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( music ) everything is everywhere these days . check out the supermarket -- orange juice from china , nuts from india , swordfish from japan , lagers from czechoslovakia , scores of european cheeses . you name it , it 's there . not when i was growing up . you 'd never taste a range of french cheeses or bohemian lager beer . at least , you could n't unless you were very rich and could go anywhere when the fancy took you . all that has changed . but it 's not just foods . got an iphone ? everyone knows it was invented and designed at cupertino in california , but who knows where the complex bits and pieces of its innards are made or assembled ? apple does n't say . the industry credits china , japan , germany , south korea and , of course , the united states itself . just think for a moment of the trillions of parts and finished goods moving cheaply around the world every second , a small portion by air , but most by sea . we call it globalization , but the man who basically made globalization a reality in our lives is too little known . this is his story . the story of the man who makes your day . in the great depression of the '30s , when millions of americans were out of work , worse than now , malcolm mclean was a 24-year-old truck driver . he got a job to take cotton bales from fayetteville in north carolina all the way to a pier in hoboken , new jersey for shipping overseas . he was glad of the work , but when he arrived he got bored out of his mind , sitting in his truck waiting and waiting and waiting on the docks as the worker ants muscled crates and bundles off other trucks and into slings that lifted the goods into the hold of the ship . on board the ship itself , with much yelling and arm waving , the stevedores then unloaded each sling and saw its contents placed in a designated position in the hold . malcolm was n't just bored , he was fuming . his income depended on getting back to north carolina to pick up more loads in his truck . out of the frustration , inspiration struck . would n't it be great , he thought , if my trailer could be lifted and placed on the ship without its cotton bales being touched . yes , it would be great . it would be revolutionary . for centuries , general non-bulk cargo had been shipped in the process he watched . it was called break bulk shipping . boxes , bales , crates handled piece by piece . what malcolm envisaged would have saved him only a day , but it would have saved everyone else something like two weeks in loading and unloading the ship . on average , it was eight days to haul and distribute break bulk shipments in the hold , plus another eight days at the other end to retrieve and distribute . all that time would have been saved if malcolm mclean could have just driven his truck onto the ship and at the other end , driven it off . well , today that concept is a reality . the concept that occurred to malcolm is known as containerization . it has done more than just save a great deal of time . it 's the reason why we have a thriving global marketplace , offering us that infinite variety of things , and it 's the reason we can move cargo from remote parts of the world at minimal cost . malcolm had his idea in 1937 . the 24-year-old truck driver sitting in his truck in hoboken was 40 before he did anything about it . by then , he 'd built his one truck into a big trucking company . he borrowed money from an enterprising vice president at citibank in new york , and set about designing the steel boxes and the decks of the ships to carry them stacked one on top of another . a lot of people thought he was crazy . inventors always attract armies of naysayers who can never remember how critical they were . for our part , we should remember malcolm mclean . his first container ship , the ideal x , sailed from shed 154 at marsh street , port newark with 58 well-filled boxes . it was the beginning of the container era , shrinking our world and enlarging human choice .

inventors always attract armies of naysayers who can never remember how critical they were . for our part , we should remember malcolm mclean . his first container ship , the ideal x , sailed from shed 154 at marsh street , port newark with 58 well-filled boxes .

who was malcolm mclean ?

( music ) sometimes when i 'm on a long plane flight , i gaze out at all those mountains and deserts and try to get my head around how vast our earth is . and then i remember that there 's an object we see every day that would literally fit one million earths inside it . the sun seems impossibly big , but in the great scheme of things , it 's a pinprick , one of about 400 billion stars in the milky way galaxy , which you can see on a clear night as a pale , white mist stretched across the sky . and it gets worse . there are maybe 100 billion galaxies detectable by our telescopes , so if each star was the size of a single grain of sand , just the milky way has enough stars to fill a 30 foot by 30 foot stretch of beach three feet deep with sand . and the entire earth does n't have enough beaches to represent the stars in the overall universe . such a beach would continue for literally hundreds of millions of miles . holy stephen hawking , that is a lot of stars . but he and other physicists now believe in a reality that is unimaginably bigger still . i mean , first of all , the 100 billion galaxies within range of our telescopes are probably a minuscule fraction of the total . space itself is expanding at an accelerating pace . the vast majority of the galaxies are separating from us so fast that light from them may never reach us . still , our physical reality here on earth is intimately connected to those distant , invisible galaxies . we can think of them as part of our universe . they make up a single , giant edifice , obeying the same physical laws and all made from the same types of atoms , electrons , protons , quarks , neutrinos that make up you and me . however , recent theories in physics , including one called string theory , are now telling us there could be countless other universes , built on different types of particles , with different properties , obeying different laws . most of these universes could never support life , and might flash in and out of existence in a nanosecond , but nonetheless , combined they make up a vast multiverse of possible universes . in up to 11 dimensions , featuring wonders beyond our wildest imagination . and the leading version of string theory predicts a multiverse made of up to 10 to the 500 universes . that 's a one followed by 500 zeroes , a number so vast that if every atom in our observable universe had its own universe and all of the atoms in all of those universes each had their own universe , and you repeated that for two more cycles , you 'd still be at a tiny fraction of the total -- namely , one trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillionth . but even that number is minuscule compared to another number : infinity . some physicists think the space-time continuum is literally infinite , and that it contains an infinite number of so-called pocket universes with varying properties . how 's your brain doing ? but quantum theory adds a whole new wrinkle . i mean , the theory 's been proven true beyond all doubt , but interpreting it is baffling . and some physicists think you can only un-baffle it if you imagine that huge numbers of parallel universes are being spawned every moment , and many of these universes would actually be very like the world we 're in , would include multiple copies of you . in one such universe , you 'd graduate with honors and marry the person of your dreams . in another , not so much . there are still some scientists who would say , hogwash . the only meaningful answer to the question of how many universes there are is one , only one universe . and a few philosophers and mystics might argue that even our own universe is an illusion . so , as you can see , right now there is no agreement on this question , not even close . all we know is , the answer is somewhere between zero and infinity . well , i guess we know one other thing : this is a pretty cool time to be studying physics . we just might be undergoing the biggest paradigm shift in knowledge that humanity has ever seen .

in up to 11 dimensions , featuring wonders beyond our wildest imagination . and the leading version of string theory predicts a multiverse made of up to 10 to the 500 universes . that 's a one followed by 500 zeroes , a number so vast that if every atom in our observable universe had its own universe and all of the atoms in all of those universes each had their own universe , and you repeated that for two more cycles , you 'd still be at a tiny fraction of the total -- namely , one trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillionth .

some string theorists believe there could be as many as 10^500 universes out there . if it ’ s to be believed , we will have moved from the idea of an earth-centered universe prior to the 16th century , to the notion of a single , sun-centered universe up until the 1920s , now to the multiverse . what ’ s the psychological impact of this progression ? what does it suggest to us about ourselves ?

this is a map of yellowstone national park for the most part the park is in wyoming but it extends a bit into montana and idaho this little 50 square miles section in idaho is what concerns us it 's called the zone of death because of a loophole that exists in the constitution of the united states if someone were to exploit that loophole they might be able to get away with murder yellowstone was established in 1872 before wyoming idaho and montana join the union it 's federal land and always has been but federal land across the u.s. is split up and divided into its corresponding state district courts except for yellowstone and this is where the loophole begins law professor brian c. kalt points out in his 2005 paper the perfect crime that yellowstone national park was assigned fully to wyoming 's district court even though small portions fall into montana and idaho unlike every other district the district of wyoming includes land in other state so kalt asks the question what happens if you 're caught for a crime you committed in that 50 square mile idea who region of the park the first thing law enforcement would do is bring you to cheyenne the hub of the district court of wyoming because the crime technically happened within wyoming 's jurisdiction but article 3 section 2 of the united states constitution says that the trial should happen in the state where you committed the crime if you 're a savvy murderer you invoke your right to a trial in idaho so they bring you back to idaho no big deal in the sixth amendment they said that they would require local juries and the language they use is that the jury has to be from the state and district where the crime was committed this is called the vicinage clause that leaves you with a sort of venn diagram you have the right to demand jury from that middle area where the state in which you committed the crime that 's idaho overlaps with the judicial jurisdiction where you committed the crime the wyoming district that has jurisdiction over yellowstone national park and here 's the problem nobody lives there there 's there 's no way for them to give you a trial and so i argue they should have to let you go this could also happen in the montana portion of the park except a few dozen people do live there so a jury could theoretically be called kalt has proposed numerous solutions to congress to fix the loophole but they have yet to act all they have to do is redraw the district line so that the district of wyoming is wyoming the district of idaho is in idaho and the district of montana in montana and if they do that it all goes away so if you 're planning a gathering of your adversaries exes and debtors maybe try yosemite

this is a map of yellowstone national park for the most part the park is in wyoming but it extends a bit into montana and idaho this little 50 square miles section in idaho is what concerns us it 's called the zone of death because of a loophole that exists in the constitution of the united states if someone were to exploit that loophole they might be able to get away with murder yellowstone was established in 1872 before wyoming idaho and montana join the union it 's federal land and always has been but federal land across the u.s. is split up and divided into its corresponding state district courts except for yellowstone and this is where the loophole begins law professor brian c. kalt points out in his 2005 paper the perfect crime that yellowstone national park was assigned fully to wyoming 's district court even though small portions fall into montana and idaho unlike every other district the district of wyoming includes land in other state so kalt asks the question what happens if you 're caught for a crime you committed in that 50 square mile idea who region of the park the first thing law enforcement would do is bring you to cheyenne the hub of the district court of wyoming because the crime technically happened within wyoming 's jurisdiction but article 3 section 2 of the united states constitution says that the trial should happen in the state where you committed the crime if you 're a savvy murderer you invoke your right to a trial in idaho so they bring you back to idaho no big deal in the sixth amendment they said that they would require local juries and the language they use is that the jury has to be from the state and district where the crime was committed this is called the vicinage clause that leaves you with a sort of venn diagram you have the right to demand jury from that middle area where the state in which you committed the crime that 's idaho overlaps with the judicial jurisdiction where you committed the crime the wyoming district that has jurisdiction over yellowstone national park and here 's the problem nobody lives there there 's there 's no way for them to give you a trial and so i argue they should have to let you go this could also happen in the montana portion of the park except a few dozen people do live there so a jury could theoretically be called kalt has proposed numerous solutions to congress to fix the loophole but they have yet to act all they have to do is redraw the district line so that the district of wyoming is wyoming the district of idaho is in idaho and the district of montana in montana and if they do that it all goes away so if you 're planning a gathering of your adversaries exes and debtors maybe try yosemite

what does the vicinage clause state ?

translator : tom carter reviewer : bedirhan cinar geckos and grasshoppers , worms and watermelons , elephants and escherichia coli , man and mushroom . all so different in form and function , but amazingly the same in how their form and function are determined . first , all these organisms are made of one or more cells , and every cell of every living thing on earth contains all the information it takes to create and duplicate and make variations of itself . that information is stored in a very long but quite simple double molecule called dna , or deoxyribonucleic acid . and the dna of every living organism is made of chains of four smaller molecules called nucleotides . what dictates the difference between a man and a mushroom is the sequence of these nucleotides in the long dna chain . the four differing nucleotide parts , called bases , are made of a few carbon , oxygen , hydrogen , nitrogen and phosphorus atoms , and the molecules look like this . and each of these four bases is attached to an identical backbone molecule , a sugar called deoxyribose - the `` d '' in dna - and a phosphate group . let 's simplify these nucleotides and show them like this . so , a single sequence of nucleotides joined by their common sugars would look like this . and the dna molecule where such sequences are stored looks like this . but how does a simple molecule dictate the form and function of millions of different living things ? you can think of dna as a great library of information , information that is used to do one thing and one thing only : direct the building of different protein molecules . and it 's the proteins that build the cells and keep them functioning and changing and reproducing . here 's where the familiar word 'gene ' comes in . if your dna is a library of information , a gene is a book in that library . a gene is a segment of the dna molecule . let 's say your body needs a particular protein , like insulin . to get it , some of your cells send a protein signal through the bloodstream to the cells in your pancreas , where insulin is made . that signal protein tells other proteins in the cell 's nuclei to open up a part of the dna double helix , the insulin gene , and start making insulin proteins . as soon as enough insulin has been produced , another signal protein comes to the pancreas ' cells that tells them to stop making insulin . it 's like looking up a book in the dna library about insulin , and then putting it back when you 're done . there are genes in dna for visible and invisible things that make up your body , like genes for eye color , protein pigments , for skin color , for hair color , for stopping and starting bone growth , for your blood type , for how many fingers or arms and legs you have , for proteins that influence how long you live . your dna probably contains between 25 thousand and 40 thousand genes , while the dna of a worm or a plant or a fruit fly contains about 12 thousand to 20 thousand genes . some of those genes have quite different sequences of nucleotides than yours , and some are similar to yours . though it happens infrequently , our own nucleotide sequences can change as the result of spontaneous or environmental damage which might remove or shift a nucleotide position . this changes the gene involved , and can then change the protein . most of these changes , called mutations , have very little effect on the organism or its descendants . some are mildly damaging , and a few can make the organism better-suited to its environment . it is these tiny changes in dna gene sequences , happening over millions of years , that create the differences among living organisms , from geckos to grasshoppers . worms to watermelons , elephants to escherichia coli , and man to mushroom .

