense with vague terms like art and craft in favor of a word like visual arts that encompasses a wider array of aesthetic production . after all , if our appreciation of objects and their makers is so conditioned by our culture and history , then art and its definition are truly in the eye of the beholder .

it turns out that in the history of art , the value placed on innovation is the exception rather than the rule . in many cultures of the world , the distinction between art and craft has never existed . in fact , some works that might be considered craft , a peruvian rug , a ming dynasty vase , a totem pole , are considered the cultures ' preeminent visual forms .

in the western world today , what are our expectations about the function of “ art ” and the role of “ artists ? ” is it the same as in other cultures ? how and why might it be different ?

has anyone ever told you , `` stand up straight ! '' or scolded you for slouching at a family dinner ? comments like that might be annoying , but they 're not wrong . your posture , the way you hold your body when you 're sitting or standing , is the foundation for every movement your body makes , and can determine how well your body adapts to the stresses on it . these stresses can be things like carrying weight , or sitting in an awkward position . and the big one we all experience all day every day : gravity . if your posture is n't optimal , your muscles have to work harder to keep you upright and balanced . some muscles will become tight and inflexbile . others will be inhibited . over time , these dysfunctional adaptations impair your body 's ability to deal with the forces on it . poor posture inflicts extra wear and tear on your joints and ligaments , increases the likelihood of accidents , and makes some organs , like your lungs , less efficient . researchers have linked poor posture to scoliosis , tension headaches , and back pain , though it is n't the exclusive cause of any of them . posture can even influence your emotional state and your sensitivity to pain . so there are a lot of reasons to aim for good posture . but it 's getting harder these days . sitting in an awkward position for a long time can promote poor posture , and so can using computers or mobile devices , which encourage you to look downward . many studies suggest that , on average , posture is getting worse . so what does good posture look like ? when you look at the spine from the front or the back , all 33 vertebrae should appear stacked in a straight line . from the side , the spine should have three curves : one at your neck , one at your shoulders , and one at the small of your back . you are n't born with this s-shaped spine . babies ' spines just have one curve like a `` c. '' the other curves usually develop by 12-18 months as the muscles strengthen . these curves help us stay upright and absorb some of the stress from activities like walking and jumping . if they are aligned properly , when you 're standing up , you should be able to draw a straight line from a point just in front of your shoulders , to behind your hip , to the front of your knee , to a few inches in front of your ankle . this keeps your center of gravity directly over your base of support , which allows you to move efficiently with the least amount of fatigue and muscle strain . if you 're sitting , your neck should be vertical , not tilted forward . your shoulders should be relaxed with your arms close to your trunk . your knees should be at a right angle with your feet flat on the floor . but what if your posture is n't that great ? try redesigning your environment . adjust your screen so it 's at or slightly below eyelevel . make sure all parts of your body , like your elbows and wrists , are supported , using ergonomic aids if you need to . try sleeping on your side with your neck supported and with a pillow between your legs . wear shoes with low heels and good arch support , and use a headset for phone calls . it 's also not enough to just have good posture . keeping your muscles and joints moving is extremely important . in fact , being stationary for long periods with good posture can be worse than regular movement with bad posture . when you do move , move smartly . keep anything you 're carrying close to your body . backpacks should be in contact with your back carried symetrically . if you sit a lot , get up and move around on occassion , and be sure to exercise . using your muscles will keep them strong enough to support you effectively , on top of all the other benefits to your joints , bones , brain and heart . and if you 're really worried , check with a physical therapist , because yes , you really should stand up straight .

has anyone ever told you , `` stand up straight ! '' or scolded you for slouching at a family dinner ?

which of the following is the besto ption for musculoskeletal health ?

we 're here on a runway because for some reason brady has printed out the first 1,000,000 digits of pi on a continuous mile long piece of paper which we are going to very carefully unravel today and go for a tour of a million digits of pi . so here 's 3.14159 which - for a fun fact - that 's as far as i 've memorised and then it carries on and you 've marked every 10 digits so there 's 100,000 marker points so we wo n't get lost , we 'll always know where we are in pi . where 's the feynman point ? is that seven hundred and something ? this the feynman point , six 9s , 999999 , so that wo n't be beaten ... there is a string of seven 3s , but that takes another 710,000 digits , so we 'll be nearly three quarters of the way down the mile of pi before we find a longer string of the same digit . and the first one is in the first two metres . absolutely incredible ! brady : do you want these ? for that . hugh : bring the staple gun back . we 've just hit 123 yards so we 're long past the familiar bits of pi . so the whole 3.14159 , that is a long time ago . you 'd think anyone who has memorised pi , we 're now in unfamiliar territory , apart from one guy . what is the world record for memorising pi , so someone recited over 125 yards of pi , someone memorised all the way to here and could n't be bothered to remember the next zero . brady : not even a third . there is a run here of seven ascending digits , there it goes , 0456789 , that is the first run of seven-digits that go up . obviously we 're missing 1 , 2 and 3 , it would have been nicer with them , but nowhere in the first million digits do you get 0 to 9 in order . hugh : that 's nearly three hours . brady : i found some heavy bases for cones , i 've got them in the back ... we 're half a mile from the start , and the trolley team , are they on the horizon ? okay , pi has just got a horizon . okay , see that 4 there , it appears every now and then , square number , kind of fun , but then from here you go , wait there 's no fours ... no four , no four , in fact there 's no fours until there , look at that , 157 digits and there are no fours for that entire run . they 've just vanished . and that is the longest run we will have in the first million digits that has one digit completely missing . with a million decimal places of pi each digit should appear approximately 100,000 time each , that makes sense , but of course it 's not exactly even , some of them do n't even make it . there are not 100,000 zeroes , zero does n't make it . 1 does n't make it . 6,7,8 all do n't make it . the champion though , is 5 . there it is , that there is the 100,000th 5 . okay we 're four hours into this and we are nearly at a million digits . so they 've been coming out a rate of a quarter of a million digits and hour , which is approximately 4,167 digits a minute , and we 're almost there . so you guys have done the hard work , do you want to wind off the last of it . and a million digits is there ! there ! alright so that is , it 's one , in case you are wondering . so there you go , we have just , i mean i think a token round of applause . applause so that is absolutely fantastic , and now the very quick process of rolling it all back up again before an aeroplane lands . brady : believe it or not we printed all million digits of pi using about eight millilitres of ink . there , that 's what 8ml looks like . that 's because of hp 's clever thermal inkjet technology combined with some very clever people here at hsa systems in denmark . to see the whole story of how and why we made this film , check out the links on the screen and below in the video description . it also includes extra footage from our day out on the runway and more curious stuff about pi itself .

applause so that is absolutely fantastic , and now the very quick process of rolling it all back up again before an aeroplane lands . brady : believe it or not we printed all million digits of pi using about eight millilitres of ink . there , that 's what 8ml looks like .

the amount of ink used in this video is just 8.16 millilitres and the paper roll weighs 20kg . if the team wants to wrap a new piece of pi around the earth 's equator ( 40,075km ) , how many digits will they now require ( assuming the printed numbers stay the same size ) ? how many gallons of ink will be needed ? and what will the new paper roll weigh ?

bees are very busy little matchmakers . wingmen in every sense of the word . you see , the bees ' side of the whole `` birds and the bees '' business is to help plants find mates and reproduce . in their work as pollinators , honeybees are integral to the production of nearly 1/3 of the food that we eat . and these bees , dutifully helping lonely plants have sex , are n't alone . but rather are part of a very complex network of matchmaking creatures , critical for the pollination of natural ecosystems and crops . plants in many natural ecosystems need help to have sex . like many of us , they 're too busy to find a relationship . they have too much photosynthesis to do , and they ca n't find the time to evolve feet and walk to a singles bar . those places are called meat markets for a reason , because plants ca n't walk . so they need matchmaker pollinators to transport their pollen grains to flowers of the same plant species , and they pay these pollinators with food . today , around 170,000 plant species receive pollination services from more than 200,000 pollinator species . pollinators include many species of bees , butterflies , moths , flies , wasps , beetles , even birds and bats , who together help pollinate many species of trees , shrubs and other flowering plants . in return , flowering plants are an abundant and diverse food source for pollinators . for instance , fossil records suggest bees may have evolved from wasps that gave up hunting after they acquired a taste for nectar . plant pollinator networks are everywhere . ecologists record these networks in the field by observing which pollinators visit which plants , or by analyzing the identity of pollen loads on their bodies . networks , registered in these ways , contain from 20 to 800 species . these networks show a repeated structure , or architecture . pollinators interact with plants in a very heterogenous way . most plants are specialists , they have only one or a few matchmakers . meanwhile , only a few generalist plants hire a diverse team of matchmakers , getting visits from almost all the pollinators of the network . the same occurs with pollinators . most are specialists that feed on only a few plant species , while a few pollinators , including the honeybee usually , are generalists , busily feeding from and matchmaking for almost all the plant species in that ecosystem . what 's interesting is that specialists and generalists across both plants and pollinators , sort themselves out in a particular pattern . most pollinator networks , for which we have data , are nested . in a nested network , specialists tend to interact more with generalists than with other specialists . this is because if you 're a specialist plant , and your only matchmaker also specializes on you as its only food source , you 're each more vulnerable to extinction . so , you 're better off specializing on a generalist pollinator that has other sources of food to ensure its persistence in bad years . the same goes if you 're a specialist pollinator . you 're better off in the long run specializing on a generalist plant that gets pollinated by other species in times when you 're not around to help . finally , in addition to nestedness , the networks are usually modular . this means that the species in a network are compartmentalized into modules of plants and animals that interact more with each other than with species in other modules . think of them like social cliques . a plant or pollinator dying off will effect the species in its module , but those effects will be less severe on the rest of the network . why 's all that important ? because plant pollinator network structure effects the stability of ecosystems . heterogeneous distribution , nestedness and modularity enable networks to better prevent and respond to extinctions . that 's critical because nature is never static . some species may not show up every year . plants flower at different times . pollinators mature on varying schedules . generalist pollinators have to adapt their preferences depending on who 's flowering when . so from one flowering season to the next , the participants and patterns of matchmaking can drastically change . with all those variables , you can understand the importance of generalist pollinators , like bees , to the stability of not only a crop harvest , but the entire network of plants and pollinators we see in nature , and rely on for life . next time you see a bee fly by , remember that it belongs to a complex network of matchmakers critical to the love lives of plants all around you .

bees are very busy little matchmakers . wingmen in every sense of the word .

how much of our food production depends on bees ?

it 's a good day to be a pirate . amaro and his four mateys , bart , charlotte , daniel , and eliza have struck gold : a chest with 100 coins . but now , they must divvy up the booty according to the pirate code . as captain , amaro gets to propose how to distribute the coins . then , each pirate , including amaro himself , gets to vote either yarr or nay . if the vote passes , or if there 's a tie , the coins are divided according to plan . but if the majority votes nay , amaro must walk the plank and bart becomes captain . then , bart gets to propose a new distribution and all remaining pirates vote again . if his plan is rejected , he walks the plank , too , and charlotte takes his place . this process repeats , with the captain 's hat moving to daniel and then eliza until either a proposal is accepted or there 's only one pirate left . naturally , each pirate wants to stay alive while getting as much gold as possible . but being pirates , none of them trust each other , so they ca n't collaborate in advance . and being blood-thirsty pirates , if anyone thinks they 'll end up with the same amount of gold either way , they 'll vote to make the captain walk the plank just for fun . finally , each pirate is excellent at logical deduction and knows that the others are , too . what distribution should amaro propose to make sure he lives ? pause here if you want to figure it out for yourself ! answer in : 3 answer in : 2 answer in : 1 if we follow our intuition , it seems like amaro should try to bribe the other pirates with most of the gold to increase the chances of his plan being accepted . but it turns out he can do much better than that . why ? like we said , the pirates all know each other to be top-notch logicians . so when each votes , they wo n't just be thinking about the current proposal , but about all possible outcomes down the line . and because the rank order is known in advance , each can accurately predict how the others would vote in any situation and adjust their own votes accordingly . because eliza 's last , she has the most outcomes to consider , so let 's start by following her thought process . she 'd reason this out by working backwards from the last possible scenario with only her and daniel remaining . daniel would obviously propose to keep all the gold and eliza 's one vote would not be enough to override him , so eliza wants to avoid this situation at all costs . now we move to the previous decision point with three pirates left and charlotte making the proposal . everyone knows that if she 's outvoted , the decision moves to daniel , who will then get all the gold while eliza gets nothing . so to secure eliza 's vote , charlotte only needs to offer her slightly more than nothing , one coin . since this ensures her support , charlotte does n't need to offer daniel anything at all . what if there are four pirates ? as captain , bart would still only need one other vote for his plan to pass . he knows that daniel would n't want the decision to pass to charlotte , so he would offer daniel one coin for his support with nothing for charlotte or eliza . now we 're back at the initial vote with all five pirates standing . having considered all the other scenarios , amaro knows that if he goes overboard , the decision comes down to bart , which would be bad news for charlotte and eliza . so he offers them one coin each , keeping 98 for himself . bart and daniel vote nay , but charlotte and eliza grudgingly vote yarr knowing that the alternative would be worse for them . the pirate game involves some interesting concepts from game theory . one is the concept of common knowledge where each person is aware of what the others know and uses this to predict their reasoning . and the final distribution is an example of a nash equilibrium where each player knows every other players ' strategy and chooses theirs accordingly . even though it may lead to a worse outcome for everyone than cooperating would , no individual player can benefit by changing their strategy . so it looks like amaro gets to keep most of the gold , and the other pirates might need to find better ways to use those impressive logic skills , like revising this absurd pirate code .

bart and daniel vote nay , but charlotte and eliza grudgingly vote yarr knowing that the alternative would be worse for them . the pirate game involves some interesting concepts from game theory . one is the concept of common knowledge where each person is aware of what the others know and uses this to predict their reasoning .

which of the following game theory concepts is not involved in the puzzle ?

translator : andrea mcdonough reviewer : jessica ruby so two guys walk into a bar . really ? no , seriously . two guys walk into a bar , an ice cream bar : dave , a physicist working on the large hadron collider at cern , the european laboratory for particle physics , and steve , a blues singer . `` dave , how 's it going ? '' `` steve , good to see you ! '' `` two scoops of chocolate almond for me . '' `` vanilla shake . '' `` hey , i just saw something about the lhc on tv . you guys found bozo in your detector ? '' `` well , not exactly . we found a boson , probably the higgs boson . '' `` what 's that ? '' `` it 's a particle . '' `` do n't you find particles all the time ? '' `` yes , but this one means that the higgs field might really exist . '' `` field ? what field ? '' `` the higgs field . it 's named after peter higgs , although many others contributed to the idea . it is n't a field , like where you grow corn , but a hypothetical , invisible kind of force field that pervades the whole universe . '' `` hmmmm , okay . if it pervades the whole universe , how come i 've never seen it ? that 's a bit strange . '' `` well , actually , it 's not that strange . think of the air around us . we ca n't see it or smell it . well , perhaps in some places we can . but we can detect its presence with sophisticated equipment , like our own bodies . so the fact that we ca n't see something just makes it a bit harder to determine whether its really there or not . '' `` alright , go on . '' `` so , we believe this higgs field is all around us , everywhere in the universe . and what it does is rather special - it gives mass to elementary particles . '' `` what 's an elementary particle ? '' `` an elementary particle is what we call particles that have no structure , they ca n't be divided , they 're the basic building blocks of the universe . '' `` i thought those were atoms . '' `` well , atoms are actually made of smaller components , protons , neutrons , and electrons . while electrons are fundamental particles , neutrons and protons are not . they are made up of other fundamental particles called quarks . '' `` sounds like russian dolls . does it ever end ? '' `` actually , we do n't really know . but our current understanding is called the standard model . in it , there are two types of fundamental particles : the fermions , that make up matter , and the bosons , that carry forces . we often order these particles according to their properties , such as mass . we can measure the masses of the particles , but we never really knew where this mass came from or why they have the masses they do . '' `` so how does this higgs field thing explain mass ? '' `` well , when a particle passes through the higgs field , it interacts and gets mass . the more it interacts , the more mass it has . '' `` ok , i kind of get that , but is it really that important ? i mean , what if there were no higgs field ? '' `` if there were no higgs field , the world would n't exist at all . there would be no stars , no planets , no air , no anything , not even that spoon or the ice cream you 're eating . '' `` oh , that would be bad . okay , but where does this higgs boson fit into things ? '' `` alright , now , you see the cherry in my shake ? '' `` can i have it ? '' `` no , not yet . we have to use it as an analogy first . '' `` oh , right , the cherry 's the higgs boson . '' `` no , not quite . the cherry is a particle moving through the higgs field , the shake . the shake gives the cherry its mass . '' `` i get it . okay , so the molecules of the shake are the higgs bosons ! '' `` well , you 're getting closer . it takes an excitation of the higgs field to produce the higgs boson . so , for example , if i were to add energy by , say , dropping this cherry in the shake , '' `` ah , then the drops that spill on the bar are the higgs bosons . '' `` almost ! the splash itself is the higgs boson . '' `` are you serious ? '' `` well , that 's what quantum mechanics teaches us . in fact , all particles are excitations of fields . '' `` okay , right . well , i kind of see why you like particle physics , it 's quite cool , strange , but cool . '' `` yeah , you could call it a bit strange , it 's not like everyday life . the higgs boson is an excitation of the higgs field . by finding the higgs boson , we know that the higgs field exists . '' `` right . so now you found it , we know this higgs field exists . you must be done . is there anything left of particle physics ? '' `` actually , we 've just begun . it 's a bit like , you know , when columbus thought he had found a new route to india . he 'd , indeed , found something new , but not quite what he was expecting . so , first , we need to make sure that the boson we found is actually the higgs boson . it seems to fit , but we need to measure its properties to be sure . '' `` how 'd you do that ? '' `` take a lot more data . this new boson lives for only a very short time before it breaks down or decays into lighter , more stable particles . by measuring these particles , you learn about the properties of the boson . '' `` and what exactly are you looking for ? '' `` well , the standard model predicts how often and in what ways the higgs boson would decay to the various , lighter particles . so we want to see if the particle we have found is the one predicted by the standard model or if it fits into other possible theoretical models . '' `` and if it fits a different model ? '' `` that would be even more exciting ! in fact , that 's how science advances . we replace old models with new ones if they better explain our observations . '' `` right , so it seems like finding this higgs boson gives a direction for exploration , a bit like that columbus guy heading west . '' `` exactly ! and this is really just the beginning . ''

what field ? '' `` the higgs field . it 's named after peter higgs , although many others contributed to the idea .

who , other than peter higgs , developed the concept of what is commonly called the “ higgs field ” ?

translator : andrea mcdonough reviewer : bedirhan cinar have you ever wondered who has the authority to make laws or punish people who break them ? when we think of power in the united states , we usually think of the president , but he does not act alone . in fact , he is only one piece of the power puzzle and for very good reason . when the american revolution ended in 1783 , the united states government was in a state of change . the founding fathers knew that they did not want to establish another country that was ruled by a king , so the discussions were centered on having a strong and fair national government that protected individual freedoms and did not abuse its power . when the new constitution was adopted in 1787 , the structure of the infant government of the united states called for three separate branches , each with their own powers , and a system of checks and balances . this would ensure that no one branch would ever become too powerful because the other branches would always be able to check the power of the other two . these branches work together to run the country and set guidelines for us all to live by . the legislative branch is described in article 1 of the u.s. constitution . many people feel that the founding fathers put this branch in the document first because they thought it was the most important . the legislative branch is comprised of 100 u.s . senators and 435 members in the u.s. house of representatives . this is better known as the u.s. congress . making laws is the primary function of the legislative branch , but it is also responsible for approving federal judges and justices , passing the national budget , and declaring war . each state gets two senators and some number of representatives , depending on how many people live in that state . the executive branch is described in article 2 of the constitution . the leaders of this branch of government are the president and vice president , who are responsible for enforcing the laws that congress sets forth . the president works closely with a group of advisors , known as the cabinet . these appointed helpers assist the president in making important decisions within their area of expertise , such as defense , the treasury , and homeland security . the executive branch also appoints government officials , commands the armed forces , and meets with leaders of other nations . all that combined is a lot of work for a lot of people . in fact , the executive branch employs over 4 million people to get everything done . the third brand of the u.s. government is the judicial branch and is detailed in article 3 . this branch is comprised of all the courts in the land , from the federal district courts to the u.s. supreme court . these courts interpret our nation 's laws and punish those who break them . the highest court , the supreme court , settles disputes among states , hears appeals from state and federal courts , and determines if federal laws are constitutional . there are nine justices on the supreme court , and , unlike any other job in our government , supreme court justices are appointed for life , or for as long as they want to stay . our democracy depends on an informed citizenry , so it is our duty to know how it works and what authority each branch of government has over its citizens . besides voting , chances are that some time in your life you 'll be called upon to participate in your government , whether it is to serve on a jury , testify in court , or petition your congress person to pass or defeat an idea for a law . by knowning the branches , who runs them , and how they work together , you can be involved , informed , and intelligent .

our democracy depends on an informed citizenry , so it is our duty to know how it works and what authority each branch of government has over its citizens . besides voting , chances are that some time in your life you 'll be called upon to participate in your government , whether it is to serve on a jury , testify in court , or petition your congress person to pass or defeat an idea for a law . by knowning the branches , who runs them , and how they work together , you can be involved , informed , and intelligent .

besides voting , in what ways can a citizen participate in his/her government ?

emily dickinson said over a century ago that `` there is no frigate like a book to take us lands away ... '' and it 's true . when we pick up a book , turn on the tv , or watch a movie , we 're carried away down the currents of story into a world of imagination . and when we land , on a shore that is both new and familiar , something strange happens . stepping onto the shore , we 're changed . we do n't retrace the footsteps of the authors or characters we followed here . no ; instead , we walk a mile in their shoes . researchers in psychology , neuroscience , child development and biology are finally starting to gain quantifiable scientific evidence , showing what writers and readers have always known : that stories have a unique ability to change a person 's point of view . scholars are discovering evidence that stories shape culture , and that much of what we believe about life comes not from fact , but from fiction - that our ideas of class , marriage and even gender are relatively new , and that many ideologies which held fast for centuries were revised within the 18th century , and redrafted in the pages of the early novel . imagine a world where class , and not hard work , decides a person 's worth ; a world where women are simply men 's more untamed copy ; a world where marriage for love is a novel notion . well , that was the world in which samuel richardson 's `` pamela '' first appeared . richardson 's love story starred a poor , serving-class heroine , who is both more superior and smarter than her upper-class suitor . the book , challenging a slew of traditions , caused quite a ruckus . there was more press for `` pamela '' than for parliament . it spawned intense debate and several counter-novels . still , for all those who could n't accept `` pamela , '' others were eager for this new fictional world . this best seller and all its literary heirs - `` pride and prejudice , '' `` jane eyre , '' and yes , even `` twilight '' - have continuously shared the same tale and taught similar lessons , which are now conventional and commonplace . similarly , novels have helped shape the minds of thought leaders across history . some scholars say that darwin 's theory of evolution is highly indebted to the plots he read and loved . his theory privileges intelligence , swiftness , and adaptability to change - all core characteristics in a hero . whether you 're reading `` harry potter '' or `` great expectations , '' you 're reading the kind of plot that inspired darwin . yet , recent studies show that his theory might not be the whole story . our sense of being a hero - one man or one woman or even one species taking on the challenges of the world - might be wrong . instead of being hardwired for competition for being the solitary heroes in our own story , we might instead be members of a shared quest . more hobbit than harry . sometimes , of course , the shoes we 've been walking in can get plain worn out . after all , we have n't walked just one mile in jane austen 's or mark twain 's shoes - we 've walked about 100 trillion miles in them . this is n't to say that we ca n't read and enjoy the classics ; we should travel with dickens , let pip teach us what to expect from ourselves , have a talk with austen and elizabeth about our prides and prejudices . we should float with twain down the mississippi , and have jim show us what it means to be good . but on our journey , we should also keep in mind that the terrain has changed . we 'll start shopping around for boots that were made for walking into a new era . take , for instance , katniss everdeen and her battle with the capitol . can `` hunger games '' lead us into thinking about capitalism in a new way ? can it teach us a lesson about why the individual should not put herself before the group ? will `` uglies '' reflect the dangers of pursuing a perfect body and letting the media define what is beautiful ? will `` seekers '' trod a path beyond global warming ? will the life-and-death struggles of toklo , kallik , lusa and the other bears chart a course for understanding animals and our place in their world ? only the future will tell which stories will engage our imagination , which tales of make-believe we 'll make tomorrow . but the good news is this : there are new stories to venture in every day , new tales that promise to influence , to create and to spark change - stories that you might even write yourself . so i guess the final question is this : what story will you try on next ?

take , for instance , katniss everdeen and her battle with the capitol . can `` hunger games '' lead us into thinking about capitalism in a new way ? can it teach us a lesson about why the individual should not put herself before the group ? will `` uglies '' reflect the dangers of pursuing a perfect body and letting the media define what is beautiful ?

give an example of how a book really challenged the way you thought about an issue , society , an individual , or a group of people .

imagine an island where 100 people , all perfect logicians , are imprisoned by a mad dictator . there 's no escape , except for one strange rule . any prisoner can approach the guards at night and ask to leave . if they have green eyes , they 'll be released . if not , they 'll be tossed into the volcano . as it happens , all 100 prisoners have green eyes , but they 've lived there since birth , and the dictator has ensured they ca n't learn their own eye color . there are no reflective surfaces , all water is in opaque containers , and most importantly , they 're not allowed to communicate among themselves . though they do see each other during each morning 's head count . nevertheless , they all know no one would ever risk trying to leave without absolute certainty of success . after much pressure from human rights groups , the dictator reluctantly agrees to let you visit the island and speak to the prisoners under the following conditions : you may only make one statement , and you can not tell them any new information . what can you say to help free the prisoners without incurring the dictator 's wrath ? after thinking long and hard , you tell the crowd , `` at least one of you has green eyes . '' the dictator is suspicious but reassures himself that your statement could n't have changed anything . you leave , and life on the island seems to go on as before . but on the hundredth morning after your visit , all the prisoners are gone , each having asked to leave the previous night . so how did you outsmart the dictator ? it might help to realize that the amount of prisoners is arbitrary . let 's simplify things by imagining just two , adria and bill . each sees one person with green eyes , and for all they know , that could be the only one . for the first night , each stays put . but when they see each other still there in the morning , they gain new information . adria realizes that if bill had seen a non-green-eyed person next to him , he would have left the first night after concluding the statement could only refer to himself . bill simultaneously realizes the same thing about adria . the fact that the other person waited tells each prisoner his or her own eyes must be green . and on the second morning , they 're both gone . now imagine a third prisoner . adria , bill and carl each see two green-eyed people , but are n't sure if each of the others is also seeing two green-eyed people , or just one . they wait out the first night as before , but the next morning , they still ca n't be sure . carl thinks , `` if i have non-green eyes , adria and bill were just watching each other , and will now both leave on the second night . '' but when he sees both of them the third morning , he realizes they must have been watching him , too . adria and bill have each been going through the same process , and they all leave on the third night . using this sort of inductive reasoning , we can see that the pattern will repeat no matter how many prisoners you add . the key is the concept of common knowledge , coined by philosopher david lewis . the new information was not contained in your statement itself , but in telling it to everyone simultaneously . now , besides knowing at least one of them has green eyes , each prisoner also knows that everyone else is keeping track of all the green-eyed people they can see , and that each of them also knows this , and so on . what any given prisoner does n't know is whether they themselves are one of the green-eyed people the others are keeping track of until as many nights have passed as the number of prisoners on the island . of course , you could have spared the prisoners 98 days on the island by telling them at least 99 of you have green eyes , but when mad dictators are involved , you 're best off with a good headstart .

after thinking long and hard , you tell the crowd , `` at least one of you has green eyes . '' the dictator is suspicious but reassures himself that your statement could n't have changed anything . you leave , and life on the island seems to go on as before .

what was it about your statement that tricked the dictator into allowing you to say it ?

for as far back as we can trace our existence , humans have been fascinated with death and resurrection . nearly every religion in the world has some interpretation of them , and from our earliest myths to the latest cinematic blockbusters , the dead keep coming back . but is resurrection really possible ? and what is the actual difference between a living creature and a dead body , anyway ? to understand what death is , we need to understand what life is . one ancient theory was an idea called vitalism , which claimed that living things were unique because they were filled with a special substance , or energy , that was the essence of life . whether it was called qi , lifeblood , or humors , the belief in such an essence was common throughout the world , and still persists in the stories of creatures who can somehow drain life from others , or some form of magical sources that can replenish it . vitalism began to fade in the western world following the scientific revolution in the 17th century . rené descartes advanced the notion that the human body was essentially no different from any other machine , brought to life by a divinely created soul located in the brain 's pineal gland . and in 1907 , dr. duncan mcdougall even claimed that the soul had mass , weighing patients immediately before and after death in an attempt to prove it . though his experiments were discredited , much like the rest of vitalism , traces of his theory still come up in popular culture . but where do all these discredited theories leave us ? what we now know is that life is not contained in some magical substance or spark , but within the ongoing biological processes themselves . and to understand these processes , we need to zoom down to the level of our individual cells . inside each of these cells , chemical reactions are constantly occurring , powered by the glucose and oxygen that our bodies convert into the energy-carrying molecule known as atp . cells use this energy for everything from repair to growth to reproduction . not only does it take a lot of energy to make the necessary molecules , but it takes even more to get them where they need to be . the universal phenomenon of entropy means that molecules will tend towards diffusing randomly , moving from areas of high concentration to low concentration , or even breaking apart into smaller molecules and atoms . so cells must constantly keep entropy in check by using energy to maintain their molecules in the very complicated formations necessary for biological functions to occur . the breaking down of these arrangements when the entire cell succumbs to entropy is what eventually results in death . this is the reason organisms ca n't be simply sparked back to life once they 've already died . we can pump air into someone 's lungs , but it wo n't do much good if the many other processes involved in the respiratory cycle are no longer functioning . similarly , the electric shock from a defibrillator does n't jump-start an inanimate heart , but resynchronizes the muscle cells in an abnormally beating heart so they regain their normal rhythm . this can prevent a person from dying , but it wo n't raise a dead body , or a monster sewn together from dead bodies . so it would seem that all our various medical miracles can delay or prevent death but not reverse it . but that 's not as simple as it sounds because constant advancements in technology and medicine have resulted in diagnoses such as coma , describing potentially reversible conditions , under which people would have previously been considered dead . in the future , the point of no return may be pushed even further . some animals are known to extend their lifespans or survive extreme conditions by slowing down their biological processes to the point where they are virtually paused . and research into cryonics hopes to achieve the same by freezing dying people and reviving them later when newer technology is able to help them . see , if the cells are frozen , there 's very little molecular movement , and diffusion practically stops . even if all of a person 's cellular processes had already broken down , this could still conceivably be reversed by a swarm of nanobots , moving all the molecules back to their proper positions , and injecting all of the cells with atp at the same time , presumably causing the body to simply pick up where it left off . so if we think of life not as some magical spark , but a state of incredibly complex , self-perpetuating organization , death is just the process of increasing entropy that destroys this fragile balance . and the point at which someone is completely dead turns out not to be a fixed constant , but simply a matter of how much of this entropy we 're currently capable of reversing .

what we now know is that life is not contained in some magical substance or spark , but within the ongoing biological processes themselves . and to understand these processes , we need to zoom down to the level of our individual cells . inside each of these cells , chemical reactions are constantly occurring , powered by the glucose and oxygen that our bodies convert into the energy-carrying molecule known as atp . cells use this energy for everything from repair to growth to reproduction . not only does it take a lot of energy to make the necessary molecules , but it takes even more to get them where they need to be .

highly organized systems like living cells should have _____ .

how is it that so many intergalactic species in movies and tv just happen to speak perfect english ? the short answer is that no one wants to watch a starship crew spend years compiling an alien dictionary . but to keep things consistent , the creators of star trek and other science-fiction worlds have introduced the concept of a universal translator , a portable device that can instantly translate between any languages . so is a universal translator possible in real life ? we already have many programs that claim to do just that , taking a word , sentence , or entire book in one language and translating it into almost any other , whether it 's modern english or ancient sanskrit . and if translation were just a matter of looking up words in a dictionary , these programs would run circles around humans . the reality , however , is a bit more complicated . a rule-based translation program uses a lexical database , which includes all the words you 'd find in a dictionary and all grammatical forms they can take , and set of rules to recognize the basic linguistic elements in the input language . for a seemingly simple sentence like , `` the children eat the muffins , '' the program first parses its syntax , or grammatical structure , by identifying the children as the subject , and the rest of the sentence as the predicate consisting of a verb `` eat , '' and a direct object `` the muffins . '' it then needs to recognize english morphology , or how the language can be broken down into its smallest meaningful units , such as the word muffin and the suffix `` s , '' used to indicate plural . finally , it needs to understand the semantics , what the different parts of the sentence actually mean . to translate this sentence properly , the program would refer to a different set of vocabulary and rules for each element of the target language . but this is where it gets tricky . the syntax of some languages allows words to be arranged in any order , while in others , doing so could make the muffin eat the child . morphology can also pose a problem . slovene distinguishes between two children and three or more using a dual suffix absent in many other languages , while russian 's lack of definite articles might leave you wondering whether the children are eating some particular muffins , or just eat muffins in general . finally , even when the semantics are technically correct , the program might miss their finer points , such as whether the children `` mangiano '' the muffins , or `` divorano '' them . another method is statistical machine translation , which analyzes a database of books , articles , and documents that have already been translated by humans . by finding matches between source and translated text that are unlikely to occur by chance , the program can identify corresponding phrases and patterns , and use them for future translations . however , the quality of this type of translation depends on the size of the initial database and the availability of samples for certain languages or styles of writing . the difficulty that computers have with the exceptions , irregularities and shades of meaning that seem to come instinctively to humans has led some researchers to believe that our understanding of language is a unique product of our biological brain structure . in fact , one of the most famous fictional universal translators , the babel fish from `` the hitchhiker 's guide to the galaxy '' , is not a machine at all but a small creature that translates the brain waves and nerve signals of sentient species through a form of telepathy . for now , learning a language the old fashioned way will still give you better results than any currently available computer program . but this is no easy task , and the sheer number of languages in the world , as well as the increasing interaction between the people who speak them , will only continue to spur greater advances in automatic translation . perhaps by the time we encounter intergalactic life forms , we 'll be able to communicate with them through a tiny gizmo , or we might have to start compiling that dictionary , after all .

finally , even when the semantics are technically correct , the program might miss their finer points , such as whether the children `` mangiano '' the muffins , or `` divorano '' them . another method is statistical machine translation , which analyzes a database of books , articles , and documents that have already been translated by humans . by finding matches between source and translated text that are unlikely to occur by chance , the program can identify corresponding phrases and patterns , and use them for future translations .