first , all these organisms are made of one or more cells , and every cell of every living thing on earth contains all the information it takes to create and duplicate and make variations of itself . that information is stored in a very long but quite simple double molecule called dna , or deoxyribonucleic acid . and the dna of every living organism is made of chains of four smaller molecules called nucleotides .

dna , although a very simple molecule , can be quite confusing . attempt to explain the parts of dna and how they fit together . what do you think is most confusing about the construction of dna ?

before the creation of humanity , the greek gods won a great battle against a race of giants called the titans . most titans were destroyed or driven to the eternal hell of tartarus . but the titan prometheus , whose name means foresight , persuaded his brother epimetheus to fight with him on the side of the gods . as thanks , zeus entrusted the brothers with the task of creating all living things . epimetheus was to distribute the gifts of the gods among the creatures . to some , he gave flight ; to others , the ability to move through water or race through grass . he gave the beasts glittering scales , soft fur , and sharp claws . meanwhile , prometheus shaped the first humans out of mud . he formed them in the image of the gods , but zeus decreed they were too remain mortal and worship the inhabitants of mount olympus from below . zeus deemed humans subservient creatures vulnerable to the elements and dependent on the gods for protection . however , prometheus envisioned his crude creations with a greater purpose . so when zeus asked him to decide how sacrifices would be made , the wily prometheus planned a trick that would give humans some advantage . he killed a bull and divided it into two parts to present to zeus . on one side , he concealed the succulent flesh and skin under the unappealing belly of the animal . on the other , he hid the bones under a thick layer of fat . when zeus chose the seemingly best portion for himself , he was outraged at prometheus 's deception . fuming , zeus forbade the use of fire on earth , whether to cook meat or for any other purpose . but prometheus refused to see his creations denied this resource . and so , he scaled mount olympus to steal fire from the workshop of hephaestus and athena . he hid the flames in a hollow fennel stalk and brought it safely down to the people . this gave them the power to harness nature for their own benefit and ultimately dominate the natural order . with fire , humans could care for themselves with food and warmth . but they could also forge weapons and wage war . prometheus 's flames acted as a catalyst for the rapid progression of civilization . when zeus looked down at this scene , he realized what had happened . prometheus had once again wounded his pride and subverted his authority . furious , zeus imposed a brutal punishment . prometheus was to be chained to a cliff for eternity . each day , he would be visited by a vulture who would tear out his liver and each night his liver would grow back to be attacked again in the morning . although prometheus remained in perpetual agony , he never expressed regret at his act of rebellion . his resilience in the face of oppression made him a beloved figure in mythology . he was also celebrated for his mischievous and inquisitive spirit , and for the knowledge , progress , and power he brought to human hands . he 's also a recurring figure in art and literature . in percy bysshe shelley 's lyrical drama `` prometheus unbound , '' the author imagines prometheus as a romantic hero who escapes and continues to spread empathy and knowledge . of his protagonist , shelley wrote , `` prometheus is the type of the highest perfection of moral and intellectual nature , impelled by the purest and the truest motives to the best and noblest ends . '' his wife mary envisaged prometheus as a more cautionary figure and subtitled her novel `` frankenstein : the modern prometheus . '' this suggests the damage of corrupting the natural order and remains relevant to the ethical questions surrounding science and technology today . as hero , rebel , or trickster , prometheus remains a symbol of our capacity to capture the powers of nature , and ultimately , he reminds us of the potential of individual acts to ignite the world .

this gave them the power to harness nature for their own benefit and ultimately dominate the natural order . with fire , humans could care for themselves with food and warmth . but they could also forge weapons and wage war .

why did the gift of fire allow humans to advance faster than the other creatures on earth ?

way before the first selfie , the ancient greeks and romans had a myth about someone a little too obsessed with his own image . in one telling , narcissus was a handsome guy wandering the world in search of someone to love . after rejecting a nymph named echo , he caught a glimpse of his own reflection in a river , and fell in love with it . unable to tear himself away , narcissus drowned . a flower marked the spot of where he died , and we call that flower the narcissus . the myth captures the basic idea of narcissism , elevated and sometimes detrimental self-involvement . but it 's not just a personality type that shows up in advice columns . it 's actually a set of traits classified and studied by psychologists . the psychological definition of narcissism is an inflated , grandiose self-image . to varying degrees , narcissists think they 're better looking , smarter , and more important than other people , and that they deserve special treatment . psychologists recognize two forms of narcissism as a personality trait : grandiose and vulnerable narcissism . there 's also narcissistic personality disorder , a more extreme form , which we 'll return to shortly . grandiose narcissism is the most familiar kind , characterized by extroversion , dominance , and attention seeking . grandiose narcissists pursue attention and power , sometimes as politicians , celebrities , or cultural leaders . of course , not everyone who pursues these positions of power is narcissistic . many do it for very positive reasons , like reaching their full potential , or helping make people 's lives better . but narcissistic individuals seek power for the status and attention that goes with it . meanwhile , vulnerable narcissists can be quiet and reserved . they have a strong sense of entitlement , but are easily threatened or slighted . in either case , the dark side of narcissism shows up over the long term . narcissists tend to act selfishly , so narcissistic leaders may make risky or unethical decisions , and narcissistic partners may be dishonest or unfaithful . when their rosy view of themselves is challenged , they can become resentful and aggressive . it 's like a disease where the sufferers feel pretty good , but the people around them suffer . taken to the extreme , this behavior is classified as a psychological disorder called narcissistic personality disorder . it affects one to two percent of the population , more commonly men . it is also a diagnosis reserved for adults . young people , especially children , can be very self-centered , but this might just be a normal part of development . the fifth edition of the american psychiatric association 's diagnostic and statistical manual describes several traits associated with narcissistic personality disorder . they include a grandiose view of oneself , problems with empathy , a sense of entitlement , and a need for admiration or attention . what makes these trait a true personality disorder is that they take over people 's lives and cause significant problems . imagine that instead of caring for your spouse or children , you used them as a source of attention or admiration . or imagine that instead of seeking constructive feedback about your performance , you instead told everyone who tried to help you that they were wrong . so what causes narcissism ? twin studies show a strong genetic component , although we do n't know which genes are involved . but environment matters , too . parents who put their child on a pedestal can foster grandiose narcissism . and cold , controlling parents can contribute to vulnerable narcissism . narcissism also seems to be higher in cultures that value individuality and self-promotion . in the united states , for example , narcissism as a personality trait has been rising since the 1970s , when the communal focus of the 60s gave way to the self-esteem movement and a rise in materialism . more recently , social media has multiplied the possibilities for self-promotion , though it 's worth noting that there 's no clear evidence that social media causes narcissism . rather , it provides narcissists a means to seek social status and attention . so can narcissists improve on those negative traits ? yes ! anything that promotes honest reflection on their own behavior and caring for others , like psychotherapy or practicing compassion towards others , can be helpful . the difficulty is it can be challenging for people with narcissistic personality disorder to keep working at self-betterment . for a narcissist , self-reflection is hard from an unflattering angle .

to varying degrees , narcissists think they 're better looking , smarter , and more important than other people , and that they deserve special treatment . psychologists recognize two forms of narcissism as a personality trait : grandiose and vulnerable narcissism . there 's also narcissistic personality disorder , a more extreme form , which we 'll return to shortly .

can you think of any characters in movies who have high levels of grandiose narcissism ? how about vulnerable narcissism ?

translator : andrea mcdonough reviewer : bedirhan cinar `` i need a hero ! '' so many people in distress have said this , but why ? what kind of hero do we need and do we even really even need a hero at all ? well , if you look at any piece of literature written for page , script , or stage , the answer is yes ! but , heroes come in all shapes and sizes , depending on what needs to be dealt with . first , you have your epic heroes . epic heroes usually come from a famous family , have super-human strength , are unusually good-looking . they take on challenges that no one else will and succeed . they have great journeys and adventures , some supernatural and some , right here on earth . beowulf does all of this . he travels across the sea with his band of warriors to help another king defeat a supernatural monster that has been terrorizing his kingdom . he defeats the monster and the monster 's mother in an epic battle , and then goes back home and becomes king himself . in his old age , he has one more monster to face , one more threat that he must keep from his people , a dragon . now , being an epic hero , of course he wins , but he is also human , and so he also dies . but he leaves behind stories to inspire others even today . next , we have our tragic heroes . tragic heroes are usually leaders or powerful characters , but the tragic hero is also majorly flawed and that flaw usually leads him down the path to a horrible and tragic death . take the story of oedipus the king , for example . one day , a young man travels to a town called thebes . on the way , he kills a man for not yielding to him on the road in the first documented case of road rage . he also defeats a magical creature and is rewarded by becoming the king of thebes , and thus , marrying their queen . well , that 's not so tragic , right ? wrong ! the queen he just married is actually his birth mother ! oedipus was supposed to have been killed as a child by a servant , but instead he was given to another family . oh , and the man he killed on the road , the previous king of thebes and his dad . so he killed his father and married his mother . now that is quite tragic . not tragic enough for you ? try this one . romeo montague is a guy born into a wealthy family and finds the love of his life at a party , juliet . but , juliet is from a different family that just so happens to hate his family . instead of being patient and working through the family feud , romeo decides he must have his love now , and his impatience leads to bloodshed and death , including his own and juliet 's . moving on to romantic heroes . now these guys might sound like they might have a better love life and chance at happiness , but that 's not always the case . these heroes are emotional and very human . but there is something magical about them . some have a miraculous birth and then are separated from their family . others use enchanted swords or get help from magical beans . they could also reject the expectations of society and adhere to their own code of morality . and in the end , the hero triumphs over evil in an idyllic way , but at great personal , emotional sacrifice . king arthur is a good example of a romantic hero . sure , he became king and married the love of his life , but he was also killed by his son , who was born out of wedlock , and had his wife cheat on him with his best friend . so , although he , too , like beowulf , was a great king , he suffered much more for the greater purpose of society , which makes him more human and relatable to us all . there are different heroes for different situations . sometimes we need the strong warrior to slay the evils of the world . at other times , we need a common person who becomes great so that they can inspire us all to be better . so do we need heroes ? absolutely ! no matter what the time or place , we still need something to believe in . they remind us of the good in each of us , and the need for hope and the importance of knowledge .

so many people in distress have said this , but why ? what kind of hero do we need and do we even really even need a hero at all ? well , if you look at any piece of literature written for page , script , or stage , the answer is yes !

there is a new type of hero called the anti-hero . can you list any examples of anti-heroes , and why they might be called that ?

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 .

where is the original statue right now ?

you work at the college library . you 're in the middle of a quiet afternoon when suddenly a shipment of 1,280 different books arrives . the books have been dropped of in one long straight line , but they 're all out of order , and the automatic sorting system is broken . to make matters worse , classes start tomorrow , which means that first thing in the morning , students will show up in droves looking for these books . how can you get them all sorted in time ? one way would be to start at one end of the line with the first pair of books . if the first two books are in order , then leave them as they are . otherwise , swap them . then , look at the second and third books , repeat the process , and continue until you reach the end of the line . at some point , you 'll come across the book that should be last , and keep swapping it with every subsequent book , moving it down the line until it reaches the end where it belongs . then , start from the beginning and repeat the process to get the second to last book in its proper place , and keep going until all books are sorted . this approach is called bubble sort . it 's simple but slow . you 'd make 1,279 comparisons in the first round , then 1,278 , and so on , adding up to 818,560 comparisons . if each took just one second , the process would take over nine days . a second strategy would be to start by sorting just the first two books . then , take the third book and compare it with the book in the second spot . if it belongs before the second book , swap them , then compare it with the book in the first spot , and swap again if needed . now you 've sorted the first three books . keep adding one book at a time to the sorted sub-line , comparing and swapping the new book with the one before it until it 's correctly placed among the books sorted so far . this is called insertion sort . unlike bubble sort , it usually does n't require comparing every pair of books . on average , we 'd expect to only need to compare each book to half of the books that came before it . in that case , the total number of comparisons would be 409,280 , taking almost five days . you 're still doing way too many comparisons . here 's a better idea . first , pick a random book . call it the partition and compare it to every other book . then , divide the line by placing all the books that come before the partition on its left and all the ones that come after it on its right . you 've just saved loads of time by not having to compare any of the books on the left to any of the ones on the right ever again . now , looking only at the books on the left , you can again pick a random partition book and separate those books that come before it from those that come after it . you can keep creating sub-partitions like this until you have a bunch of small sub-lines , each of which you 'd sort quickly using another strategy , like insertion sort . each round of partitioning requires about 1,280 comparisons . if your partitions are pretty balanced , dividing the books into 128 sub-lines of ten would take about seven rounds , or 8,960 seconds . sorting these sub-lines would add about 22 seconds each . all in all , this method known as quicksort could sort the books in under three and a half hours . but there 's a catch . your partitions could end up lopsided , saving no time at all . luckily , this rarely happens . that 's why quicksort is one of the most efficient strategies used by programmers today . they use it for things like sorting items in an online store by price , or creating a list of all the gas stations close to a given location sorted by distance . in your case , you 're done quick sorting with time to spare . just another high-stakes day in the library .

if your partitions are pretty balanced , dividing the books into 128 sub-lines of ten would take about seven rounds , or 8,960 seconds . sorting these sub-lines would add about 22 seconds each . all in all , this method known as quicksort could sort the books in under three and a half hours .

which of the following sorting algorithms was not covered in this video ?

many people in the united states and latin america have grown up celebrating the anniversary of christopher columbus 's voyage , but was he an intrepid explorer who brought two worlds together or a ruthless exploiter who brought colonialism and slavery ? and did he even discover america at all ? it 's time to put columbus on the stand in history vs. christopher columbus . `` order , order in the court . wait , am i even supposed to be at work today ? '' cough `` yes , your honor . from 1792 , columbus day was celebrated in many parts of the united states on october 12th , the actual anniversary date . but although it was declared an official holiday in 1934 , individual states are n't required to observe it . only 23 states close public services , and more states are moving away from it completely . '' cough `` what a pity . in the 70s , we even moved it to the second monday in october so people could get a nice three-day weekend , but i guess you folks just hate celebrations . '' `` uh , what are we celebrating again ? '' `` come on , your honor , we all learned it in school . christopher columbus convinced the king of spain to send him on a mission to find a better trade route to india , not by going east over land but sailing west around the globe . everyone said it was crazy because they still thought the world was flat , but he knew better . and when in 1492 he sailed the ocean blue , he found something better than india : a whole new continent . '' `` what rubbish . first of all , educated people knew the world was round since aristotle . secondly , columbus did n't discover anything . there were already people living here for millennia . and he was n't even the first european to visit . the norse had settled newfoundland almost 500 years before . '' `` you do n't say , so how come we 're not all wearing those cow helmets ? '' `` actually , they did n't really wear those either . '' cough `` who cares what some vikings did way back when ? those settlements did n't last , but columbus 's did . and the news he brought back to europe spread far and wide , inspiring all the explorers and settlers who came after . without him , none of us would be here today . '' `` and because of him , millions of native americans are n't here today . do you know what columbus did in the colonies he founded ? he took the very first natives he met prisoner and wrote in his journal about how easily he could conquer and enslave all of them . '' `` oh , come on . everyone was fighting each other back then . did n't the natives even tell columbus about other tribes raiding and taking captives ? '' `` yes , but tribal warfare was sporadic and limited . it certainly did n't wipe out 90 % of the population . '' `` hmm . why is celebrating this columbus so important to you , anyway ? '' `` your honor , columbus 's voyage was an inspiration to struggling people all across europe , symbolizing freedom and new beginnings . and his discovery gave our grandparents and great-grandparents the chance to come here and build better lives for their children . do n't we deserve a hero to remind everyone that our country was build on the struggles of immigrants ? '' `` and what about the struggles of native americans who were nearly wiped out and forced into reservations and whose descendants still suffer from poverty and discrimination ? how can you make a hero out of a man who caused so much suffering ? '' `` that 's history . you ca n't judge a guy in the 15th century by modern standards . people back then even thought spreading christianity and civilization across the world was a moral duty . '' `` actually , he was pretty bad , even by old standards . while governing hispaniola , he tortured and mutilated natives who did n't bring him enough gold and sold girls as young as nine into sexual slavery , and he was brutal even to the other colonists he ruled , to the point that he was removed from power and thrown in jail . when the missionary , bartolomé de las casas , visited the island , he wrote , 'from 1494 to 1508 , over 3,000,000 people had perished from war , slavery and the mines . who in future generations will believe this ? ' '' `` well , i 'm not sure i believe those numbers . '' `` say , are n't there other ways the holiday is celebrated ? '' `` in some latin american countries , they celebrate the same date under different names , such as día de la raza . in these places , it 's more a celebration of the native and mixed cultures that survived through the colonial period . some places in the u.s. have also renamed the holiday , as native american day or indigenous people 's day and changed the celebrations accordingly . '' `` so , why not just change the name if it 's such a problem ? '' `` because it 's tradition . ordinary people need their heroes and their founding myths . ca n't we just keep celebrating the way we 've been doing for a century , without having to delve into all this serious research ? it 's not like anyone is actually celebrating genocide . '' `` traditions change , and the way we choose to keep them alive says a lot about our values . '' `` well , it looks like giving tired judges a day off is n't one of those values , anyway . '' traditions and holidays are important to all cultures , but a hero in one era may become a villain in the next as our historical knowledge expands and our values evolve . and deciding what these traditions should mean today is a major part of putting history on trial .

there were already people living here for millennia . and he was n't even the first european to visit . the norse had settled newfoundland almost 500 years before . ''

who were the first europeans to visit the americas ?

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 .

two of the main properties of neural stem cells are their ability to proliferate to produce more cells and to differentiate into neurons and glial cells . what are some of the deleterious effects that would result from abnormal regulation of either of these two processes ?

you know , back in the '40s and '50s , the original standard television had a 4 to 3 width to height ratio . that shape was chosen to be a slight rectangle , but still mostly square , thus having the maximal screen area for the given dimensions . and that 's still the ratio on many tvs and computer monitors in today 's homes . the problem is , hardly anybody today treats video content in a 4 to 3 ratio . see , this whole problem started when people wanted to watch movies from the theater in the comfort of their own homes . movie screens are considerably larger than our home television . more important , the screen is completely different rectangle and ca n't mathematically fit on our tv screens without manipulation . a typical tv is one and a third times wider than it is tall some movie screens could be up to three times as wide as it is tall . so what 're we going to do to make it fit ? well , we have all kinds of options . well , we could squeeze and stretch and mangle everything onto the screen , to make it all fill up , and everyone would look ridiculously thin and compressed . the good news is the sound would be just fine , although i do n't think people would be too happy about that option , particularly the actors in the movie . we could just cut a chunk of the original movie like a cookie cutter and just see that frame of the movie . the problem with that would be people and objects would be speaking from off the screen , or , even worse , they might be cut in half . some movie editors use what 's called the `` pan and scan '' technique to allow the full height of the tv screen to be used , but pick and choose what section of the original movie should be shown on your screen thus eliminating the annoying cutting of people . imagine that job : staring at a 4 to 3 hole watching movies all day , deciding for everyone which piece of the screen is the most important part for people to see . now let 's do a little quick math . if we compare a major cinematic film produced on a 2.35 to 1 aspect frame with my standard 4 to 3 tv screen , we find out that only 55 % of the movie can actually fit on the screen at any one time . just over half ! you 've seen the disclaimer at the beginning of the movie on tv or dvd that says , `` this film has been modified from its original format to fit on your tv screen . '' well , what it should say is , `` we are only displaying 55 % of the movie of our choosing . '' now for all the full-screen tv lovers , this is your dilemma : do you want to see all the movie , or is 55 % good enough ? how about new tvs ? around the start of the century , some widescreen tvs emerged in a 16 to 9 , or 1.78 times wider than it is tall . well , this screen fits the movie a little better , but still only shows 75 % of the original movie at one time . suppose someone made a tv for your living room that was actually 2.35 to 1 to show those full movies ? well , the tv with the same height as the most current 50-inch tvs - that tv would be close to six feet long . and on top of that , you 'd only use the full screen when you watched movies . most of the other content would have to be stretched , or have empty space on the sides of the screen . of course , there is one more option . we can just shrink the movie screen proportionally , to fit the width of your home television . we can mathematically scale the original to fit exactly the width of the screen and this 'll preserve the entire movie screen , but show the infamous black bars along the top and bottom that so many television watchers abhor . of course , now you can argue that we 're only using 75 % of that screen . and that is where the real question is : do you want your full screen , or do you want to see the entire movie ? most likely , you just need a bigger tv .

now let 's do a little quick math . if we compare a major cinematic film produced on a 2.35 to 1 aspect frame with my standard 4 to 3 tv screen , we find out that only 55 % of the movie can actually fit on the screen at any one time . just over half !

if you take a major cinematic film ( produced in 2.35:1aspect frame ) and compare it with a television ( 4:3 screen ) , we find that how much of the original movie can fit on the television screen ?

some of the best opportunities to learn are the moments in which we are perplexed . those moments in which you begin to wonder and question . these moments have happened throughout history . and have led to some truly amazing discoveries . take this story , for example . there once was a fellow named archimedes . he was born in 287 b.c . in the city of syracuse in sicily . he was a greek mathematician , physicist , engineer , inventor , and astronomer . one day , archimedes was summoned by the king of sicily to investigate if he had been cheated by a goldsmith . the king said he had given a goldsmith the exact amount of gold needed to make a crown . however , when the crown was ready , the king suspected that the goldsmith cheated and slipped some silver into the crown , keeping some of the gold for himself . the king asked archimedes to solve the problem . but there was a catch : he could n't do any damage to the crown . one day , while taking his bath , archimedes noticed that the water level in the bathtub rose and overflowed as he immersed himself into the tub . he suddenly realized that how much water was displaced depended on how much of his body was immersed . this discovery excited him so much that he jumped out of the tub and ran through the streets naked , shouting `` eureka ! '' which comes from the ancient greek meaning `` i found it . '' what did he find ? well , he found a way to solve the king 's problem . you see , archimedes needed to check the crown 's density to see if it was the same as the density of pure gold . density is a measure of an object 's mass divided by its volume . pure gold is very dense , while silver is less dense . so if there was silver in the crown , it would be less dense than if it were made of pure gold . but no matter what it was made of , the crown would be the same shape , which means the same volume . so if archimedes could measure the mass of the crown first , and then measure its volume , he could find out how dense it was . but it is not easy to measure a crown 's volume - it has an irregular shape , that 's different from a simple box or ball . you ca n't measure its size and multiply like you might for other shapes . the solution , archimedes realized , was to give the crown a bath . by placing it in water and seeing how much water was displaced , he could measure the volume , and he 'd calculate the density of the crown . if the crown was less dense than pure gold , then the goldsmith most definitely cheated the king . when archimedes went back to the king and did his test , the story says , he found that the goldsmith had indeed cheated the king , and slipped some silver in . these days , using the way an object displaces water to measure volume is called archimedes ' principle . the next time you take a bath , you can see archimedes ' principle in action , and maybe you 'll have a genius idea of your own .

some of the best opportunities to learn are the moments in which we are perplexed . those moments in which you begin to wonder and question .

salata says that some of the best opportunities to learn are the moments in which we are ...