`` statistical machine translation '' is based :

as we walk through our daily environments , we 're surrounded by exotic creatures that are too small to see with the naked eye . we usually imagine these microscopic organisms , or microbes , as asocial cells that float around by themselves . but in reality , microbes gather by the millions to form vast communities known as biofilms . natural biofilms are like miniature jungles filled with many kinds of microbes from across the web of life . bacteria and archaea mingle with other microbes like algae , fungi , and protozoa , forming dense , organized structures that grow on almost any surface . when you pad across a river bottom , touch the rind of an aged cheese , tend your garden soil , or brush your teeth , you 're coming into contact with these invisible ecosystems . to see how biofilms come about , let 's watch one as it develops on a submerged river rock . this type of biofilm might begin with a few bacteria swimming through their liquid environment . the cells use rotating flagella to propel towards the surface of the rock , which they attach to with the help of sticky appendages . then , they start producing an extracellular matrix that holds them together as they divide and reproduce . before long , microcolonies arise , clusters of cells sheathed in this slimy , glue-like material . microcolonies grow to become towers , while water channels flow around them , functioning like a basic circulatory system . but why do microbes build such complex communities when they could live alone ? for one thing , microbes living in a biofilm are rooted in a relatively stable microenvironment where they may have access to a nutrient source . there 's also safety in numbers . out in the deep , dark wilderness of the microbial world , isolated microbes face serious risks . predators want to eat them , immune systems seek to destroy them , and there are physical dangers , too , like running out of water and drying up . however , in a biofilm , the extracellular matrix shields microbes from external threats . biofilms also enable interactions between individual cells . when microbes are packed against each other in close proximity , they can communicate , exchange genetic information , and engage in cooperative and competitive social behaviors . take the soil in your garden , home to thousands of bacterial species . as one species colonizes a plant root , its individual cells might differentiate into various subpopulations , each carrying out a specific task . matrix producers pump out the extracellular goo , swimmers assemble flagella and are free to move about or migrate , and spore-formers produce dormant , tough endospores that survive starvation , temperature extremes , and harmful radiation . this phenomenon is called division of labor . ultimately , it gives rise to a sophisticated system of cooperation that 's somewhat like a multicellular organism in itself . but because biofilms often contain many different microbes that are n't closely related to each other , interactions can also be competitive . bacteria launch vicious attacks on their competitors by secreting chemicals into the environment , or by deploying molecular spears to inject nearby cells with toxins that literally blow them up . in the end , competition is all about resources . if one species eliminates another , it keeps more space and food for itself . although this dramatic life cycle occurs beyond the limits of our vision , microbial communities provide humans and other species with tangible , and sometimes even delicious , benefits . microbes make up a major fraction of the biomass on earth and play a critical role within the global ecosystem that supports all larger organisms , including us . they produce much of the oxygen we breath , and are recruited to clean up environmental pollution , like oil spills , or to treat our waste water . not to mention , biofilms are normal and flavor enhancing parts of many of the foods we enjoy , including cheese , salami , and kombucha . so the next time you brush your teeth , bite into that cheese rind , sift through garden soil , or skip a river stone , look as close as you can . imagine the microbial jungles all around you waiting to be discovered and explored .

predators want to eat them , immune systems seek to destroy them , and there are physical dangers , too , like running out of water and drying up . however , in a biofilm , the extracellular matrix shields microbes from external threats . biofilms also enable interactions between individual cells .

which of these activities can occur inside biofilm communities ?

many of my friends , teachers , romantic partners and even my parents have all told me to stop fidgeting , `` trace stop shaking your leg . '' but i did n't even know i was doing it mom , geez ! fidgeting friends once upon a time , psychologist sir francis galton was sitting in a lecture , got bored and decided to watch the audience instead of listen to the speaker . ( been there ! ) according to him , these elderly victorian lecture-goers were , `` swaying from side-to-side '' at about `` 1 fidget a minute . '' when the audience 's attention was aroused , he noticed their fidgeting would lessen . in his paper , published in nature , titled `` the measure of fidget '' galton determined people must fidget out of boredom ! this was before discussions about hyperactivity or sugar , or before the television ruined our attention span . this was 1885 ! 130 years ago , people fidgeted . it 's definitely not caused by over-caffeinated , adhd-prone , coddled millennials . instead , fidgeting seems to be part of human nature . the dictionary defines fidgeting as `` small movements , especially of the hands and feet , caused by nervousness or impatience , '' but science has another explanation ; it 's a way to keep my brain active and focused . yep , you heard me , fidgeting may equal focus . hashtag science , yo . when brains are stressed we do n't pay as close attention , and we do n't learn as much ! cognitive load theory says to think of the brain like a cpu ; when too much is going on the brain ca n't focus . so , to offload some of that stress , the brain might trigger our fidgeting ! lower stress is highly associated with better learning and memory performance , so fidgeting can help us learn ! though science is n't sure… because maybe it 's just men… for some reason men fidget twice as often as women , and a 2005 study from the university of hertfordshire found fidgeting can reduce levels of the stress hormone cortisol , which should lower stress . a study in plos one , however , that benefit seems to fall on men who fidgeted . the fidgeting men they tested performed better on cognitive tests and had lower stress , but fidgeting women did neither . another study with adhd kids further muddies the fidgeting waters , as fidgeting does n't help everyone all the time . a study in the journal of abnormal psychology assessed the working memory of young fidgeting boys . when adhd kids were put in a swivel chair and allowed to spin , they performed better on memory tests . however , kids without adhd performed worse when they were allowed to spin , and better when they stayed still . it would seem , though fidgeting may lower stress and help learning , there 's a level where the benefits to our attention and learning disappear . for example , drawing random doodles , kicking feet , or shaking legs may be fine , but drawing specific pictures or walking around the room is too distracting and benefits are lost . so , perhaps boys with adhd need to fidget ? what about girls ? do they get any benefit ? well , a study from september 2015 in the american journal of preventive medicine , looked at 13,000 uk women 12 years apart and found adults who fidgeted , also burned calories ! their results found fidgeters had quote `` better health outcomes , '' than their still counterparts . and another study in medicine & amp ; amp ; science in sports & amp ; amp ; exercise found fidgeting can burn up to 144 calories a day ! that 's more than a can of pop ! some researchers believe fidgeting seems to be an adaptation to our more sedentary lifestyle . but a study in frontiers in psychology looking at memory retention of lectures , and fidgeting… found almost the same as galton in 1885 . if you track the number of fidgets per minute , it 's a good indicator of audience boredom . fidgeting seems to be a representation of our animal brains working hard to keep on task and learning . it can be irksome , but as long as it 's not distracting to others , it 's not necessarily bad , and is ( at least ) burning some calories ! sometimes we 're just… fidgety widgety . do you fidget ? how ? pen clicker ? leg shaker ? finger tapper ? nail biter ? whatchoo got ? tell us your fidgeting functions down below . fidgeting might be annoying to some , but sitting is killing you . yep . your chair . it 's slowing killing you right now . find out more in this video

whatchoo got ? tell us your fidgeting functions down below . fidgeting might be annoying to some , but sitting is killing you . yep .

what are the modern scientific explanations that might explain fidgeting ?

nothing stuck to mafia boss john gotti who evaded justice for years by bribing and threatening jurors and witnesses . that earned him the name the teflon don after one of the slipperiest materials on earth . teflon was in the spacesuits the apollo crew wore for the moon landing , in pipes and valves used in the manhattan project , and maybe in your kitchen as the nonstick coating on frying pans and cookie sheets . so what is this slippery solid , and why does n't anything stick to it ? teflon is a brand name for polytetrafluoroethylene , or ptfe . it was stumbled upon accidentally in 1938 by a 27-year-old american chemist named roy plunkett while he was trying to develop a non-toxic refrigerant fluid for dupont , a chemicals company . the strange , white substance that formed inside his lab canister was chemically inert , meaning it would n't react with other substances . it also had an extremely low coefficient of friction , making other materials slide right off it . teflon 's properties make it perfect when you need something slippery , chemical resistant , or waterproof , which means it has a lot of applications . it can be found all over the place , as a coating on raincoats , industrial ball bearings , artificial joints , circuit boards , and even the rocky mountains-themed roof of the denver international airport . the incredible properties of ptfe come from its molecular structure . it 's a polymer , meaning it 's made of long chains of repeating units of atoms strung together . a ptfe chain has a backbone of carbon atoms , each of which is attached to two fluorines . the fluorine atoms surround the carbon like armor , spiraling around the chain , and the bond between carbon and fluorine is incredibly tight . like a couple that ignores everyone except each other , carbon and fluorine interact so strongly that the normal , intermolecular forces that help substances stick to each other do n't stand a chance . even the famously adhesive feet of geckos usually ca n't get a grip . but wait ! if ptfe does n't stick to anything , how can it be so firmly attached to something like a pan ? one method involves sandblasting the pan or etching it with chemicals to make it rough . then , a special primer is applied , which acts like glue . its exact composition is a trade secret guarded by each manufacturer . the pan is sprayed with liquid ptfe and heated to around 800 degrees fahrenheit . the layers then solidify into a smooth , slick coating . when you later cook eggs in this ptfe-coated pan , the extra tight carbon-fluorine bonds just ignore the water and fat and protein molecules in the eggs . without those interactions , the food just slides around without sticking . you might wonder if it 's safe to cook in a ptfe-coated pan . the answer is yes , if you 're careful . ptfe is stable at moderate temperatures , like you 'd use to cook eggs or fish , but above 500 degrees fahrenheit , it starts to degrade , and heating it further releases fumes that can make you feel sick . an empty pan can reach 500 degrees fast over high heat , but most kitchens are ventilated well enough to dissipate the fumes . people used to also think that accidentally consuming ptfe that flaked off a scratched pan was bad for you , but the current consensus is that it 's harmless . because ptfe does n't interact with other chemicals very well , it is n't thought to break down inside your body . whether it 's safe to manufacture teflon is another story . dupont and its spin-off company chemours now face lawsuits worth millions of dollars . they 've been accused of polluting the environment for decades and exposing employees and local communities to health risks associated with a toxic chemical called pfoa . that chemical was involved in manufacturing teflon . as for john gotti , in 1992 , the mob boss was finally convicted of five counts of murder , among other charges . that prompted the head of the fbi office in new york city to announce , `` the teflon is gone . the don is covered in velcro , and all the charges stuck . ''

that earned him the name the teflon don after one of the slipperiest materials on earth . teflon was in the spacesuits the apollo crew wore for the moon landing , in pipes and valves used in the manhattan project , and maybe in your kitchen as the nonstick coating on frying pans and cookie sheets . so what is this slippery solid , and why does n't anything stick to it ?

which property of teflon made it ideal for coating the valves and seals in pipes carrying toxic fluids ( e.g. , uranium hexafluoride ) in the manhattan project during world war ii ?

translator : jessica ruby reviewer : caroline cristal russia , with the largest territory in the world , has roughly the same total population as nigeria , a country 1/16 its size . but this similarity wo n't last long . one of the populations is rapidly growing , while the other is slowly declining . what can this tell us about the two countries ? population statistics are some of the most important data social scientists and policy experts have to work with . but understanding a country 's situation and making accurate predictions requires knowing not just the total size of the population but its internal characteristics , such as age and gender distribution . so , how can we keep track of all that data in a way that makes it easy to comprehend ? complex data is more easily interpreted through visualization , and one of the ways that demographers represent the internal distribution of a population is the population pyramid . here , the data is divided by gender with females on one side and males on the other . the population numbers are shown for each five-year age interval , starting from 0-4 and continuing up to 100 and up . these intervals are grouped together into pre-reproductive ( 0-14 ) , reproductive ( 15-44 ) , and post-reproductive years ( 45 and up ) . such a population pyramid can be a powerful predictor of future population trends . for example , rwanda 's population pyramid shows it to be a fast-growing country , with most of the population being in the youngest age groups at the bottom of the pyramid . the number will grow rapidly in the coming years . as today 's children reach their reproductive years and have children of their own , the total population is almost certain to double within the next few decades . for our second example , let 's look at canada , where most of the population is clustered around the middle of the graph . because there are less people in the pre-reproductive age groups than there are in the reproductive ones , the population will grow more slowly , as the number of people reaching their reproductive years decreases . finally , let 's look at japan . because the majority of its population is in its post-reproductive years and the number of people is smaller at each younger interval , this means that at current rates of reproduction the population will begin to decline as fewer and fewer people reach reproductive age . comparing these three population pyramids side by side shows us three different stages in a demographic transition , as a country moves from a pre-industrial society to one with an industrial or post-industrial economy . countries that have only recently begun the process of industrialization typically see an increase in life expectancy and a fall in child mortality rates as a result of improvements in medicine , sanitation , and food supply . while birth rates remain constant , leading to a population boom . developing countries that are farther along in the industrialization process begin to see a fall in birth rates , due to factors such as increased education and opportunities for women outside of child-rearing and a move from rural to urban living that makes having large families less economically advantageous . finally , countries in advanced stages of industrialization reach a point where both birth and death rates are low , and the population remains stable or even begins to decline . now , let 's take a look at the projected population pyramids for the same three countries in 2050 . what do these tell us about the expected changes in each country 's population , and what kinds of factors can alter the shape of these future pyramids ? a population pyramid can be useful not only as a predictor of a country 's future but as a record of its past . russia 's population pyramid still bears the scars of world war ii , which explains both the fewer numbers of elderly men compared to elderly women and the relatively sudden population increase as soldiers returned from the war and normal life resumed . china 's population pyramid reflects the establishment of the one child policy 35 years before , which prevented a population boom such as that of rwanda but also led to sex-selective abortions , resulting in more male children than female children . finally , the pyramid for the united states shows the baby boom that followed world war ii . as you can see , population pyramids tell us far more about a country than just a set of numbers , by showing both where it 's been and where it 's headed within a single image . and in today 's increasingly interconnected world , facing issues such as food shortages , ecological threats , and economic disparities , it is increasingly important for both scientists and policy makers to have a rich and complex understanding of populations and the factors affecting them .

such a population pyramid can be a powerful predictor of future population trends . for example , rwanda 's population pyramid shows it to be a fast-growing country , with most of the population being in the youngest age groups at the bottom of the pyramid . the number will grow rapidly in the coming years .

what services would a fast growth country in comparison to a slow growth country need to consider increasing for the benefit of its people ?

we 've all seen the movies where a monster , created by a scientist in a laboratory , escapes to wreak havoc on the outside world . but what if the monster was not some giant rampaging beast , destroying a city , but just a tiny amount of seaweed with the potential to disrupt entire coastal ecosystems ? this is the story of caulerpa taxifolia , originally a naturally occurring seaweed native to tropical waters . in the 1980s , one strain was found to thrive in colder environments . this trait , combined with its beautiful , bright green color and ability to grow quickly without maintenance made it ideal for aquariums , which it helped keep clean by consuming nutrients and chemicals in the water . further selective breeding made it even heartier , and soon it was used in aquariums around the world . but it was not long before a sample of this aquarium-developed super algae turned up in the mediterranean sea near the famed oceanographic museum of monaco . the marine biologist who found it believed that the museum had accidentally realeased it into the ocean along with aquarium waters , while museum directors claimed it had be carried into the area by ocean currents . regardless of how it ended up there , the non-native caulerpa multiplied rapidly , having no natural predators due to releasing a toxin that keeps fish away . and like some mythical monster , even a tiny piece that broke off could grow into a whole new colony . through water currents and contact with boat anchors and fishing lines , it fragmented and spread throughout mediterranean coastal cities covering coral reefs . so what was the result of this invasion ? well , it depends on who you ask . many scientists warned that the spread of caulerpa reduces biodiversity by crowding out native species of seaweed that are eaten by fish , with the biologist who first discovered its presence dubbing it killer algae . other studies instead claim that the algae actually had a beneficial effect by consuming chemical pollutants -- one reason the aquariums strain was developed . but the disruption of a natural ecosystem by an introduced foreign species can have unpredictable and uncontrollable effects that may not be immediately visible . so when culerpa taxifolia was discovered at carlsbad 's agua hedionda lagoon , near san diego in the year 2000 , having most likely come from the dumping of home aquarium water into a connecting storm drain , it was decided to stop it before it spread . tarps were placed over the culerpa colonies and chlorine injected inside . although this method killed all other marine life trapped under the tarps , it did succeed in eradicating the algae and native eelgrass was able to emerge in its place . by responding quickly , authorities in california were able to prevent culerpa from propagating . but another occurrence of the strain , in the coastal wetlands of southeast australia , was left unchecked and allowed to spread . and unfortunately , a tarp can not cover the mediterranean sea or the australian coast . invasive species are not a new problem , and can indeed occur naturally . but when such species are the results of human directed selective breeding or genetic modification and then released into the natural environment , their effect on ecosystems can be far more radical and irreversible . with the proliferation of new technologies and multiple threats to the environment , it is more important than ever for scientists to monitor and evaluate the risks and dangers , and for the rest of us to remember that what starts in our backyard can effect ecosystems half a world away .

but what if the monster was not some giant rampaging beast , destroying a city , but just a tiny amount of seaweed with the potential to disrupt entire coastal ecosystems ? this is the story of caulerpa taxifolia , originally a naturally occurring seaweed native to tropical waters . in the 1980s , one strain was found to thrive in colder environments .

since a small amount of the caulerpa seaweed can be detached and then start growing in a new location things like boat anchors , scuba gear , fishing lines , and even disturbance by hand removal can lead to the unintended spread of this seaweed . what kind of challenges come up when trying to tell people they can no longer enjoy boating , fishing or other recreational activities in an area that has been infested with caulerpa taxifolia ?

... and i 'm scratching , and i like to hide . oh , i am such a good spider . i will turn this way , and i will , let 's see ... i will hide now . ah , with a scratch scratch scratch scratch scratch scratch scratch ! and i will flatten myself like this ! and now i 'm hiding , and i can see you . i like looking at you ... but wait a minute . if i can see you then you can see me ... meh , and it *is* a bit drafty in here , i must say . so maybe i 'm not hidden . i will turn this way . yes ? and i will – i will scratch scratch scratch scratch scratch scratch scratch scratch ! and that will bury myself again , and i will flatten my legs this time that was the problem last time – my legs were not flattened , so i flat – no ! but i still bury– oh hon hon hon hon honn hon hon honnnn ! here is the secret key ! i can not be you , that they you can not see me ... i am hidden !

... and i 'm scratching , and i like to hide . oh , i am such a good spider .

what is a narrative voice ?

translator : tom carter reviewer : bedirhan cinar she 's only a few feet away . the closer he gets , the more nervous he becomes , the budding zit on his nose growing bigger and bigger until it practically eclipses his face . she looks at him hovering nearby , sees the massive zit , and giggles . he slumps away , feeling sick . stress can sure make a mess , and it happens to both teens and adults . but how does it happen ? let 's rewind to before the zit , to before justin even sees his crush . already late for school , justin got to class just in time to hear the teacher say `` pop quiz . '' he had n't done his homework the night before , and felt more unprepared than the ambushed world war ii soldiers he was supposed to write about . a sudden rush of panic swept over his body , leaving him with sweaty palms , a foggy mind and a racing heart . he stumbled out of class in a daze , and ran straight into his all-time crush , spiking up his stress . stress is a general biological response to a potential danger . in primitive caveman terms , stress can make you fight for your life , or run for your life , if , for example , you 're confronted by a hungry saber-tooth tiger . special chemicals called stress hormones run through your body , giving you more oxygen and power to run away from danger or to face it and fight for your life , hence the term `` fight or flight . '' but when you do n't fight , or take flight , you face the plight . when we 're taking final exams , sitting in traffic or pondering pollution , we internalize stress . it all begins in the brain . the hypothalamus , the master controller of your hormones , releases something called corticotropin-releasing hormone . this triggers the pituitary gland , a pea-sized gland found at the base of the brain , to release adrenocorticotropic hormone which then stimulates the adrenal gland sitting on top of the kidneys to release cortisol , the major stress hormone . these natural chemicals are a great help when you need to run away quickly , or do superhuman feats of courage , but when you 're simply sitting , these stress hormones collect in the body and affect your overall health . stress hormones increase inflammation in the body , suppress the immune system , which makes you more susceptible to infection by acne-causing bacteria , and can even increase oil production in the skin . and this is the perfect storm for forming a pimple . cortisol is a major stress hormone involved in making skin cells churn out oily lipids from special glands called sebaceous glands . but when there 's too much of these oily lipids , called sebum , they can plug up the swollen , inflamed pores and trap the pesky , acne-causing bacteria inside , where they set up house and thrive . add a dash of inflammatory neuropeptides released by the nervous system when you 're -- well , nervous -- and angry zits follow . to make matters worse , justin is a boy , meaning he 's got more testosterone than girls . testosterone is another hormone that increases oil production in the skin . so , his already oily skin , together with a boost in oil and inflammation from stress , is the perfect environment for bacteria to swell , swell , swell up into a major zit . so what could 've justin done to avoid the big pimple ? stressful situations are unavoidable . but we can try to change our responses so that we 're not so stressed in the end . and had he been confident in approaching her , she might not have noticed the pimple , or he might not have had one .

and this is the perfect storm for forming a pimple . cortisol is a major stress hormone involved in making skin cells churn out oily lipids from special glands called sebaceous glands . but when there 's too much of these oily lipids , called sebum , they can plug up the swollen , inflamed pores and trap the pesky , acne-causing bacteria inside , where they set up house and thrive .

what major stress hormone increases inflammation and makes sebaceous glands produce more oil in the skin ?

what could octopuses possibly have in common with us ? after all , they do n't have lungs , spines , or even a plural noun we can all agree on . but what they do have is the ability to solve puzzles , learn through observation , and even use tools , just like some other animals we know . and what makes octopus intelligence so amazing is that it comes from a biological structure completely different from ours . the 200 or so species of octopuses are mollusks belonging to the order cephalopoda , greek for head-feet . those heads contain impressively large brains , with a brain to body ratio similar to that of other intelligent animals , and a complex nervous system with about as many neurons as that of a dog . but instead of being centralized in the brain , these 500 million neurons are spread out in a network of interconnected ganglia organized into three basic structures . the central brain only contains about 10 % of the neurons , while the two huge optic lobes contain about 30 % . the other 60 % are in the tentacles , which for humans would be like our arms having minds of their own . this is where things get even more interesting . vertebrates like us have a rigid skeleton to support our bodies , with joints that allow us to move . but not all types of movement are allowed . you ca n't bend your knee backwards , or bend your forearm in the middle , for example . cephalopods , on the other hand , have no bones at all , allowing them to bend their limbs at any point and in any direction . so shaping their tentacles into any one of the virtually limitless number of possible arrangements is unlike anything we are used to . consider a simple task , like grabbing and eating an apple . the human brain contains a neurological map of our body . when you see the apple , your brain 's motor center activates the appropriate muscles , allowing you to reach out with your arm , grab it with your hand , bend your elbow joint , and bring it to your mouth . for an octopus , the process is quite different . rather than a body map , the cephalopod brain has a behavior library . so when an octopus sees food , its brain does n't activate a specific body part , but rather a behavioral response to grab . as the signal travels through the network , the arm neurons pick up the message and jump into action to command the movement . as soon as the arm touches the food , a muscle activation wave travels all the way through the arm to its base , while the arm sends back another wave from the base to the tip . the signals meet halfway between the food and the base of the arm , letting it know to bend at that spot . what all this means is that each of an octopus 's eight arms can essentially think for itself . this gives it amazing flexibility and creativity when facing a new situation or problem , whether its opening a bottle to reach food , escaping through a maze , moving around in a new environment , changing the texture and the color of its skin to blend into the scenery , or even mimicking other creatures to scare away enemies . cephalopods may have evolved complex brains long before our vertebrate relatives . and octopus intelligence is n't just useful for octopuses . their radically different nervous system and autonomously thinking appendages have inspired new research in developing flexible robots made of soft materials . and studying how intelligence can arise along such a divergent evolutionary path can help us understand more about intelligence and consciousness in general . who knows what other forms of intelligent life are possible , or how they process the world around them .

and octopus intelligence is n't just useful for octopuses . their radically different nervous system and autonomously thinking appendages have inspired new research in developing flexible robots made of soft materials . and studying how intelligence can arise along such a divergent evolutionary path can help us understand more about intelligence and consciousness in general .

the use of nature as a model for developing new technology is called biomimicry . name three examples of technology inspired by nature .

translator : andrea mcdonough reviewer : jessica ruby imagine a place so dark you ca n't see the nose on your face . eyes opened or closed , it 's all the same because the sun never shines there . up ahead , you see a light . when you creep in to investigate , a blue light flits around you . `` i could watch this forever , '' you think . but you ca n't because the mouth of an anglerfish has just sprung open and eaten you alive . you are just one of many creatures at the bottom of the ocean who learn too late to appreciate the power of bioluminescence . bioluminescence refers to the ability of certain living things to create light . the human body can make stuff like ear wax and toe nails , but these organisms can turn parts of their body into glow sticks . it 's like nature made them ready to rave . why ? in one way or another , bioluminescence improves a living thing 's chances of survival . take the firefly . it 's ability to glow green helps it attract a mate on a warm , summer night , but it 's just one of many living things that can glow . the railroad worm , phrixothrix hirtus , can light up its body in two colors : red and green . would you eat something that looks like an airport runway ? neither would any sensible predator . the flashing lights keep the worm safe . then there 's the deep sea shrimp , acantherphyra purpurea . when it feels threatened , it spews a cloud of glowing goo from its mouth . who does n't run the other way when they 've just been puked on ? plus , that puke attracts bigger predators who want to eat the shrimp 's enemy . so what if you ca n't bioluminesce ? no problem ! there are other ways for living things to make bioluminescence work for them , even if they were n't born with the equipment to glow . let 's revisit the anglerfish moments before it tried to eat you . that glowing bait on top of its head ? it comes from a pocket of skin called the esca . the esca holds bioluminescent bacteria . the anglerfish ca n't glow there by itself , so it holds a sack of glowing bacteria instead . remember the firefly ? it can actually make itself glow . inside its lantern are two chemicals , a luciferin and a luciferase . when firefly luciferase and luciferin mix together in the presence of oxygen and fuel for the cell , called atp , the chemical reaction gives off energy in the form of light . once scientists figured out how the firefly creates its luciferase and luciferin , they used genetic engineering to make this light-producing reaction occur inside other living things that ca n't glow . for example , they inserted the genes , or instructions , for a cell to create firefly luciferase and luciferin into a tobacco plant . once there , the tobacco plant followed the instructions slipped into its dna and lit up like a christmas tree . the beauty of bioluminescence , unlike the light from the sun or an incandescent bulb , is that it 's not hot . it takes place in a range of temperatures that do n't burn a living thing . and unlike a glow stick , which fades out as the chemicals inside get used up , bioluminescent reactions use replenishable resources . that 's one reason engineers are trying to develop bioluminescent trees . just think , if planted on the side of highways , they could light the way , using only oxygen and other freely available , clean resources to run . talk about survival advantage ! that could help our planet live longer . do you find yourself thinking of other ways to put bioluminescence to good use ? that glow stick you swing at a rave may help you find a mate , but how else can bioluminescence improve your survival ? if you start thinking in this way , you have seen the light .

why ? in one way or another , bioluminescence improves a living thing 's chances of survival . take the firefly .

are bioluminescence and fluorescence the same thing ?

we are here in the basement of the royal society in london , the royal society is the uk national academy for sciences and we are here because there is an exhibition about rutherford . we are interested in the element rutherfordium which is right here at the bottom of the periodic table number 104 , and with these elements only tiny amounts , relatively few atoms have been made so we can ’ t tell you about how it is used in light bulbs or something like that because it has not been used for anything . people are really excited if they make one or two atoms of it . so instead we are going to tell you a bit about rutherford after whom it ’ s named . and rutherford is famous because he did a whole series of experiments , or he and his co-workers , that really explained the structure of atoms and so the periodic table for the first time really began to make sense . over here you can see there is a picture of rutherford here in his lab with one of his co-workers and this is a very famous picture . rutherford , who came from new zealand , had a very loud voice and the experiments were rather sensitive , if you talked too loud the apparatus started shaking and it did not work properly , so his students put up a big notice in the lab saying talk softly please . but i am not sure that it stopped him and i use this picture when i am talking to my students about safety , you ’ ve always got to be really safe when you are working as a chemist . first of all you can see that rutherford is smoking in the lab and then he is not wearing safety glasses , nor is his colleague , and then they have a whole series of wires and all sorts of things to trip over . so it is really surprising that they managed to get their experiments to work without some sort of serious accident . perhaps they did break things and never told us about it . anyway rutherford ’ s work was recognised by him winning the nobel prize and here , and it is quite exciting , there is a replica of the nobel prize . the nobel prize is a gold medal but here they have shown it as two half-medals , underneath there is nothing to see , so you can see both of the sides . so on one side there is the portrait of alfred nobel , whose money and foundation , still to this day , pays for prize money , when he received this it would have been presented to him by the swedish king in a huge ceremony in stockholm . now what i can ’ t remember is whether he got the nobel prize for physics or chemistry . i have a feeling… chemistry ! yes . i have a feeling that he got it for chemistry which was particularly funny because rutherford didn ’ t like chemistry . he said that there is just physics and stamp collecting and he did not really respect chemistry so perhaps the chemists got their revenge by giving him the nobel prize for chemistry . now rutherford had very strong views about the hours his students should work and they were not allowed to work after 6 o ’ clock at night in the lab and his chief technician would go round the lab at 6 o ’ clock and switch off all the apparatus and chase everybody out of the lab . and even though they did this , 11 of his students won nobel prizes ; this must be one of the records for any single research group to this day . and of course when they went home having had dinner and drank wine in the college then they started working writing papers . but it is very interesting that if you read letters from visiting american scientists they could not understand how rutherford ’ s lab was so successful because the people came in at 10 o ’ clock in the morning they went home at 6 , and did not seem to do any work at all , but they discovered all these wonderful things . what ’ s your policy on your students working then ? well i always encourage my students to work but i find that if i encourage them too hard , it has the opposite effect , just like parents telling children to do their homework but by and large when people are enthusiastic about their science it is difficult to stop them working too much . as part of this exhibition they have got some postcards of rutherford and this one has got , i think it is really terrific , shows rutherford in the sea . but i really like this because it shows that famous scientists sometimes take time off and they don ’ t always behave like white-coated figures in labs , but they do have a human side as well .

we are here in the basement of the royal society in london , the royal society is the uk national academy for sciences and we are here because there is an exhibition about rutherford . we are interested in the element rutherfordium which is right here at the bottom of the periodic table number 104 , and with these elements only tiny amounts , relatively few atoms have been made so we can ’ t tell you about how it is used in light bulbs or something like that because it has not been used for anything . people are really excited if they make one or two atoms of it .

does rutherfordium have any applications in our daily lives ?