if someone called you scum , you 'd probably be offended , but scientifically , they might not be far off . have you ever thought about where your food comes from ? you might say it comes from plants , animals , or even fungi , but you 'd probably rather not think about the rotting organisms and poop that feed those plants , animals , and fungi . so really , you and most of the matter in your body are just two or three degrees of separation from things like pond scum . all species in an ecosystem , from the creatures in a coral reef to the fish in a lake to the lions on the savannah , are directly or indirectly nourished by dead stuff . most of the organic matter in our bodies , if we trace it back far enough , comes from co2 and water through photosynthesis . plants use the energy from sunlight to transform carbon dioxide and water from the environment into glucose and oxygen . that glucose is then transformed into more complex organic molecules to form leaves , stems , roots , fruit , and so on . the energy stored in these organic molecules supports the food chains with which we 're familiar . you 've probably seen illustrations like this or this . these green food chains start with living plants at their base . but in real-life terrestrial ecosystems , less than 10 % of plant matter is eaten while it 's still alive . what about the other 90 ? well , just look at the ground on an autumn day . living plants shed dead body parts : fallen leaves , broken branches , and even underground roots . many plants are lucky enough to go their whole lives without being eaten , eventually dying and leaving remains . all of these uneaten , undigested , and dead plant parts , that 90 % of terrestrial plant matter ? that becomes detritus , the base of what we call the brown food chain , which looks more like this . what happens to plants also happens to all other organisms up the food chain : some are eaten alive , but most are eaten only when they 're dead and rotting . and all along this food chain , living things shed organic matter and expel digestive waste before dying and leaving their remains to decay . all that death sounds grim , right ? but it 's not . all detritus is ultimately consumed by microbes and other scavengers , so it actually forms the base of the brown food chain that supports many other organisms , including us . scientists are learning that this detritus is an unexpectedly huge energy source , fueling most natural ecosystems . but the interactions within an ecosystem are even more complex than that . what a food chain really represents is a single pathway of energy flow . and within any ecosystem , many of these flows are linked together to form a rich network of interactions , or food web , with dead matter supporting that network at every step . the resulting food web is so connected that almost every species is no more than two degrees from detritus , even us humans . you probably do n't eat rotting things , poop , or pond scum directly , but your food sources probably do . many animals we eat either feed directly on detritus themselves , like pork , poultry , mushrooms , shellfish , or catfish and other bottom feeders , or they are fed animal by-products . so , if you 're thinking nature is full of waste , you 're right . but one organism 's garbage is another 's gold , and all that rotting dead stuff ultimately provides the energy that nourishes us and most of life on earth , as it passes through the food web . now that 's some food for thought .

you 've probably seen illustrations like this or this . these green food chains start with living plants at their base . but in real-life terrestrial ecosystems , less than 10 % of plant matter is eaten while it 's still alive . what about the other 90 ?

what percentage , on average , of living plant biomass on land is consumed alive by herbivores ?

translator : andrea mcdonough reviewer : bedirhan cinar you look down and see a yellow pencil lying on your desk . your eyes , and then your brain , are collecting all sorts of information about the pencil : its size , color , shape , distance , and more . but , how exactly does this happen ? the ancient greeks were the first to think more or less scientifically about what light is and how vision works . some greek philosophers , including plato and pythagoras , thought that light originated in our eyes and that vision happened when little , invisible probes were sent to gather information about far-away objects . it took over a thousand years before the arab scientist , alhazen , figured out that the old , greek theory of light could n't be right . in alhazen 's picture , your eyes do n't send out invisible , intelligence-gathering probes , they simply collect the light that falls into them . alhazen 's theory accounts for a fact that the greek 's could n't easily explain : why it gets dark sometimes . the idea is that very few objects actually emit their own light . the special , light-emitting objects , like the sun or a lightbulb , are known as sources of light . most of the things we see , like that pencil on your desk , are simply reflecting light from a source rather than producing their own . so , when you look at your pencil , the light that hits your eye actually originated at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye , which is pretty cool when you think about it . but , what exactly is the stuff that is emitted from the sun and how do we see it ? is it a particle , like atoms , or is it a wave , like ripples on the surface of a pond ? scientists in the modern era would spend a couple of hundred years figuring out the answer to this question . isaac newton was one of the earliest . newton believed that light is made up of tiny , atom-like particles , which he called corpuscles . using this assumption , he was able to explain some properties of light . for example , refraction , which is how a beam of light appears to bend as it passes from air into water . but , in science , even geniuses sometimes get things wrong . in the 19th century , long after newton died , scientists did a series of experiments that clearly showed that light ca n't be made up of tiny , atom-like particles . for one thing , two beams of light that cross paths do n't interact with each other at all . if light were made of tiny , solid balls , then you would expect that some of the particles from beam a would crash into some of the particles from beam b . if that happened , the two particles involved in the collision would bounce off in random directions . but , that does n't happen . the beams of light pass right through each other as you can check for yourself with two laser pointers and some chalk dust . for another thing , light makes interference patterns . interference patterns are the complicated undulations that happen when two wave patterns occupy the same space . they can be seen when two objects disturb the surface of a still pond , and also when two point-like sources of light are placed near each other . only waves make interference patterns , particles do n't . and , as a bonus , understanding that light acts like a wave leads naturally to an explanation of what color is and why that pencil looks yellow . so , it 's settled then , light is a wave , right ? not so fast ! in the 20th century , scientists did experiments that appear to show light acting like a particle . for instance , when you shine light on a metal , the light transfers its energy to the atoms in the metal in discrete packets called quanta . but , we ca n't just forget about properties like interference , either . so these quanta of light are n't at all like the tiny , hard spheres newton imagined . this result , that light sometimes behaves like a particle and sometimes behaves like a wave , led to a revolutionary new physics theory called quantum mechanics . so , after all that , let 's go back to the question , `` what is light ? '' well , light is n't really like anything we 're used to dealing with in our everyday lives . sometimes it behaves like a particle and other times it behaves like a wave , but it is n't exactly like either .

for example , refraction , which is how a beam of light appears to bend as it passes from air into water . but , in science , even geniuses sometimes get things wrong . in the 19th century , long after newton died , scientists did a series of experiments that clearly showed that light ca n't be made up of tiny , atom-like particles .

colm says , `` even geniuses sometimes get things wrong . '' what other major scientific principles did scientists get wrong for centuries and centuries ? when were these principles correctly proven ?

translator : andrea mcdonough reviewer : bedirhan cinar tap dance : one of america 's major contributions to the world of percussive dance , born out of the melding of african and european dance traditions . there 's so many variations within tap dance , as many approaches as there have been tap dancers . and there have been a lot ! since its birth , over 125 years ago , tap dance has grown up in the world of american popular entertainment . from minstral shows and vaudeville , to night clubs , musical theater , and movie musicals , tap dance has held a featured role . and your approach depends on when in the history 's lineage you decide to connect . the landscape of american entertainment shifted in the 1950s and 60s . big bands became cost-prohibitive , rock and roll was becoming a popular music , and american musical theater moved towards a format incorporating ballet with narrative rather than the extension of variety shows that it had been in the past . all these factors pushed tap dancing to the fringes of the entertainment world . tap dance still existed ; there were dancers , but it was outside of the popular discourse . there were fewer and fewer places to dance and very little need for new tap dancers , so those who have been dancing in the 20s , 30s , and 40s , really had no one to pass along the art form to . in the 1970s , a multifaceted resurgence began . modern dancers became interested in the older tap dancers , drawing them out of retirement to teach . grassroots-organized tap festivals began to spring up , featuring the older tap dancers teaching the technique and the history of the craft . older dancers also came out of retirement to perform with groups such as the copasetics and the original hoofers , traveling the world . even broadway regained interest in the form , with gregory hines becoming a public figure for tap dance on the stage and in feature films . since then , the resurgence has spawned a more popular interest , with savion glover at the nexus of the crowd . considered the quintessential tap dancer , glover presents the form as a pure musician . since the 1990s , and thanks in a large part to the work of savion glover , we 've seen a rise in young people 's interest in tap dance . i 'm part of that generation . today , as we begin to rediscover the craft , we continue to look back and take examples of what tap dance was from past generations , at the same time , discovering our own unique approaches . there is so much freedom today . we can take what exists and apply past examples within our own unique context - today 's perspective on tap dance . it all really boils down to two pieces of metal on a leather-soled shoe , the wood to dance on , an audience to watch and listen , and something to say . it 's the balancing of these elements that is a tap dancer 's craft work .

and your approach depends on when in the history 's lineage you decide to connect . the landscape of american entertainment shifted in the 1950s and 60s . big bands became cost-prohibitive , rock and roll was becoming a popular music , and american musical theater moved towards a format incorporating ballet with narrative rather than the extension of variety shows that it had been in the past .

what things happened in the 1950 's and 60 's that caused a major shift in american entertainment ?

translator : tom carter reviewer : bedirhan cinar carbon dioxide , or co2 , is the main greenhouse gas in climate change . so how does co2 get into our atmosphere ? well , carbon is part of a cycle . it starts with the sun , which heats the earth 's surface with more energy in one hour than the whole world uses in a year . plants , which are kind of like biological chefs , take that sunlight , and then suck in some co2 from the air , mix them together , and bam ! they create a stored form of energy , in the form of carbohydrates such as glucose and sucrose . the process is called photosynthesis . when animals like us eat those plants our stomachs convert that food back into energy for our own growth . greenhouse gases are a byproduct of this process , and are released through waste . if those plants die , they decompose , and tiny microorganisms break down those carbohydrates and again , release greenhouse gases as a byproduct . as you see , energy originates from the sun . it is then transferred as it moves through the food chain . but sometimes , carbon based organisms like plants or animals get stuck in the earth . when this happens , they 're compressed under tons of pressure , and turned into carbon-based fossil fuels like oil , coal or natural gas . since the industrial revolution , humans have been pulling those fossil fuels out of the ground and burning them , activating the stored energy to make electricity and power engines . but the thing is it also releases millions of years worth of stored co2 back into the air . in addition , humans breathe in oxygen and breathe out co2 . but plants do the opposite . trees suck up huge amounts of co2 , which balances the cycle . thus , deforestation reduces the plants that store co2 . we 're attacking the cycle from both sides . think of it like a computer . a computer can operate a few programs at a time , right ? normally , when you 've finished with a document , you save , and you close it , so as not to overwork the computer . then , imagine you stopped closing your documents . so they were all open at once . your computer would n't be able to process it all . it would start to slow down , and then to freeze , and eventually it would crash . which might be where our environment is heading if we keep overloading the carbon cycle . so is there any way to rebalance the ecosystem ? what about technology ? technology is defined as a technique to solve a problem . and so , sustainable technologies are those whose output is equal to their input . they do not create negative externalities , such as co2 , in the present or the future . they sort of cancel themselves out to solve the problem . to achieve this , we need to invent sustainable technologies . if we put all the ideas and technologies ever created into one circle , then invention is the pushing of the boundaries of that circle . and the area outside of the circle is infinite , meaning the potential for invention is limitless . think about some of the incredible clean technologies we have today . [ wind ; electric & amp ; amp ; solar cars ; biogas ] [ biofuels ; photosynthetic algae ; compost ] all those ideas have one thing in common . they all came from people . people innovate . people create . it 's the limitless potential of creative people to build unimagined technologies that is going to stop climate change and rebalance the ecosystem . and that is something to be hopeful about .

but sometimes , carbon based organisms like plants or animals get stuck in the earth . when this happens , they 're compressed under tons of pressure , and turned into carbon-based fossil fuels like oil , coal or natural gas . since the industrial revolution , humans have been pulling those fossil fuels out of the ground and burning them , activating the stored energy to make electricity and power engines . but the thing is it also releases millions of years worth of stored co2 back into the air .

burning fossil fuels creates energy because :

the human brain is one of the most sophisticated organs in the world , a supercomputer made of billions of neurons that processes and controls all of our senses , thoughts , and actions . but there was something charles darwin found even more impressive : the brain of an ant , which he called one of the most marvelous atoms of matter in the world . if you find it hard to believe that something so tiny could have a complex brain , you 're not alone . in his project to classify and describe all living things , swedish naturalist carl linnaeus assumed insects had no brains at all . he was wrong , but understandably so . insect brains are not only miniscule , but in many respects , they function differently than our own . one of the most noticeable differences is that an insect that loses its head can still walk , scratch itself , breathe , and even fly . this is because while our nervous system works like a monarchy , with the brain calling the shots , the insect nervous system works more like a decentralized federation . many insect activities , like walking or breathing , are coordinated by clusters of neurons , also known as ganglia , along their bodies . together with the brain , these local ganglia form the insect nervous system . while an insect can do a lot with just its local ganglia , the brain is still crucial for its survival . an insect 's brain lets it perceive the world through sight and smell . it also chooses suitable mates , remembers locations of food sources and hives , regulates communication , and even coordinates navigation over huge distances . and this vast diversity of behaviors is controlled by an organ the size of the head of a pin , with less than one million neurons , compared to our 86 billion . but even though the insect brain is organized very differently from ours , there are some striking similarities . for example , most insects have smell detectors on their antennae , similar to those found in human noses . and our primary olfactory brain regions look and function rather similarly , with clusters of neurons activated and deactivated in precise timing to code for specific scents . scientists have been astonished by these similarities because insects and humans are not very closely related . in fact , our last common ancestor was a simple worm-like creature that lived more than 500 million years ago . so how did we end up with such similar brain structures when our evolution took almost entirely different paths ? scientists call this phenomenon convergent evolution . it 's the same principle behind birds , bats , and bees separately evolving wings . similar selective pressures can cause natural selection to favor the same evolutionary strategy in species with vastly different evolutionary pasts . by studying the comparison between insect and human brains , scientists can thus understand which of our brain functions are unique , and which are general solutions to evolutionary problems . but this is not the only reason scientists are fascinated by insect brains . their small size and simplicity makes it easier to understand exactly how neurons work together in the brain . this is also valuable for engineers , who study the insect brain to help design control systems for everything from self-flying airplanes to tiny search-and-rescue roach bots . so , size and complexity are not always the most impressive things . the next time you try to swat a fly , take a moment to marvel at the efficiency of its tiny nervous system as it outsmarts your fancy brain .

by studying the comparison between insect and human brains , scientists can thus understand which of our brain functions are unique , and which are general solutions to evolutionary problems . but this is not the only reason scientists are fascinated by insect brains . their small size and simplicity makes it easier to understand exactly how neurons work together in the brain .

which features of insect brains are of particular interest for robotics engineers ?

hi , i ’ m john green , and this is crash course world history . let ’ s begin today with a question . why am i alive ? also , why don ’ t i have any eyes ? ah , that ’ s better . the way we answer that question ends up organizing all kinds of other thoughts , like what we should value , and how we should behave , and if we should eat meat , and whether we should dump that boy who is very nice , but insanely clingy , in a way that he can not possibly think is attractive . all of which adds up- uh , mr. green , mr. green , uh , are you talking about me ? yes , i ’ m talking about you , me from the past . i ’ m telling you that one of the reasons we study history is so that you can be a less terrible boyfriend , but more on that momentarily . [ theme music ] today we ’ re going to talk about civilizations , but in order to do that , we have to talk about talking about civilizations , because it ’ s a problematic word . so problematic , in fact , that i have to turn to camera 2 to discuss it . certain conglomerations of humans are seen as civilizations , whereas , say , nomadic cultures generally aren ’ t , unless , you are -- say it with me -- the mongols by calling some groups civilizations , you imply that all other social orders are uncivilized , which is basically just another way of saying that they ’ re savages or barbarians . side note : originally greek , the word barbarian denoted anyone who did not speak ancient greek , because to the greeks , all other languages sounded like bar bar bar bar bar bar . so , that is to say that we are all essentially barbarians , except for the classics majors , which is worth remembering when we ’ re discussing civilizations . civilizations are like most of the things we like to study , they ’ re intellectual constructs . no one woke up in the city of thebe ’ s in egypt one morning and said , “ what a beautiful morning , i sure am living at the height of egyptian civilization. ” still , they ’ re useful constructs , particularly when you ’ re comparing one civilization to another . they ’ re less useful when you ’ re comparing a civilization to a non-civilization type social order , which is why we will try to avoid that . and yes , i am getting to the good boyfriend stuff . patience , grasshopper . so what is a civilization ? well , diagnosing a civilization is a little like like diagnosing an illness . if you have four or more of the following symptoms , you might be a civilization . surplus production . once one person can make enough food to feed several people , it becomes possible to build a city , another symptom of civilization . it also leads to the specialization of labor , which in turn leads to trade . like , if everybody picks berries for a living , there ’ s no reason to trade , because i have berries , and you have berries , but if i pick berries for a living and you make hammers , suddenly , we have cause to trade . civilizations are also usually associated with social stratification , centralized government , shared values , generally in the form of religion , and writing . and at least in the early days , they were almost always associated with rivers . these days you can just bisect a segment of land horizontally and vertically , and boom , build a city . but 5000 years ago , civilizations were almost always associated with rivers . whether that ’ s the tigris and euphrates , the yellow river , the nile , the amazon basin , the coatzacoalcos - gaaah ! i was doing so good until i got to coatzacoalcos ! ( computer says : coatzacoalcos ) coatzacoalcos . maybe . why river valleys ? they ’ re flat , they ’ re well watered , and when they flood , they deposit nutrient-rich silt . we ’ ll have more to say about most of these civilizations later , but let ’ s talk about this guy , the indus valley civilization , ‘ cause it ’ s my all time favorite . the indus valley civilization was located in the flood plain of the indus and sarawati rivers , and it was about the best place in the world to have an ancient civilization because the rivers flooded very reliably twice a year , which meant that it had the most available calories per acre of pretty much anywhere on the planet . we know the indus valley civilization flourished a long time ago . probably around 3000 bce . why is that question literally hanging over my head ? but people of the indus valley were trading with mesopotamians as early as 3500 bce . we also know that it was the largest of the ancient civilizations . archaeologists have discovered more than 1500 sites . so what do we know about this civilization ? let ’ s go to the thought bubble . everything we know about the indus valley civilization comes from archaeology , because while they did use written language , we don ’ t know how to read it , and no rosetta stone has thus appeared to help us learn it . i meant the other rosetta stone , thought bubble , yeah . although , come to think of it , either would be acceptable . so here ’ s what we know , they had amazing cities . harappa and mohenjo daro are the best known , with dense , multi-story homes constructed out of uniformly sized bricks along perpendicular streets . i mean this wasn ’ t some ancient world version of houston , more like chicago . this means they must have had some form of government and zoning , but we don ’ t know what gave this government its authority . cities were oriented to catch the wind and provide a natural form of air conditioning . and they were clean . most homes were connected to a centralized drainage system that used gravity to carry waste and water out of the city in big sewer ditches that ran under the main avenues , a plumbing system that would have been the envy of many 18th century european cities . also , in mohenjo daro , the largest public building was not a temple or a palace , but a public bath , which historians call the great bath . we don ’ t know what the great bath was used for , but since later indian culture placed a huge emphasis on ritual purity , which is the basis for the caste system , some historians have speculated that the bath might have been like a giant baptismal pool . also , they traded . one of the coolest things that the indus valley civilization produced were seals used as identification markers on goods and clay tablets . these seals contained the writing that we still can ’ t decipher , and a number of fantastic designs , many featuring animals and monsters . one of the most famous and frightening is of a man with what looks like water buffalo horns on his head , sitting cross-legged between a tiger and a bull . we don ’ t know what ’ s really going on here , but it ’ s safe to say that this was a powerful dude , because he seems to be able to control the tiger . how do these seals let us know that they traded ? well , because we found them in mesopotamia , not the indus valley . plus , archaeologists have found stuff like bronze in the indus valley that is not native to the region . so what did they trade ? cotton cloth . still such a fascinating export , incidentally that it will be the subject of the 40th and final video in this very series . but here ’ s the most amazing thing about the indus valley people . they were peaceful . despite archaeologists finding 1500 sites , they have found very little evidence of warfare , almost no weapons . thanks thought bubble . ok , before we talk about the fascinating demise of the indus valley civilization . it ’ s time for the open letter . magic ! i wonder what the secret compartment has for me today ? oh ! fancy clothes . i guess the secret compartment didn ’ t think i was dressed up enough for the occasion . an open letter to historians . dear historians , the great bath ? really ? the great bath ? i ’ m trying to make history fascinating , and you give me a term that evokes scented candles , bath salts and frederic fekkai hair products ? i know sometimes the crushingly boring names of history aren ’ t your fault . you didn ’ t name the federalist papers or the austro-hungarian empire or adam smith . but when you do get a chance to name something , you go with the great bath ? not the epic bath of mohenjo daro , or the bath to end all baths , or the pool that ruled , or the moist mystery of mohenjo daro or the wet wonder ? the great bath ? really ? you can do better . best wishes , john green . so what happened to these people ? well , here ’ s what didn ’ t happen to them . they didn ’ t morph into the current residents of that area of the world , hindu indians or muslim pakistanis . those people probably came from the caucasus . instead , sometime around 1750 bce , the indus valley civilization declined until it faded into obscurity . why ? historians have three theories . one : conquest ! turns out to be a terrible military strategy not to have any weapons , and it ’ s possible people from the indus valley were completely overrun by people from the caucasus . two : environmental disaster ! it ’ s possible they brought about their own end by destroying their environment . three : earthquake ! the most interesting theory is that a massive earthquake changed the course of the rivers so much that a lot of the tributaries dried up . without adequate water supplies for irrigation , the cities couldn ’ t sustain themselves , so people literally picked up and headed for greener pastures . well , probably not pastures , it ’ s unlikely they became nomads . they probably just moved to a different plain an continued their agricultural ways . i am already boring you and i haven ’ t even told you yet how to be a better boyfriend and/or girlfriend . i ’ m going to do that now . so we don ’ t know why the indus valley civilization ended , but we also don ’ t really know why it started . why did these people build cities , and dig swimming pools , and make unnecessarily ornate seals ? were they motivated by hunger , fear , a desire for companionship , the need to be near their sacred spaces , or a general feeling that city life was just more awesome than foraging ? thinking about what motivated them to structure their life as they did helps us to think about how we structure our own lives . in short , you ’ re clingy because you ’ re motivated by fear and a need for companionship , and she finds it annoying because it ’ s enough work having to be responsible for herself without having to also be responsible for you . also , you ’ re not really helping her by clinging , and from the indus valley in the bronze age , to school life today , human life is all about collaboration . trading cloth for bronze , building cities together , and collaborating to make sure that human lives are tilted to catch the wind . next week we will travel here to discuss the hot mess o ’ potamia , but in the meantime , if you have any questions , leave them in comments , and our team of semi-trained semi-professionals will do their best to answer them . also , you ’ ll find some suggested resources in the video info below , he said , pointing at his pants . thanks for watching , and we ’ ll see you next week !

they were peaceful . despite archaeologists finding 1500 sites , they have found very little evidence of warfare , almost no weapons . thanks thought bubble .

what concept are you finding difficult to understand ?

is she turning towards you or away from you ? no one can agree . she 's the mysterious subject of dutch master johannes vermeer 's `` girl with the pearl earring , '' a painting often referred to as the 'mona lisa of the north . ' belonging to a dutch style of idealized , sometimes overly expressive paintings known as tronies , the `` girl with the pearl earring '' has the allure and subtlety characteristic of vermeer 's work . but this painting stands apart from the quiet narrative scenes that we observe from afar in many of vermeer 's paintings . a girl reading a letter . a piano lesson . a portrait artist at work . these paintings give us a sense of intimacy while retaining their distance , a drawn curtain often emphasizes the separation . we can witness a milkmaid serenely pouring a bowl of milk , but that milk is n't for us . we 're only onlookers . the studied composition in vermeer 's paintings invokes a balanced harmony . with the checkered floor in many of his works , vermeer demonstrates his command of perspective and foreshortening . that 's a technique that uses distortion to give the illusion of an object receding into the distance . other elements , like sight lines , mirrors , and light sources describe the moment through space and position . the woman reading a letter by an open window is precisely placed so the window can reflect her image back to the viewer . vermeer would even hide the leg of an easel for the sake of composition . the absence of these very elements brings the `` girl with the pearl earring '' to life . vermeer 's treatment of light and shadow , or chiaroscuro , uses a dark , flat background to further spotlight her three-dimensionality . instead of being like a set piece in a theatrical narrative scene , she becomes a psychological subject . her eye contact and slightly parted lips , as if she is about to say something , draw us into her gaze . traditional subjects of portraiture were often nobility or religious figures . so why was vermeer painting an anonymous girl ? in the 17th century , the city of delft , like the netherlands in general , had turned against ruling aristocracy and the catholic church . after eight decades of rebellion against spanish power , the dutch came to favor the idea of self-rule and a political republic . cities like delft were unsupervised by kings or bishops , so many artists like vermeer were left without traditional patrons . fortunately , business innovation spearheaded by the dutch east india company transformed the economic landscape in the netherlands . it created a merchant class and new type of patron . wishing to be represented in the paintings they financed , these merchants preferred middle class subjects depicted in spaces that looked like their own homes surrounded by familiar objects . the maps that appear in vermeer 's paintings , for example , were considered fashionable and worldly by the merchant class of what is known as the dutch golden age . the oriental turban worn by the `` girl with the pearl earring '' also emphasizes the worldliness of the merchant class , and the pearl itself , a symbol of wealth , is actually an exaggeration . vermeer could n't have afforded a real pearl of its size . it was likely just a glass or tin drop varnished to look like a pearl . this mirage of wealth is mirrored in the painting itself . in greater context , the pearl appears round and heavy , but a detailed view shows that it 's just a floating smudge of paint . upon close inspection , we are reminded of vermeer 's power as an illusion maker . while we may never know the real identity of the `` girl with the pearl earring , '' we can engage with her portrait in a way that is unforgettable . as she hangs in her permanent home in the mauritshuis museum in the hague , her presence is simultaneously penetrating and subtle . in her enigmatic way , she represents the birth of a modern perspective on economics , politics , and love .