when we think of classic works of art , the most common setting we imagine them in is a museum . but what we often forget is that much of this art was not produced with a museum setting in mind . what happens to an artwork when it 's taken out of its originally intended context ? take the example of michelangelo 's statue of david , depicting the boy hero who slew the giant philistine , goliath , armed with only his courage and his slingshot . when michelangelo began carving a block of pure white marble to communicate this famous biblical story , the city of florence intended to place the finished product atop their grand cathedral . not only would the 17 foot tall statue be easily visible at this height , but its placement alongside 11 other statues of old testament heroes towering over onlookers would have a powerful religious significance , forcing the viewer to stare in awe towards the heavens . but by the time michelangelo had finished the work , in 1504 , the plans for the other statues had fallen through , and the city realized that lifting such a large sculpture to the roof would be more difficult than they had thought . furthermore , the statue was so detailed and lifelike , down to the bulging veins in david 's arm and the determination on his face , that it seemed a shame to hide it so far from the viewer . a council of politicians and artists convened to decide on a new location for the statue . ultimately voting to place it in front of the palazzo della signoria , the town hall and home of the new republican government . this new location transformed the statue 's meaning . the medici family , who for generations had ruled the city through their control of banking , had recently been exiled , and florence now saw itself as a free city , threatened on all sides by wealthy and powerful rivals . david , now the symbol of heroic resistance against overwhelming odds , was placed with his intense stare , now a look of stern warning , focused directly towards rome , the home of cardinal giovanni de medici . though the statue itself had not been altered , its placement changed nearly every aspect of it from a religious to a political significance . though a replica of david still appears at the palazzo , the original statue was moved in 1873 to the galleria dell'accademia , where it remains today . in the orderly , quiet environment of the museum , alongside numerous half-finished michelangelo sculptures , overt religious and political interpretations fall away , giving way to detached contemplation of michelangelo 's artistic and technical skill . but even here , the astute viewer may notice that david 's head and hand appear disproportionately large , a reminder that they were made to be viewed from below . so , not only does context change the meaning and interpretation of an artwork throughout its history , sometimes it can make that history resurface in the most unexpected ways .

ultimately voting to place it in front of the palazzo della signoria , the town hall and home of the new republican government . this new location transformed the statue 's meaning . the medici family , who for generations had ruled the city through their control of banking , had recently been exiled , and florence now saw itself as a free city , threatened on all sides by wealthy and powerful rivals .

what meaning would michelangelo ’ s statue of david have if it appeared outside of your favorite sports team ’ s arena ?

translator : jessica ruby reviewer : caroline cristal you may not realize it , but from the moment you got out of bed today to the point where you sat down to watch this video , you 've essentially been swimming . why ? because air is a fluid just like water . it has waves and eddies . it flows . and when you push air out of the way , it rushes around you into a wake . so why do n't we notice it most of the time ? we commonly think of air as empty space . but while one cubic centimeter of interstellar space , the volume in the tip of your pinky finger , contains roughly one atom , the same volume of air has about 10 quintillion molecules . if that sounds hard to wrap your head around , it happens to be about the same as the number of insects alive on the planet , all crawling , climbing , and flying over each other in an enormous , tightly packed swarm . when this swarm of molecules runs into things , it exerts a force , pressing against the boundaries of the fluid , like water pressing against the glass of a bottle . this is known as air pressure . and while air is lighter than water , all those molecules still get pretty heavy , with the total air filling a typical school gym , weighing about as much as an adult elephant . so when you walk into a gym , how come you 're not immediately crushed by the elephant of air in the room ? well , first of all , because most of it is pressing on the floor and the walls , and the part that is pressing on you is pushed back by the pressure inside you ! you see , the air , as well as the water and everything else , that fills our bodies exerts an amount of pressure equal to that of the air outside . of course , this is no accident . it 's precisely what allows us to survive in the normal atmosphere , and what makes it more difficult at high altitudes or deep water . and we normally do n't feel the air pressing on us because it 's generally uniform . so even though different amounts of air molecules are hitting you at different times , the swarm is so thick that all those little differences average out . what happens when air pressure is n't uniform ? this means that the molecules are pushing harder in one region of air than another , driving the air flow from the higher pressure region to the lower . we feel this flow directly as wind , and the pressure systems that meteorologists are always going on about are responsible for other weather changes , from the mundane to the catastrophic . but differences in air pressure do more than just let us complain about the weather ; they 're the very reason we 're alive . we breathe by lowering the pressure in our lungs , allowing air to rush in . so the next time you take a deep breath , think of the unfathomable number of air molecules you 're commanding to move . we look up at the night sky to ponder the infinity of space , but unless you 're watching this video from that deep space , there are more air molecules in and around your body than there are grains of sand in all the world 's beaches and deserts , stars in the visible universe , or both of those numbers combined . the vastness of the universe is right in front of you and inside you .

when this swarm of molecules runs into things , it exerts a force , pressing against the boundaries of the fluid , like water pressing against the glass of a bottle . this is known as air pressure . and while air is lighter than water , all those molecules still get pretty heavy , with the total air filling a typical school gym , weighing about as much as an adult elephant . so when you walk into a gym , how come you 're not immediately crushed by the elephant of air in the room ?

the air in a typical gymnasium can weigh as much as ________ .

translator : andrea mcdonough reviewer : bedirhan cinar i am going to start with a challenge . i want you to imagine each of these two scenes in as much detail as you can . scene number one : `` they gave us a hearty welcome . '' well , who are the people who are giving a hearty welcome ? what are they wearing ? what are they drinking ? ok , scene two : `` they gave us a cordial reception . '' how are these people standing ? what expressions are on their faces ? what are they wearing and drinking ? fix these pictures in your mind 's eye and then jot down a sentence or two to describe them . we 'll come back to them later . now on to our story . in the year 400 c.e . the celts in britain were ruled by romans . this had one benefit for the celts : the romans protected them from the barbarian saxon tribes of northern europe . but then the roman empire began to crumble , and the romans withdrew from britain . with the romans gone , the germanic tribes , the angles , saxons , jutes , and frisians quickly sailed across the water , did away with the celts , and formed kingdoms in the british isles . for several centuries , these tribes lived in britain , and their germanic language , anglo saxon , became the common language , what we call old english . although modern english speakers may think old english sounds like a different language , if you look and listen closely , you 'll find many words that are recognizable . for example , here is what the lord 's prayer looks like in old english . at first glance , it may look unfamiliar , but update the spelling a bit , and you 'll see many common english words . so the centuries passed with britains happily speaking old english , but in the 700 's , a series of viking invasions began , which continued until a treaty split the island in half . on one side were the saxons . on the other side were the danes who spoke a language called old norse . as saxons fell in love with their cute danish neighbors and marriages blurred the boundaries , old norse mixed with old english , and many old norse words like freckle , leg , root , skin , and want are still a part of our language . 300 years later , in 1066 , the norman conquest brought war again to the british isles . the normans were vikings who settled in france . they had abandoned the viking language and culture in favor of a french lifestyle , but they still fought like vikings . they placed a norman king on the english throne and for three centuries , french was the language of the british royalty . society in britain came to have two levels : french-speaking aristocracy and old english-speaking peasants . the french also brought many roman catholic clergymen with them who added latin words to the mix . old english adapted and grew as thousands of words flowed in , many having to do with government , law , and aristocracy . words like council , marriage , sovereign , govern , damage , and parliament . as the language expanded , english speakers quickly realized what to do if they wanted to sound sophisticated : they would use words that had come from french or latin . anglo saxon words seemed so plain like the anglo saxon peasants who spoke them . let 's go back to the two sentences you thought about earlier . when you pictured the hearty welcome , did you see an earthy scene with relatives hugging and talking loudly ? were they drinking beer ? were they wearing lumberjack shirts and jeans ? and what about the cordial reception ? i bet you pictured a far more classy and refined crowd . blazers and skirts , wine and caviar . why is this ? how is it that phrases that are considered just about synonymous by the dictionary can evoke such different pictures and feelings ? `` hearty '' and `` welcome '' are both saxon words . `` cordial '' and `` reception '' come from french . the connotation of nobility and authority has persisted around words of french origin . and the connotation of peasantry , real people , salt of the earth , has persisted around saxon words . even if you never heard this history before , the memory of it persists in the feelings evoked by the words you speak . on some level , it 's a story you already knew because whether we realize it consciously or only subconsciously , our history lives in the words we speak and hear .

we 'll come back to them later . now on to our story . in the year 400 c.e .

this lecture , when given in a classroom , is entitled : “ the words tell the story. ” what is meant by that title ?

would n't it be great if we could be invisible ? ha , right ? i mean , we could spy on people without being noticed and do whatever we want without being held responsible . now , magicians have figured out how to utilize full-sized mirrors to bend light in order to create disappearing illusions . scientists have created metamaterials to guide rays of light around tiny , two-dimensional objects . cameras can also film what is behind you and project the image so you appear invisible from the front . however , none of these options can make an object as large as a person appear invisible for all angles and distances while its moving . but if you are truly invisible , as in from within , here are a few problems you may not have thought about before . to move around undetected by other people , you would have to be totally naked . even if it 's freezing outside ! you ca n't carry anything , including your wallet and keys , otherwise people would just see your wallet and keys floating around . drivers and people on the street ca n't see you either , therefore they can and will run into you at some point . oh , and you better not wear any perfume or make any noise breathing , otherwise they 'll know you 're there . and , just because you start off invisible , does n't mean you 'll stay that way . what if someone accidentally spills scolding hot coffee on you ? and what if it rains ? but if you think only liquid can make you visible , you 're wrong . dust consists of dead skin cells from humans , soil particles , and fibers from clothes made from cotton and other materials . dust sticks to the moisture on our skin when we sweat and the tiny hairs on our skin when we are dry . so , even if you are invisible , dust would still land on every part of you . we usually do n't notice the dust on our skin because we ca n't see a thin layer of dust on top of our skin color . but , if you 're invisible , people would see a human-shaped blob of dust walking around with extremely dirty soles . gross ! what do you think the world looks like if you are invisible ? well , the answer is nothing . the reason you ca n't see in the dark is because there is no light . to see an apple , light has to hit the apple and return it to your eyes . then , the retinas in your eyes catch the light reflection for your brain to interpret into the image of an apple . if you 're invisible , then , by definition , light would travel through you or around you instead of bouncing off you for people to see . but that means that retinas in your eyes are not catching the light , either . therefore , your brain has nothing to interpret into an image . can you see your reflection without a mirror to stop the light ? no . so , when you ca n't be seen by others , you also can not see . ouch ! now , have you given any thought as of whether the invisibility is permanent ? if it is , how can you receive medical treatment from a doctor if you 're injured ? the doctor would n't know where to apply ointments or bandages because they can not access your injury . for that matter , you ca n't see it either . i mean , what if you have an illness or an infection ? how can the doctor diagnose you without being able to see the color change or inflammation ? and what if everyone is permanently invisible ? well , think about how boring the world would be without seeing people on the streets , on tv , or at home on your computer like right now . it 's lonely being invisible . now , which superpower physics lesson will you explore next ? shifting body size and content , super speed , flight , super strength , immortality , and invisibility .

cameras can also film what is behind you and project the image so you appear invisible from the front . however , none of these options can make an object as large as a person appear invisible for all angles and distances while its moving . but if you are truly invisible , as in from within , here are a few problems you may not have thought about before .

as of 2013 , who has been able to make an object as large as a person appear “ completely ” invisible from all angles and distances while it is moving ?

meet the nurdles . they may be tiny , look harmless , and sound like a bunch of cartoon characters , but do n't be fooled . these little guys are plotting ocean domination . nurdles are some of the planet 's most pervasive pollutants , found in lakes , rivers , and oceans across the globe . the tiny factory-made pellets form the raw material for every plastic product we use . and each year , billions of pounds of nurdles are produced , melted , and molded into toys , bottles , buttons , bags , pens , shoes , toothbrushes , and beads . they are everywhere . and they come in many guises , multi-colored and many-shaped , they range in size from just a few millimeters to mere specks that are only visible through a microscope . but their real advantage in the quest for ocean domination is their incredible endurance , which allows them to persist in an environment for generations because their artificial makeup makes them unable to biodegrade . so , just as long as they do n't get into the environment , we have nothing to worry about , right ? the problem is nurdles have a crafty way of doing exactly this . produced in several countries and shipped to plastic manufacturing plants the world over , nurdles often escape during the production process , carried by runoff to the coast or during shipping when they 're mistakenly tipped into the waves . once in the water , nurdles are swiftly carried by currents , ultimately winding up in huge circulating ocean systems called gyres , where they convene to plan their tactics . the earth has five gyres that act as gathering points , but the headquarters of nurdle ocean domination are in the pacific ocean , where the comparative enormity of the gyre and the resulting concentration of pollution is so huge that it 's known as the great pacific garbage patch . here , nurdles have good company . this gyre draws in all kinds of pollution , but because they do n't biodegrade , plastics dominate , and they come from other sources besides nurdles , too . you know those tiny beads you see in your face wash or your toothpaste ? they 're often made of plastic , and after you flush them down the drain , some also end up in this giant garbage patch , much to the delight of the nurdles , building up their plastic army there . and then there are the large pieces of unrecycled plastic litter , like bottles and carrier bags , transported by runoff from land to sea . over time , these plastic chunks turn into a kind of nurdle , too , but one that 's been worn down by the elements , not made in a factory . and as if they were n't threatening enough , the rough , pitted surfaces of these microplastics , the name we give to all those collective plastic bits , water-born chemicals stick , or adhere , to them , making them toxic . this gathering has grown so immense that the oceanic garbage patch can shift from around the size of texas to something the size of the united states . but while this toxic tornado is circulating , the birds , fish , filter feeders , whales , and crustaceans around it are just going about their daily business , which means they 're looking for food . unfortunately for them , tiny bits of floating plastic look a lot like fish eggs and other enticing bits of food . but once ingested , microplastics have a very different and terrible habit of sticking around . inside an animal 's stomach , they not only damage its health with a cocktail of toxins they carry but can also lead to starvation because although nurdles may be ingested , they 're never digested , tricking an animal into feeling like it 's continually full and leading to its eventual death . when one organism consumes another , microplastics and their toxins are then passed up through the food chain . and that 's how , bit by bit , nurdles accomplish their goal , growing ever more pervasive as they wipe out marine life and reshape the ocean 's ecosystems . so , how to break this cycle ? the best solution would be to take plastics out of the equation altogether . that 'll take a lot of time but requires only small collective changes , like more recycling , replacing plastics with paper and glass , and ditching that toothpaste with the microbeads . if we accomplish these things , perhaps over time fewer and fewer nurdles will turn up at that giant garbage patch , their army of plastics will grow weaker , and they 'll surrender the ocean to its true keepers once more .

once in the water , nurdles are swiftly carried by currents , ultimately winding up in huge circulating ocean systems called gyres , where they convene to plan their tactics . the earth has five gyres that act as gathering points , but the headquarters of nurdle ocean domination are in the pacific ocean , where the comparative enormity of the gyre and the resulting concentration of pollution is so huge that it 's known as the great pacific garbage patch . here , nurdles have good company .

the largest nurdle headquarters is the great pacific garbage patch , located in :

a handful of species on earth share a seemingly mysterious trait : a menstrual cycle . we 're one of the select few . monkeys , apes , bats , humans , and possibly elephant shrews are the only mammals on earth that menstruate . we also do it more than any other animal , even though its a waste of nutrients and can be a physical inconvenience . so where 's the sense in this uncommon biological process ? the answer begins with pregnancy . during this process , the body 's resources are cleverly used to shape a suitable environment for a fetus , creating an internal haven for a mother to nurture her growing child . in this respect , pregnancy is awe-inspiring , but that 's only half the story . the other half reveals that pregnancy places a mother and her child at odds . as for all living creatures , the human body evolved to promote the spread of its genes . for the mother , that means she should try to provide equally for all her offspring . but a mother and her fetus do n't share exactly the same genes . the fetus inherits genes from its father , as well , and those genes can promote their own survival by extracting more than their fair share of resources from the mother . this evolutionary conflict of interests places a woman and her unborn child in a biological tug-of-war that plays out inside the womb . one factor contributing to this internal tussle is the placenta , the fetal organ that connects to the mother 's blood supply and nourishes the fetus while it grows . in most mammals , the placenta is confined behind a barrier of maternal cells . this barrier lets the mother control the supply of nutrients to the fetus . but in humans and a few other species , the placenta actually penetrates right into the mother 's circulatory system to directly access her blood stream . through its placenta , the fetus pumps the mother 's arteries with hormones that keep them open to provide a permanent flow of nutrient-rich blood . a fetus with such unrestricted access can manufacture hormones to increase the mother 's blood sugar , dilate her arteries , and inflate her blood pressure . most mammal mothers can expel or reabsorb embryos if required , but in humans , once the fetus is connected to the blood supply , severing that connection can result in hemorrhage . if the fetus develops poorly or dies , the mother 's health is endangered . as it grows , a fetus 's ongoing need for resources can cause intense fatigue , high blood pressure , and conditions like diabetes and preeclampsia . because of these risks , pregnancy is always a huge , and sometimes dangerous , investment . so it makes sense that the body should screen embryos carefully to find out which ones are worth the challenge . this is where menstruation fits in . pregnancy starts with a process called implantation , where the embryo embeds itself in the endometrium that lines the uterus . the endometrium evolved to make implantation difficult so that only the healthy embryos could survive . but in doing so , it also selected for the most vigorously invasive embryos , creating an evolutionary feedback loop . the embryo engages in a complex , exquisitely timed hormonal dialogue that transforms the endometrium to allow implantation . what happens when an embryo fails the test ? it might still manage to attach , or even get partly through the endometrium . as it slowly dies , it could leave its mother vulnerable to infection , and all the time , it may be emitting hormonal signals that disrupt her tissues . the body avoids this problem by simply removing every possible risk . each time ovulation does n't result in a healthy pregnancy , the womb gets rid of its endometrial lining , along with any unfertilized eggs , sick , dying , or dead embryos . that protective process is known as menstruation , leading to the period . this biological trait , bizarre as it may be , sets us on course for the continuation of the human race .

the body avoids this problem by simply removing every possible risk . each time ovulation does n't result in a healthy pregnancy , the womb gets rid of its endometrial lining , along with any unfertilized eggs , sick , dying , or dead embryos . that protective process is known as menstruation , leading to the period .

each time ovulation does not result in a healthy pregnancy , what occurs ?

space : it 's where things happen . time : it 's when things happen . we can measure where things are and when things take place , but in modern physics , we realize when and where are actually part of the same question . because when it comes to understanding the universe , we need to replace three-dimensional space plus time with a single concept : four-dimensional space-time . we 'll explore and explain space-time in this series of animations . animations ? yeah . well , we 're not very animated are we ? sure we are ! look , i can go from here to here . whoa ! how 'd you get from here to there ? how fast did you go ? did you run ? walk ? did you even go in a straight line ? ah ! to answer that , you 'll need to make our cartoon physics look more like physics physics . you 'll need more panels . more panels , please ! okay , in each panel , andrew 's in a slightly different place . so i can see each one records where andrew is at a different time . that 's great . but it would be easier to see what 's going on if we could cut out all the hundreds of panels and stack them up like a flip book . right , now let 's flip through the book so that we can see one panel after another getting through 24 in every second . see ! i told you it was an animation . now you can see me walking along . drawing all those panels and putting them into a flip book is just one way of recording the way i 'm moving . it 's how animation , or even movies , work . as it turns out , at my walking speed , it takes two seconds to get past each fence post , and they 're spaced four meters apart . so we can calculate my velocity -- how fast i 'm moving through space - - is two meters per second . but i could 've worked that out from the panels without flipping through them . from the edge of the flip book , you can see all of the copies of the fence posts and all of the copies of andrew and he 's in a slightly different place in each one . now we can predict everything that will happen to andrew when we flip through 24 pages every second , including his speed of motion , just by looking . no need to flip through at all . the edge of this flip book is known as a space-time diagram of andrew 's journey through , you guessed it , space and time . we call the line that represents andrew 's journey his world line . if i jog instead of walking , i might be able to get past a fence post every second . he 's not very athletic . anyway , when we look at this new flip book from the edge , we can do the same analysis as before . the world line for andrew jogging is more tilted over than the world line for andrew walking . we can tell he 's going twice as fast as before without flipping the panels . but here 's the clever bit . in physics , it 's always good to view things from other perspectives . after all , the laws of physics should be the same for everyone or no one will obey them . so let 's rethink our cartoon and have the camera follow andrew jogging along as the fence posts approach and pass behind him . still viewing it as a flip book of panels , we do n't need to redraw anything . we simply move all of the cutout frames slightly until andrew 's tilted world line becomes completely vertical . to see why , let 's flip it . yes , now i 'm stationery , just jogging on the spot , in the center of the panel . on the edge of the flip book , my world line was going straight upwards . the fence posts are coming past me . it 's now their world lines that are tilted . this rearrangement of the panels is known as a galilean transformation , and it lets us analyze physics from someeone else 's perspective . in this case , mine . after all , it 's always good to see things from other points of view , especially when the viewers are moving at different speeds . so long as the speeds are n't too high . if you 're a cosmic ray moving at the speed of light , our flip book of your point of view falls apart . to stop that from happening , we 'll have to glue panels together . instead of a stack of separate panels , we 'll need a solid block of space-time , which we 'll come to in the next animation .

that 's great . but it would be easier to see what 's going on if we could cut out all the hundreds of panels and stack them up like a flip book . right , now let 's flip through the book so that we can see one panel after another getting through 24 in every second .

we showed the worldlines of objects moving at a constant speed . what would a worldline look like for someone who starts out sitting down , walks across the room , then sits down again ? what would a worldline look like for a smoothly accelerating car ? try thinking of other objects that you could draw worldlines for , and draw them . get your classmates to guess what it is you ’ ve drawn .

have you ever been waiting in line at the grocery store , innocently perusing the magazine rack , when a song pops into your head ? not the whole song , but a fragment of it that plays and replays until you find yourself unloading the vegetables in time to the beat . you 've been struck by an earworm , and you 're not alone . over 90 % of people are plagued by earworms at least once a week , and about a quarter of people experience them several times a day . they tend to burrow in during tasks that do n't require much attention , say , when waiting on water to boil or a traffic light to change . this phenomenon is one of the mind 's great mysteries . scientists do n't know exactly why it 's so easy for tunes to get stuck in our heads . from a psychological perspective , earworms are an example of mental imagery . this imagery can be visual , like when you close your eyes and imagine a red wagon , or it can be auditory , like when you imagine the sound of a baby screaming , or oil sizzling in a pan . earworms are a special form of auditory imagery because they 're involuntary . you do n't plug your ears and try to imagine `` who let the dogs out , '' or , well , you probably do n't . it just intrudes onto your mental soundscape and hangs around like an unwanted house guest . earworms tend to be quite vivid and they 're normally made up of a tune , rather than , say , harmonies . a remarkable feature of earworms is their tendency to get stuck in a loop , repeating again and again for minutes or hours . also remarkable is the role of repetition in sparking earworms . songs tend to get stuck when we listen to them recently and repeatedly . if repetition is such a trigger , then perhaps we can blame our earworms on modern technology . the last hundred years have seen an incredible proliferation of devices that help you listen to the same thing again and again . records , cassettes , cds , or streamed audio files . have these technologies bread some kind of unique , contemporary experience , and are earworms just a product of the late 20th century ? the answer comes from an unlikely source : mark twain . in 1876 , just one year before the phonograph was invented , he wrote a short story imagining a sinister takeover of an entire town by a rhyming jingle . this reference , and others , show us that earworms seem to be a basic psychological phenomenon , perhaps exacerbated by recording technology but not new to this century . so yes , every great historical figure , from shakespeare to sacajawea , may well have wandered around with a song stuck in their head . besides music , it 's hard to think of another case of intrusive imagery that 's so widespread . why music ? why do n't watercolors get stuck in our heads ? or the taste of cheesy taquitos ? one theory has to do with the way music is represented in memory . when we listen to a song we know , we 're constantly hearing forward in time , anticipating the next note . it 's hard for us to think about one particular musical moment in isolation . if we want to think about the pitch of the word `` you '' in `` happy birthday , '' we have to start back at `` happy , '' and sing through until we get to `` you . '' in this way , a tune is sort of like a habit . just like once you start tying your shoe , you 're on automatic until you tighten the bow , once a tune is suggested because , for example , someone says , `` my umbrella , '' we have to play through until it reaches a natural stopping point , `` ella , ella , ella . '' but this is largely speculation . the basic fact remains we do n't know exactly why we 're susceptible to earworms . but understanding them better could give us important clues to the workings of the human brain . maybe the next time we 're plagued by a taylor swift tune that just wo n't go away , we 'll use it as the starting point for a scientific odyssey that will unlock important mysteries about basic cognition . and if not , well , we can just shake it off .

have these technologies bread some kind of unique , contemporary experience , and are earworms just a product of the late 20th century ? the answer comes from an unlikely source : mark twain . in 1876 , just one year before the phonograph was invented , he wrote a short story imagining a sinister takeover of an entire town by a rhyming jingle .

a story by mark twain is one piece of evidence that :

every spring , hundreds of adventure-seekers dream of climbing qomolangma , also known as mount everest . at base camp , they hunker down for months waiting for the chance to scale the mountain 's lofty , lethal peak . but why do people risk life and limb to climb everest ? is it the challenge ? the view ? the chance to touch the sky ? for many , the draw is everest 's status as the highest mountain on earth . there 's an important distinction to make here . mauna kea is actually the tallest from base to summit , but at 8850 meters above sea level , everest has the highest altitude on the planet . to understand how this towering formation was born , we have to peer deep into our planet 's crust , where continental plates collide . the earth 's surface is like an armadillo 's armor . pieces of crust constantly move over , under , and around each other . for such huge continental plates , the motion is relatively quick . they move two to four centimeters per year , about as fast as fingernails grow . when two plates collide , one pushes into or underneath the other , buckling at the margins , and causing what 's known as uplift to accomodate the extra crust . that 's how everest came about . 50 million years ago , the earth 's indian plate drifted north , bumped into the bigger eurasian plate , and the crust crumpled , creating huge uplift . mountain everest lies at the heart of this action , on the edge of the indian-eurasian collision zone . but mountains are shaped by forces other than uplift . as the land is pushed up , air masses are forced to rise as well . rising air cools , causing any water vapor within it to condense and form rain or snow . as that falls , it wears down the landscape , dissolving rocks or breaking them down in a process known as weathering . water moving downhill carries the weathered material and erodes the landscape , carving out deep valleys and jagged peaks . this balance between uplift and erosion gives a mountain its shape . but compare the celestial peaks of the himalayas to the comforting hills of appalachia . clearly , all mountains are not alike . that 's because time comes into the equation , too . when continental plates first collide , uplift happens fast . the peaks grow tall with steep slopes . over time , however , gravity and water wear them down . eventually , erosion overtakes uplift , wearing down peaks faster than they 're pushed up . a third factor shapes mountains : climate . in subzero temperatures , some snowfall does n't completely melt away , instead slowly compacting until it becomes ice . that forms the snowline , which occurs at different heights around the planet depending on climate . at the freezing poles , the snowline is at sea level . near the equator , you have to climb five kilometers before it gets cold enough for ice to form . gathered ice starts flowing under its own immense weight forming a slow-moving frozen river known as a glacier , which grinds the rocks below . the steeper the mountains , the faster ice flows , and the quicker it carves the underlying rock . glaciers can erode landscapes swifter than rain and rivers . where glaciers cling to mountain peaks , they sand them down so fast , they lop the tops off like giant snowy buzzsaws . so then , how did the icy mount everest come to be so tall ? the cataclysmic continental clash from which it arose made it huge to begin with . secondly , the mountain lies near the tropics , so the snowline is high , and the glaciers relatively small , barely big enough to widdle it down . the mountain exists in a perfect storm of conditions that maintain its impressive stature . but that wo n't always be the case . we live in a changing world where the continental plates , earth 's climate , and the planet 's erosive power might one day conspire to cut mount everest down to size . for now , at least , it remains legendary in the minds of hikers , adventurers , and dreamers alike .

the earth 's surface is like an armadillo 's armor . pieces of crust constantly move over , under , and around each other . for such huge continental plates , the motion is relatively quick .

pieces of the earth ’ s crust move :

it may seem like the semicolon is struggling with an identity crisis . it looks like a comma crossed with a period . maybe that 's why we toss these punctuation marks around like grammatical confetti . we 're confused about how to use them properly . in fact , it 's the semicolon 's half-half status that makes it useful . it 's stronger than a comma , and less final than a period . it fills the spaces in between , and for that reason , it has some specific and important tasks . for one , it can clarify ideas in a sentence that 's already festooned with commas . `` semicolons : at first , they may seem frightening , then , they become enlightening , finally , you 'll find yourself falling for these delightful punctuation marks . '' even though the commas separate different parts of the sentence , it 's easy to lose track of what belongs where . but then the semicolon edges in to the rescue . in list-like sentences , it can exert more force than commas do , cutting sentences into compartments and grouping items that belong together . the semicolon breaks things up , but it also builds connections . another of its tasks is to link together independent clauses . these are sentences that can stand on their own , but when connected by semicolons , look and sound better because they 're related in some way . `` semicolons were once a great mystery to me . i had no idea where to put them . '' technically , there 's nothing wrong with that . these two sentences can stand alone . but imagine they appeared in a long list of other sentences , all of the same length , each separated by periods . things would get monotonous very fast . in that situation , semicolons bring fluidity and variation to writing by connecting related clauses . but as beneficial as they are , semicolons do n't belong just anywhere . there are two main rules that govern their use . firstly , unless they 're being used in lists , semicolons should only connect clauses that are related in some way . you would n't use one here , for instance : `` semicolons were once a great mystery to me ; i 'd really like a sandwich . '' periods work best here because these are two totally different ideas . a semicolon 's job is to reunite two independent clauses that will benefit from one another 's company because they refer to the same thing . secondly , you 'll almost never find a semicolon willingly stationed before coordinating conjunctions : the words , `` and , '' `` but , '' `` for , '' `` nor , '' `` or , '' `` so , '' and `` yet . '' that 's a comma 's place , in fact . but a semicolon can replace a conjunction to shorten a sentence or to give it some variety . ultimately , this underappreciated punctuation mark can give writing clarity , force , and style , all encompassed in one tiny dot and squiggle that 's just waiting to be put in the right place .

periods work best here because these are two totally different ideas . a semicolon 's job is to reunite two independent clauses that will benefit from one another 's company because they refer to the same thing . secondly , you 'll almost never find a semicolon willingly stationed before coordinating conjunctions : the words , `` and , '' `` but , '' `` for , '' `` nor , '' `` or , '' `` so , '' and `` yet . ''

one of the semicolon 's grammatical functions is to :

today lots of girls play sports . but , for a long time , girls were not encouraged to kick , throw , run , jump , shoot , slide , or hit like boys . so , why did things change ? and how much have they changed ? are girls and boys treated equally when it comes to sports ? to begin to answer these questions , we have to look back . in 1972 , congress passed a law called title ix , which protected girls and women from discrimination in schools , colleges , and universities . this included discrimination in school-sponsored sports . at that time , only 15 % of college athletes were women , and in high schools , only 7 % of athletes were girls . female athletes did n't get a lot of support either and often had to provide their own uniforms and equipment . it was title ix that forced school administrators to make sports more equal . but what does equal mean in sports ? the government developed rules to measure equality under two general categories : participation and treatment . in the early days of title ix , the number of girls playing sports was so low that it would have been very difficult for schools to suddenly provide exactly the same number of opportunities for girls and boys . instead , the government wrote rules that gave schools three options , or tests , to demonstrate fairness in opportunities for girls . the three tests are proportionality , progress , and satisfied interests . a school can pick which test to follow . proportionality means that girls should receive the same percentage of athletic opportunities as the percentage of girls in the student body . so , if 51 % of students are girls , then girls should have approximately 51 % of the opportunities to play sports . the second test , progress , requires schools to make up for the days when girls had fewer opportunities by adding new sports for girls on a regular basis . the third test asks if girls interested in athletics are satisfied . under this test , a school must regularly ask female students what sports they are interested in and also take into consideration the popularity of certain sports in the area where the school is located . it must , then , add teams according to the girls ' interests . another important part of title ix is that it does n't just look at how many athletic opportunities are available to each sex but whether those opportunities are of equal quality . specifically , title ix requires equality between boys and girls teams for things like equipment and supplies , publicity , the scheduling of games and practice times , and the quality and number of coaches . girls should also have equal access to locker rooms , practice spaces , and competitive facilities , as well as medical services . so , if the best time to play basketball is on friday nights because that 's when most parents and fans can come , then the girls and boys teams should take turns playing on friday night . if boys teams play in a stadium with lights , scoreboards , and concession stands , then girls teams must have the same opportunity , either by sharing those facilities or getting their own of equal quality . but , as we all know , just because a law exists does n't mean that everybody follows it . school officials are responsible for making sure there is fairness in sports , but you can help , too , by keeping an eye on your own school . look around . are there a lot more boys than girls who play sports ? is the boys ' soccer field better than the girls ' ? are athletic trainers available to all teams equally ? does the baseball team get new uniforms every year , while the softball team gets them every three years ? if you think there might be inequality in your schools , you can approach a school administrator , a parent , or the office of civil rights , a government agency that makes sure schools comply with title ix because equality is important for everyone , both on the field and off .

it must , then , add teams according to the girls ' interests . another important part of title ix is that it does n't just look at how many athletic opportunities are available to each sex but whether those opportunities are of equal quality . specifically , title ix requires equality between boys and girls teams for things like equipment and supplies , publicity , the scheduling of games and practice times , and the quality and number of coaches .

washington high school has an equal number of female and male students . girls receive forty percent of the athletic opportunities and boys receive sixty percent of athletic opportunities . what can whs do to ensure compliance with title ix ?