is she turning towards you or away from you ? no one can agree .

what is a tronie ?

many people in the united states and latin america have grown up celebrating the anniversary of christopher columbus 's voyage , but was he an intrepid explorer who brought two worlds together or a ruthless exploiter who brought colonialism and slavery ? and did he even discover america at all ? it 's time to put columbus on the stand in history vs. christopher columbus . `` order , order in the court . wait , am i even supposed to be at work today ? '' cough `` yes , your honor . from 1792 , columbus day was celebrated in many parts of the united states on october 12th , the actual anniversary date . but although it was declared an official holiday in 1934 , individual states are n't required to observe it . only 23 states close public services , and more states are moving away from it completely . '' cough `` what a pity . in the 70s , we even moved it to the second monday in october so people could get a nice three-day weekend , but i guess you folks just hate celebrations . '' `` uh , what are we celebrating again ? '' `` come on , your honor , we all learned it in school . christopher columbus convinced the king of spain to send him on a mission to find a better trade route to india , not by going east over land but sailing west around the globe . everyone said it was crazy because they still thought the world was flat , but he knew better . and when in 1492 he sailed the ocean blue , he found something better than india : a whole new continent . '' `` what rubbish . first of all , educated people knew the world was round since aristotle . secondly , columbus did n't discover anything . there were already people living here for millennia . and he was n't even the first european to visit . the norse had settled newfoundland almost 500 years before . '' `` you do n't say , so how come we 're not all wearing those cow helmets ? '' `` actually , they did n't really wear those either . '' cough `` who cares what some vikings did way back when ? those settlements did n't last , but columbus 's did . and the news he brought back to europe spread far and wide , inspiring all the explorers and settlers who came after . without him , none of us would be here today . '' `` and because of him , millions of native americans are n't here today . do you know what columbus did in the colonies he founded ? he took the very first natives he met prisoner and wrote in his journal about how easily he could conquer and enslave all of them . '' `` oh , come on . everyone was fighting each other back then . did n't the natives even tell columbus about other tribes raiding and taking captives ? '' `` yes , but tribal warfare was sporadic and limited . it certainly did n't wipe out 90 % of the population . '' `` hmm . why is celebrating this columbus so important to you , anyway ? '' `` your honor , columbus 's voyage was an inspiration to struggling people all across europe , symbolizing freedom and new beginnings . and his discovery gave our grandparents and great-grandparents the chance to come here and build better lives for their children . do n't we deserve a hero to remind everyone that our country was build on the struggles of immigrants ? '' `` and what about the struggles of native americans who were nearly wiped out and forced into reservations and whose descendants still suffer from poverty and discrimination ? how can you make a hero out of a man who caused so much suffering ? '' `` that 's history . you ca n't judge a guy in the 15th century by modern standards . people back then even thought spreading christianity and civilization across the world was a moral duty . '' `` actually , he was pretty bad , even by old standards . while governing hispaniola , he tortured and mutilated natives who did n't bring him enough gold and sold girls as young as nine into sexual slavery , and he was brutal even to the other colonists he ruled , to the point that he was removed from power and thrown in jail . when the missionary , bartolomé de las casas , visited the island , he wrote , 'from 1494 to 1508 , over 3,000,000 people had perished from war , slavery and the mines . who in future generations will believe this ? ' '' `` well , i 'm not sure i believe those numbers . '' `` say , are n't there other ways the holiday is celebrated ? '' `` in some latin american countries , they celebrate the same date under different names , such as día de la raza . in these places , it 's more a celebration of the native and mixed cultures that survived through the colonial period . some places in the u.s. have also renamed the holiday , as native american day or indigenous people 's day and changed the celebrations accordingly . '' `` so , why not just change the name if it 's such a problem ? '' `` because it 's tradition . ordinary people need their heroes and their founding myths . ca n't we just keep celebrating the way we 've been doing for a century , without having to delve into all this serious research ? it 's not like anyone is actually celebrating genocide . '' `` traditions change , and the way we choose to keep them alive says a lot about our values . '' `` well , it looks like giving tired judges a day off is n't one of those values , anyway . '' traditions and holidays are important to all cultures , but a hero in one era may become a villain in the next as our historical knowledge expands and our values evolve . and deciding what these traditions should mean today is a major part of putting history on trial .

without him , none of us would be here today . '' `` and because of him , millions of native americans are n't here today . do you know what columbus did in the colonies he founded ?

why might native americans living today be uncomfortable with columbus day as it has been celebrated through most of the 20th century ?

take a look at the water in this glass . refreshing , hydrating , and invaluable to your survival . before you take a sip , though , how do you know that the water inside is free from disease-causing organisms and pollutants ? one out of ten people in the world ca n't actually be sure that their water is clean and safe to drink . why is that ? inadequate sanitation , poor protection of drinking water sources , and improper hygiene often lead to sewage and feces-contaminated water . that 's the ideal breeding ground for dangerous bacteria , viruses , and parasites . and the effects of these pathogens are staggering . diarrheal disease from unsafe water is one of the leading causes of death around the world for children under five . and according to a u.n. report from 2010 , microbial water-borne illnesses killed more people per year than war . proper treatment processes , though , can address these threats . they usually have three parts : sedimentation , filtration , and disinfection . once water has been collected in a treatment facility , it 's ready for cleaning . the first step , sedimentation , just takes time . the water sits undisturbed , allowing heavier particles to sink to the bottom . often , though , particles are just too small to be removed by sedimentation alone and need to be filtered . gravity pulls the water downward through layers of sand that catch leftover particles in their pores , prepping the water for its final treatment , a dose of disinfectant . chemicals , primarily forms of chlorine and ozone , are mixed in to kill off any pathogens and to disinfect pipes and storage systems . chlorine is highly effective in destroying water 's living organisms , but its use remains government-regulated because it has potentially harmful chemical byproducts . and if an imbalance of chlorine occurs during the disinfection process , it can trigger other chemical reactions . for example , levels of chlorine byproducts , like trihalomethanes , could skyrocket , leading to pipe corrosion and the release of iron , copper , and lead into drinking water . water contamination from these and other sources including leaching , chemical spills , and runoffs , has been linked to long-term health effects , like cancer , cardiovascular and neurological diseases , and miscarriage . unfortunately , analyzing the exact risks of chemically contaminated water is difficult . so while it 's clear that disinfectants make us safer by removing disease-causing pathogens , experts have yet to determine the full scope of how the chemical cocktail in our drinking water really impacts human health . so how can you tell whether the water you have access to , whether from a tap or otherwise , is drinkable ? firstly , too much turbidity , trace organic compounds , or high-density heavy metals like arsenic , chromium , or lead , mean that the water is unsuitable for consumption . a lot of contaminants , like lead or arsenic , wo n't be obvious without tests , but some clues , like cloudiness , brown or yellow coloration , a foul odor , or an excessive chlorine smell can indicate the need to investigate further . water testing kits can go a step further and confirm the presence of many different contaminants and chemicals . with many types of contamination , there are ways of treating water where it 's used instead of close to its source . point-of-use treatment has actually been around for thousands of years . ancient egyptians boiled away many organic contaminants with the sun 's heat . and in ancient greece , hippocrates designed a bag that trapped bad tasting sediments from water . today , point-of-use processes usually involve ionization to lower mineral content . they also use adsorption filtration , where a porous material called activated carbon strains the water to remove contaminants and chemical byproducts . while it 's not always an effective long-term solution , point-of-use treatment is portable , easy to install , and adaptable . and in regions where large-scale systems are unavailable , or where water has been contaminated further along its journey , these systems can mean the difference between life and death . clean water remains a precious and often scarce commodity . there are nearly 800 million of us who still do n't have regular access to it . the good news is that continued developments in water treatment , both on a large and small scale , can alleviate a lot of unsafe conditions . implementing proper systems where they 're needed and paying careful attention to the ones already in place will fulfill one of the most basic of our human needs .

before you take a sip , though , how do you know that the water inside is free from disease-causing organisms and pollutants ? one out of ten people in the world ca n't actually be sure that their water is clean and safe to drink . why is that ?

many people in the world have no access to clean drinking water . what may be the cause of this ?

it was a night like any other night , except here i was climbing the platonic peaks like romeo on a second date . ( ugh ) i was there for the dame . she had eyes like imaginary numbers and curves that went on forever . said she wanted to go home . said i could help . said the pay was good . did n't say anything about climbing a ... voice : `` who 's there ? '' manny brot : `` manny brot , private eye . '' voice : `` what are you doing here ? '' `` a pretty number sent me to find a stolen dingus . '' voice : `` well , to enter the cave , you must answer my riddles three . '' what was it with riddles , and why do they always come in threes ? `` is it an egg ? '' `` no . why would it be an egg ? '' `` it 's usually an egg . '' `` what can i hold in my hand , but has zero area ? '' `` is it a dodo egg ? '' `` it 's not an egg ! '' i took out the rock that had nearly brained me before and gave it a hard ponder . the size of the rising bump on my conk said to me that this thing had area , and a lot of it . but what if i carved out a triangle from this side here ? as any mook could see , this triangle had a quarter of the area of the full triangle . i did the same thing again with each of the smaller triangles . again , a quarter of the remaining area -- gone . and i just kept going . after an infinite number of cuts , i was satisfied that my triangle had zero area . a bounded shape with zero area . now , it 's not often that i surprise myself , but my own two mitts had created something crazy , and new . `` very good . ( ahem ) now , show me a shape with finite area , but an infinitely long perimeter . '' `` let me get this straight . if i want to make a snip in the border of this shape , smooth it out , and lay it on the ground ... `` `` it would go on for ... `` `` wait 'til i 'm through , and then you can talk . it would go on forever . '' `` are you through ? '' `` yeah . '' `` so show me that shape then . '' mmm ... i had n't been this stuck since the rubik 's cube fiasco of '58 . all the shapes i knew had perimeters . circles : 2πr . triangles : sum of their sides . what 's this ? an angle . an angle from heaven . what if i were to pinch each side , like so . a third of the way through , just so . and do it again , and again , and again . after each pinch , the perimeter got a third longer because where there had been three line segments , now there were four . as for the area , every pinch made more triangles , that 's true . but those triangles were getting smaller and smaller . you could say that the area was converging , approaching a fixed number , while the perimeter was just getting bigger and bigger , uncontrollably ballooning like an overindulgent birthday clown . after infinity pinches , flimflam , there it was : finite area , but infinite perimeter . now that is a piece of work . `` oh , you 're good . ( ahem ) riddle three : show me a picture that if i magnify it under my microscope , i 'll keep seeing the original picture , no matter how much i zoom in . '' `` you 're a strange little man . '' `` thank you . '' i was out of ideas , so i looked at my muse , my complex dora . voice : `` who 's the dame ? '' and then it hit me . `` she 's a heart breaker , my fractal femme fatale . will she do ? '' `` yes , she 'll do just fine . '' ( lightning ) it was dark , and at first i thought the cave was empty , but then i noticed : the box . the dame had played me like a triangle . she had told me she wanted to go home . ( lightning ) what she really wanted was to bring her home here . the fractals spread everywhere . most of them the same no matter how deep you looked at them , like dora 's mugshot . some had infinitely long perimeters , others were objects with no area or volume , all of them created through infinite repetition . so , you wanted to know what fractals are ? well , kid , they 're the stuff that dreams are made of . ( music )

( lightning ) what she really wanted was to bring her home here . the fractals spread everywhere . most of them the same no matter how deep you looked at them , like dora 's mugshot .