in 1978 , louise brown became the world 's first baby to be born by in vitro fertilization , or ivf . her birth revolutionized the field of reproductive medicine . given that approximately one in eight heterosexual couples has difficulty conceiving , and that homosexual couples and single parents often need clinical help to make a baby , the demand for ivf has been growing . ivf is so common , that more than 5 million babies have been born through this technology . ivf works by mimicking the brilliant design of sexual reproduction . in order to understand ivf , we first need to take a look at the natural process of baby making . believe it or not , it all starts in the brain . roughly fifteen days before fertilization can happen , the anterior pituitary gland secretes follicle stimulating hormone , fsh , which ripens a handful of follicles of the ovary that then release estrogen . each follicle contains one egg , and on average , only one follicle becomes fully mature . as it grows and continues to release estrogen , this hormone not only helps coordinate growth and preparation of the uterus , it also communicates to the brain how well the follicle is developing . when the estrogen level is high enough , the anterior pituitary releases a surge of luteinizing hormone , lh , which triggers ovulation and causes the follicle to rupture and release the egg . once the egg leaves the ovary , it is directed into the fallopian tube by the finger-like fimbriae . if the egg is not fertilized by sperm within 24 hours , the unfertilized egg will die , and the entire system will reset itself , preparing to create a new egg and uterine lining the following month . the egg is the largest cell in the body and is protected by a thick , extracellular shell of sugar and protein called the zona pellucida . the zona thwarts the entry and fusion of more than one sperm , the smallest cell in the body . it takes a man two to three months to make sperm , and the process constantly renews . each ejaculation during sexual intercourse releases more than 100 million sperm . but only 100 or so will ultimately make it to the proximity of the egg , and only one will successfully penetrate through the armor of the zona pellucida . upon successful fertilization , the zygote immediately begins developing into an embryo , and takes about three days to reach the uterus . there , it requires another three or so days to implant firmly into the endometrium , the inner lining of the uterus . once implanted , the cells that are to become the placenta secrete a hormone that signals to the ovulated follicle that there is a pregnancy in the uterus . this helps rescue that follicle , now called the corpus luteum , from degenerating as it normally would do in that stage of the menstrual cycle . the corpus luteum is responsible for producing the progesterone required to maintain the pregnancy until six to seven weeks of gestation , when the placenta develops and takes over , until the baby is born approximately 40 weeks later . now , how do you make a baby in a lab ? in patients undergoing ivf , fsh is administered at levels that are higher than naturally occuring to cause a controlled overstimulation of the ovaries so that they ultimately produce multiple eggs . the eggs are then retrieved just before ovulation would occur , while the woman is under anesthesia , through an aspirating needle that is guided by ultrasound . most sperm samples are produced by masturbation . in the laboratory , the identified eggs are stripped of surrounding cells and prepared for fertilization in a petri dish . fertilization can occur by one of two techniques . in the first , the eggs are incubated with thousands of sperm and fertilization occurs naturally over a few hours . the second technique maximizes certainty of fertilization by using a needle to place a single sperm inside the egg . this is particularly useful when there is a problem with the quality of the sperm . after fertilization , embryos can be further screened for genetic suitability , frozen for later attempted pregnancies , or delivered into the woman 's uterus via catheter . common convention is to transfer the embryo three days after fertilization , when the embryo has eight cells , or on day five , when the embryo is called a blastocyst , and has hundreds of cells . if the woman 's eggs are of poor quality due to age or toxic exposures , or have been removed due to cancer , donor eggs may be used . in the case that the intended mother has a problematic uterus , or lacks one , another woman , called the gestational carrier or surrogate , can use her uterus to carry the pregnancy . to increase the odds of success , which are as high as 40 % for a woman younger than 35 , doctors sometimes transfer multiple embryos at once , which is why ivf results in twins and triplets more often than natural pregnancies . however , most clinics seek to minimize the chances of multiple pregnancies , as they are riskier for mothers and babies . millions of babies , like louise brown , have been born from ivf and have had normal , healthy lives . the long-term health consequences of ovarian stimulation with ivf medicines are less clear , though so far , ivf seems safe for women . because of better genetic testing , delayed childbearing , increased accessibility and diminishing cost , it 's not inconceivable that artificial baby making via ivf and related techniques could outpace natural reproduction in years to come .

her birth revolutionized the field of reproductive medicine . given that approximately one in eight heterosexual couples has difficulty conceiving , and that homosexual couples and single parents often need clinical help to make a baby , the demand for ivf has been growing . ivf is so common , that more than 5 million babies have been born through this technology .

what proportion of heterosexual couples have difficulty conceiving ?

have you ever tried to picture an ideal world ? one without war , poverty , or crime ? if so , you 're not alone . plato imagined an enlightened republic ruled by philosopher kings , many religions promise bliss in the afterlife , and throughout history , various groups have tried to build paradise on earth . thomas more 's 1516 book `` utopia '' gave this concept a name , greek for `` no place . '' though the name suggested impossibility , modern scientific and political progress raised hopes of these dreams finally becoming reality . but time and time again , they instead turned into nightmares of war , famine , and oppression . and as artists began to question utopian thinking , the genre of dystopia , the not good place , was born . one of the earliest dystopian works is jonathan swift 's `` gulliver 's travels . '' throughout his journey , gulliver encounters fictional societies , some of which at first seem impressive , but turn out to be seriously flawed . on the flying island of laputa , scientists and social planners pursue extravagant and useless schemes while neglecting the practical needs of the people below . and the houyhnhnm who live in perfectly logical harmony have no tolerance for the imperfections of actual human beings . with his novel , swift established a blueprint for dystopia , imagining a world where certain trends in contemporary society are taken to extremes , exposing their underlying flaws . and the next few centuries would provide plenty of material . industrial technology that promised to free laborers imprisoned them in slums and factories , instead , while tycoons grew richer than kings . by the late 1800 's , many feared where such conditions might lead . h. g. wells 's `` the time machine '' imagined upper classes and workers evolving into separate species , while jack london 's `` the iron heel '' portrayed a tyrannical oligarchy ruling over impoverished masses . the new century brought more exciting and terrifying changes . medical advances made it possible to transcend biological limits while mass media allowed instant communication between leaders and the public . in aldous huxley 's `` brave new world '' , citizens are genetically engineered and conditioned to perform their social roles . while propaganda and drugs keep the society happy , it 's clear some crucial human element is lost . but the best known dystopias were not imaginary at all . as europe suffered unprecedented industrial warfare , new political movements took power . some promised to erase all social distinctions , while others sought to unite people around a mythical heritage . the results were real-world dystopias where life passed under the watchful eye of the state and death came with ruthless efficiency to any who did n't belong . many writers of the time did n't just observe these horrors , but lived through them . in his novel `` we '' , soviet writer yevgeny zamyatin described a future where free will and individuality were eliminated . banned in the u.s.s.r. , the book inspired authors like george orwell who fought on the front lines against both fascism and communism . while his novel `` animal farm '' directly mocked the soviet regime , the classic `` 1984 '' was a broader critique of totalitarianism , media , and language . and in the u.s.a. , sinclair lewis 's `` it ca n't happen here '' envisioned how easily democracy gave way to fascism . in the decades after world war ii , writers wondered what new technologies like atomic energy , artificial intelligence , and space travel meant for humanity 's future . contrasting with popular visions of shining progress , dystopian science fiction expanded to films , comics , and games . robots turned against their creators while tv screens broadcast deadly mass entertainment . workers toiled in space colonies above an earth of depleted resources and overpopulated , crime-plagued cities . yet politics was never far away . works like `` dr. strangelove '' and `` watchmen '' explored the real threat of nuclear war , while `` v for vendetta '' and `` the handmaid 's tale '' warned how easily our rights could disappear in a crisis . and today 's dystopian fiction continues to reflect modern anxieties about inequality , climate change , government power , and global epidemics . so why bother with all this pessimism ? because at their heart , dystopias are cautionary tales , not about some particular government or technology , but the very idea that humanity can be molded into an ideal shape . think back to the perfect world you imagined . did you also imagine what it would take to achieve ? how would you make people cooperate ? and how would you make sure it lasted ? now take another look . does that world still seem perfect ?

and as artists began to question utopian thinking , the genre of dystopia , the not good place , was born . one of the earliest dystopian works is jonathan swift 's `` gulliver 's travels . '' throughout his journey , gulliver encounters fictional societies , some of which at first seem impressive , but turn out to be seriously flawed .

what was the basic formula for dystopia established by jonathan swift in `` gulliver ’ s travels '' ?

you probably know that all stuff is made up of atoms and that an atom is a really , really , really , really tiny particle . every atom has a core , which is made up of at least one positively charged particle called a proton , and in most cases , some number of neutral particles called neutrons . that core is surrounded by negatively charged particles called electrons . the identity of an atom is determined only by the number of protons in its nucleus . hydrogen is hydrogen because it has just one proton , carbon is carbon because it has six , gold is gold because it has 79 , and so on . indulge me in a momentary tangent . how do we know about atomic structure ? we ca n't see protons , neutrons , or electrons . so , we do a bunch of experiments and develop a model for what we think is there . then we do some more experiments and see if they agree with the model . if they do , great . if they do n't , it might be time for a new model . we 've had lots of very different models for atoms since democritus in 400 bc , and there will almost certainly be many more to come . okay , tangent over . the cores of atoms tend to stick together , but electrons are free to move , and this is why chemists love electrons . if we could marry them , we probably would . but electrons are weird . they appear to behave either as particles , like little baseballs , or as waves , like water waves , depending on the experiment that we perform . one of the weirdest things about electrons is that we ca n't exactly say where they are . it 's not that we do n't have the equipment , it 's that this uncertainty is part of our model of the electron . so , we ca n't pinpoint them , fine . but we can say there 's a certain probability of finding an electron in a given space around the nucleus . and that means that we can ask the following question : if we drew a shape around the nucleus such that we would be 95 % sure of finding a given electron within that shape , what would it look like ? here are a few of these shapes . chemists call them orbitals , and what each one looks like depends on , among other things , how much energy it has . the more energy an orbital has , the farther most of its density is from the nucleus . by they way , why did we pick 95 % and not 100 % ? well , that 's another quirk of our model of the electron . past a certain distance from the nucleus , the probability of finding an electron starts to decrease more or less exponentially , which means that while it will approach zero , it 'll never actually hit zero . so , in every atom , there is some small , but non-zero , probability that for a very , very short period of time , one of its electrons is at the other end of the known universe . but mostly electrons stay close to their nucleus as clouds of negative charged density that shift and move with time . how electrons from one atom interact with electrons from another determines almost everything . atoms can give up their electrons , surrendering them to other atoms , or they can share electrons . and the dynamics of this social network are what make chemistry interesting . from plain old rocks to the beautiful complexity of life , the nature of everything we see , hear , smell , taste , touch , and even feel is determined at the atomic level .

but we can say there 's a certain probability of finding an electron in a given space around the nucleus . and that means that we can ask the following question : if we drew a shape around the nucleus such that we would be 95 % sure of finding a given electron within that shape , what would it look like ? here are a few of these shapes .

which of the following statements is true :

every day , a sea of decisions stretches before us . some are small and unimportant , but others have a larger impact on our lives . for example , which politician should i vote for ? should i try the latest diet craze ? or will email make me a millionaire ? we 're bombarded with so many decisions that it 's impossible to make a perfect choice every time . but there are many ways to improve our chances , and one particularly effective technique is critical thinking . this is a way of approaching a question that allows us to carefully deconstruct a situation , reveal its hidden issues , such as bias and manipulation , and make the best decision . if the critical part sounds negative that 's because in a way it is . rather than choosing an answer because it feels right , a person who uses critical thinking subjects all available options to scrutiny and skepticism . using the tools at their disposal , they 'll eliminate everything but the most useful and reliable information . there are many different ways of approaching critical thinking , but here 's one five-step process that may help you solve any number of problems . one : formulate your question . in other words , know what you 're looking for . this is n't always as straightforward as it sounds . for example , if you 're deciding whether to try out the newest diet craze , your reasons for doing so may be obscured by other factors , like claims that you 'll see results in just two weeks . but if you approach the situation with a clear view of what you 're actually trying to accomplish by dieting , whether that 's weight loss , better nutrition , or having more energy , that 'll equip you to sift through this information critically , find what you 're looking for , and decide whether the new fad really suits your needs . two : gather your information . there 's lots of it out there , so having a clear idea of your question will help you determine what 's relevant . if you 're trying to decide on a diet to improve your nutrition , you may ask an expert for their advice , or seek other people 's testimonies . information gathering helps you weigh different options , moving you closer to a decision that meets your goal . three : apply the information , something you do by asking critical questions . facing a decision , ask yourself , `` what concepts are at work ? '' `` what assumptions exist ? '' `` is my interpretation of the information logically sound ? '' for example , in an email that promises you millions , you should consider , `` what is shaping my approach to this situation ? '' `` do i assume the sender is telling the truth ? '' `` based on the evidence , is it logical to assume i 'll win any money ? '' four : consider the implications . imagine it 's election time , and you 've selected a political candidate based on their promise to make it cheaper for drivers to fill up on gas . at first glance , that seems great . but what about the long-term environmental effects ? if gasoline use is less restricted by cost , this could also cause a huge surge in air pollution , an unintended consequence that 's important to think about . five : explore other points of view . ask yourself why so many people are drawn to the policies of the opposing political candidate . even if you disagree with everything that candidate says , exploring the full spectrum of viewpoints might explain why some policies that do n't seem valid to you appeal to others . this will allow you to explore alternatives , evaluate your own choices , and ultimately help you make more informed decisions . this five-step process is just one tool , and it certainly wo n't eradicate difficult decisions from our lives . but it can help us increase the number of positive choices we make . critical thinking can give us the tools to sift through a sea of information and find what we 're looking for . and if enough of us use it , it has the power to make the world a more reasonable place .

we 're bombarded with so many decisions that it 's impossible to make a perfect choice every time . but there are many ways to improve our chances , and one particularly effective technique is critical thinking . this is a way of approaching a question that allows us to carefully deconstruct a situation , reveal its hidden issues , such as bias and manipulation , and make the best decision .

what is one advantage of critical thinking ?

one of the most amazing facts in physics is this : everything in the universe , from light to electrons to atoms , behaves like both a particle and a wave at the same time . all of the other weird stuff you might have heard about quantum physics , schrodinger 's cat , god playing dice , spooky action at a distance , all of it follows directly from the fact that everything has both particle and wave nature . this might sound crazy . if you look around , you 'll see waves in water and particles of rock , and they 're nothing alike . so why would you think to combine them ? physicists did n't just decide to mash these things together out of no where . rather , they were led to the dual nature of the universe through a process of small steps , fitting together lots of bits of evidence , like pieces in a puzzle . the first person to seriously suggest the dual nature of light was albert einstein in 1905 , but he was picking up an earlier idea from max planck . planck explained the colors of light emitted by hot objects , like the filament in a light bulb , but to do it , he needed a desperate trick : he said the object was made up of oscillators that could only emit light in discrete chunks , units of energy that depend on the frequency of the light . planck was never really happy with this , but einstein picked it up and ran with it . he applied planck 's idea to light itself , saying that light , which everybody knew was a wave , is really a stream of photons , each with a discrete amount of energy . einstein himself called this the only truly revolutionary thing he did , but it explains the way light shining on a metal surface knocks loose electrons . even people who hated the idea had to agree that it works brilliantly . the next puzzle piece came from ernest rutherford in england . in 1909 , ernest marsden and hans geiger , working for rutherford , shot alpha particles at gold atoms and were stunned to find that some bounced straight backwards . this showed that most of the mass of the atom is concentrated in a tiny nucleus . the cartoon atom you learn in grade school , with electrons orbiting like a miniature solar system , that 's rutherford 's . there 's one little problem with rutherford 's atom : it ca n't work . classical physics tells us that an electron whipping around in a circle emits light , and we use this all the time to generate radio waves and x-rays . rutherford 's atoms should spray x-rays in all directions for a brief instant before the electron spirals in to crash into the nucleus . but niels bohr , a danish theoretical physicist working with rutherford , pointed out that atoms obviously exist , so maybe the rules of physics needed to change . bohr proposed that an electron in certain special orbits does n't emit any light at all . atoms absorb and emit light only when electrons change orbits , and the frequency of the light depends on the energy difference in just the way planck and einstein introduced . bohr 's atom fixes rutherford 's problem and explains why atoms emit only very specific colors of light . each element has its own special orbits , and thus its own unique set of frequencies . the bohr model has one tiny problem : there 's no reason for those orbits to be special . but louis de broglie , a french phd student , brought everything full circle . he pointed out that if light , which everyone knew is a wave , behaves like a particle , maybe the electron , which everyone knew is a particle , behaves like a wave . and if electrons are waves , it 's easy to explain bohr 's rule for picking out the special orbits . once you have the idea that electrons behave like waves , you can go look for it . and within a few years , scientists in the us and uk had observed wave behavior from electrons . these days we have a wonderfully clear demonstration of this : shooting single electrons at a barrier with slits cut in it . each electron is detected at a specific place at a specific time , like a particle . but when you repeat the experiment many times , all the individual electrons trace out a pattern of stripes , characteristic of wave behavior . the idea that particles behave like waves , and vice versa , is one of the strangest and most powerful in physics . richard feynman famously said that this illustrates the central mystery of quantum mechanics . everything else follows from this , like pieces of a puzzle falling into place .

the idea that particles behave like waves , and vice versa , is one of the strangest and most powerful in physics . richard feynman famously said that this illustrates the central mystery of quantum mechanics . everything else follows from this , like pieces of a puzzle falling into place .

a popular image of science is of the lone genius who invents a new theory in isolation purely by thinking about it . does the story of quantum mechanics suggest that this is a good model of science ?

in 1861 , two scientists got into a very brainy argument . specifically , they had opposing ideas of how speech and memory operated within the human brain . ernest aubertin , with his localistic model , argued that a particular region or the brain was devoted to each separate process . pierre gratiolet , on the other hand , argued for the distributed model , where different regions work together to accomplish all of these various functions . the debate they began reverberated throughout the rest of the century , involving some of the greatest scientific minds of the time . aubertin and his localistic model had some big names on his side . in the 17th century , rené descartes had assigned the quality of free will and the human soul to the pineal gland . and in the late 18th century , a young student named franz joseph gall had observed that the best memorizers in his class had the most prominent eyes and decided that this was due to higher development in the adjacent part of the brain . as a physician , gall went on to establish the study of phrenology , which held that strong mental faculties corresponded to highly developed brain regions , observable as bumps in the skull . the widespread popularity of phrenology throughout the early 19th century tipped the scales towards aubertin 's localism . but the problem was that gall had never bothered to scientifically test whether the individual brain maps he had constructed applied to all people . and in the 1840 's , pierre flourens challenged phrenology by selectively destroying parts of animal brains and observing which functions were lost . flourens found that damaging the cortex interfered with judgement or movement in general , but failed to identify any region associated with one specific function , concluding that the cortex carried out brain functions as an entire unit . flourens had scored a victory for gratiolet , but it was not to last . gall 's former student , jean-baptiste bouillaud , challenged flourens ' conclusion , observing that patients with speech disorders all had damage to the frontal lobe . and after paul broca 's 1861 autopsy of a patient who had lost the power to produce speech , but not the power to understand it , revealed highly localized frontal lobe damage , the distributed model seemed doomed . localism took off . in the 1870 's , karl wernicke associated part of the left temporal lobe with speech comprehension . soon after , eduard hitzig and gustav fritsch stimulated a dog 's cortex and discovered a frontal lobe region responsible for muscular movements . building on their work , david ferrier mapped each piece of cortex associated with moving a part of the body . and in 1909 , korbinian brodmann built his own cortex map with 52 separate areas . it appeared that the victory of aubertin 's localistic model was sealed . but neurologist karl wernicke had come up with an interesting idea . he reasoned that since the regions for speech production and comprehension were not adjacent , then injuring the area connecting them might result in a special type of language loss , now known as receptive aphasia . wernicke 's connectionist model helped explain disorders that did n't result from the dysfunction of just one area . modern neuroscience tools reveal a brain more complex than gratiolet , aubertin , or even wernicke imagined . today , the hippocampus is associated with two distinct brain functions : creating memories and processing location in space . we also now measure two kinds of connectivity : anatomical connectivity between two adjoining regions of cortex working together , and functional connectivity between separated regions working together to accomplish one process . a seemingly basic function like vision is actually composed of many smaller functions , with different parts of the cortex representing shape , color and location in space . when certain areas stop functioning , we may recognize an object , but not see it , or vice versa . there are even different kinds of memory for facts and for routines . and remembering something like your first bicycle involves a network of different regions each representing the concept of vehicles , the bicycle 's shape , the sound of the bell , and the emotions associated with that memory . in the end , both gratiolet and aubertin turned out to be right . and we still use both of their models to understand how cognition happens . for example , we can now measure brain activity on such a fine time scale that we can see the individual localized processes that comprise a single act of remembering . but it is the integration of these different processes and regions that creates the coherent memory we experience . the supposedly competing theories prove to be two aspects of a more comprehensive model , which will in turn be revised and refined as our scientific techologies and methods for understanding the brain improve .

modern neuroscience tools reveal a brain more complex than gratiolet , aubertin , or even wernicke imagined . today , the hippocampus is associated with two distinct brain functions : creating memories and processing location in space . we also now measure two kinds of connectivity : anatomical connectivity between two adjoining regions of cortex working together , and functional connectivity between separated regions working together to accomplish one process .

you have learned about two models of how the brain functions . in developing these models , scientists used different approaches to come to their conclusions . discuss two of them . has science made a final declaration about which is right ? will it ever ?

we 've all seen the movies where a monster , created by a scientist in a laboratory , escapes to wreak havoc on the outside world . but what if the monster was not some giant rampaging beast , destroying a city , but just a tiny amount of seaweed with the potential to disrupt entire coastal ecosystems ? this is the story of caulerpa taxifolia , originally a naturally occurring seaweed native to tropical waters . in the 1980s , one strain was found to thrive in colder environments . this trait , combined with its beautiful , bright green color and ability to grow quickly without maintenance made it ideal for aquariums , which it helped keep clean by consuming nutrients and chemicals in the water . further selective breeding made it even heartier , and soon it was used in aquariums around the world . but it was not long before a sample of this aquarium-developed super algae turned up in the mediterranean sea near the famed oceanographic museum of monaco . the marine biologist who found it believed that the museum had accidentally realeased it into the ocean along with aquarium waters , while museum directors claimed it had be carried into the area by ocean currents . regardless of how it ended up there , the non-native caulerpa multiplied rapidly , having no natural predators due to releasing a toxin that keeps fish away . and like some mythical monster , even a tiny piece that broke off could grow into a whole new colony . through water currents and contact with boat anchors and fishing lines , it fragmented and spread throughout mediterranean coastal cities covering coral reefs . so what was the result of this invasion ? well , it depends on who you ask . many scientists warned that the spread of caulerpa reduces biodiversity by crowding out native species of seaweed that are eaten by fish , with the biologist who first discovered its presence dubbing it killer algae . other studies instead claim that the algae actually had a beneficial effect by consuming chemical pollutants -- one reason the aquariums strain was developed . but the disruption of a natural ecosystem by an introduced foreign species can have unpredictable and uncontrollable effects that may not be immediately visible . so when culerpa taxifolia was discovered at carlsbad 's agua hedionda lagoon , near san diego in the year 2000 , having most likely come from the dumping of home aquarium water into a connecting storm drain , it was decided to stop it before it spread . tarps were placed over the culerpa colonies and chlorine injected inside . although this method killed all other marine life trapped under the tarps , it did succeed in eradicating the algae and native eelgrass was able to emerge in its place . by responding quickly , authorities in california were able to prevent culerpa from propagating . but another occurrence of the strain , in the coastal wetlands of southeast australia , was left unchecked and allowed to spread . and unfortunately , a tarp can not cover the mediterranean sea or the australian coast . invasive species are not a new problem , and can indeed occur naturally . but when such species are the results of human directed selective breeding or genetic modification and then released into the natural environment , their effect on ecosystems can be far more radical and irreversible . with the proliferation of new technologies and multiple threats to the environment , it is more important than ever for scientists to monitor and evaluate the risks and dangers , and for the rest of us to remember that what starts in our backyard can effect ecosystems half a world away .

but the disruption of a natural ecosystem by an introduced foreign species can have unpredictable and uncontrollable effects that may not be immediately visible . so when culerpa taxifolia was discovered at carlsbad 's agua hedionda lagoon , near san diego in the year 2000 , having most likely come from the dumping of home aquarium water into a connecting storm drain , it was decided to stop it before it spread . tarps were placed over the culerpa colonies and chlorine injected inside .

the california coastal town that found caulerpa in agua hedionda lagoon and became the first place in the world to eradicate it is called :

when french mathematician laurent schwartz was in high school , he started to worry that he was n't smart enough to solve math problems . maybe you know a similar feeling . you sit down to take a math test , and you feel your heart beat faster and your palms start to sweat . you get butterflies in your stomach , and you ca n't concentrate . this phenomenon is called math anxiety , and if it happens to you , you 're not alone . researchers think about 20 % of the population suffers from it . some psychologists even consider it a diagnosable condition . but having mathematical anxiety does n't necessarily mean you 're bad at math - not even close . laurent schwartz went on to win the fields medal , the highest award in mathematics . people might think that they 're anxious about math because they 're bad at it , but it 's often the other way around . they 're doing poorly in math because they 're anxious about it . some psychologists think that 's because math anxiety decreases a cognitive resource called working memory . that 's the short-term memory system that helps you organize the information you need to complete a task . worrying about being able to solve math problems , or not doing well on a test , eats up working memory , leaving less of it available to tackle the math itself . people can suddenly struggle with even basic math skills , like arithmetic , that they 've otherwise mastered . academic anxiety certainly is n't limited to math , but it does seem to happen much more frequently , and cause more harm in that subject . so why would that be ? researchers are n't yet sure , but some studies suggest that the way children are exposed to math by their parents and teachers play a large part . if parents talk about math like something challenging and unfamiliar , children can internalize that . teachers with math anxiety are also likely to spread it to their students . pressure to solve problems quickly dials up stress even more . and in some cultures , being good at math is a sign of being smart in general . when the stakes are that high , it 's not surprising that students are anxious . even maryam mirzakhani , an influential mathematician who was the first woman to win the fields medal , felt unconfident and lost interest in mathematics because her math teacher in middle school did n't think she was talented . so if you experience mathematical anxiety , what can you do ? relaxation techniques , like short breathing exercises , have improved test performance in students with math anxiety . writing down your worries can also help . this strategy may give you a chance to reevaluate a stressful experience , freeing up working memory . and if you have the chance , physical activity , like a brisk walk , deepens breathing and helps relieve muscle tension , preventing anxiety from building . you can also use your knowledge about the brain to change your mindset . the brain is flexible , and the areas involved in math skills can always grow and develop . this is a psychological principle called the growth mindset . thinking of yourself as someone who can grow and improve can actually help you grow and improve . if you 're a teacher or parent of young children , try being playful with math and focusing on the creative aspects . that can build the numerical skills that help students approach math with confidence later on . importantly , you should give children the time and space to work through their answers . and if you 're an administrator , make sure your teachers have the positive attitudes and mathematical confidence necessary to inspire confidence in all of their students . also , do n't let anyone spread the myth that boys are innately better than girls at math . that is completely false . if you experience math anxiety , it may not help to just know that math anxiety exists . or perhaps it 's reassuring to put a name to the problem . regardless , if you take a look around yourself , the odds are good that you 'll see someone experiencing the same thing as you . just remember that the anxiety is not a reflection of your ability , but it is something you can conquer with time and awareness .

they 're doing poorly in math because they 're anxious about it . some psychologists think that 's because math anxiety decreases a cognitive resource called working memory . that 's the short-term memory system that helps you organize the information you need to complete a task .

how does math anxiety affect working memory , and why do such changes in working memory interfere with math performance ?

here 's a conundrum : identical twins originate from the same dna , so how can they turn out so different even in traits that have a significant genetic component ? for instance , why might one twin get heart disease at 55 , while her sister runs marathons in perfect health ? nature versus nurture has a lot to do with it , but a deeper related answer can be found within something called epigenetics . that 's the study of how dna interacts with the multitude of smaller molecules found within cells , which can activate and deactivate genes . if you think of dna as a recipe book , those molecules are largely what determine what gets cooked when . they are n't making any conscious choices themselves , rather their presence and concentration within cells makes the difference . so how does that work ? genes in dna are expressed when they 're read and transcribed into rna , which is translated into proteins by structures called ribosomes . and proteins are much of what determines a cell 's characteristics and function . epigenetic changes can boost or interfere with the transcription of specific genes . the most common way interference happens is that dna , or the proteins it 's wrapped around , gets labeled with small chemical tags . the set of all of the chemical tags that are attached to the genome of a given cell is called the epigenome . some of these , like a methyl group , inhibit gene expression by derailing the cellular transcription machinery or causing the dna to coil more tightly , making it inaccessible . the gene is still there , but it 's silent . boosting transcription is essentially the opposite . some chemical tags will unwind the dna , making it easier to transcribe , which ramps up production of the associated protein . epigenetic changes can survive cell division , which means they could affect an organism for its entire life . sometimes that 's a good thing . epigenetic changes are part of normal development . the cells in an embryo start with one master genome . as the cells divide , some genes are activated and others inhibited . over time , through this epigenetic reprogramming , some cells develop into heart cells , and others into liver cells . each of the approximately 200 cell types in your body has essentially the same genome but its own distinct epigenome . the epigenome also mediates a lifelong dialogue between genes and the environment . the chemical tags that turn genes on and off can be influenced by factors including diet , chemical exposure , and medication . the resulting epigenetic changes can eventually lead to disease , if , for example , they turn off a gene that makes a tumor-suppressing protein . environmentally-induced epigenetic changes are part of the reason why genetically identical twins can grow up to have very different lives . as twins get older , their epigenomes diverge , affecting the way they age and their susceptibility to disease . even social experiences can cause epigenetic changes . in one famous experiment , when mother rats were n't attentive enough to their pups , genes in the babies that helped them manage stress were methylated and turned off . and it might not stop with that generation . most epigenetic marks are erased when egg and sperm cells are formed . but now researchers think that some of those imprints survive , passing those epigenetic traits on to the next generation . your mother 's or your father 's experiences as a child , or choices as adults , could actually shape your own epigenome . but even though epigenetic changes are sticky , they 're not necessarily permanent . a balanced lifestyle that includes a healthy diet , exercise , and avoiding exposure to contaminants may in the long run create a healthy epigenome . it 's an exciting time to be studying this . scientists are just beginning to understand how epigenetics could explain mechanisms of human development and aging , as well as the origins of cancer , heart disease , mental illness , addiction , and many other conditions . meanwhile , new genome editing techniques are making it much easier to identify which epigenetic changes really matter for health and disease . once we understand how our epigenome influences us , we might be able to influence it , too .

for instance , why might one twin get heart disease at 55 , while her sister runs marathons in perfect health ? nature versus nurture has a lot to do with it , but a deeper related answer can be found within something called epigenetics . that 's the study of how dna interacts with the multitude of smaller molecules found within cells , which can activate and deactivate genes . if you think of dna as a recipe book , those molecules are largely what determine what gets cooked when . they are n't making any conscious choices themselves , rather their presence and concentration within cells makes the difference .

epigenetics describe the interaction of dna with :

how old is the earth ? well , by counting the number of isotopes in a sample of rock that 's undergone radioactive decay , geologists have estimated the earth 's birthday , when it first formed from a solar nebula , to be 4.6 billion years ago . but just how long is that really ? here 's some analogies that might help you understand . for example , let 's imagine the entire history of earth until the present day as a single calendar year . on january 1st , the earth begins to form . by march 3rd , there 's the first evidence of single-celled bacteria . life remains amazingly unicellular until november 11th when the first multicellular organisms , known as the ediacaran fauna , come along . shortly thereafter , on november 16th at 6:08 p.m. is the cambrian explosion of life , a major milestone , when all of the modern phyla started to appear . on december 10th at 1:26 p.m. , the dinosaurs first evolve but are wiped out by an asteroid just two weeks later . on december 31st , the mighty roman empire rises and falls in just under four seconds . and columbus sets sail for what he thinks is india at three seconds to midnight . if you try to write the history of the earth using just one page per year , your book would be 145 miles thick , more than half the distance to the international space station . the story of the 3.2 million year-old australopithecine fossil known as lucy would be found on the 144th mile , just over 500 feet from the end of the book . the united states of america 's declaration of independence would be signed in the last half-inch . or if we compared geologic time to a woman stretching her arms to a span of six feet , the simple act of filing her nails would wipe away all of recorded human history . finally , let 's imagine the history of the earth as your life : from the moment you 're born to your first day of high school . your first word , first time sitting up , and first time walking would all take place while life on earth was comprised of single-celled organisms . in fact , the first multicellular organism would n't evolve until you were 12 years old and starting 7th grade , right around the time your science teacher is telling the class how fossils are formed . the dinosaurs do n't appear until three months into 8th grade and are soon wiped out right around spring break . three days before 9th grade begins , when you realize summer is over and you need new school supplies , lucy , the australopithecine , is walking around africa . as you finish breakfast and head outside to catch your bus 44 minutes before school , the neanderthals are going extinct throughout europe . the most recent glacial period ends as your bus drops you off 16 minutes before class . columbus sets sail 50 seconds before class as you 're still trying to find the right classroom . the declaration of independence is signed 28 seconds later as you look for an empty seat . and you were born 1.3 seconds before the bell rings . so , you see , the earth is extremely , unbelievably old compared to us humans with a fossil record hiding incredible stories to tell us about the past and possibly the future as well . but in the short time we 've been here , we 've learned so much and will surely learn more over the next decades and centuries , near moments in geological time .