fractals can be found in nature , from the pattern of arteries that pump blood through your body to the spiral arms of the milky way galaxy . what other natural fractals can you think of ?

approximately 7 million people around the world die from heart attacks every year , and cardiovascular disease , which causes heart attacks and other problems like strokes , is the world 's leading killer . so what causes a heart attack ? like all muscles , the heart needs oxygen , and during a heart attack , it ca n't get enough . fatty deposits , or plaques , develop on the walls of our coronary arteries . those are the vessels that supply oxygenated blood to the heart . these plaques grow as we age , sometimes getting chunky , hardened , or enflamed . eventually , the plaques can turn into blockages . if one of the plaques ruptures or cracks , a blood clot will form around it in minutes , and a partially closed artery can become completely blocked . blood flow is cut off to the cardiac muscle and the oxygen-starved cells start to die within several minutes . this is a myocardial infarction , or heart attack . things can rapidly deteriorate in the absence of treatment . the injured muscle may not be able to pump blood as well , and its rhythm might be thrown off . in the worst case scenario , a heart attack can cause sudden death . and how do you know that someone is having a heart attack ? the most common symptom is chest pain caused by the oxygen-deprived heart muscle . patients describe it as crushing or vice-like . it can radiate to the left arm , jaw , back , or abdomen . but it 's not always as sudden and dramatic as it is in the movies . some people experience nausea or shortness of breath . symptoms may be less prominent in women and the elderly . for them , weakness and tiredness may be the main signal . and surprisingly , in many people , especially those with diabetes , which affects the nerves that carry pain , a heart attack may be silent . if you think that someone might be having a heart attack , the most important thing is to respond quickly . if you have access to emergency medical services , call them . they 're the fastest way to get to a hospital . taking aspirin , which thins the blood , and nitroglycerin , which opens up the artery , can help keep the heart attack from getting worse . in the emergency room , doctors can diagnose a heart attack . they commonly use an electrocardiogram to measure the heart 's electrical activity and a blood test to assess heart muscle damage . the patient is then taken to a high-tech cardiac suite where tests are done to locate the blockages . cardiologists can reopen the blocked artery by inflating it with a balloon in a procedure called an angioplasty . frequently , they also insert a metal or polymer stent that will hold the artery open . more extensive blockages might require coronary artery bypass surgery . using a piece of vein or artery from another part of the body , heart surgeons can reroute blood flow around the blockage . these procedures reestablish circulation to the cardiac muscle , restoring heart function . heart attack treatment is advancing , but prevention is vital . genetics and lifestyle factors both affect your risk . and the good news is that you can change your lifestyle . exercise , a healthy diet , and weight loss all lower the risk of heart attacks , whether you 've had one before or not . doctors recommend exercising a few times a week , doing both aerobic activity and strength training . a heart-healthy diet is low in sugar and saturated fats , which are both linked to heart disease . so what should you eat ? lots of fiber from vegetables , chicken and fish instead of red meat , whole grains and nuts like walnuts and almonds all seem to be beneficial . a good diet and exercise plan can also keep your weight in a healthy range , which will lower your heart attack risk as well . and of course , medications can also help prevent heart attacks . doctors often prescribe low-dose aspirin , for example , particularly for patients who 've already had a heart attack and for those known to be at high risk . and drugs that help manage risk factors , like high blood pressure , cholesterol , and diabetes , will make heart attacks less likely , too . heart attacks may be common , but they do n't have to be inevitable . a healthy diet , avoiding tobacco use , staying fit , and enjoying plenty of sleep and lots of laughter all go a long way in making sure your body 's most important muscle keeps on beating .

the injured muscle may not be able to pump blood as well , and its rhythm might be thrown off . in the worst case scenario , a heart attack can cause sudden death . and how do you know that someone is having a heart attack ? the most common symptom is chest pain caused by the oxygen-deprived heart muscle .

lifestyle modifications can prevent the risk of a future heart attack . what advice would you give someone in your family about this ?

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 .

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 .

in this analogy , adding more students is analogous to :

now and then i think of what i learned in high school like ap bio and british literature is that igneous or metamorphic ? i do n't need to write a nine bic and i 'll admit i do n't know shit about millard fillmore why did i have to learn this stuff ? it is never common -- had they never used it for nothing ? why did we have to read the scarlet letter ? puritans are boring even when one is a slut there 's actually one thing i still know eli whitney he invented the cotton gin definitely do not need that , though now it 's just a study that i used to know now it 's just a study that i used to know now and then i think of all the things i 've taught you every handout with a far side cartoon apropo you do n't want to live that way forgetting every word i say you said you 'd never let it go i guess mnemonic devices just were n't enough for you though you really freaking pissed me off i worked so hard to teach you something , now you do n't know nothing what does the comment symbolize ? or anything beyond the first three digits of pi and what about sohcahtoa or asexual reproduction of a protozoa i guess you did n't need that though now it 's just a study that you used to know a study i used to know now it 's just a study that you used to know i used to know a study

now and then i think of what i learned in high school like ap bio and british literature is that igneous or metamorphic ? i do n't need to write a nine bic and i 'll admit i do n't know shit about millard fillmore why did i have to learn this stuff ?

math problem : in high school , students are in class for approximately 1,000 hours per year . how many years of school have you attended ? approximately how many hours have you been a student in a classroom ?

when you think of archimedes ' `` eureka ! '' moment , you probably think of this . as it turns out , it may have been more like this . in the third century bc , hieron , king of the sicilian city of syracuse , chose archimedes to supervise an engineering project of unprecedented scale . hieron commissioned a sailing vessel 50 times bigger than a standard ancient warship , named the syracusia after his city . hieron wanted to construct the largest ship ever , which was destined to be given as a present for egypt 's ruler , ptolemy . but could a boat the size of a palace possibly float ? in archimedes 's day , no one had attempted anything like this . it was like asking , `` can a mountain fly ? '' king hieron had a lot riding on that question . hundreds of workmen were to labor for years on constructing the syracusia out of beams of pine and fir from mount etna , ropes from hemp grown in spain , and pitch from france . the top deck , on which eight watchtowers were to stand , was to be supported not by columns , but by vast wooden images of atlas holding the world on his shoulders . on the ship 's bow , a massive catapult would be able to fire 180 pound stone missiles . for the enjoyment of its passengers , the ship was to feature a flower-lined promenade , a sheltered swimming pool , and bathhouse with heated water , a library filled with books and statues , a temple to the goddess aphrodite , and a gymnasium . and just to make things more difficult for archimedes , hieron intended to pack the vessel full of cargo : 400 tons of grain , 10,000 jars of pickled fish , 74 tons of drinking water , and 600 tons of wool . it would have carried well over a thousand people on board , including 600 soldiers . and it housed 20 horses in separate stalls . to build something of this scale , only for that to sink on its maiden voyage ? well , let 's just say that failure would n't have been a pleasant option for archimedes . so he took on the problem : will it sink ? perhaps he was sitting in the bathhouse one day , wondering how a heavy bathtub can float , when inspiration came to him . an object partially immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object . in other words , if a 2,000 ton syracusia displaced exactly 2,000 tons of water , it would just barely float . if it displaced 4,000 tons of water , it would float with no problem . of course , if it only displaced 1,000 tons of water , well , hieron would n't be too happy . this is the law of buoyancy , and engineers still call it archimedes ' principle . it explains why a steel supertanker can float as easily as a wooden rowboat or a bathtub . if the weight of water displaced by the vessel below the keel is equivalent to the vessel 's weight , whatever is above the keel will remain afloat above the waterline . this sounds a lot like another story involving archimedes and a bathtub , and it 's possible that 's because they 're actually the same story , twisted by the vagaries of history . the classical story of archimedes ' eureka ! and subsequent streak through the streets centers around a crown , or corona in latin . at the core of the syracusia story is a keel , or korone in greek . could one have been mixed up for the other ? we may never know . on the day the syracusia arrived in egypt on its first and only voyage , we can only imagine how residents of alexandria thronged the harbor to marvel at the arrival of this majestic , floating castle . this extraordinary vessel was the titanic of the ancient world , except without the sinking , thanks to our pal , archimedes .

of course , if it only displaced 1,000 tons of water , well , hieron would n't be too happy . this is the law of buoyancy , and engineers still call it archimedes ' principle . it explains why a steel supertanker can float as easily as a wooden rowboat or a bathtub .

what was the principle archimedes discovered ?

translator : tom carter reviewer : bedirhan cinar take an adjective such as `` implacable , '' or a verb like `` proliferate , '' or even another noun , `` crony , '' and add a suffix , such as `` -ity , '' or `` -tion , '' or `` -ism . '' you 've created a new noun . `` implacability , '' `` proliferation , '' `` cronyism . '' sounds impressive , right ? wrong ! you 've just unleashed a flesh-eating zombie . nouns made from other parts of speech are called nominalizations . academics love them . so do lawyers , bureaucrats , business writers . i call them zombie nouns , because they consume the living . they cannibalize active verbs , they suck the lifeblood from adjectives , and they substitute abstract entities for human beings . here 's an example . `` the proliferation of nominalizations in a discursive formation may be an indication of a tendency towards pomposity and abstraction . '' huh ? this sentence contains no fewer than seven nominalizations , yet it fails to tell us who is doing what . when we eliminate , or reanimate , most of the zombie nouns , so `` tendency '' becomes `` tend , '' `` abstraction '' becomes `` abstract , '' then we add a human subject and some active verbs , the sentence springs back to life . `` writers who overload their sentences with nominalizations tend to sound pompous and abstract . '' only one zombie noun -- the key word `` nominalizations '' -- has been allowed to remain standing . at their best , nominalizations help us express complex ideas , perception , intelligence , epistemology . at their worst , they impede clear communication . to get a feeling for how zombie nouns work , release a few of them into a lively sentence and watch them sap all its energy . george orwell played this game in his essay `` politics in the english language . '' he started with a well-known verse from the book of ecclesiastes in the bible . it says `` i returned and saw under the sun , that the race is not to the swift , nor the battle to the strong , neither yet bread to the wise , nor yet riches to men of understanding , nor yet favor to men of skill ; but time and chance happeneth to them all . '' now here 's orwell 's modern english version . `` objective considerations of contemporary phenomena compel the conclusion that success or failure in competitive activities exhibits no tendency to be commensurate with innate capacity , but that a considerable element of the unpredictable must invariably be taken into account . '' the bible passage speaks to our senses and emotions with concrete nouns , descriptions of people , and punchy , abstract nouns such as `` race , '' `` battle , '' `` riches , '' `` time , '' `` chance . '' not a zombie among them . orwell 's satirical translation , on the other hand , is teeming with nominalizations and other vague abstractions . the zombies have taken over , and the humans have fled the village . zombie nouns do their worst damage when they gather in jargon-generating packs and swallow every noun , verb and adjective in sight . so `` globe '' becomes `` global , '' becomes `` globalize , '' becomes `` globalization . '' the grandfather of all nominalizations , antidisestablishmentarianism , contains at least two verbs , three adjectives , and six other nouns inside its distended belly . a paragraph heavily populated by nominalizations will send your readers straight to sleep . rescue them from the zombie apocalypse with vigorous verb-driven sentences that are concrete and clearly structured . you want your sentences to live , not to join the living dead .

wrong ! you 've just unleashed a flesh-eating zombie . nouns made from other parts of speech are called nominalizations . academics love them .