but just how long is that really ? here 's some analogies that might help you understand . for example , let 's imagine the entire history of earth until the present day as a single calendar year .

how does understanding the past help us understand the present ?

in 1796 , the scientist edward jenner injected material from a cowpox virus into an eight-year-old boy with a hunch that this would provide the protection needed to save people from deadly outbreaks of the related smallpox virus . it was a success . the eight-year-old was inoculated against the disease and this became the first ever vaccine . but why did it work ? to understand how vaccines function , we need to know how the immune system defends us against contagious diseases in the first place . when foreign microbes invade us , the immune system triggers a series of responses in an attempt to identify and remove them from our bodies . the signs that this immune response is working are the coughing , sneezing , inflammation and fever we experience , which work to trap , deter and rid the body of threatening things , like bacteria . these innate immune responses also trigger our second line of defense , called adaptive immunity . special cells called b cells and t cells are recruited to fight microbes , and also record information about them , creating a memory of what the invaders look like , and how best to fight them . this know-how becomes handy if the same pathogen invades the body again . but despite this smart response , there 's still a risk involved . the body takes time to learn how to respond to pathogens and to build up these defenses . and even then , if a body is too weak or young to fight back when it 's invaded , it might face very serious risk if the pathogen is particularly severe . but what if we could prepare the body 's immune response , readying it before someone even got ill ? this is where vaccines come in . using the same principles that the body uses to defend itself , scientists use vaccines to trigger the body 's adaptive immune system , without exposing humans to the full strength disease . this has resulted in many vaccines , which each work uniquely , separated into many different types . first , we have live attenuated vaccines . these are made of the pathogen itself but a much weaker and tamer version . next , we have inactive vaccines , in which the pathogens have been killed . the weakening and inactivation in both types of vaccine ensures that pathogens do n't develop into the full blown disease . but just like a disease , they trigger an immune response , teaching the body to recognize an attack by making a profile of pathogens in preparation . the downside is that live attenuated vaccines can be difficult to make , and because they 're live and quite powerful , people with weaker immune systems ca n't have them , while inactive vaccines do n't create long-lasting immunity . another type , the subunit vaccine , is only made from one part of the pathogen , called an antigen , the ingredient that actually triggers the immune response . by even further isolating specific components of antigens , like proteins or polysaccharides , these vaccines can prompt specific responses . scientists are now building a whole new range of vaccines called dna vaccines . for this variety , they isolate the very genes that make the specific antigens the body needs to trigger its immune response to specific pathogens . when injected into the human body , those genes instruct cells in the body to make the antigens . this causes a stronger immune response , and prepares the body for any future threats , and because the vaccine only includes specific genetic material , it does n't contain any other ingredients from the rest of the pathogen that could develop into the disease and harm the patient . if these vaccines become a success , we might be able to build more effective treatments for invasive pathogens in years to come . just like edward jenner 's amazing discovery spurred on modern medicine all those decades ago , continuing the development of vaccines might even allow us to treat diseases like hiv , malaria , or ebola , one day .

by even further isolating specific components of antigens , like proteins or polysaccharides , these vaccines can prompt specific responses . scientists are now building a whole new range of vaccines called dna vaccines . for this variety , they isolate the very genes that make the specific antigens the body needs to trigger its immune response to specific pathogens .

vaccines do not only protect those who get vaccinated , but others as well . is this true ? why or why not ?

shall i ask for a show of hands or a clapping of people in different generations ? i 'm interested in how many are three to 12 years old . ( laughter ) none , huh ? ( laughter ) all right . i 'm going to talk about dinosaurs . do you remember dinosaurs when you were that age ? ( applause ) dinosaurs are kind of funny , you know . ( laughter ) we 're going to kind of go in a different direction right now . i hope you all realize that . so i 'll just give you my message up front : try not to go extinct . ( laughter ) that 's it . ( laughter ) people ask me a lot -- in fact , one of the most asked questions i get is , why do children like dinosaurs so much ? what 's the fascination ? and i usually just say , `` well , dinosaurs were big , different and gone . '' they 're all gone . well that 's not true , but we 'll get to the goose in a minute . so that 's sort of the theme : big , different and gone . the title of my talk : shape-shifting dinosaurs : the cause of a premature extinction . now i assume that we remember dinosaurs . and there 's lots of different shapes . lots of different kinds . a long time ago , back in the early 1900s , museums were out looking for dinosaurs . they went out and gathered them up . and this is an interesting story . every museum wanted a little bigger or better one than anybody else had . so if the museum in toronto went out and collected a tyrannosaur , a big one , then the museum in ottawa wanted a bigger one , and a better one . and that happened for all museums . so everyone was out looking for all these bigger and better dinosaurs . and this was in the early 1900s . by about 1970 , some scientists were sitting around and they thought , `` what in the world -- look at these dinosaurs , they 're all big . where are all the little ones ? '' ( laughter ) and they thought about it and they even wrote papers about it : `` where are the little dinosaurs ? '' ( laughter ) well , go to a museum , you 'll see , see how many baby dinosaurs there are . people assumed -- and this was actually a problem -- people assumed that if they had little dinosaurs , if they had juvenile dinosaurs , they 'd be easy to identify . you 'd have a big dinosaur and a littler dinosaur . ( laughter ) but all they had were big dinosaurs . and it comes down to a couple of things . first off , scientists have egos , and scientists like to name dinosaurs . they like to name anything . everybody likes to have their own animal that they named . ( laughter ) and so every time they found something that looked a little different , they named it something different . and what happened , of course , is we ended up with a whole bunch of different dinosaurs . in 1975 , a light went on in somebody 's head . dr. peter dodson at the university of pennsylvania actually realized that dinosaurs grew kind of like birds do , which is different than the way reptiles grow . and in fact , he used the cassowary as an example . and it 's kind of cool -- if you look at the cassowary , or any of the birds that have crests on their heads , they grow to about 80 percent adult size before the crest starts to grow . now think about that . they 're basically retaining their juvenile characteristics very late in what we call ontogeny . so allometric cranial ontogeny is relative skull growth . so you can see that if you actually found one that was 80 percent grown and you did n't know that it was going to grow up to a cassowary , you would think they were two different animals . so this was a problem , and peter dodson pointed this out using some duck-billed dinosaurs then called hypacrosaurus . and he showed that if you were to take a baby and an adult and make an average of what it should look like , if it grew in sort of a linear fashion , it would have a crest about half the size of the adult . but the actual subadult at 65 percent had no crest at all . so this was interesting . so this is where people went astray again . i mean , if they 'd have just taken that , taken peter dodson 's work , and gone on with that , then we would have a lot less dinosaurs than we have . but scientists have egos ; they like to name things . and so they went on naming dinosaurs because they were different . now we have a way of actually testing to see whether a dinosaur , or any animal , is a young one or an older one . and that 's by actually cutting into their bones . but cutting into the bones of a dinosaur is hard to do , as you can imagine , because in museums , bones are precious . you go into a museum , and they take really good care of them . they put them in foam , little containers . they 're very well taken care of . they do n't like it if you come in and want to saw them open and look inside . ( laughter ) so they do n't normally let you do that . ( laughter ) but i have a museum and i collect dinosaurs and i can saw mine open . so that 's what i do . ( applause ) so if you cut open a little dinosaur , it 's very spongy inside , like a . and if you cut into an older dinosaur , it 's very massive . you can tell it 's mature bone . so it 's real easy to tell them apart . so what i want to do is show you these . in north america in the northern plains of the united states and the southern plains of alberta and saskatchewan , there 's this unit of rock called the hell creek formation that produces the last dinosaurs that lived on earth . and there are 12 of them that everyone recognizes -- i mean the 12 primary dinosaurs that went extinct . and so we will evaluate them . and that 's sort of what i 've been doing . so my students , my staff , we 've been cutting them open . now as you can imagine , cutting open a leg bone is one thing , but when you go to a museum and say , `` you do n't mind if i cut open your dinosaur 's skull , do you ? '' they say , `` go away . '' ( laughter ) so here are 12 dinosaurs . and we want to look at these three first . so these are dinosaurs that are called pachycephalosaurus . and everybody knows that these three animals are related . and the assumption is that they 're related like cousins or whatever . but no one ever considered that they might be more closely related . in other words , people looked at them and they saw the differences . and you all know that if you are going to determine whether you 're related to your brother or your sister , you ca n't do it by looking at differences . you can only determine relatedness by looking for similarities . so people were looking at these and they were talking about how different they are . pachycephalosaurus has a big , thick dome on its head , and it 's got some little bumps on the back of its head , and it 's got a bunch of gnarly things on the end of its nose . and then stygimoloch , another dinosaur from the same age , lived at the same time , has spikes sticking out the back of its head . it 's got a little , tiny dome , and it 's got a bunch of gnarly stuff on its nose . and then there 's this thing called dracorex hogwartsia . guess where that came from ? dragon . so here 's a dinosaur that has spikes sticking out of its head , no dome and gnarly stuff on its nose . nobody noticed the gnarly stuff sort of looked alike . but they did look at these three and they said , `` these are three different dinosaurs , and dracorex is probably the most primitive of them . and the other one is more primitive than the other . '' it 's unclear to me how they actually sorted these three of them out . but if you line them up , if you just take those three skulls and just line them up , they line up like this . dracorex is the littlest one , stygimoloch is the middle-size one , pachycephalosaurus is the largest one . and one would think , that should give me a clue . ( laughter ) but it did n't give them a clue . ( laughter ) because , well we know why . scientists like to name things . so if we cut open dracorex -- i cut open our dracorex -- and look , it was spongy inside , really spongy inside . i mean , it is a juvenile and it 's growing really fast . so it is going to get bigger . if you cut open stygimoloch , it is doing the same thing . the dome , that little dome , is growing really fast . it 's inflating very fast . what 's interesting is the spike on the back of the dracorex was growing very fast as well . the spikes on the back of the stygimoloch are actually resorbing , which means they 're getting smaller as that dome is getting bigger . and if we look at pachycephalosaurus , pachycephalosaurus has a solid dome and its little bumps on the back of its head were also resorbing . so just with these three dinosaurs , as a scientist , we can easily hypothesize that it is just a growth series of the same animal . which of course means that stygimoloch and dracorex are extinct . ( laughter ) ok. ( laughter ) which of course means we have 10 primary dinosaurs to deal with . so a colleague of mine at berkeley -- he and i were looking at triceratops . and before the year 2000 -- now remember , triceratops was first found in the 1800s -- before 2000 , no one had ever seen a juvenile triceratops . there 's a triceratops in every museum in the world , but no one had ever collected a juvenile . and we know why , right ? because everybody wants to have a big one . so everyone had a big one . so we went out and collected a whole bunch of stuff and we found a whole bunch of little ones . they 're everywhere , they 're all over the place . so we have a whole bunch of them at our museum . ( laughter ) and everybody says it 's because i have a little museum . when you have a little museum , you have little dinosaurs . ( laughter ) if you look at the triceratops , you can see it 's changing , it 's shape-shifting . as the juveniles are growing up , their horns actually curve backwards . and then as they get older , the horns grow forward . and that 's pretty cool . if you look along the edge of the frill , they have these little triangular bones that actually grow big as triangles and then they flatten against the frill pretty much like the spikes do on the pachycephalosaurs . and then , because the juveniles are in my collection , i cut them open ... ( laughter ) and look inside . and the little one is really spongy . and the middle-size one is really spongy . but what was interesting was the adult triceratops was also spongy . and this is a skull that is two meters long . it 's a big skull . but there 's another dinosaur that is found in this formation that looks like a triceratops , except it 's bigger , and it 's called torosaurus . and torosaurus , when we cut into it , has mature bone . but it 's got these big holes in its shield . and everybody says , `` a triceratops and a torosaurus ca n't possibly be the same animal because one of them 's bigger than the other one . '' ( laughter ) `` and it has holes in its frill . '' and i said , `` well do we have any juvenile torosauruses ? '' and they said , `` well , no , but it has holes in its frill . '' so one of my graduate students , john scannella , looked through our whole collection and he actually discovered that the hole starting to form in triceratops and , of course it 's open , in torosaurus -- so he found the transitional ones between triceratops and torosaurus , which was pretty cool . so now we know that torosaurus is actually a grown-up triceratops . now when we name dinosaurs , when we name anything , the original name gets to stick and the second name is thrown out . so torosaurus is extinct . triceratops , if you 've heard the news , a lot of the newscasters got it all wrong . they thought torosaurus should be kept and triceratops thrown out , but that 's not going to happen . ( laughter ) all right , so we can do this with a bunch of dinosaurs . i mean , here 's edmontosaurus and anatotitan . anatotitan : giant duck . it 's a giant duck-bill dinosaur . here 's another one . so we look at the bone histology . the bone histology tells us that edmontosaurus is a juvenile , or at least a subadult , and the other one is an adult , and we have an ontogeny . and we get rid of anatotitan . so we can just keep doing this . and the last one is t. rex . so there 's these two dinosaurs , t. rex and nanotyrannus . ( laughter ) again , it makes you wonder . ( laughter ) but they had a good question . they were looking at them and they said , `` one 's got 17 teeth , and the biggest one 's got 12 teeth . and that does n't make any sense at all , because we do n't know of any dinosaurs that gain teeth as they get older . so it must be true -- they must be different . '' so we cut into them . and sure enough , nanotyrannus has juvenile bone and the bigger one has more mature bone . it looks like it could still get bigger . and at the museum of the rockies where we work , i have four t. rexes , so i can cut a whole bunch of them . but i did n't have to cut any of them really , because i just lined up their jaws and it turned out the biggest one had 12 teeth and the next smallest one had 13 and the next smallest had 14 . and of course , nano has 17 . and we just went out and looked at other people 's collections and we found one that has sort of 15 teeth . so again , real easy to say that tyrannosaurus ontogeny included nanotyrannus , and therefore we can take out another dinosaur . ( laughter ) so when it comes down to our end cretaceous , we have seven left . and that 's a good number . that 's a good number to go extinct , i think . now as you can imagine , this is not very popular with fourth-graders . ( laughter ) fourth-graders love their dinosaurs , they memorize them . and they 're not happy with this . ( laughter ) thank you very much . ( applause )

and the middle-size one is really spongy . but what was interesting was the adult triceratops was also spongy . and this is a skull that is two meters long .

why was the adult triceratops skull that jack horner cut into in his lab also spongy ?

imagine waking up the morning of prom , or your wedding day , or a big job interview… and sure enough , you look in the mirror to find your forehead is covered in zits ! it ’ s happened to lots of us . acne , or acne vulgaris , is the most common skin disease in humans . it affects about 80 % of people at some point in their lives . most people get acne between the ages of 11 and 30 , but sometimes older people continue to struggle with it , too . acne happens when follicles and pores become clogged with dead skin cells and oils . and … it sucks . but by studying how acne forms , doctors have developed ways to prevent and treat it . it all starts with your skin : a complex organ made up of two layers and lots of nerves , blood vessels , and glands . your skin cells regenerate about once a month , so you constantly have dead skin cells sloughing off , and new skin cells rising to the surface . this whole skin-replacement thing isn ’ t much of a problem , on its own . but lots of these dead skin cells come out through your pores . and pores make things more complicated . skin pores are essentially just openings for tiny hairs . hair follicles , the root ends of the hairs , are embedded in your skin and surrounded by clusters of sebaceous glands , special glands that produce sebum . sebum is that oily , waxy stuff that comes out of your pores . it helps keep your skin waterproof and moisturized : it keeps excess water out of your body , and it keeps water already inside you from getting out through your skin . so , sebum is important . but things can go very wrong if your sebum production gets out of whack . when your body doesn ’ t produce enough sebum , your skin can dry out , making you more susceptible to bacterial or fungal infections . but if your body produces too much sebum , it can build up inside your pores , trap dead skin cells , and cause a blockage . increased sebum production is one of the major factors involved in the development of acne . increased keratin production is another one . keratin is a protein produced by your hair follicles . it gives structure to each strand of hair , as well as the top layer of your skin . but when the hair follicles produce too much keratin , the extra protein binds together dead skin cells , so they can ’ t just shed out of the pore like they normally would . you end up with a blockage that then traps more dead skin cells , plus sebum . once the pore is officially clogged , it becomes a breeding ground for colonies of bacteria — especially propionibacterium acnes . that ’ s a species of commensal bacteria , which basically means it ’ s friendly . it naturally lives on your skin , and it ’ s not harmful … most of the time . the commensal bacteria that make up your microbiome probably even help prevent other , more harmful bacteria from colonizing on your skin . so having colonies of propionibacterium acnes living on you isn ’ t a bad thing . you want them there — as long as they stay on the surface of your skin . when the bacteria find their way deep into skin pores where they don ’ t belong , that ’ s when they can cause an infection . and infections often cause inflammation . when you get an infection , your immune system responds by increasing blood flow to the area and sending extra immune cells and enzymes to fight off the infection . different combinations of symptoms cause different kinds of acne , with names you ’ ve probably heard before : blackheads , whiteheads , pimples , pustules … technically , they all mean different things . the scientific term for a clogged pore is a comedo , which actually used to mean a parasitic worm . people started using the term to refer to a clogged pore because the stuff that comes out when you squeeze it looks kind of like a worm . when the main symptom is just that the pore is clogged , without much inflammation , that ’ s either a blackhead or a whitehead . blackheads are what it ’ s called when the comedo is open . the trapped sebum and dead skin cells become oxidized , which turns the surface of the clogged material into a dark color , kind of like how silver tarnishes . when the comedo closes , skin cells grow over the top of the plug and stop this oxidation from happening , so the whitish color of the sebum shows through . that ’ s called a whitehead . when there ’ s a comedo plus an infection that causes inflammation , that ’ s a different kind of acne : pimples ! the typical reddish bumpy kind are more specifically called papules . if the inflammation gets really bad , sometimes the bumps start leaking fluid or bacteria-filled pus . those kind are categorized as pustules , and they ’ re usually a much brighter red , or sometimes white from the oozing fluid . the most severe kind of acne is generally called cystic acne . that ’ s when the infection takes root in the deepest layers of the skin . sometimes the infection causes more solid bumps to form , called nodules . and sometimes the infection causes pus-filled bumps , called cysts . so that ’ s how acne happens . but what causes it in the first place ? what makes healthy pores become clogged , infected , and sometimes ooze-y ? again , there are a few different factors involved . genetics seem to be important , for one thing . so if your parents had acne , you ’ re more likely to have it too . hormones also have a huge influence on acne — specifically , androgen hormones , like testosterone , which influence the development of both the male and female reproductive systems . which explains why acne is so much more of a problem during puberty . androgen hormones are linked to sebum production . so during puberty , when the hormones are highly active , there ’ s an increase in sebum production . increased stress has been thought to increase hormone production , as well . so if you find yourself breaking out the day before a big test , that ’ s probably why . when you ’ re stressed , you produce more hormones , which then increases your sebum production . since sebum is an oil , a lot of people say that greasy foods will cause acne . sometimes you ’ ll also hear that dairy makes it worse , or even more specific foods , like chocolate . but the truth is , scientists aren ’ t really sure how or whether diet and acne are connected . there have been lots of studies investigating this , and some do suggest a possible link . but others don ’ t . we need more comprehensive , controlled trials with plenty of subjects before we can come to any real conclusions . doctors do acknowledge that there ’ s anecdotal evidence , and they say that if changing your diet has helped with your acne , then it makes sense for you to stick with it . there just isn ’ t enough evidence to support the idea that diet has a role in acne in general . but we do know that exposure to other topical oils , like some cosmetics or moisturizers , can cause acne by blocking your pores with extra oils and trapping sebum . it ’ s easy to avoid the problem , though — just look for products that say they ’ re non-comedogenic , which means that they shouldn ’ t clog your pores . but the natural oil on your face isn ’ t really a problem . you ’ ll often hear that you should wash your face a lot to help prevent acne , but acne isn ’ t caused by dirt or by the natural oil that ’ s already on the surface of your skin . and washing your face too much can actually irritate your skin , making acne worse . to treat acne , the goal is to reduce the factors that come together to cause breakouts . the one thing you shouldn ’ t do is pop a zit . the big risk is that you ’ ll push the infection out of the hair follicle and into the surrounding skin , instead of out to the surface . plus , you ’ ll irritate the area , causing more inflammation and making the acne take longer to heal . you might also spread bacteria to non-affected pores . instead , treatments try to lower sebum production , stop dead cells from clumping together in the pore as much , prevent bacterial growth , and lower inflammation . treatments can range from mild to aggressive , depending on how severe the symptoms are . for mild acne like blackheads and whiteheads , you can usually use topical over-the-counter medications . one of the most effective is benzoyl peroxide , a chemical compound that ’ s really good at killing bacteria . it decomposes into super reactive forms of oxygen , which bind to and destroy the molecules the bacteria need to survive . another common treatment is salicylic acid , which doesn ’ t kill the bacteria , but stops them from replicating . it can also break down skin cells and keratin to help unclog the pores inflammatory acne , like papular pimples or cystic acne , sometimes needs stronger treatment to reduce the inflammation . that usually means prescription meds . # # # antibiotics — the kind that are also used to treat other bacterial infections , from strep throat to urinary tract infections — can be used to treat acne . they stop bacterial growth and reduce inflammation . another kind of treatment involves retinoids , which are compounds related to vitamin a. retinoids work by binding to skin cell receptors to remove dead skin cells and encourage healthy skin cell growth . so retinoids work really well to unclog pores full of dead skin cells . they ’ re anti-inflammatory , too . in severe cystic acne cases , stronger retinoids actually work at the deeper layers of skin to reduce the size of the oil glands so they produce less sebum . and since hormones are a big factor in sebum production , using birth control or corticosteroids can regulate female hormones and reduce the amount of androgen hormones being produced . fewer androgen receptors at work means less sebum production , which means less acne . sometimes , severe , cystic acne will leave scarring , but there are ways to reduce it . these procedures don ’ t necessarily treat or prevent the acne itself , but they can reduce the bumps and scars left over from bad breakouts . dermabrasion uses a gentle sanding tool to wear down layers of the skin that have scarred over from cystic acne , but it only works for people with lighter skin . this procedure has mostly been replaced by laser resurfacing , which uses laser pulses to remove skin layer by layer until the scar has smoothed out . then there are chemical peels , which use compounds like salicylic acid or retinoic acid to perform what ’ s basically a controlled injury to the top layer of skin , killing the top layer of cells . the dead skin cells peel off , revealing healthy skin cells underneath . luckily , most people grow out of the acne-ridden years of puberty , though some people will continue to have acne well into their 40s and 50s . but even though a bad breakout might make you self-conscious , it ’ s normal , it ’ s treatable , and it ’ s not life-threatening . so take care of your skin , talk to your doctor about prescription treatments if you want them , and trust that your acne will probably get better with age . and then you get to look forward to wrinkles ! thanks for watching this episode of scishow , brought to you by our patrons on patreon . if you want to help support this show , just go to patreon.com/scishow . and don ’ t forget to go to youtube.com/scishow and subscribe !

but we do know that exposure to other topical oils , like some cosmetics or moisturizers , can cause acne by blocking your pores with extra oils and trapping sebum . it ’ s easy to avoid the problem , though — just look for products that say they ’ re non-comedogenic , which means that they shouldn ’ t clog your pores . but the natural oil on your face isn ’ t really a problem .

skin products that are 'non-comedogenic ' claim to not do what ?

this is a 20-minute vhs tape about a lego character called jack stone . when it came out in 2001 , it was the first real computer-animated lego movie . … but it hasn ’ t aged that well . `` incredible ! '' `` fantastic . '' thirteen years later , the lego movie looked like this : let ’ s watch that again . this is 2001 . `` there you have it . '' and this is 2014 . `` yes , that 's me . '' that is a huge difference . here ’ s how they made it happen . “ my name is grant freckelton , i ’ m a production designer at animal logic. ” he ’ s overseen the animation style of movies like legend of the guardians , 300 , and more recently , the lego movie , with co-directors chris miller and phil lord . “ chris and phil were determined to sort of make sure the audience was confused about what they were seeing . you know is it actually stop motion , or is it cg film ? ” and that became a big debate . before the movie came out , there was a lot of conversation about whether the movie was stop motion or computer animation . `` it is , i would say 99 % cg animation , but it respects the rules of stop motion animation , and is designed to emulate that style. ” to understand what made that style so unique , you have to look back at what lego movies used to look like . early productions for themes like bionicle , star wars , and batman helped establish the whimsical feel of lego movies — but the animation didn ’ t fit the physics of the toy itself . “ there was this tendency to sort of treat the plastic like it was flexible rubber , which meant that the characters could flex and move a lot more than they might be able to in real life. ” that style is typical of more traditional computer animation , like what you ’ d expect to see in a pixar movie . take a shot like this , for example . the background isn ’ t made of actual blocks , plastic limbs are bending in ways they couldn ’ t , and the faces are a bizarre blend of skin-like texture and lego geometry . it doesn ’ t look like a scene you could make at home with your own legos . compare that to scenes from the lego movie , where everything — gunshots , smoke , water , fire , explosions , clouds , even mud on the camera lens — are all made up of lego pieces as they look in real life . “ we respected the hardness of the plastic by not necessarily bending on the elbow , which you can ’ t do on a real lego minifig. ” that means that any movement you see onscreen simulates the adjustment or replacement of an individual lego piece . a joint or facial expression will never actually bend or stretch — it ’ ll either move slightly or be replaced by another piece . early lego movies lacked that level of discipline . they struggled because they fought back against the limitations of the medium instead of embracing them . but the creators of the lego movie saw things differently . “ characters that have limitations force you to find solutions and charming ways of doing things in different ways . i mean , look at r2-d2 : he ’ s like , the ultimate limited character , he ’ s basically a bin with wheels that makes beeping noises , and that ’ s all he 's got to work with . and yet he ’ s a really charming character and everybody loves him . same with bb-8 . and other characters . same with the muppets , they ’ re essentially sock puppets with googly eyes that you do n't really have much control over . but it ’ s from those limitations that you actually get a lot of charm. ” every now and then , the lego movie animators would let some joints overextend slightly to make room for a nod or a shrug of the shoulders ... but overall , sticking to the plastic rule made for a believable movie . you can freeze frame any part of the lego movie and look at a scene that you could practically make at home . “ we were always trying to echo and hark back to how a child might make a film . so we would alternate between thinking like responsible filmmakers working on a large-budget warner brothers animated film , and then we would suddenly approach a scene as if we were like a kid animating in their basement. ” but the history of lego movies actually does start with kids animating in their basements . in 1973 , two danish cousins , aged 10 and 12 , shot a short film called journey to the moon on super 8 film . they made it for their grandparents ’ 50th wedding anniversary — and it ’ s widely considered to be the first time anyone made a motion picture with lego blocks . note that the “ people ” in this film are just little cylinder blocks — this was before any version of the minifigure design came out . movies like this came to be known as “ brickfilms. ” when fans were making these at home , they shot them in traditional stop motion . footage was usually shot “ on twos , ” which meant that they would take 12 pictures — adjusting the characters every other frame — to make one second of film . shooting “ on ones ” meant taking 24 pictures per second — this was usually reserved for making faster movements like running look smoother . when the danish cousins sent their movie to the managing director of the lego group , they were rewarded with a tour of the lego factory and sent home with large lego sets . but lego hasn ’ t always had the most positive reaction to homemade fan films like this one . between 1985 and 1989 , a teenage animator named lindsay fleay worked on a 16-minute short called the magic portal . he used borrowed equipment to shoot it in his parents ’ basement . before entering festivals and competitions , fleay sent the film to lego to see if they were interested in doing something with it . at first , lego responded with a letter of approval . but soon , the company started expressing legal concerns and issued a letter demanding fleay surrender all copies of the film within seven days . lego ultimately backed down , but fleay had already missed out on most major film festivals by then . fleay actually went on to work at animal logic . he left before production on lego projects began , but his movie had a huge influence on the world of brickfilms . “ if you look at the live action portion of the lego movie , you 'll see finn , the little kid , holds up a sort of cardboard tube and across the side is written magic portal . '' the lego movie , of course , was a huge technical feat . there are 15,080,330 animated lego pieces and 182 unique minifigures in the movie . early mockups of buildings and vehicles were drafted on a free software called lego digital designer later on , in the animation software maya , each brick was given profiles for fingerprints , dents , seam lines , scratches , and dust . it ’ s hard to imagine what the lego movie would be if it weren ’ t for the legacy of these early home experiments . where most animated films use soft lighting modeled after paintings , the lego movie ’ s lighting was harsh , replicating the actual lamps that animators like fleay used . playful non-stop motion interludes — like levitation via fishing line — were part of journey to the moon long before they appeared in the lego movie . even the final break from the lego world into the real world to meet a human creator parallels the magic portal really closely . ah , my film ! it ’ s easy to miss on-screen , but the lego movie pays tribute to fan films in the background of this scene — these four clips are shorts submitted by fans . “ look at all these things that people built ! ” the homage was a nod to the fans . by doing that , the movie embraced the idea that amateur creators matter — and sometimes , the way they handle source material is far better than the way major studios are used to doing it . if you want to try any of this at home , you can actually use the same software that the animators of the lego movie used . it ’ s called lego digital designer , it ’ s totally free off the internet . when i talked to grant freckelton , he challenged me to make this sort of pig-drawn carriage . i tried . i got the pigs , i got the wheels , but not much else . it ’ s very , very difficult .

before the movie came out , there was a lot of conversation about whether the movie was stop motion or computer animation . `` it is , i would say 99 % cg animation , but it respects the rules of stop motion animation , and is designed to emulate that style. ” to understand what made that style so unique , you have to look back at what lego movies used to look like . early productions for themes like bionicle , star wars , and batman helped establish the whimsical feel of lego movies — but the animation didn ’ t fit the physics of the toy itself .

what style of animation did most fans use to make their brickfilms ?

during a long day spent roaming the forest in search of edible grains and herbs , the weary divine farmer shennong accidentally poisoned himself 72 times . but before the poisons could end his life , a leaf drifted into his mouth . he chewed on it and it revived him , and that is how we discovered tea . or so an ancient legend goes at least . tea does n't actually cure poisonings , but the story of shennong , the mythical chinese inventor of agriculture , highlights tea 's importance to ancient china . archaeological evidence suggests tea was first cultivated there as early as 6,000 years ago , or 1,500 years before the pharaohs built the great pyramids of giza . that original chinese tea plant is the same type that 's grown around the world today , yet it was originally consumed very differently . it was eaten as a vegetable or cooked with grain porridge . tea only shifted from food to drink 1,500 years ago when people realized that a combination of heat and moisture could create a complex and varied taste out of the leafy green . after hundreds of years of variations to the preparation method , the standard became to heat tea , pack it into portable cakes , grind it into powder , mix with hot water , and create a beverage called muo cha , or matcha . matcha became so popular that a distinct chinese tea culture emerged . tea was the subject of books and poetry , the favorite drink of emperors , and a medium for artists . they would draw extravagant pictures in the foam of the tea , very much like the espresso art you might see in coffee shops today . in the 9th century during the tang dynasty , a japanese monk brought the first tea plant to japan . the japanese eventually developed their own unique rituals around tea , leading to the creation of the japanese tea ceremony . and in the 14th century during the ming dynasty , the chinese emperor shifted the standard from tea pressed into cakes to loose leaf tea . at that point , china still held a virtual monopoly on the world 's tea trees , making tea one of three essential chinese export goods , along with porcelain and silk . this gave china a great deal of power and economic influence as tea drinking spread around the world . that spread began in earnest around the early 1600s when dutch traders brought tea to europe in large quantities . many credit queen catherine of braganza , a portuguese noble woman , for making tea popular with the english aristocracy when she married king charles ii in 1661 . at the time , great britain was in the midst of expanding its colonial influence and becoming the new dominant world power . and as great britain grew , interest in tea spread around the world . by 1700 , tea in europe sold for ten times the price of coffee and the plant was still only grown in china . the tea trade was so lucrative that the world 's fastest sailboat , the clipper ship , was born out of intense competition between western trading companies . all were racing to bring their tea back to europe first to maximize their profits . at first , britain paid for all this chinese tea with silver . when that proved too expensive , they suggested trading tea for another substance , opium . this triggered a public health problem within china as people became addicted to the drug . then in 1839 , a chinese official ordered his men to destroy massive british shipments of opium as a statement against britain 's influence over china . this act triggered the first opium war between the two nations . fighting raged up and down the chinese coast until 1842 when the defeated qing dynasty ceded the port of hong kong to the british and resumed trading on unfavorable terms . the war weakened china 's global standing for over a century . the british east india company also wanted to be able to grow tea themselves and further control the market . so they commissioned botanist robert fortune to steal tea from china in a covert operation . he disguised himself and took a perilous journey through china 's mountainous tea regions , eventually smuggling tea trees and experienced tea workers into darjeeling , india . from there , the plant spread further still , helping drive tea 's rapid growth as an everyday commodity . today , tea is the second most consumed beverage in the world after water , and from sugary turkish rize tea , to salty tibetan butter tea , there are almost as many ways of preparing the beverage as there are cultures on the globe .

the japanese eventually developed their own unique rituals around tea , leading to the creation of the japanese tea ceremony . and in the 14th century during the ming dynasty , the chinese emperor shifted the standard from tea pressed into cakes to loose leaf tea . at that point , china still held a virtual monopoly on the world 's tea trees , making tea one of three essential chinese export goods , along with porcelain and silk .

in what dynasty did the emperor change tea making from pressed form to the loose leaves we use today ?

translator : andrea mcdonough reviewer : bedirhan cinar ever see a medieval painting of baby jesus sitting or standing on his mother 's lap and wonder why she 's so large ? paintings like cimabue 's enthroned madonna with angels or duccio 's maesta also appear out of proportion . if mary were to stand up , it seems , the angels in the picture would be as tall as her shin bone , and her torso would be disproportionately small when compared to her legs . maybe you thought the artist simply was n't skilled enough to paint realistically or lacked the mathematical skill of perspective . but that 's not the full story . to understand why , we need to go back to the late fifth century when the city of rome was attacked by the goths . rome was built in marble and meant to last forever . it represented , for many years , the pinnacle of human civilization , so its destruction left a huge void . theologians , who preached about a world beyond the physical , began attracting an audience as rome crumbled , and christianity started to fill the void left by the empire . as a replacement for the physical beauty of rome , christianity offered a metaphysical beauty of virtue and an eternal heaven that could not be destroyed as rome had . after the fall of rome , early medieval theologians turned away from physical beauty , rejecting it in favor of inner-beauty . they maintained that while the physical world was temporary , virtue and religion were permanent . beautiful objects could lead to a misguided worship of the object rather than the worship of goodness . it is said that the early sixth century preacher , st. benedict , upon thinking of a beautiful woman , threw himself into a thorn patch , and through his suffering , regained his focus on spiritual beauty . he feared his desire for the beautiful woman would distract him from his desire to love god . as european civilization transitioned away from empires and towards religion , monasteries became the gatekeepers of knowledge , which meant that classical books that praised physical pleasures were not copied or protected . without protection , they became the victims of natural decay , fire , flooding , or pests . and without the help of monks transcribing new copies , these texts and the philosophies they carried disappeared in western europe and were replaced by the works of people like st. benedict , which brings us back to these depictions of jesus and mary . because christianity had so fervently rejected physical beauty , these medieval artists purposefully avoided aesthetically pleasing forms . at first , decorations for churches or palaces were limited to interesting geometric patterns , which could be pleasing without inspiring sinful thoughts of physical pleasure . as the medieval period progressed , depictions of jesus and mary were tolerated , but the artist clearly made an effort to veil mary and give her disproportionately large legs , with those enormous shin bones . the fear remained that a beautiful illustration of mary might inspire the viewer to love the painting or the physical form of mary , rather than the virtue she 's meant to represent . so even though it may be fun to think we can paint more realistically than cimabuey or duccio , we need to remember that they had different goals when picking up a paintbrush .

and without the help of monks transcribing new copies , these texts and the philosophies they carried disappeared in western europe and were replaced by the works of people like st. benedict , which brings us back to these depictions of jesus and mary . because christianity had so fervently rejected physical beauty , these medieval artists purposefully avoided aesthetically pleasing forms . at first , decorations for churches or palaces were limited to interesting geometric patterns , which could be pleasing without inspiring sinful thoughts of physical pleasure .

because those in power did n't want people to worship physical beauty , artists did n't paint many people . do you think there is anything in art today that 's similar to portraiture in medieval times ? if so , what is it ? if not , explain why .

sunken relics , ghostly shipwrecks , and lost cities . these are n't just wonders found in fictional adventures . beneath the ocean 's surface , there are ruins where people once roamed and shipwrecks loaded with artifacts from another time . this is the domain of underwater archaeology , where researchers discover and study human artifacts that slipped into the sea . they 're not on a treasure hunt . underwater archaeology reveals important information about ancient climates and coastlines , it tells us how humans sailed the seas , and what life was like millennia ago . so what exactly can we find ? at shallow depths mingled in with modern-day items , we 've discovered all sorts of ancient artifacts . this zone contains evidence of how our ancestors fished , how they repaired their ships , disposed of their trash , and even their convicted pirates , who were buried below the tide line . and it 's not just our recent history . 800,000-year old footprints were found along the shore in norfolk , britain . in these shallow depths , the remains of sunken cities also loom up from the sea floor , deposited there by earthquakes , tsunamis , and earth 's sinking plates . almost every sunken city can be found at these shallow depths because the sea level has changed little in the several thousand years that city-building civilizations have existed . for instance , in shallow waters off the coast of italy lies baia , a roman seaside town over 2,000 years old . there , it 's possible to swim among the ruins of structures built by rome 's great families , senators , and emperors . and then there are shipwrecks . as ships grow too old for use , they 're usually abandoned near shore in out-of-the-way places like estuaries , rivers , and shallow bays . archaeologists use these like a timeline to map a harbor 's peaks and declines , and to get clues about the historic art of shipbuiding . at roskilde in denmark , for example , five purposefully sunken vessels reveal how vikings crafted their fearsome long ships 1,000 years ago . when we descend a bit further , we reach the zone where the deepest human structures lie , like ancient harbor walls and quays . we also see more shipwrecks sunk by storms , war , and collisions . we 're still excavating many of these wrecks today , like blackbeard 's ship , which is revealing secrets about life as an 18th century pirate . but past 50 feet , there are even deeper , better preserved shipwrecks , like the wreck at antikythera , which sank during the 1st century bc . when it was discovered , it contained statues , trade cargo , and also the earliest known computer , a mysterious device called the antikythera mechanism that kept track of astronomical changes and eclipses . today , it gives archaeologists vital information about the knowledge possessed by the ancient greeks . it is in this zone that we also begin to find aircraft and submarines , such as those from the world wars . plunging as deep as 200 feet , we can find some of the earliest and rarest signs of human history . prior to 5,000 years ago , there was a lot more dry land because glaciers trapped much of the water that now forms the sea . our ancestors spread across these lands , and so on the sea floor , we find their camps , stone tools , and the bones of animals they hunted . these sites give us invaluable knowledge about our ancestor 's migration patterns , hunting methods , and technologies . in the deepest zone , no human has ever walked . this area has been submerged since well before mankind evolved . the only artifacts we find are those that have drifted down from above , like nasa 's saturn v rocket engines at 14,000 feet , and the deepest shipwrecks . the ocean is like a huge underwater museum that constantly adds to our knowledge about humanity . with only a fraction of it explored , discoveries are sure to continue long into the future .

our ancestors spread across these lands , and so on the sea floor , we find their camps , stone tools , and the bones of animals they hunted . these sites give us invaluable knowledge about our ancestor 's migration patterns , hunting methods , and technologies . in the deepest zone , no human has ever walked .

shallow archaeological sites are easier to access and there are a great number of them , but they are often damaged over the years by storms and treasure seekers . deep sites are hard to find and difficult to access , but are untouched time capsules . should science focus on one type , or are both important ?

translator : andrea mcdonough reviewer : bedirhan cinar the universe , rather beautiful , is n't it ? it 's quite literally got everything , from the very big to the very small . sure , there are some less than savory elements in there , but on the whole , scholars agree that its existence is probably a good thing . such a good thing that an entire field of scientific endeavor is devoted to its study . this is known as cosmology . cosmologists look at what 's out there in space and piece together the tale of how our universe evolved : what it 's doing now , what it 's going to be doing , and how it all began in the first place . it was edwin hubble who first noticed that our universe is expanding , by noting that galaxies seem to be flying further and further apart . this implied that everything should have started with the monumental explosion of an infinitely hot , infinitely small point . this idea was jokingly referred to at the time as the `` big bang , '' but as the evidence piled up , the notion and the name actually stuck . we know that after the big bang , the universe cooled down to form the stars and galaxies that we see today . cosmologists have plenty of ideas about how this happened . but we can also probe the origins of the universe by recreating the hot , dense conditions that existed at the beginning of time in the laboratory . this is done by particle physicists . over the past century , particle physicists have been studying matter and forces at higher and higher energies . firstly with cosmic rays , and then with particle accelerators , machines that smash together subatomic particles at great energies . the greater the energy of the accelerator , the further back in time they can effectively peek . today , things are largely made up of atoms , but hundreds of seconds after the big bang , it was too hot for electrons to join atomic nuclei to make atoms . instead , the universe consisted of a swirling sea of subatomic matter . a few seconds after the big bang , it was hotter still , hot enough to overpower the forces that usually hold protons and neutrons together in atomic nuclei . further back , microseconds after the big bang , and the protons and neutrons were only just beginning to form from quarks , one of the fundamental building blocks of the standard model of particle physics . further back still , and the energy was too great even for the quarks to stick together . physicists hope that by going to even greater energies , they can see back to a time when all the forces were one and the same , which would make understanding the origins of the universe a lot easier . to do that , they 'll not only need to build bigger colliders , but also work hard to combine our knowledge of the very , very big with the very , very small and share these fascinating insights with each other and with , well , you . and that 's how it should be ! because , after all , when it comes to our universe , we 're all in this one together .

cosmologists look at what 's out there in space and piece together the tale of how our universe evolved : what it 's doing now , what it 's going to be doing , and how it all began in the first place . it was edwin hubble who first noticed that our universe is expanding , by noting that galaxies seem to be flying further and further apart . this implied that everything should have started with the monumental explosion of an infinitely hot , infinitely small point .

how did we first work out that the universe was expanding ?

muhammad ali spent years training to become the greatest boxer the world had ever seen , but only moments to create the shortest poem . ali captivated harvard 's graduating class in 1975 with his message of unity and friendship . when he finished , the audience wanted more . they wanted a poem . ali delivered what is considered the shortest poem ever . `` me , we . '' or is it `` me , weeee '' ? no one 's really sure . regardless , if these two words are a poem , then what exactly makes a poem a poem ? poets themselves have struggled with this question , often using metaphors to approximate a definition . is a poem a little machine ? a firework ? an echo ? a dream ? poetry generally has certain recognizable characteristics . one - poems emphasize language 's musical qualities . this can be achieved through rhyme , rhythm , and meter , from the sonnets of shakepeare , to the odes of confucius , to the sanskrit vedas . two - poems use condensed language , like literature with all the water wrung out of it . three - poems often feature intense feelings , from rumi 's spiritual poetry to pablo neruda 's `` ode to an onion . '' poetry , like art itself , has a way of challenging simple definitions . while the rhythmic patterns of the earliest poems were a way to remember stories even before the advent of writing , a poem does n't need to be lyrical . reinhard döhl 's “ apfel ” and eugen gomringer 's `` silencio '' toe the line between visual art and poetry . meanwhile , e.e . cummings wrote poems whose shapes were as important as the words themselves , in this case amplifying the sad loneliness of a single leaf falling through space . if the visual nature of poetry faded into the background , perhaps we 'd be left with music , and that 's an area that people love to debate . are songs poems ? many do n't regard songwriters as poets in a literary sense , but lyrics from artists like paul simon , bob dylan , and tupac shakur often hold up even without the music . in rap , poet elements like rhyme , rhythm , and imagery are inseparable from the form . take this lyric from the notorious b.i.g . `` i can hear sweat trickling down your cheek your heartbeat sound like sasquatch feet thundering , shaking the concrete . '' so far , all the examples we 've seen have had line breaks . we can even imagine the two words of ali 's poem organizing in the air - me , we . poetry has a shape that we can usually recognize . its line breaks help readers navigate the rhythms of a poem . but what if those line breaks disappeared ? would it lose its essence as a poem ? maybe not . enter the prose poem . prose poems use vivid images and wordplay but are formatted like paragraphs . when we look at poetry less as a form and more as a concept , we can see the poetic all around us : spiritual hymns , the speeches of orators like martin luther king , jr. , jfk , and winston churchill , and surprising places like social media . in 2010 , journalist joanna smith tweeted updates from the earthquake in haiti . `` was in b-room getting dressed when heard my name . tremor . ran outside through sliding door . all still now . safe . roosters crowing . '' smith uses language in a way that is powerful , direct , and filled with vivid images . compare her language to a haiku , the ancient japanese poetic form that emphasizes bursts of brief intensity with just three lines of five , seven , and five syllables . the waters of poetry run wide and deep . poetry has evolved over time , and perhaps now more than ever , the line between poetry , prose , song , and visual art has blurred . however , one thing has not changed . the word poetry actually began in verb form , coming from the ancient greek poiesis , which means to create . poets , like craftsman , still work with the raw materials of the world to forge new understandings and comment on what it is to be human in a way only humans can . dartmouth researchers tested this idea by asking robots to pen poetry . a panel of judges sorted through stacks of sonnets to see if they could distinguish those made by man and machine . you may be happy to know that while scientists have successfully used artificial intelligence in manufacturing , medicine , and even journalism , poetry is a different story . the robots were caught red-handed 100 % of the time .

three - poems often feature intense feelings , from rumi 's spiritual poetry to pablo neruda 's `` ode to an onion . '' poetry , like art itself , has a way of challenging simple definitions . while the rhythmic patterns of the earliest poems were a way to remember stories even before the advent of writing , a poem does n't need to be lyrical .

in what way was joanna smith ’ s tweet like a poem ?

it was much more exciting than i thought . you see the flames . our first video of fluorine was a bit disappointing . there wasn ’ t any , just a few bits of glassware and some funny stories . so at the moment i ’ m in the office of professor eric hope who is one of the country ’ s specialists in fluorine chemistry . he knows how to handle this terrific element safely . i have no idea what to do . i ’ m quite excited to see what happens . one of the things you said in that original video was , on youtube , was that fluorine was one of the few elements that you hadn ’ t seen so i thought there are actually relatively few chemists who have seen fluorine . so what i want to do is produce and show you elemental fluorine . fluorine is slowly released ; you see the pressure slowly going up . the reason that people know about fluorine is that it is one of the really reactive elements . it will react with all the elements of the periodic table , except neon and helium . it will react with gold , it ’ ll react with silver , it ’ ll react with platinum . platinum hexafluoride is bright red as it ’ s a gas . ok so fluorine is going into the apparatus , it ’ s going into this tube . martyn , you can ’ t see anything can you ? i can ’ t see anything at all . you can ’ t see anything at all , and that ’ s because there ’ s only a little under 2 atmospheres of fluorine in there . it ’ s a very pale yellow colour as a gas . a bit disappointed but i suppose it ’ s like oxygen or nitrogen , you can ’ t really see it . but perhaps if we condense it as a liquid then i ’ ll see it properly . ok so now i ’ m going to cool this down with liquid nitrogen to -196oc . i ’ m going to do it slowly . it will take a little while . ok martyn , do you want to help me with this ? yep . so what i want to do is for you to take that flask away and i ’ ll slide this one in . so if you slide it away and back up again . and there we have , oh maybe two inches of liquid fluorine . you can go right up that , there ’ s no problem with that if you want to . just , clear a bit of condensation off there . yeah i ’ m really surprised i thought it would be pale green and its dark yellow . if i ’ d been shown it i ’ d thought it was liquid chlorine . but i ’ ve never seen liquid chlorine either . i ’ m quite pleased with that . so , basically i ’ ve got another fluorine cylinder filled up from the roof with about 5 atmospheres of fluorine in it . so this is now going to release the fluorine . and what i ’ ve got in this demonstration here is just a scouring pad . it ’ s a metal scouring pad , iron wool . it burnt a hole right through the iron wool . it ’ s extraordinary . the iron looks as if it ’ s rusted but the rusty colour is actually iron fluoride or maybe a bit of iron oxide from the hot iron reacting with the oxygen in the air . well the reason that fluorine makes such strong bonds is because it is a small atom and the nucleus is relatively highly charged because it ’ s right on the right-hand side of the periodic table but the electrons don ’ t shield this nucleus . so it is very , so-called , electronegative . it attracts electrons to itself from other elements . i ’ ve changed the prop now for some just normal barbeque briquettes which is pure carbon . so we haven ’ t done anything . this is cold charcoal and cold gas , and the gas just touching it is enough to start the fire . think of that : just the cold gas setting things on fire . most chemists are really too frightened to work with fluorine . you can ’ t use it in glass vessels . it doesn ’ t attack glass but if the glass is a tiny bit wet and most glass has moisture absorbed into it , then the fluorine form hydrogen fluoride and it reacts with the water and the hydrogen fluoride just eats through the glass . so you need to use equipment made out of metal , usually nickel , and the fluorine reacts with the surface of the nickel , the first time you use it and then you get a layer on the surface that protects the rest of the metal . so this is again fluorine with sulphur . so you are going to oxidise the sulphur , probably to sulphur tetrafluoride or sulphur hexafluoride . fluorine has this reputation for being very reactive and very dangerous and something to be careful about . but aren ’ t their fluorine atoms in my toothpaste ? your toothpaste contains fluoride and , just in the same way that you can eat sodium chloride , table salt which contains chlorine , you can use fluorides and once the fluorine has got an extra electron , for example from the tin in tin fluoride , which is often used in toothpaste or sodium fluoride . it ’ s got what it wants and it ’ s not very reactive . and the way it works with teeth is that the enamel of your teeth is a compound of calcium called appetite , which normally the appetite in your teeth can dissolve quite easily in acid . for example , if you eat sweets or drink some fizzy drinks then you have enough acid to start dissolving the surface of your teeth . but if you brush your teeth with fluoride , some of the appetite , which contains oh groups , some of these are replaced with fluoride and you make a material called fluoral appetite which is much less soluble in acid so it can ’ t attacked so easily , so you don ’ t get holes in your teeth .

i ’ m quite pleased with that . so , basically i ’ ve got another fluorine cylinder filled up from the roof with about 5 atmospheres of fluorine in it . so this is now going to release the fluorine . and what i ’ ve got in this demonstration here is just a scouring pad .

fluorine is the best example of an element that can attract electrons towards itself . what is the name of this chemical property ?

all year long , researchers at hundreds of hospitals around the world collect samples from flu patients and send them to top virology experts with one goal : to design the vaccine for the next flu season . but why do we need a new one every year ? vaccines for diseases like mumps and rubella offer a lifetime of protection with two shots early in life . what 's so special about the flu ? two factors make the flu a tough target . first , there are more than 100 subtypes of the influenza virus , and the ones in circulation change from season to season . and second , the flu 's genetic code allows it to mutate more quickly than many other viruses . the flu spreads by turning a host 's own cells into viral production factories . when the virus is engulfed by a host cell , it expels its genetic material , which makes its way to the nucleus . there , cellular machinery that normally copies the host 's genes starts replicating viral genes instead , creating more and more copies of the virus . new viruses are repackaged and crammed into the cell until it bursts , sending freshly minted influenza viruses out to infect additional cells . most viruses follow this script . the trick with the flu is that its genetic material is n't dna but a similar compound called rna . and rna viruses can mutate much faster . when cells synthesize dna , a built-in proofreader recognizes and corrects mistakes , but the rna synthesis mechanism does n't have this fail-safe . if errors creep in , they stick around creating new variants of the virus . why is this a problem ? because vaccines depend on recognition . the flu vaccine includes some of the same substances , called antigens , found on the surface of the virus itself . the body identifies those fragments as foreign and responds by producing compounds called antibodies , tailor-made to match the antigens . when a vaccinated person encounters the actual virus , the preprogrammed antibodies help the immune system identify the threat and mobilize quickly to prevent an infection . those antigens are different for every strain of influenza . if vaccination has prepared the immune system for one strain , a different one may still be able to sneak by . even within the same strain of flu , those rapid genetic mutations can change the surface compounds enough that the antibodies may not recognize them . to make things even more complicated , sometimes two different strains combine to create an entirely new hybrid virus . all of this makes vaccinating for the flu like trying to hit a moving transforming target . that 's why scientists are constantly collecting data about which strains are circulating and checking to see how much those strains have mutated from previous years ' versions . twice annually , the world health organization pulls together experts to analyze all that data , holding one meeting for each hemisphere . the scientists determine which strains to include in that season 's vaccine , picking four for the quadrivalent vaccine in use today . in spite of the flu 's evasive maneuvers , in recent years , the group 's predictions have been almost always correct . even when flu strains mutate further , the vaccine is often close enough that a vaccinated person who catches the flu anyway will have a milder and shorter illness than they would otherwise . vaccination also helps protect other people in the community who may not be medically eligible for the shot by preventing those around them from carrying the virus . this is called herd immunity . the flu shot ca n't give you the flu . it contains an inactivated virus that is n't capable of making you sick . you might feel tired and achy after getting it , but that 's not an infection . it 's your normal immune response to the vaccine . some parts of the world use , instead of a shot , an inhaled vaccine that contains a weakened live virus . this is also safe for the vast majority of people . only those with impaired immune systems would be at risk , but they 're typically not given live vaccines . meanwhile , scientists are working to develop a universal flu vaccine that would protect against any strain , even mutated ones . but until then , the hunt for next year 's vaccine is on .

twice annually , the world health organization pulls together experts to analyze all that data , holding one meeting for each hemisphere . the scientists determine which strains to include in that season 's vaccine , picking four for the quadrivalent vaccine in use today . in spite of the flu 's evasive maneuvers , in recent years , the group 's predictions have been almost always correct .

what are the types of flu vaccine available today ?

if you 've had surgery , you might remember starting to count backwards from ten , nine , eight , and then waking up with the surgery already over before you even got to five . and it might seem like you were asleep , but you were n't . you were under anesthesia , which is much more complicated . you were unconscious , but you also could n't move , form memories , or , hopefully , feel pain . without being able to block all those processes at once , many surgeries would be way too traumatic to perform . ancient medical texts from egypt , asia and the middle east all describe early anesthetics containing things like opium poppy , mandrake fruit , and alcohol . today , anesthesiologists often combine regional , inhalational and intravenous agents to get the right balance for a surgery . regional anesthesia blocks pain signals from a specific part of the body from getting to the brain . pain and other messages travel through the nervous system as electrical impulses . regional anesthetics work by setting up and electrical baracade . they bind to the proteins in neurons ' cell membranes that let charged particles in and out , and lock out positively charged particles . one compound that does this is cocaine , whose painkilling effects were discovered by accident when an ophthalmology intern got some on his tongue . it 's still occasionally used as an anesthetic , but many of the more common regional anesthetics have a similar chemical structure and work the same way . but for major surgeries where you need to be unconscious , you 'll want something that acts on the entire nervous system , including the brain . that 's what inhalational anesthetics do . in western medicine , diethyl ether was the first common one . it was best known as a recreational drug until doctors started to realize that people sometimes did n't notice injuries they received under the influence . in the 1840s , they started sedating patients with ether during dental extractions and surgeries . nitrous oxide became popular in the decades that followed and is still used today . although ether derivatives , like sevoflurane , are more common . inhalational anesthesia is usually supplemented with intravenous anesthesia , which was developed in the 1870s . common intravenous agents include sedatives , like propofol , which induce unconsciousness , and opioids , like fentanyl , which reduce pain . these general anesthetics also seem to work by affecting electrical signals in the nervous system . normally , the brain 's electrical signals are a chaotic chorus as different parts of the brain communicate with each other . that connectivity keeps you awake and aware . but as someone becomes anesthetized , those signals become calmer and more organized , suggesting that different parts of the brain are n't talking to each other anymore . there 's a lot we still do n't know about exactly how this happens . several common anesthetics bind to the gaba-a receptor in the brain 's neurons . they hold the gateway open , letting negatively charged particles flow into the cell . negative charge builds up and acts like a log jam , keeping the neuron from transmitting electrical signals . the nervous system has lots of these gated channels , controlling pathways for movement , memory , and consciousness . most anesthetics probably act on more than one , and they do n't act on just the nervous system . many anesthetics also affect the heart , lungs , and other vital organs . just like early anesthetics , which included familiar poisons like hemlock and aconite , modern drugs can have serious side effects . so an anesthesiologist has to mix just the right balance of drugs to create all the features of anesthesia , while carefully monitoring the patient 's vital signs , and adjusting the drug mixture as needed . anesthesia is complicated , but figuring out how to use it allowed for the development of new and better surgical techniques . surgeons could learn how to routinely and safely perform c-sections , reopen blocked arteries , replace damaged livers and kidneys , and many other life-saving operations . and each year , new anesthesia techniques are developed that will ensure more and more patients survive the trauma of surgery .

in the 1840s , they started sedating patients with ether during dental extractions and surgeries . nitrous oxide became popular in the decades that followed and is still used today . although ether derivatives , like sevoflurane , are more common .

the following is not a method of taking anesthesia used today :

how do schools of fish swim in harmony ? and how do the tiny cells in your brain give rise to the complex thoughts , memories , and consciousness that are you ? oddly enough , those questions have the same general answer : emergence , or the spontaneous creation of sophisticated behaviors and functions from large groups of simple elements . like many animals , fish stick together in groups , but that 's not just because they enjoy each other 's company . it 's a matter of survival . schools of fish exhibit complex swarming behaviors that help them evade hungry predators , while a lone fish is quickly singled out as easy prey . so which brilliant fish leader is the one in charge ? actually , no one is , and everyone is . so what does that mean ? while the school of fish is elegantly twisting , turning , and dodging sharks in what looks like deliberate coordination , each individual fish is actually just following two basic rules that have nothing to do with the shark : one , stay close , but not too close to your neighbor , and two , keep swimmming . as individuals , the fish are focused on the minutiae of these local interactions , but if enough fish join the group , something remarkable happens . the movement of individual fish is eclipsed by an entirely new entity : the school , which has its own unique set of behaviors . the school is n't controlled by any single fish . it simply emerges if you have enough fish following the right set of local rules . it 's like an accident that happens over and over again , allowing fish all across the ocean to reliably avoid predation . and it 's not just fish . emergence is a basic property of many complex systems of interacting elements . for example , the specific way in which millions of grains of sand collide and tumble over each other almost always produces the same basic pattern of ripples . and when moisture freezes in the atmosphere , the specific binding properties of water molecules reliably produce radiating lattices that form into beautiful snowflakes . what makes emergence so complex is that you ca n't understand it by simply taking it apart , like the engine of a car . taking things apart is a good first step to understanding a complex system . but if you reduce a school of fish to individuals , it loses the ability to evade predators , and there 's nothing left to study . and if you reduce the brain to individual neurons , you 're left with something that is notoriously unreliable , and nothing like how we think and behave , at least most of the time . regardless , whatever you 're thinking about right now is n't reliant on a single neuron lodged in the corner of your brain . rather , the mind emerges from the collective activities of many , many neurons . there are billions of neurons in the human brain , and trillions of connections between all those neurons . when you turn such a complicated system like that on , it could behave in all sorts of weird ways , but it does n't . the neurons in our brain follow simple rules , just like the fish , so that as a group , their activity self-organizes into reliable patterns that let you do things like recognize faces , successfully repeat the same task over and over again , and keep all those silly little habits that everyone likes about you . so , what are the simple rules when it comes to the brain ? the basic function of each neuron in the brain is to either excite or inhibit other neurons . if you connect a few neurons together into a simple circuit , you can generate rhythmic patterns of activity , feedback loops that ramp up or shut down a signal , coincidence detectors , and disinhibition , where two inhibitory neurons can actually activate another neuron by removing inhibitory brakes . as more and more neurons are connected , increasingly complex patterns of activity emerge from the network . soon , so many neurons are interacting in so many different ways at once that the system becomes chaotic . the trajectory of the network 's activity can not be easily explained by the simple local circuits described earlier . and yet , from this chaos , patterns can emerge , and then emerge again and again in a reproducible manner . at some point , these emergent patterns of activity become sufficiently complex , and curious to begin studying their own biological origins , not to mention emergence . and what we found in emergent phenomena at vastly different scales is that same remarkable characteristic as the fish displayed : that emergence does n't require someone or something to be in charge . if the right rules are in place , and some basic conditions are met , a complex system will fall into the same habits over and over again , turning chaos into order . that 's true in the molecular pandemonium that lets your cells function , the tangled thicket of neurons that produces your thoughts and identity , your network of friends and family , all the way up to the structures and economies of our cities across the planet .

the movement of individual fish is eclipsed by an entirely new entity : the school , which has its own unique set of behaviors . the school is n't controlled by any single fish . it simply emerges if you have enough fish following the right set of local rules .

what determines how a school of fish will behave ?

[ go project films ] i think that facing death changes people ... which is what happened with me . before this experience , i was a completely different person with a completely different dream . my last dream which was to treat cancer and right now my dream of changing the world in another way . [ welcome to canada ] [ over 4.8 million syrians are refugees living in neighboring countries . ] [ 6.5 million more are displaced within syria . ] [ in november 2015 , the government of canada promised ] [ to resettle 25,000 syrian refugees within 6 months . ] [ the 2400 court motel in vancouver is one of 9 temporary housing sites ] [ for the newly arrived refugees . ] [ may 2016 , vancouver , canada ] staying at the motel is this hard transitional stage . you are homesick and you 're also thinking about remaining family members overseas living under horrendous circumstances . i try my best to introduce the new reality . i try my best to ease the impact of their resettlement process as refugees , as someone who did n't choose to come here , as someone who had to come here . hi , my name is mohammed from immigrant services society of british columbia , iss of bc contacting you regarding your place on craigslist . [ tell me we have three children . ] you 're looking at the two bedroom or the three bedroom ? - two bedroom , two bedroom . - two bedroom ? okay . - oh , two bedroom ? - the two bedroom , yeah . how many people you have ? a family of five people with three small kids . - yeah , that too many . - that is too many ? [ she 's telling you that 's too many people . ] [ okay , tell her thank you ... they are young . ] thank you . i 'm with my clients right now . so i 'm helping him . he wants to share with you , the kids are so small and the ages are ... the place is too small for five people . oh , oh , i see . [ - she 's saying the house is too small to fit five people . ] [ - what about the 3 bedroom ... what 's the rental cost ? ] okay , what about the three bedroom that you have ? $ 3,500 a month . that will be expensive for a new immigrant family . is it possible for you to see the kids and ... i can not accommodate five people in that place . yeah , thank you so much . i 'm sorry . [ the two bedroom house , it 's too small to accommodate five people . ] [ the other house with 3 bedrooms , it 's too expensive , it 's $ 3,500 a month . ] moving to canada is not easy at all . my job is all about providing first language services [ oh my god . ] to the newly arrived refugees . [ we 're going to try and find you another house . ] i 'm the person who welcomes them and i will help them with everything that they will need in their resettlement process . it 's really hard to explain the reality on the ground in syria . it keeps on changing on a daily basis . syrians are just caught up in the middle of this non-sense chaos . many of them have spent many years in refugee camps in neighboring countries trying to just wait for this crazy war to finish . when they realized it 's going to be much longer , this syrian refugee crisis started . [ this is a transitional stage and it 's very difficult . ] [ i was just like you when i came here . ] [ the same reception center , same counselor ] [ and even signed the same papers . ] [ attended the same orientation , and was looking for a house . ] [ so you have been through this before . ] [ the exact same thing . ] [ -i would not encourage you to work right away ] [ -of course not , i need to learn the language first . ] [ excellent thinking . focus on english . ] [ your life starts tomorrow . ] [ god willing , we will start a new life tomorrow . ] before 2011 , before everything has started , we were living a happy life . i was born in al-hasakah , syria , a very peaceful city , a city of so many languages , ethnic components , and religious components with the idea and the notion of accepting others . i was in my fourth year of my medical studies in syria , i was trying my best to become a doctor , and my dream was to treat cancer . my generation was dreaming of having freedom , having some basic things that the average canadian would not think about . [ filmed by mohammed in homs , syria ] we never thought we could have faced such a brutal , barbaric response from your own government , just for gathering in the street and shouting the word `` freedom . '' we were just standing there and surprisingly they started shooting and people started falling ... at that point everyone started running , everyone who had survived it , started running , and some people were just on the ground covered with blood . i 'm calling you regarding clients of mine who are moving to your place tomorrow morning . [ -what 's happening in aleppo is breaking my heart . ] [ -a lot of problems are happening there . ] yeah , because we 're in the middle of , you know , arranging all the transportation needed for all of these families . all righty . thank you so much . [ this boy is dying . ] [ i want my brother . where is my mother and father ? ] [ where is my mom ? ] [ say , `` there is no god but god . '' ] for syrians , it is so normal to open your facebook and see the death of your friend on social media . it is something that is really hard and that is really difficult to accept , to observe , and to even think about . [ there is no power except what lies in god 's hands . ] i 'm about to turn 27 next month . in this small lifetime , i have been arrested three times . i have been in five different detention places . the first thing that they did in the detention center was hanging me from the ceiling . they had handcuffs on my hands like this and they had a chain coming down from the ceiling , and they have hooked that chain to my hands like this , and they kept me like this for three days . after spending three days like this , the actual torture started . they spent so many days practicing all kinds of torture on me , and on other syrian people , in that detention center . i can never forget this old man who was sleeping next to me ... he used to say , `` you see all of this ... one day , all of this will be just a story that you will be telling to other people . '' after 120 days of torture , i was finally released ... i was finally able to see sunlight again . the only thing that i wanted to do is talk to my family . i just wanted to see them but also say goodbye to them ... get the hell out of there and never look back . i took a taxi from damascus to beirut where there was no shelling , no explosions , just a normal life ... three hours away from where i was , from where i was tortured , it was unbelievable for me . iss of bc kingsway . good morning . syrians in lebanon are not allowed to work , are not allowed to go to school . syrians in lebanon are simply not welcomed . the best job that i could find was washing cars from 9 am to 9 pm for $ 20 a day . i was just struggling to have a life . my whole life changed with a single phone call . i pick up the phone , it was this same phone . so i pick up and i was told that , `` this is the canadian embassy calling for mohammed alsaleh , '' i was like , `` yes , speaking . '' so they told me , `` we have an application on your behalf to come to canada , are you interested ? '' and i was like , `` yes , i 'm . '' [ in november 2014 mohammed was granted asylum in canada and arrived in vancouver . ] [ to date thousands of syrian families have arrived in canada . ] each syrian family is thinking about someone who 's left behind ... if it was a brother , if it was a mother , or if it was a father . this is something that i can see among the people that i 'm helping , and this is something that i can relate to on a personal level because of the situation of my family . my family had to illegally cross the border between syria and turkey . they had to crawl in the mud in order to make it to safety . come on , pick up . [ hello . ] [ hello ... hello . ] [ hello , mama . ] [ how are you , mother ? ] [ i swear we miss you . we miss you so much . ] [ me too . i miss you so so much . ] [ shahad , what is this beautiful hair ? ] [ this is the new style , with these bangs . ] [ wow , look , look your hair is so long now . ] when i last saw my family , my youngest sister was seven , right now she is ten , and i do n't know how old would she be when i meet her . it 's really hard to know that you might not be able to meet them . [ look at how my hair looks . ] [ güzel ! güzel like the turkish say . ] [ are you learning turkish ? ] [ a little bit , not much yet . ] [ we try a little bit when we go out , things like that . ] [ -great . ] [ even though we are in turkey , the situation is tough here . ] [ we are always stressed and tired . life is hard here . ] [ what 's important is that you guys are safe and sound ] [ and you are not in danger , ] [ and we do n't have to worry about your life being in danger . ] [ and that 's the most important thing right now , ] [ to let these few months pass while everything is processed and you get here . ] [ god willing , because the situation here is n't comfortable and one does n't feel at home . ] [ -yes , yes . -you always feel like something is missing . ] [ god willing , we will all be together soon here in canada . ] [ that 's what we hope for . hopefully everything will work out . ] [ i miss you so so so much . ] in order for people to get settled and to feel like home , i think the only missing part is time . they just need time . [ speaking foreign language ] [ welcome , welcome to our new house . ] [ a hundred congratulations on the new house , it 's a lovely home . ] [ god bless you , it 's lovely having you all here . ] my first client was a family of 13 people who have just came to canada . [ the best thing you did was to get this property . ] [ here you can play , whatever you want is here . ] i was telling them , `` you 're safe now . one year ago , i was standing exactly where you are and right now i 'm helping you , so do n't worry everything 's going to be fine . '' i want everyone to realize how tremendous , how beautiful it is to offer people a place to call home ... which is something priceless that i really , really appreciate having right now . it 's heart breaking to see the country that you grew up in get destroyed . i 'm one of the ones lucky enough to come back from the dead , to tell their stories , to share their suffering with the rest of the world , which is something that i think is part of my obligation toward syrians and toward canadians . [ mohammed continues to support his family as he works to bring them safely to canada . ] [ according to the un , approximately 250,000 people ] [ have been killed in syria and 13.5 million people are in urgent need of humanitarian assistance . ] [ to date , 29,817 syrian refugees have been welcomed to canada . ] [ 2016 go project films ]

[ go project films ] i think that facing death changes people ... which is what happened with me . before this experience , i was a completely different person with a completely different dream .

what do you find most compelling about mohammed 's story ? do you think his story , told through the medium of a short documentary film , might provide an important way for people to learn about the syrian conflict from a humanistic perspective ? why or why not ?

have you ever heard the term , `` tip of the iceberg '' ? you know that icebergs are mostly underwater , their immense bulk hidden beneath the water . but why is that so ? well , the density of pure ice is less than that of sea water . usually only 1/9 of the volume of an iceberg is above the water . the shape of the underwater portion is difficult to discern by looking at the above-surface portion . this has led to the expression , `` tip of the iceberg . '' here are some thing you might not know about the icy islands . the life of an iceberg begins many thousands of years before it reaches the ocean . unlike sea ice or pack ice , which form when the ocean freezes , glaciers are made of fresh water . for thousands of years , these glaciers build layer upon layer of ice , constantly compressing , moving , adding snow , compressing , and moving again as they inch along like a frozen river . it is the force of gravity that pulls them towards the sea , where a glacier may calve off to become an iceberg or continue to spread up as an ice shelf or an ice tongue . once an iceberg breaks away from the glacier or ice shelf , it will usually live for three to six years , floating around , carried by the currents and tidal movements of the ocean . as it floats along , it is battered by waves , melts , and smashes into land and sometimes other icebergs . some icebergs are so unstable that they have more dramatic ends , heaving up , collapsing , and sometimes even exploding . and as they fall apart , many icebergs make all sorts of strange sounds . when a piece of iceberg melts , it makes a fizzing sound , called bergie seltzer . this sound is made when the water-ice interface reaches compressed air bubbles trapped in the ice . as this happens , each bubble bursts , making a popping sound . there are six official size classifications for icebergs . the smallest icebergs are called growlers . they can be up the size of your car and are very dangerous for ships and boats because usually they sit just at the waterline where they are not easy to spot . next are the bergy bits - yes , that is their scientific name - which can be up to the size of your home . the other four sizes are small , medium , large , and very large . so just how big is a very large iceberg ? officially , any iceberg looming larger than 270 feet high above sea level and 670 feet long is considered very large . that 's 27 stories of looming , blue ice . and how do icebergs get that blue color anyways ? when snow on the glacier is compressed over many hundreds of years , the weight of the snow forces the air bubbles out of the ice , creating pure ice with very little air trapped inside . this compression is seen when the glacier calves , creating a blue iceberg . an iceberg that has not experienced as much compression and has a large amount of air and surface edges reflects light as white . although they form in far northern or southern areas , icebergs can float thousands of miles . an iceberg from the arctic floated as far south as bermuda . antarctic icebergs are mostly trapped in the circumpolar current , never giving them a chance to float north . however , they have been known to interrupt shipping lanes between australia , south america , and south africa . for all their travelling , many people think that these slabs of ice are barren of life , but these seemingly sterile ice slabs also harbor their own complex ecosystems and they shape the ecosystems that they pass through . they become mobile , floating ecosystems . even in the coldest seas , icebergs are always melting , at least a little bit . this melting has a major impact on the ocean around an iceberg . the fresh water from the berg creates a pool of fresh water that can extend a nautical mile away from the iceberg . this water is colder than the surrounding sea water , and the temperature variation creates thermal currents in the vicinity of the iceberg . life thrives on and around an iceberg . young icefish hide in small ice holes to avoid predators , while a variety of invertebrates , like jellyfish and siphonophores , congregate in the area . many of them come to feed on krill , tiny shrimp-like creatures . snow petrels nest on the icebergs and feed on the sea life nearby . whales and seals and penguins seem to like them too . and even now that you know all this , we 're still at the tip of the iceberg . there are all sorts of things we do n't know about icebergs . perhaps you 'll be the one to see a little deeper .

for all their travelling , many people think that these slabs of ice are barren of life , but these seemingly sterile ice slabs also harbor their own complex ecosystems and they shape the ecosystems that they pass through . they become mobile , floating ecosystems . even in the coldest seas , icebergs are always melting , at least a little bit .

icebergs become mobile floating ecosystems ; describe some of the creatures that thrive because of them . what are the attributes of an iceberg that attract these creatures ?

what is the shape of a molecule ? well , a molecule is mostly empty space . almost all of its mass is concentrated in the extremely dense nuclei of its atoms . and its electrons , which determine how the atoms are bonded to each other , are more like clouds of negative charge than individual , discrete particles . so , a molecule does n't have a shape in the same way that , for example , a statue has a shape . but for every molecule , there 's at least one way to arrange the nuclei and electrons so as to maximize the attraction of opposite charges and minimize the repulsion of like charges . now , let 's assume that the only electrons that matter to a molecule 's shape are the outermost ones from each participating atom . and let 's also assume that the electron clouds in between atoms , in other words , a molecule 's bonds , are shaped kind of like sausages . remember that nuclei are positively charged and electrons are negatively charged , and if all of a molecule 's nuclei were bunched up together or all of its electrons were bunched up together , they would just repel each other and fly apart , and that does n't help anyone . in 1776 , alessandro volta , decades before he would eventually invent batteries , discovered methane . now , the chemical formula of methane is ch4 . and this formula tells us that every molecule of methane is made up of one carbon and four hydrogen atoms , but it does n't tell us what 's bonded to what or how they atoms are arranged in 3d space . from their electron configurations , we know that carbon can bond with up to four other atoms and that each hydrogen can only bond with one other atom . so , we can guess that the carbon should be the central atom bonded to all the hydrogens . now , each bond represents the sharing of two electrons and we draw each shared pair of electrons as a line . so , now we have a flat representation of this molecule , but how would it look in three dimensions ? we can reasonably say that because each of these bonds is a region of negative electric charge and like charges repel each other , the most favorable configuration of atoms would maximize the distance between bonds . and to get all the bonds as far away from each other as possible , the optimal shape is this . this is called a tetrahedron . now , depending on the different atoms involved , you can actually get lots of different shapes . ammonia , or nh3 , is shaped like a pyramid . carbon dioxide , or co2 , is a straight line . water , h2o , is bent like your elbow would be bent . and chlorine trifluoride , or clf3 , is shaped like the letter t. remember that what we 've been doing here is expanding on our model of atoms and electrons to build up to 3d shapes . we 'd have to do experiments to figure out if these molecules actually do have the shapes we predict . spoiler alert : most of the do , but some of them do n't . now , shapes get more complicated as you increase the number of atoms . all the examples we just talked about had one obviously central atom , but most molecules , from relatively small pharmaceuticals all the way up to long polymers like dna or proteins , do n't . the key thing to remember is that bonded atoms will arrange themselves to maximize the attraction between opposite charges and minimize the repulsion between like charges . some molecules even have two or more stable arrangements of atoms , and we can actually get really cool chemistry from the switches between those configurations , even when the composition of that molecule , that 's to say the number and identity of its atoms , has not changed at all .

in 1776 , alessandro volta , decades before he would eventually invent batteries , discovered methane . now , the chemical formula of methane is ch4 . and this formula tells us that every molecule of methane is made up of one carbon and four hydrogen atoms , but it does n't tell us what 's bonded to what or how they atoms are arranged in 3d space . from their electron configurations , we know that carbon can bond with up to four other atoms and that each hydrogen can only bond with one other atom .

the chemical formula of a molecule tell us ________ .

meet our chemist , harriet . she has a chemical reaction that needs to occur more quickly . a chemist has some processes at her disposal that can help her speed up her reaction , and she knows of five ways . and to remember them , she thinks back to her days as a high school student , and the day she got a date for the dance . harriet was in high school , studying between classes . she had lost track of time and was going to be late to class . unbeknownst to her , harold , who was just around the corner , was running late , too . they both sprinted to class and , as it happened , sprinted directly into one another . now , this was no small collision . they ran squarely into one another in such a way that he knocked the books right out of her hand . `` i 'm sorry , '' he said . `` let me help you with your books . '' he kindly helped her re-collect her belongings , and politely offered to walk her to class . and you 'll never guess who went together to the dance later that year . yup , those two . so as we can see from this example , the key to getting a date for the dance is to collide with someone and knock the books out of their hands . now , you 're probably already aware that not all collisions lead to dates for the dance , thankfully . the collisions must have two important characteristics : one , correct orientation that allows books to be knocked from one 's hands ; and two , enough energy to knock the books out . shortly after this incident , harriet decided to tell me , her chemistry teacher , all about it . i noticed some interesting parallels between her story and chemical reaction rates , which happened to be what she was studying in the hallway the day of the collision . together , we decided to set out on two missions . harriet wanted to help all chemistry students and chemists remember how to speed up the rate of chemical reactions and i , being the nice guy that i am , decided to make it my mission to help create educational environments in which more book-dropping collisions can take place to increase future chemists ' chances of getting a date for the dance . in order to facilitate this improved dance-date-getting process , i propose five changes to all schools that parallel harriet 's five ways to increase chemical reaction rates . first , i propose that we shrink the size of the hallways . this will make it more difficult to safely navigate the hallways and will cause more collisions than in larger hallways . and by increasing the number of collisions , we increase the likelihood that some of those collisions will have the correct alignment and enough energy to create a date to the dance . now , chemically speaking , this is equivalent to lowering the volume of a reaction vessel or a reaction mixture . in doing so , the individual particles are closer together , and more collisions will occur . more collisions means a greater likelihood that collisions with the appropriate energy and configuration will happen . second , i propose increasing the overall population of the school . more students equals more collisions . by increasing the number of particles available for collision , we create an environment where more collisions can take place . third , we must reduce the time allowed between classes -- heck , let 's just cut it in half . in doing so , students will need to move more quickly to get from one class to the next . this increase in velocity will help make sure collisions have the appropriate amount of energy necessary to ensure book-dropping . this is analogous to increasing the temperature of the reaction mixture . higher temperature means particles are moving faster . faster-moving particles means more energy , and a greater likelihood of the reaction-causing collision . fourth , students must stop traveling in packs . by traveling in packs , the students on the outside of the pack insulate those in the middle from undergoing any collisions . by splitting up , each student has more area exposed that is available for a collision from a passing student . when particles travel in packs , the surface area is very small , and only the outside particles can collide . however , by breaking up the clumps into individual particles , the total surface area is increased , and each particle has an exposed surface that can react . fifth and finally , we hire a matchmaker . is this colliding and book-dropping too violent ? is there an easier way to get a date that requires less initial energy ? then a matchmaker will help with this . the matchmaker makes it easier for a couple to get together , by coordinating the match . our matchmaker is like a catalyst . chemical catalysts function by lowering the activation energy -- in other words , by lowering the energy required to start a reaction . they do this by bringing two particles together and orienting them correctly in space so that the two can meet at the correct configuration and allow a reaction to take place . so , to sum up : if a future chemist wants a date for the dance , he must collide with another person and knock the books out of their hands . and if a chemist wants to make a chemical reaction occur , the particles must collide in the correct orientation with an appropriate amount of energy . and both of these processes can be accelerated , using the five methods i 've described .

the matchmaker makes it easier for a couple to get together , by coordinating the match . our matchmaker is like a catalyst . chemical catalysts function by lowering the activation energy -- in other words , by lowering the energy required to start a reaction .

in this analogy , hiring a matchmaker is analogous to :

cancer is like a car crash . your body typically regulates the speed at which your cells divide , but sometimes , cancer cuts the brake lines , and your cells divide too quickly , accumulating mutations that cause them to veer away from their original function , form dangerous tumors , and land you in the hospital . cancer is basically an inability of the body to control the speed at which cells divide . when cells divide too quickly , they can often accumulate mutations that cause them to ignore their original function in the body , forming tumors . in turn , these tumors may interfere with the natural processes of the body , such as digestion and respiration , potentially leading to death . typically , your body has a number of genetic mechanisms to control how fast your cells divide . one of these genes is brca1 , which stands for breast cancer susceptibility gene 1 . brca1 belongs to a class of genes called tumor suppressor genes . tumor suppressor genes are involved in regulating how fast a cell divides . normally , cell division follows an orderly process called the cell cycle , which is basically the life cycle of a cell . within the cell cycle is a series of checkpoints , where proteins , such as the one produced by brca1 , regulate how fast the cell may proceed . how does it do this ? brca1 helps repair some forms of mutation in your dna . if your dna is damaged , brca1 keeps the cell from dividing until the mutation is repaired . you have two copies of the brca1 gene in every cell of your body . one copy you inherited from mom , the other from dad . this redundancy is a good a thing because you only need one functioning brca1 gene in a cell to regulate the cell cycle . but it 's important to note that while these copies have a similar function they 're not necessarily the same . in fact , there are hundreds of variations , or alleles , of brca1 . some regulate the cell cycle more effectively than others . in other words , some people are born with better regulating and repair mechanisms than others . and in some cases , mutations may render brca1 ineffective . when this happens , cells with damaged dna are allowed to divide . as they divide , these cells may accumulate additional mutations . these mutations may cause the cell to become less specialized and stop performing its original function in the tissue . if this occurs , then there 's a greater chance they 'll develop into cancer cells . while we all have the gene , such as brca1 , that can cause cancer , it 's only when these genes fail at their function that problems develop . having an ineffective or mutated version of brca1 can increase your susceptibility to cancer , much like driving with bad brakes increases the risk of an accident .

these mutations may cause the cell to become less specialized and stop performing its original function in the tissue . if this occurs , then there 's a greater chance they 'll develop into cancer cells . while we all have the gene , such as brca1 , that can cause cancer , it 's only when these genes fail at their function that problems develop .

which of the following occurs during the development of cancer ?

so here i ’ ve got a really nice sample of silicon , alright ? ok. i ’ m going to take it out of the bottle… of the… i ’ m going to have to wash my hands after this . so silicon is a very common element , it ’ s particularly found in sand which is the oxide of silica ; that ’ s the compound of oxygen and silicon . it is also found in a variety of minerals which contain silicon , oxygen and another metal which are known as silicates . and silicates occur in an enormous number of different minerals . it ’ s sort of the part of science that unless you are a specialist you find quite boring but if you really go into it like everything else it becomes really quite interesting . so this is a piece of polycrystalline silicon . it ’ s a really quite fantastic element and it ’ s very often used , or in fact it ’ s used very regularly to make electronic components . all of the computers that we use and actually the camera that you are recording me on now are based upon silicon technology . silicon is also extremely important and the basis of most of the electronic devices we use : my watch , your video camera , and also in computers . and if we look over here , i have got here this is an example of a silicon wafer ; you can see at the back this is silicon . so the silicon is grown as a single crystal from which we can make very highly-refined architectures on silicon chips , but you see here we have a polycrystalline sample so it is very pretty the way that it interacts with the light and you can see the different grain sizes . so let me take it out . did martyn show you the single crystal , the wafer ? yeah , he ’ s got a single chip , yeah , yeah . cause if you can get the light coming off it , you can get all sorts of different coloured affects . here you can see , this is pure silicon on the back and on the front , people have grown chips these are the pentium 4 chips for the computer , i think , i am not absolutely sure but i think these are the chips and these are the connectors on either side . so there are a whole lot of these chips and they grow a large number of them at once . these are chopped up and tested and the ones that worked are put into computers and the ones that are no good are just chucked and so this is a fantastically delicate piece of engineering making these . this is so-called 20cm wafer . they now make silicon chips on a 30cm wafer which is about this size and you can get a large number more on them . if you get a single crystal of this silicon structure , it can diffract the light and change the light so that it diffracts and bends off at different angles so that you get like a rainbow effect off it . it ’ s really quite beautiful . a compound of silicon , silicon nitride is extremely tough and very light so it ’ s very difficult to break and silicon nitride for example is used in the impellers in turbo chargers in cars . so when you put your foot down on the accelerator it will spin up very fast because it is very light but it is very strong so it won ’ t very suddenly fall to bits as it is revving up inside your engine . right i must put that there because i want to put that back in a bag .

ok. i ’ m going to take it out of the bottle… of the… i ’ m going to have to wash my hands after this . so silicon is a very common element , it ’ s particularly found in sand which is the oxide of silica ; that ’ s the compound of oxygen and silicon . it is also found in a variety of minerals which contain silicon , oxygen and another metal which are known as silicates .

what is the name of inert silicon polymers that can be found in implants ?

in the winter of 1995 , scientists pointed the hubble telescope at an area of the sky near the big dipper , a spot that was dark and out of the way of light pollution from surrounding stars . the location was apparently empty , and the whole endeavor was risky . what , if anything , was going to show up ? over ten consecutive days , the telescope took close to 150 hours of exposure of that same area . and what came back was nothing short of spectacular : an image of over 1,500 distinct galaxies glimmering in a tiny sliver of the universe . now , let 's take a step back to understand the scale of this image . if you were to take a ballpoint pen and hold it at arm 's length in front of the night sky , focusing on its very tip , that is what the hubble telescope captured in its first deep field image . in other words , those 3,000 galaxies were seen in just a tiny speck of the universe , approximately one two-millionth of the night sky . to put all this in perspective , the average human measures about 1.7 meters . with earth 's diameter at 12,700 kilometers , that 's nearly 7.5 million humans lined up head to toe . the apollo 8 astronauts flew a distance of 380,000 kilometers to the moon . and our relatively small sun has a diameter of about 1.4 million kilometers , or 110 times the earth 's diameter . a step further , the milky way holds somewhere between 100 to 400 billion stars , including our sun . and each glowing dot of a galaxy captured in the deep field image contains billions of stars at the very least . almost a decade after taking the deep field image , scientists adjusted the optics on the hubble telescope and took another long exposure over a period of about four months . this time , they observed 10,000 galaxies . half of these galaxies have since been analyzed more clearly in what 's known as the extreme deep field image , or xdf . by combining over ten years of photographs , the xdf shows galaxies so distant that they 're only one ten-billionth the brightness that the human eye can perceive . so , what can we learn about the universe from the deep field images ? in a study of the universe , space and time are inextricably linked . that 's because of the finite speed of light . so the deep field images are like time machines to the ancient universe . they reach so far into space and time that we can observe galaxies that existed over 13 billion years ago . this means we 're looking at the universe as it was less than a billion years after the big bang , and it allows scientists to research galaxies in their infancy . the deep field images have also shown that the universe is homogeneous . that is , images taken at different spots in the sky look similar . that 's incredible when we think about how vast the universe is . why would we expect it to be the same across such huge distances ? on the scale of a galaxy , let alone the universe , we 're smaller than we can readily comprehend , but we do have the capacity to wonder , to question , to explore , to investigate , and to imagine . so the next time you stand gazing up at the night sky , take a moment to think about the enormity of what is beyond your vision , out in the dark spaces between the stars .

this means we 're looking at the universe as it was less than a billion years after the big bang , and it allows scientists to research galaxies in their infancy . the deep field images have also shown that the universe is homogeneous . that is , images taken at different spots in the sky look similar .

the hubble deep field image illustrates provides a visual aide when thinking about the size of the universe , the size of the cosmos , and the size of humans . has this video changed your ideas about scale ? if so , how ?

[ music ] science is coming . [ music ] the game of thrones universe is one of the most brilliantly complex and utterly frustrating fictional universes ever created . but it is a fictional universe , and the only rule of a fictional universe is that it is self-consistent . it does n't have to agree with our science , or logic , or even our commonly agreed-upon moral code that says killing people is not a good thing . there is only one god in that universe , and his name is gurm . but despite that , many things in game of thrones can be linked to the real , actual world , drawing inspiration as if through the thirsty roots of a weirwood tree . many of these connections are interpreted by fans , but some have been verified by the bearded one himself . there are the many competing religious philosophies , the many , many , many similarities to real-life historical characters or the fact that they look like us ? but we are not going to be talking about those ... here 's where i would give you a spoilers warning , but . . . come on . you clicked on this . spoilers are coming . why are the seasons so crazy ? in the game of thrones universe winters and summers are known to last years at a time and apparently show up when they damn well please . we know that the summer/winter cycle normally averages around 5 or 6 years apiece , and as the story begins the most recent summer has stretched to nearly ten years . on earth , seasons are caused by our axial tilt leaning one side of earth toward or away from the sun during our annual trip around it , but george 's world is n't so predictable . the maesters of the citadel are the geeks of westeros , who are supposed to calculate when the next polar doom will arrive . westeros is n't an industrial society , but the architecture , metallurgy , and medicine we see in the known world suggests that these guys are a fairly scientific bunch . many theories have attempted to explain the reason for these seasons , but most of them collapse faster than a greyjoy 's loyalty . we know that the westeros-ian world has a moon , and that it used to have two . maybe their moon is n't as large as ours so the planet 's axis , unstabilized by lunar gravity , wobbles like a broken top . but , according to astronomers , moons do n't stabilize planets , rather a moonless planet should spin more evenly than one with a moon . then what if its orbit , instead of a nearly circular ellipse , like ours , was extremely elongated ? well that does n't work either . while it could cause extreme seasons , they 'd still show up on a regular schedule . even complex combinations of orbital stretches and wobbles , like earth 's milankovitch cycles , could be predicted by any society that knows basic algebra . well , then maybe it 's tugged on by the gravity of a neighboring planet , or its sun has a variable output . george r.r . martin did write his first novel about a planet falling away from its parent star . it 's most likely that the game of thrones planet . . . it needs a name . planet hodor ! lives in a very strange solar system , around a pair of stars . last april , a group of graduate students from johns hopkins university published a paper showing that if the world of game of thrones was subject to the complex dynamics of three celestial bodies orbiting each other , predicting a planet 's seasons would be impossible . this has interesting implications for tatooine . . ? of course , it could also be due to magic , which is cheating . and what about that world anyway ? at the amazing planetary science blog generation anthropocene , miles traer and mike osborne have constructed a detailed geologic history of westeros stretching back more than 500 million years into the fictional past . they determined that , since the north is cold enough to maintain a wall of ice , which we 'll come back to , year-round , it must be near this planet 's arctic circle , and since the south is warm enough to be covered by deserts , which primarily exist near earth 's 30th parallel that planet hodor has a radius of 4,297 miles or about 10 % wider than earth . we know that the first men crossed into westeros on a land bridge near dorne , and like africa and south america , the coastlines of westeros and essos seem to fit like puzzle pieces . they were probably unzipped beginning 25 million years ago by a spreading rift , like the one in the middle of our atlantic ocean . and 40 million years ago , westeros was likely covered by a huge ice sheet , which retreated as glaciers , cutting the great valleys south of winterfell and the riverlands between harrenhal and the twins . the description of the jagged black mountains sounds a lot like our own rocky mountains , which were born around 60-80 million years ago . this would also mark the birth of the mountains of the moon and the high westerlands , as north and south westeros smashed together just like the fault beneath the himalayas . that violent uplift is what exposed all that lannister gold from its origin deep within the crust . that era also would have borne the iron islands . . . but we have a different iron to talk about . valyrian steel was an alloy forged in the ancient empire of the valyrians , lighter and stronger than regular steel , and whose secrets were lost during the great doom , when volcanoes torched valyria , and its dragons , into charcoal . that valyrian steel was forged with dragon fire , which is not actually a thing , but it 's almost certainly a reference to damscus steel , an ancient steel alloy developed in india around 300 bc . like valyrian steel , the secrets of its forgery were lost to history forever . speaking of dragon fire . . . what if dragons could exist ? how could a living thing breathe flames ? my buddy kyle hill came up with an interesting theory . like the tiny bombardier beetle , dragons could secrete reactive `` hypergolic '' chemicals that , when mixed , react violently and shoot out of an orifice like rocket fuel . and if dragons chewed on certain rocks and metals , which i imagine are like cupcakes to them , they could coat their teeth in minerals , creating a spark with rows of deadly knife-like flint and steel . unfortunately , our idea of a fire-breathing flying dragon is about to come crashing back down to earth , because physics . as bran stark found out the hard way , gravity seems to work in westeros just like it does here . and that means the mother of dragons ' kids are grounded . the largest bird that ever lived was the giant teratorn , with a wingspan of 7 meters . not big enough . dragons are probably more like pterosaurs . but even the largest of those , quetzalcoatlus , maxed out at 11 meters from wingtip to wingtip and 250 kg . but daenarys ' dragons are bigger than that by the time they hit puberty , and dragon lore says they never stop growing . even with a pterosaur 's hollow bones , ability to gallop on all fours to take off and huge stretchy wings , even hodor could figure out that the dragons do n't work . unless , yeah . . . magic . the wall ? wo n't work . a sheer cliff of solid ice stacked 700 feet tall would melt at the bottom under its own weight and would fall apart unless it was sloped wildfire ? works . `` greek fire '' was an ancient precursor to napalm made from petroleum , sulfur , saltpeter and was the most potent weapon of its time . add a little trimethyl borate , and you 've got a flaming death that 's ready for st. patrick 's day . milk of poppy ? works . our opiate drugs from morphine to vicodin to even heroin are all derived from the poppy plant . dire wolf ? works . the extinct canis dirus was the largest wolf to ever exist , covering north and south america , thousands have been found in the la brea tar pits alone . of course , the universe of game of thrones would live . . . or die . . . just fine whether or not it agrees with our science . but by combining the two , as raymond chandler said , the truth of art keeps science from becoming inhuman , and the truth of science keeps art from becoming ridiculous what do you think ? does bringing science into a fantasy story kill the wonder like a guest at the red wedding ? or does it help the fictional world . . . truly `` exist '' in our own ? i think it makes the story richer than a lannister . let me know what you think in the comments . and remember , a hanson always pay their debts . subscribe , and i will pay you back with a new video every week . valar morcurious .

martin did write his first novel about a planet falling away from its parent star . it 's most likely that the game of thrones planet . .

why would n't a super elongated ellipse account for the longer and unpredictable seasons on the game of thrones planet ?

in 1985 , 16-year-old douglas casa , ran the championship 10,000 meter track race at the empire state games . suddenly , with just 200 meters to go , he collapsed , got back up and then collapsed again on the final straightaway , with his body temperature at dangerous levels . he had suffered an exertional heat stroke . fortunately , with immediate and proper treatment , he survived the potentially fatal episode and has since helped save 167 people in similar circumstances . from ancient soldiers on the battlefield to modern day warriors on the gridiron , exertional heat stroke , or sunstroke , has long been a serious concern . and unlike classical heat stroke , which affects vulnerable people such as infants and the elderly during heat waves , exertional heat stroke is caused by intense exercise in the heat , and is one of the top three killers of athletes and soldiers in training . when you exercise , nearly 80 % of the energy you use is transformed into heat . in normal circumstances , this is what 's known as compensable heat stress . and your body can dissipate the heat as quickly as it 's generated through cooling methods like the evaporation of sweat . but with uncompensable heat stress , your body is unable to lose enough heat due to overexertion or high temperatures in humidity , which raises your core temperature beyond normal levels . this causes the proteins and cell membranes to denature , creating cells that no longer function properly and begin to leak their contents . if these leaky cells proliferate through the body , the results can be devastating . including liver damage , blood clot formation in the kidneys , damage to the gastrointestinal tract and even the failure of vital organs . so how do you diagnose an exertional heat stroke ? the main criterion is a core body temperature greater than 40 degrees celsius observed along with physical symptoms such as increased heart rate , low blood pressure and rapid breathing or signs of central nervous system disfunction such as confused behavior , aggression or loss of consciousness . the most feasible and accurate way to assess core body temperature is with a rectal thermometer as other common temperature-taking methods are not accurate in these circumstances . as far as treatment goes , the most important thing to remember is cool first , transport second . because the human body can withstand a core temperature above 40 degrees celsius for about 30 minutes before cell damage sets in , it 's essential to initiate rapid cooling on site in order to lower it as quickly as possible . after any athletic or protective gear has been removed from the victim , place them in an ice water tub while stirring the water and monitoring vitals continuously . if this is not possible , dousing in ice water and applying wet towels over the entire body can help . but before you start anything , emergency services should be called . as you wait , it 's important to keep the victim calm while cooling as much surface area as possible until emergency personnel arrive . if medical staff are available on site , cooling should continue until a core temperature of 38.9 degrees celsius is reached . the sun is known for giving life , but it can also take life away if we 're not careful , even affecting the strongest among us . as dr. jj levick wrote of exertional heat stroke in 1859 , `` it strikes down its victim with his full armor on . youth , health and strength oppose no obstacle to its power . '' but although this condition is one of the top three leading causes of death in sports , it has been 100 % survivable with proper care .

from ancient soldiers on the battlefield to modern day warriors on the gridiron , exertional heat stroke , or sunstroke , has long been a serious concern . and unlike classical heat stroke , which affects vulnerable people such as infants and the elderly during heat waves , exertional heat stroke is caused by intense exercise in the heat , and is one of the top three killers of athletes and soldiers in training . when you exercise , nearly 80 % of the energy you use is transformed into heat .

what effect does extreme heat have on cells ?

there 's a common misconception that if you like to meticulously organize your things , keep your hands clean , or plan out your weekend to the last detail , you might have ocd . in fact , ocd , which stands for obsessive compulsive disorder , is a serious psychiatric condition that is frequently misunderstood by society and mental health professionals alike . so let 's start by debunking some myths . myth one : repetitive or ritualistic behaviors are synonymous with ocd . as its name suggests , obsessive compulsive disorder has two aspects : the intrusive thoughts , images , or impulses , known as obsessions , and the behavioral compulsions people engage in to relieve the anxiety the obsessions cause . the kinds of actions that people often associate with ocd , like excessive hand washing , or checking things repeatedly , may be examples of obsessive or compulsive tendencies that many of us exhibit from time to time . but the actual disorder is far more rare and can be quite debilitating . people affected have little or no control over their obsessive thoughts and compulsive behaviors , which tend to be time consuming and interfere with work , school or social life to the point of causing significant distress . this set of diagnostic criteria is what separates people suffering from ocd from those who may just be a bit more meticulous or hygiene obsessed than usual . myth two : the main symptom of ocd is excessive hand washing . although hand washing is the most common image of ocd in popular culture , obsessions and compulsions can take many different forms . obsessions can manifest as fears of contamination and illness , worries about harming others , or preoccupations with numbers , patterns , morality , or sexual identity . and compulsions can range from excessive cleaning or double checking , to the fastidious arrangement of objects , or walking in predetermined patterns . myth three : individuals with ocd do n't understand that they are acting irrationally . many individuals with ocd actually understand the relationship between their obsessions and compulsions quite well . being unable to avoid these thoughts and actions despite being aware of their irrationality is part of the reason why ocd is so distressing . ocd sufferers report feeling crazy for experiencing anxiety based on irrational thoughts and finding it difficult to control their responses . so what exactly causes ocd ? the frustrating answer is we do n't really know . however , we have some important clues . ocd is considered a neurobiological disorder . in other words , research suggests that ocd sufferers brains are actually hardwired to behave in a certain fashion . research has implicated three regions of the brain variously involved in social behavior and complex cognitive planning , voluntary movement , and emotional and motivational responses . the other piece of the puzzle is that ocd is associated with low levels of serotonin , a neurotransmitter that communicates between brain structures and helps regulate vital processes , such as mood , aggression , impulse control , sleep , appetite , body temperature and pain . but are serotonin and activity in these brain regions the sources of ocd or symptoms of an unknown underlying cause of the disorder . we probably wo n't know until we have a much more intimate understanding of the brain . the good news is there are effective treatments for ocd , including medications , which increase serotonin in the brain by limiting its reabsorption by brain cells , behavioral therapy that gradually desensitizes patients to their anxieties , and in some cases , electroconvulsive therapy , or surgery , when ocd does n't respond to other forms of treatment . knowing that your own brain is lying to you while not being able to resist its commands can be agonizing . but with knowledge and understanding comes the power to seek help , and future research into the brain may finally provide the answers we 're looking for .

ocd sufferers report feeling crazy for experiencing anxiety based on irrational thoughts and finding it difficult to control their responses . so what exactly causes ocd ? the frustrating answer is we do n't really know .

which of the following are treatment options for ocd ?

translator : andrea mcdonough reviewer : bedirhan cinar have you heard the one about thomas jefferson and the louisiana territory ? thomas jefferson , author of the declaration of independence , was not a fan of the new constitution presented in 1787 . he was very worried that the constitution gave too much power to the new , national government , and not enough power to the states , an issue known as `` big government '' . jefferson only reluctantly agreed to support it when his friend , james madison , promised to propose a bill of rights after it was ratified . but jefferson 's fears about big government did not go away . for example , secretary of the treasury , alexander hamilton , proposed a national bank in 1790 , and jefferson knew there was no provision in the constitution to permit such a thing . hamilton claimed some sort of implied powers mumbo-jumbo . sure , it was n't written in the constitution , but the constitution implied that it could be done . but , jefferson was n't buying it . nonetheless , the bank was established by hamilton and president washington . when jefferson was sworn in as president in 1801 , he pledged to reduce the size and scope of the national government . but , of course , things did n't go exactly as he had planned . spain secretly transferred the louisiana territory to france right beneath jefferson 's nose . when congress found out , they quickly began discussions with france to buy a piece of the territory along the mississippi river for about $ 2 million . but , there was one little problem : jefferson knew there was no provision in the constitution to buy foreign territory . so what was a strict constructionist to do ? first , he tried to get an amendment to the constitution passed that would expressly permit the purchase , but congress was n't willing to do it . then , without permission , the u.s. negotiators in france cut a deal for all of the territory for a cool $ 15 million dollars . that new land doubled the size of the nation ! now jefferson was really stuck . he knew that the territory would be a great acquisition for the country , providing lots of new land for farmers and other settlers , but how could he constitutionally justify it ? in the end , jefferson turned to the argument used by his old foe alexander hamilton . he claimed that the power to purchase the territory is implied in the constitution 's treaty-making power . this was the exact argument that he had mocked openly a decade before , so it must have crushed his pride to have to use it . but more importantly , he may have committed the biggest big government play ever ! how ironic is it that one of the biggest opponents of big government doubled the size of the young country and did so while openly questioning its constitutionality ? at $ 15 million , which is about three cents an acre , it has been called by many the greatest real estate deal in the history of the united states .

but , of course , things did n't go exactly as he had planned . spain secretly transferred the louisiana territory to france right beneath jefferson 's nose . when congress found out , they quickly began discussions with france to buy a piece of the territory along the mississippi river for about $ 2 million .

the louisiana territory was initially transferred by ______________ to _______________ .

how old is the earth ? well , by counting the number of isotopes in a sample of rock that 's undergone radioactive decay , geologists have estimated the earth 's birthday , when it first formed from a solar nebula , to be 4.6 billion years ago . but just how long is that really ? here 's some analogies that might help you understand . for example , let 's imagine the entire history of earth until the present day as a single calendar year . on january 1st , the earth begins to form . by march 3rd , there 's the first evidence of single-celled bacteria . life remains amazingly unicellular until november 11th when the first multicellular organisms , known as the ediacaran fauna , come along . shortly thereafter , on november 16th at 6:08 p.m. is the cambrian explosion of life , a major milestone , when all of the modern phyla started to appear . on december 10th at 1:26 p.m. , the dinosaurs first evolve but are wiped out by an asteroid just two weeks later . on december 31st , the mighty roman empire rises and falls in just under four seconds . and columbus sets sail for what he thinks is india at three seconds to midnight . if you try to write the history of the earth using just one page per year , your book would be 145 miles thick , more than half the distance to the international space station . the story of the 3.2 million year-old australopithecine fossil known as lucy would be found on the 144th mile , just over 500 feet from the end of the book . the united states of america 's declaration of independence would be signed in the last half-inch . or if we compared geologic time to a woman stretching her arms to a span of six feet , the simple act of filing her nails would wipe away all of recorded human history . finally , let 's imagine the history of the earth as your life : from the moment you 're born to your first day of high school . your first word , first time sitting up , and first time walking would all take place while life on earth was comprised of single-celled organisms . in fact , the first multicellular organism would n't evolve until you were 12 years old and starting 7th grade , right around the time your science teacher is telling the class how fossils are formed . the dinosaurs do n't appear until three months into 8th grade and are soon wiped out right around spring break . three days before 9th grade begins , when you realize summer is over and you need new school supplies , lucy , the australopithecine , is walking around africa . as you finish breakfast and head outside to catch your bus 44 minutes before school , the neanderthals are going extinct throughout europe . the most recent glacial period ends as your bus drops you off 16 minutes before class . columbus sets sail 50 seconds before class as you 're still trying to find the right classroom . the declaration of independence is signed 28 seconds later as you look for an empty seat . and you were born 1.3 seconds before the bell rings . so , you see , the earth is extremely , unbelievably old compared to us humans with a fossil record hiding incredible stories to tell us about the past and possibly the future as well . but in the short time we 've been here , we 've learned so much and will surely learn more over the next decades and centuries , near moments in geological time .

the united states of america 's declaration of independence would be signed in the last half-inch . or if we compared geologic time to a woman stretching her arms to a span of six feet , the simple act of filing her nails would wipe away all of recorded human history . finally , let 's imagine the history of the earth as your life : from the moment you 're born to your first day of high school . your first word , first time sitting up , and first time walking would all take place while life on earth was comprised of single-celled organisms . in fact , the first multicellular organism would n't evolve until you were 12 years old and starting 7th grade , right around the time your science teacher is telling the class how fossils are formed . the dinosaurs do n't appear until three months into 8th grade and are soon wiped out right around spring break .

100,000 years in the geologic history of earth would be considered

[ go project films ] [ wind sounds ] [ a film by emmanuel vaughan-lee ] [ wind sounds ] [ engine sounds ] [ yukon river , alaska ] [ engine sounds ] [ engine sounds continue ] [ i 'm hungry . where 's the fish ? ] [ the yup'ik peoples have lived off king salmon for centuries . ] [ since 1998 the king salmon have been disappearing . ] [ ♪ music ♪ ] [ male speaker ] i 've been fishing all my life . in fact i used to fish with my dad . [ scraping sounds ] [ ♪ music ♪ ] i do n't know . [ ♪ music ♪ ] [ ♪ music continues ♪ ] [ ♪ music continues ♪ ] we have nine kids , thirty-three grandchildren . we 've been blessed by our children . they help us out . warm gear , life jackets , do n't forget . [ footsteps sounds ] every one of my grandkids , since they were small , they 've been with me in the camp . do n't forget your rubber gloves . but they all work , even the littlest ones . [ rustling sounds ] [ boat horn sounds ] [ ♪ music ♪ ] [ water and engine sounds ] when i was young , average fish was like thirty pounds . [ ♪ music ♪ ] but now you 're lucky if you get eighteen pounder , fifteen pound king . nobody can explain that . but they can guess . they can talk . [ ♪ music ♪ ] [ ♪ music continues ♪ ] [ fire crackling sounds ] right now for subsistence , average person can take maybe ten kings and they 're satisfied . [ fire crackling sounds ] salmon is a way of our life . i hope it does n't go away . [ ♪ music ♪ ] i remember when i was growing up , i used to hear— elders will talk . they said , `` people will change , the weather will change . '' it 's true , i see it now . there 's no stopping it . [ ♪ music ♪ ] [ ♪ music continues ♪ ] [ seagull sounds ] it 's hard . for our younger people , it 's very hard . they got ta have that money to pay for the gas . got ta have gas to go out and try to get your subsistence . if there 's no more salmon , there will be no more work , i know . [ ♪ music ♪ ] [ seagull sounds ] [ ♪ music continues ♪ ] [ seagull sounds continue ] [ ♪ music ♪ ] [ water sounds ] yeah , i take my grandchildren out fishing . i teach them how to check net and how to set net and how to use the current . [ ♪ music ♪ ] [ ♪ music continues ♪ ] [ ♪ music continues ♪ ] [ ♪ music continues ♪ ] [ ♪ music continues ♪ ] i feel good when i teach them something they can remember . [ ♪ music ♪ ] [ ♪ music continues ♪ ] because we 're not going to be around forever . we 'll be gone . [ rustling and rattling sounds ] this is how they used , long time ago , no cooking pot , they cooked it out on open fire . it sure beats cup of noodles . so far they 're okay , the grandchildren . [ ♪ music ♪ ] but we 're not there all the time to watch them . [ ♪ music ♪ ] [ ♪ music continues ♪ ] i know my grandchildren will teach their kids how to fish . they will . i know they will . [ ♪ music ♪ ] [ ♪ music continues ♪ ] [ ♪ music continues ♪ ] [ yukon kings ] [ kuigpiim taryaquii ] [ ♪ music ♪ ] [ directed by emmanuel vaughan-lee ] [ produced by dorothée royal-hedinger ] [ emmanuel vaughan-lee ] [ edited by adam loften ] [ director of photography ] [ andrew david watson ] [ music by h. scott salinas ] [ guitars : h. scott salinas ] [ matthew atticus berger ] [ cello : artyom manukyan ] [ sound design/mix by d. chris smith ] [ assistant camera : elias koch ] [ color grading : leo hallal ] [ special thanks : the waska family ] [ kwik'pak fisheries ] [ ©2012 goprojectfilms.com ]

[ the yup'ik peoples have lived off king salmon for centuries . ] [ since 1998 the king salmon have been disappearing . ] [ ♪ music ♪ ] [ male speaker ] i 've been fishing all my life .

since what year did the king salmon begin to disappear ?

we 've decided to make a new video about aluminium because it 's a long time over five years since we made the first one and ... we did n't say very much . aluminium is a surprisingly abundand element . if you look at this periodic table here , where the area of the different elements gives you a rough idea of the abundance you can see that aluminium is one of the most abundant metals up there with sodium , magnesium and calcium . more aluminum than potassium ; about the same or perhaps even more than iron . we 're never going to run out of aluminium . the problem with aluminium is that you do n't find aluminium metal in nature as a metal . it 's always tied up with other compounds ; mostly with oxygen , in clays . you know what clays are , the sort of muddy stuff that you get stuck on your shoes when it 's raining . to get the aluminium out of the clay , that is , to break the aluminium/oxygen bonds , which are very strong ; requires a lot of energy , which comes from electricity . so , making aluminium is very energy intensive . that 's why people like to recycle aluminium because once you 've got it , it 's worth preserving ; but it 's fantastically important because aluminium is a very light metal . and it 's often used as an alloy because the aluminium alloys are stronger than the aluminium itself , so , if you 're using it for aircraft or some other use like that where you want to combine lightness with strength then the stronger you can make it , the better . but when it was first made , in the 19th century , isolated as a metal it was terrifically valuable and there are stories of the french emperor serving his honored guests with aluminium plates or aluminium cutlery while the less important people had silver or gold ; but those times have passed and now you can get cupcakes and things like that surrounded by foil of aluminium . aluminium is a very good metal for making things because it has a very thin coating of aluminium oxide on the surface which prevents it [ from ] reacting with things . but as soon as that coating goes it becomes very reactive . alfred worden : hadley base , do you read houston ? david scott : yeah . now , 5 by , joe . worden : okay . worden : and i guess we 're standing by for your high-gain alignment per the checklist . scott : okay , stand by . you may have seen our video where we put copper chloride in one of these cupcake holders ... [ first of all i 'm going to dissolve some up and make a fairly concentrated solution . i 'm going to place this here . ] ... and what came out was this , or rather the copper chloride came out through the hole . [ it starts boiling really quite nicely . now , imagine i was doing this for my children who were quite small at that time , and ... voosh ! ] and the aluminium was completely dissolved up forming aluminium chloride and copper metal . in my own research , aluminium is quite important ; quite a lot of our equipment uses aluminium . not so much for the high pressure tubing that we use because quite a lot of my reaserch involves high pressures but we use it for the metal blocks that we put round the tubing so that we can heat it up . aluminium has a good electrical conductivity , and it 's also easy to machine . this is a piece of equipment here where we have a tube going down the middle . you can see the diameter of the tube here . around it is an aluminium block and an electrical heater . now , this particular case there was an accident , or a mishap , because the thermocouple that was controlling the temperature of this fell out . so , the heater got hotter and hotter , and eventually , the aluminium melted and poured down here . and i think this is really beautiful . well , fortunately , i was not in the lab or i would 've got very angry with my students but i think when it happened it was quite exciting ; this would have been glowing almost red because the melting point of aluminium is around 500 degrees centigrade . but then once it formed originally it was very shiny but quickly , it again developed the surface layer of aluminium oxide . if you have fine particles of aluminium and blow them into a flame ... ... then they will burn quite spectacularly and you form aluminium oxide . now , on the face of it , aluminium oxide sounds a rather boring compound but it 's really very useful and we use it quite a lot in our research in all sorts of different ways . it looks like a white powder . not very exciting . but in our group this aluminium oxide has been a fantastic catalyst all sorts of reactions that we did n't expect have gone with this material . my students keep it in a bottle almost like a magic catalyst and i 've only been given a little to show you . it acts as a solid acid which can be used at very high temperature and will get various acid-catalyzed reactions of organic compounds . it will make ethers , we have made various alkynes and a whole series of different compounds and my students still use it very much . if you melt the aluminium oxide , which we ca n't do here but can be done industrially , you can make single crystals which are transparent like glass and then you can grow a single crystal tube , like this one , which because it 's a single crystal , it 's terrifically strong . it 's the defects that make something weak and so if you have just one crystal there are no defects and so it 's very strong . so you can put a very high pressure inside this tube without it blowing up . brady : but you could make that tube out of metal , professor . professor : but , if you have a metal then you ca n't see what 's going on inside , and we 're using these tubes for photochemical reactions . so , we take a light like this , and shine it on the chemicals going through the tube under high pressure and we can convert one chemical into another . we can do this very efficiently because the light is absorbed by the molecules that we want to react and so we dont waste the energy on everything else . and using leds , which are a very efficient light source , you can get a process that is very energy efficient and it all depends on having this sapphire tube . this is synthetic sapphire . the real sapphire , the gems , have impurities in them , of other metals , which give them the nice colors , particularly the blue . princess kate has a blue sapphire ring which belonged to her husband 's mother , princess di , before her . and so , these are very valuable ones . but synthetic sapphire is also expensive but not in the same class as a natural gem . brady : what can nature do that the guys at the sapphire factory ca n't do ? professor : nature has time . the people who grow this will take hours or days or perhaps weeks to grow it . nature can spend thousands or millions of years growing a particular gem and therefore they can heat it up and cool it down in natural surroundings , in volcanoes ... or whatever far more slowly than people can afford to do industrially . there 's a lot of argument whether you should call it aluminum or aluminium now , there is n't a totally correct one because both forms are acceptable . but , all or nearly all chemists use aluminium because it 's very important to use a standardized nomenclature right across the world . and i think aluminium sounds nicer . student : hi professor , my question is is it aluminum or aluminium ? 'cause i want to know what to call my aluminium model . apparantly , there was a decision in 1990 by iupac the international union of pure and applied chemistry that it should definately be called a l u m i n i u m but then they relented three years later and said you could use aluminum as well . but if you 're a serious chemist you really need to say aluminium , because otherwise people wo n't find your papers , your publications , when they search because they 'll almost certainly put an `` i '' ' in the name . aluminium is frequently used or used [ to be ] frequently used kkfor sauce pans , for cooking in because it 's easy to make , easy to machine and particularly when people used electric stoves it was easy to make a flat bottom so that you got good contact between the electric element and the sauce pan . the problem with aluminium sauce pans is that if you 're cooking some fairly acidic food , for example boiling lemons or rhubarb something like that which is quite acidic you can dissolve some of the aluminium and people got quite worried about getting aluminium in their food . also , if you cook red cabbage , which is an indicator ; blue for alkali , red for acid , then if you boil it in an aluminium sauce pan it goes blue . and earlier in my carreer i used a red cabbage together with a white one to make a union jack , a u.k. flag with a mixture of red and blue-red cabbage and the white from the white cabbage . unfortionately , i 've lost the photo ; brady is very cross with me . but it was quite fun cooking it in the kitchen . i did it once myself , but it was such a lot of work that the second time a got one of my students to do it .

more aluminum than potassium ; about the same or perhaps even more than iron . we 're never going to run out of aluminium . the problem with aluminium is that you do n't find aluminium metal in nature as a metal . it 's always tied up with other compounds ; mostly with oxygen , in clays .

why do the professor ’ s students find aluminium oxide ( alumina ) such a useful catalyst ?

have you ever heard the term , `` tip of the iceberg '' ? you know that icebergs are mostly underwater , their immense bulk hidden beneath the water . but why is that so ? well , the density of pure ice is less than that of sea water . usually only 1/9 of the volume of an iceberg is above the water . the shape of the underwater portion is difficult to discern by looking at the above-surface portion . this has led to the expression , `` tip of the iceberg . '' here are some thing you might not know about the icy islands . the life of an iceberg begins many thousands of years before it reaches the ocean . unlike sea ice or pack ice , which form when the ocean freezes , glaciers are made of fresh water . for thousands of years , these glaciers build layer upon layer of ice , constantly compressing , moving , adding snow , compressing , and moving again as they inch along like a frozen river . it is the force of gravity that pulls them towards the sea , where a glacier may calve off to become an iceberg or continue to spread up as an ice shelf or an ice tongue . once an iceberg breaks away from the glacier or ice shelf , it will usually live for three to six years , floating around , carried by the currents and tidal movements of the ocean . as it floats along , it is battered by waves , melts , and smashes into land and sometimes other icebergs . some icebergs are so unstable that they have more dramatic ends , heaving up , collapsing , and sometimes even exploding . and as they fall apart , many icebergs make all sorts of strange sounds . when a piece of iceberg melts , it makes a fizzing sound , called bergie seltzer . this sound is made when the water-ice interface reaches compressed air bubbles trapped in the ice . as this happens , each bubble bursts , making a popping sound . there are six official size classifications for icebergs . the smallest icebergs are called growlers . they can be up the size of your car and are very dangerous for ships and boats because usually they sit just at the waterline where they are not easy to spot . next are the bergy bits - yes , that is their scientific name - which can be up to the size of your home . the other four sizes are small , medium , large , and very large . so just how big is a very large iceberg ? officially , any iceberg looming larger than 270 feet high above sea level and 670 feet long is considered very large . that 's 27 stories of looming , blue ice . and how do icebergs get that blue color anyways ? when snow on the glacier is compressed over many hundreds of years , the weight of the snow forces the air bubbles out of the ice , creating pure ice with very little air trapped inside . this compression is seen when the glacier calves , creating a blue iceberg . an iceberg that has not experienced as much compression and has a large amount of air and surface edges reflects light as white . although they form in far northern or southern areas , icebergs can float thousands of miles . an iceberg from the arctic floated as far south as bermuda . antarctic icebergs are mostly trapped in the circumpolar current , never giving them a chance to float north . however , they have been known to interrupt shipping lanes between australia , south america , and south africa . for all their travelling , many people think that these slabs of ice are barren of life , but these seemingly sterile ice slabs also harbor their own complex ecosystems and they shape the ecosystems that they pass through . they become mobile , floating ecosystems . even in the coldest seas , icebergs are always melting , at least a little bit . this melting has a major impact on the ocean around an iceberg . the fresh water from the berg creates a pool of fresh water that can extend a nautical mile away from the iceberg . this water is colder than the surrounding sea water , and the temperature variation creates thermal currents in the vicinity of the iceberg . life thrives on and around an iceberg . young icefish hide in small ice holes to avoid predators , while a variety of invertebrates , like jellyfish and siphonophores , congregate in the area . many of them come to feed on krill , tiny shrimp-like creatures . snow petrels nest on the icebergs and feed on the sea life nearby . whales and seals and penguins seem to like them too . and even now that you know all this , we 're still at the tip of the iceberg . there are all sorts of things we do n't know about icebergs . perhaps you 'll be the one to see a little deeper .

have you ever heard the term , `` tip of the iceberg '' ? you know that icebergs are mostly underwater , their immense bulk hidden beneath the water .

what does the term “ tip of the iceberg ” refer to ?

unfortunately , i know very little about dubnium , i am not sure anybody knows much about it , but it is named after the russian atomic research establishment , dubna . in these artificial elements , the elements are either named after somebody who is famous like rutherford for rutherfordium or in the place where an element was first discovered , but often where there is argument about who discovered the element first , then it is more equitable to name it after scientists .

unfortunately , i know very little about dubnium , i am not sure anybody knows much about it , but it is named after the russian atomic research establishment , dubna . in these artificial elements , the elements are either named after somebody who is famous like rutherford for rutherfordium or in the place where an element was first discovered , but often where there is argument about who discovered the element first , then it is more equitable to name it after scientists .

where was dubnium discovered ?

welcome to the ted-ed beta website tour . i 'm logan smalley , i 'm bedirhan cinar , i 'm jordan reeves , and i 'm stephanie lo . we represent the ted-ed team . we 're going to tell you about how the website is organized , about the lessons that surround each video , how you can customize or flip your own lesson , and how you can measure the lesson 's effect on your class or the world . towards the end of the tour , we 'll reveal one more major feature that directly affects every person viewing this video . let 's get started with the home page . on the home page , you 'll find original ted-ed videos , each is a lesson recorded by an actual educator that 's visualized by a professional animator . you can nominate educators and animators in the `` get involved '' section of the site . the ted-ed library can be browsed through two different lenses . learners can use the `` series '' view to browse videos thematically and based on their own curiosity . and teachers can use the browse by `` subject '' view to find the perfect short video to show in class or to assign as homework . every video on ted-ed is accompanied by a lesson . these lessons do n't replace good teaching , but they can be supplementary resources for students and teachers around the world . let 's look at this one , created by a teacher in the us and an animator in the uk . when you arrive on the lesson page , simply click play ; the video will continue to play as you navigate the lesson 's sections that surround it . in the `` quick quiz '' section , you 'll find multiple-choice questions that check for basic comprehension of the video . you get real-time feedback on your answers and if you get one wrong , you can use the video hint . you 'll find open-answer questions in the `` think '' section . and in the `` dig deeper '' section , you 'll find additional resources for exploring the topic . you can complete the lessons anonymously , but if you log in , you can track your own learning across the site . just visit the `` recent activity '' feed , and you 'll find answers you 've saved to lessons that you 've already started or completed . and now to one of the most powerful features of the ted-ed website : flipping a lesson . flipping a featured lesson allows you to edit each of the lesson 's sections . you can edit the title as it relates to your class . you can use the `` let 's begin '' section to provide instructions or context for the lesson . you can select or deselect any `` quick quiz '' question . in the `` think '' section , you can add your own open-answer questions . and in the `` dig deeper '' section , you can use the resources provided or add your own . when you finish flipping a lesson , it 'll publish to a new and unique url . and because the link is unique , it can measure the progress of any learner you share it with . you can use it to measure participation and accuracy of any individual student 's answers . so that 's how you flip a featured ted-ed video , we 've got one more major feature to tell you about . using the ted-ed platform , you can flip any video from youtube . that means you can create a lesson around any ted talk , any tedx talk , but also any of the other thousands of great educational videos on youtube , including the ones that you yourself could record , upload and flip . and through flipping these lessons , together we 'll create a free and remarkable library of lessons worth sharing .

so that 's how you flip a featured ted-ed video , we 've got one more major feature to tell you about . using the ted-ed platform , you can flip any video from youtube . that means you can create a lesson around any ted talk , any tedx talk , but also any of the other thousands of great educational videos on youtube , including the ones that you yourself could record , upload and flip .

which ted-ed or youtube video will you flip first ?

so i 'm here today to encourage you to think about new york city , and not just as one of humanity 's greatest achievements , but as home to native wildlife that are subject to a grand evolutionary experiment . so take this forested hillside in northern manhattan , for example . this is one of the last areas left in the city where there 's clean spring water seeping out of the ground . you could drink this out of your hands and you 'd be ok . these tiny little areas of seeping water contain huge populations of northern dusky salamanders . these guys were common in the city maybe 60 years ago , but now they 're just stuck on this single hillside and a few places in staten island . not only do they suffer the indignity of being stuck on this hillside , but we divided the hillside in two on two different occasions with bridges crossing from the bronx into manhattan . but they 're still there , on either side of the bridges , where you see the red arrows -- about 180th street , 167th street . my lab has found that if you just take a few segments of dna from salamanders in those two locations , you can tell which side of the bridge they came from . we built this single piece of infrastructure that 's changed their evolutionary history . we can go study these guys , we just go to the hillside we know where they are , we flip over rocks so we can catch them . there are a lot of other things in new york city , though , that are not that easy to capture , such as this guy , a coyote . we caught him on an automatic camera trap in an undisclosed location ; i 'm not allowed to talk about it yet . but they 're moving into new york city for the first time . they 're very flexible , intelligent animals . this is one of this year 's pups checking out one of our cameras . and my colleagues and i are very interested in understanding how they 're going to spread through the area , how they 're going to survive here and maybe even thrive . and they 're probably coming to a neighborhood near you , if they 're not already there . some things are too fast to be caught by hand . we ca n't pick them up on the cameras , so we set up traps around new york city and the parks . this is one of our most common activities . here 's some of my students and collaborators getting the traps out and ready . this guy , we catch in almost every forested area in new york city . this is the white-footed mouse -- not the mouse you find running around your apartment . this is a native species , been here long before humans . you find them in forests and meadows . because they 're so common in forested areas in the city , we 're using them as a model to understand how species are adapting to urban environments . so if you think back 400 years ago , the five boroughs would 've been covered in forests and other types of vegetation . this mouse would 've been everywhere [ in ] huge populations that showed few genetic differences across the landscape . but if you look at the situation today , they 're just stuck in these little islands of forest scattered around the city . just using 18 short segments of dna , we can pretty much take a mouse somebody could give us a mouse , not tell us where it was from , and we could determine what park it came from . that 's how different they 've become . you 'll notice in the middle of this figure , there are some mixed-up colors . there are a few parks in the city that are still connected to each other with strips of forest , so the mice can run back and forth and spread their genes , so they do n't become different . but throughout the city , they 're mostly becoming different in the parks . so i 'm telling you they 're different , but what does that mean ? what 's changing about their biology ? to answer this question , we 're sequencing thousands of genes from our city mice and comparing those to thousands of genes from the country mice , so , their ancestors outside of new york city in these big , more wilderness areas . now , genes are short segments of dna that code for amino acids . and amino acids are the building blocks of proteins . if a single base pair changes in a gene , you can get a different amino acid , which will then change the shape and structure of the protein . if you change the structure of a protein , you often change something about what it does in the organism . now if that change leads to a longer life or more babies for a mouse , something evolutionary biologists call fitness , then that single base-pair change will spread quickly in an urban population . so this crazy figure is called a manhattan plot , because it kind of looks like a skyline . each dot represents one gene , and the higher the dot is in the plot , the more different it is between city and country mice . the ones kind of at the tips of the skyscrapers are the most different , especially those above the red line . and these genes encode for things like immune response to disease , because there might be more disease in very dense , urban populations ; metabolism , how the mice use energy ; and heavy-metal tolerance . you guys can probably predict that new york city soils are pretty contaminated with lead and chromium and that sort of thing . and now our hard work is really starting . we 're going back into the wilds of new york city parks , following the lives of individual mice and seeing exactly what these genes are doing for them . and i would encourage you guys to try to look at your parks in a new way . i 'm not going to be the next charles darwin , but one of you guys might be , so just keep your eyes open . thank you . ( applause )

so i 'm here today to encourage you to think about new york city , and not just as one of humanity 's greatest achievements , but as home to native wildlife that are subject to a grand evolutionary experiment . so take this forested hillside in northern manhattan , for example . this is one of the last areas left in the city where there 's clean spring water seeping out of the ground .

when two bridges were built on a hillside in northern manhattan , what happened to the northern dusky salamanders that lived there ?

it 's midnight and all is still , except for the soft skittering of a gecko hunting a spider . geckos seem to defy gravity , scaling vertical surfaces and walking upside down without claws , adhesive glues or super-powered spiderwebs . instead , they take advantage of a simple principle : that positive and negative charges attract . that attraction binds together compounds , like table salt , which is made of positively charged sodium ions stuck to negatively charged chloride ions . but a gecko 's feet are n't charged and neither are the surfaces they 're walking on . so , what makes them stick ? the answer lies in a clever combination of intermolecular forces and stuctural engineering . all the elements in the periodic table have a different affinity for electrons . elements like oxygen and fluorine really , really want electrons , while elements like hydrogen and lithium do n't attract them as strongly . an atom 's relative greed for electrons is called its electronegativity . electrons are moving around all the time and can easily relocate to wherever they 're wanted most . so when there are atoms with different electronegativities in the same molecule , the molecules cloud of electrons gets pulled towards the more electronegative atom . that creates a thin spot in the electron cloud where positive charge from the atomic nuclei shines through , as well as a negatively charged lump of electrons somewhere else . so the molecule itself is n't charged , but it does have positively and negatively charged patches . these patchy charges can attract neighboring molecules to each other . they 'll line up so that the positive spots on one are next to the negative spots on the other . there does n't even have to be a strongly electronegative atom to create these attractive forces . electrons are always on the move , and sometimes they pile up temporarily in one spot . that flicker of charge is enough to attract molecules to each other . such interactions between uncharged molecules are called van der waals forces . they 're not as strong as the interactions between charged particles , but if you have enough of them , they can really add up . that 's the gecko 's secret . gecko toes are padded with flexible ridges . those ridges are covered in tiny hair-like structures , much thinner than human hair , called setae . and each of the setae is covered in even tinier bristles called spatulae . their tiny spatula-like shape is perfect for what the gecko needs them to do : stick and release on command . when the gecko unfurls its flexible toes onto the ceiling , the spatulae hit at the perfect angle for the van der waals force to engage . the spatulae flatten , creating lots of surface area for their positively and negatively charged patches to find complimentary patches on the ceiling . each spatula only contributes a minuscule amount of that van der waals stickiness . but a gecko has about two billion of them , creating enough combined force to support its weight . in fact , the whole gecko could dangle from a single one of its toes . that super stickiness can be broken , though , by changing the angle just a little bit . so , the gecko can peel its foot back off , scurrying towards a meal or away from a predator . this strategy , using a forest of specially shaped bristles to maximize the van der waals forces between ordinary molecules has inspired man-made materials designed to imitate the gecko 's amazing adhesive ability . artificial versions are n't as strong as gecko toes quite yet , but they 're good enough to allow a full-grown man to climb 25 feet up a glass wall . in fact , our gecko 's prey is also using van der waals forces to stick to the ceiling . so , the gecko peels up its toes and the chase is back on .

those ridges are covered in tiny hair-like structures , much thinner than human hair , called setae . and each of the setae is covered in even tinier bristles called spatulae . their tiny spatula-like shape is perfect for what the gecko needs them to do : stick and release on command . when the gecko unfurls its flexible toes onto the ceiling , the spatulae hit at the perfect angle for the van der waals force to engage .

how do the setae and spatulae help the gecko stick ?