sword calls nominalizations “ zombie nouns ” because they

in the summer of 1963 , a high school teacher changed the way the world looked at `` the wizard of oz . '' his name was henry littlefield , and he was teaching an american history class . he 'd made it to the late 19th century , a time called the gilded age , but he was struggling to keep his class interested in the complex social and economic issues of the time . then one night , while he was reading `` the wonderful wizard of oz '' to his daughters , he had an idea . in the 1890s , farmers wanted to add silver to the gold standard to put more money in circulation and make it easier for farmers to borrow . in the book , dorothy walked to the emerald city on the yellow brick road in her silver shoes . the movie 's ruby red slippers started out as silver . silver and gold on the road to prosperity . l. frank baum had published the book in 1900 at the height of the gilded age , and the analogy did n't seem out of the question . no one else had seen these connections , but that did n't deter littlefield . he taught his class about the gilded age using the book , and soon he and his students were finding more connections . for instance , in the late 1890s , the u.s. had recently recovered from the civil war and integrated vast new territories , bringing an era of prosperity for some . but while industry and finance in the north and east prospered , farmers across the south and midwest struggled . this led to the populist movement , uniting farmers and workers against urban elites . by 1896 , the movement had grown into the people 's party , and its support of democrat williams jennings bryan put him in reach of the presidency . meanwhile in oz , claimed littlefield , dorothy is a typical american girl whose hard life in kansas is literally turned upside down by powerful forces outside her control . the munchkins are the common people oppressed by the witch of the east , banks and monopolies . the scarecrow is the farmer , considered naive but actually quite resourceful , the tin woodman is the industrial worker dehumanized by factory labor , and the cowardly lion is william jennings bryan who could be an influential figure if only he were brave enough to adopt the populist 's radical program . together , they travel along a golden yellow road towards a grand city whose ruler 's power turns out to be built on illusions . littlefield published some of these observations in an essay . his claim that this fantasy was actually a subversive critique of american capitalism appealed to many people in 1960s . other scholars took up the theme , and the proposed analogies and connections multiplied . they suggested that dorothy 's dog toto represented the teetotalers of the prohibition party . oz was clearly the abbreviation for ounces , an important unit in the silver debate . the list goes on . by the 1980s , this understanding of the book was accepted so widely that several american history textbooks mentioned it in discussions of late 19th century politics . but is the theory right ? l. frank baum 's introduction claims the book is just an innocent children 's story . could he have been deliberately throwing people off the trail ? and is it fair to second guess him so many decades later ? there 's no definitive answer , which is part of why authorial intent is a complex , tangled , fun question to unravel . and some recent scholars have interpreted `` the wonderful wizard of oz '' in the opposite way as littlefield . they claim it 's a celebration of the new urban consumer culture . historian william leach argued that the dazzling emerald city of oz was meant to acclimate people to the shiny , new america . in the end , all we know for sure is that baum , inspired by european folk legends , had set out to create one for american children . and whether or not he intended any hidden meanings , its continuing relevance suggests he succeeded in creating a fairytale america can call its own .

there 's no definitive answer , which is part of why authorial intent is a complex , tangled , fun question to unravel . and some recent scholars have interpreted `` the wonderful wizard of oz '' in the opposite way as littlefield . they claim it 's a celebration of the new urban consumer culture .

`` the wonderful wizard of oz '' was published in :

sharks have been celebrated as powerful gods by some native cultures . for example , fijians believe the shark god dakuwaqa , could protect fisherman from the dangers at sea . and today , sharks are recognized as apex predators of the world 's ocean and include some of the earth 's longest living vertebrates . what is it that makes these fish worthy of our ancient legends and so successful in the seas ? much of their hunting prowess stems from a unique set of biological traits honed for more than 400 million years . their cartilaginous skeletons are less dense than bony ones and require less energy to move . large oily livers lend buoyancy to their streamlined bodies , and while trunk muscles of bony fishes attach directly to their skeletons , those of sharks also join to their skin . this special design transforms them into pressurized tubes whose springy skin can efficiently transmit muscular forces to the tail . shark skin has additional remarkable features . despite its smooth external appearance , at the micro level , it has a coarse texture thanks to thousands of tiny teeth-like scales called dermal denticles . each denticle is coated in a substance called enameloid , which turns the skin into a tough shield . plus the structure of denticles varies across the body in such a way as to reduce noise and drag when the shark moves through water . as for the teeth in their mouths , sharks can produce up to 50,000 in a lifetime . on average , they can lose one tooth a week , and each time that happens , it 's rapidly replaced . thanks to a layer of fluoride coating their teeth , sharks also avoid cavities . but teeth are n't the same in all sharks . they can vary across species and by diet . some are dense and flattened , useful for crushing mollusks . others are needle-like for gripping fish . the mouths of great whites contain pointy lower teeth for holding prey and triangular serrated upper teeth for slicing . this variety enables sharks to target prey in a diversity of ocean environments . many species also have another peculiar trait - the ability to launch their jaws out of their mouths , open them extra wide , and grab prey by surprise . over the course of evolution , shark brains have expanded , coupled with the growth of their sensory organs . modern-day sharks can smell a few drops of blood and hear sounds underwater from 800 meters away . they 're particularly well-tuned to low frequencies , including those emitted by dying fish . and like cats , they have reflective membranes called tapeta lucida at the backs of their eyes that dramatically improve their vision in low light . as if these heightened abilities were n't enough , sharks have even honed a sixth sense . they 're able to hunt using a network of electrosensory cells called ampullae of lorenzini . these cells are filled with hypersensitive jelly which allows them to detect electrical signals from prey , including the slightest twitch of a muscle . some of the most iconic shark species , like great whites , makos , porbeagles , and salmon sharks owe their success to another surprising trait : warm blood inside a cold-blooded creature . inside their bodies , they have bundles of arteries and veins called rete mirabile . here , venous blood warmed up by the shark 's working muscles passes right next to arteries carrying cold , oxygen-rich blood from the gills . this arrangement transfers heat to the blood that gets cycled back to the body 's vital organs . warmer muscles enable faster , more powerful swimming , while warmer bellies aid digestion , and the more rapid development of young in utero . and warmer eyes and brains keep the sharks alert in cold waters . with these amazing adaptations , there 's more to revere than fear from the 500 shark species roaming our oceans . unfortunately , one-third of these species are threatened due to overfishing . after millions of years in the making , these apex predators may be meeting their greatest challenge yet .

this special design transforms them into pressurized tubes whose springy skin can efficiently transmit muscular forces to the tail . shark skin has additional remarkable features . despite its smooth external appearance , at the micro level , it has a coarse texture thanks to thousands of tiny teeth-like scales called dermal denticles .

list some advantages the shark has due to the ability to maintain warmth .

you might have seen this symbol before , whether it 's as a temporary tattoo or at a chinese temple . it 's called the yin-yang symbol . it comes from taoism , a religion born in china and it has far more meaning than you probably realize . the yin is the dark swirl , and the yang is the light one , and each side has a dot of the opposite color , which gives a clue to the meaning of yin and yang . everything contains the seed of its opposite . darth vadar has the seed of goodness , and luke has the potential to follow his father to the dark side . like luke and his father , yin and yang are not total opposites , they are relative to each other . taoists believe that the universe is made up of energies , vibrations , and matter , which behave differently in different contexts . something can be yin or yang depending on , well , depending on lots of things . so , while wheat that 's growing is yang , when it 's being reaped , it 's yin . a wave 's crest is yang , and the trough is yin . villages on the sunny side of a valley in china have names like liuyang or shiyang , but on the shady side , for example , of the yangtze river valley , there 's jiangyin . the brake is yin to the gas pedal 's yang . an eggshell is yang , the egg inside is yin . you think you 're getting it ? yang is harder , stronger , brighter , and faster , but one can turn into the other or are two sides of the same coin . the sunbeams are yang in comparison to the shadows . the pitch is yang , the catch is yin . the yang starts an action , and the yin receives it , completes it . yin is the inside space of a cup ; it would n't be a cup without it . yang is the cup . the coffee 's heat , however , is yang , and its blackness is yin . yang goes berserk sometimes , but there 's some very powerful yins , too , if they do n't quite go berserk . yin is the darker swirl , the female , but there is a white dot in it . and yang is the lighter , the male , but it has a black dot . water flowing calmly in a river is yin , but when it goes over the waterfall , it 's very yang . toothpicks are yin compared with a telephone pole . the back of a person is more yin than the front . the top of a person is the yang end . taoism teaches that there is a power in the universe . it 's higher , deeper , and truer than any other force . they call it the tao . it means the way . like the force in star wars , the tao has two sides . unlike other religions where the higher power is all good , and perhaps has an all-evil rival , taoism teaches that we need to learn from both yin and yang . and unlike religions with gods that are personal , the higher power in taoism is not . taoists believe that living in harmony with the way , a person will not have to fight against the universe 's natural flow . so , for example , listen more , argue less . be ready to back up or undo something , and you will make even faster progress . do n't worry about being the best , be who you are . live simply . complications take you away from the tao . `` the wise person is flexible , '' taoists say . learning to use the tao is what taoism is all about , and that 's why you should know your yin from your yang .

the back of a person is more yin than the front . the top of a person is the yang end . taoism teaches that there is a power in the universe .

which of the following is on the yang side of a person :

if i say , `` venice , '' do you imagine yourself gliding down the grand canal , serenaded by a gondolier ? there 's no doubt that the gondola is a symbol of venice , italy , but how did this curious banana-shaped black boat get its distinctive look ? the origins of the venetian gondola are lost to history , but by the 1500s , some 10,000 gondolas transported dignitaries , merchants and goods through the city 's canals . in fact , venice teemed with many types of handmade boats , from utilitarian rafts to the doge 's own ostentatious gilded barge . like a modern day taxi system , gondolas were leased to boatmen who made the rounds of the city 's ferry stations . passengers paid a fare to be carried from one side of the grand canal to the other , as well as to other points around the city . but gondoliers soon developed a bad rap . historical documents describe numerous infractions involving boatmen , including cursing , gambling , extorting passengers -- even occasional acts of violence . to minimize the unpredictability of canal travel , venetian citizens who could afford it purchased their own gondolas , just as a celebirty might use a private car and driver today . these wealthy venetians hired two private gondoliers to ferry them around the city and maintain their boats . the gondolas soon became a status symbol , much like an expensive car , with custom fittings , carved and gilded ornamentation , and seasonal fabrics , like silk and velvet . however , the majority of gondolas seen today are black because in 1562 , venetian authorities decreed that all but ceremonial gondolas be painted black in order to avoid sinfully extravagant displays . apparently , venetian authorities did not believe in `` pimping their rides . '' still , some wealthy venetians chose to pay the fines in order to maintain their ornamental gondolas , a small price to keep up appearances . the distinctive look of the gondola developed over many centuries . each gondola was constructed in a family boatyard called a squero . > from their fathers and grandfathers , sons learned how to select and season pieces of beech , cherry , elm , fir , larch , lime , mahogany , oak and walnut . the gondola makers began with a wooden template that may have been hammered into the workshop floor generations earlier . > from this basic form , they attached fore and aft sterns , then formed the longitudinal planks and ribs that made up the frame of a boat designed to glide through shallow , narrow canals . a gondola has no straight lines or edges . its familiar profile was achieved through an impressive fire and water process that involved warping the boards with torches made of marsh reeds set ablaze . however , the majority of the 500 hours that went into building a gondola involved the final stages : preparing surfaces and applying successive coats of waterproof varnish . the varnish was a family recipe , as closely guarded as one for risotto or a homemade sauce . yet even with the woodwork finished , the gondola was still not complete . specialized artisans supplied their gondola-making colleagues with elaborate covered passenger compartments , upholstery and ornaments of steel and brass . oar makers became integral partners to the gondola makers . the venetian oarlock , or fórcola , began as a simple wooden fork , but evolved into a high-precision tool that allowed a gondolier to guide the oar into many positions . by the late 1800s , gondola makers began to make the left side of the gondola wider than the right as a counter balance to the force created by a single gondolier . this modification allowed rowers to steer from the right side only , and without lifting the oar from the water . while these modifications improved gondola travel , they were not enough to keep pace with motorized boats . today , only about 400 gondolas glide through the waterways of venice , and each year , fewer authentic gondolas are turned out by hand . but along the alleys , street signs contain words in venetian dialect for the locations of old boatyards , oar makers and ferry stations , imprinting the memory of the boat-building trades that once kept life in the most serene republic gliding along at a steady clip .

its familiar profile was achieved through an impressive fire and water process that involved warping the boards with torches made of marsh reeds set ablaze . however , the majority of the 500 hours that went into building a gondola involved the final stages : preparing surfaces and applying successive coats of waterproof varnish . the varnish was a family recipe , as closely guarded as one for risotto or a homemade sauce .

the majority of the 500 hours that went into building a traditional gondola involved :

in 479 bc , when persian soldiers besieged the greek city of potidaea , the tide retreated much farther than usual , leaving a convenient invasion route . but this was n't a stroke of luck . before they had crossed halfway , the water returned in a wave higher than anyone had ever seen , drowning the attackers . the potiidaeans believed they had been saved by the wrath of poseidon . but what really saved them was likely the same phenomenon that has destroyed countless others : a tsunami . although tsunamis are commonly known as tidal waves , they 're actually unrelated to the tidal activity caused by the gravitational forces of the sun and moon . in many ways , tsunamis are just larger versions of regular waves . they have a trough and a crest , and consist not of moving water , but the movement of energy through water . the difference is in where this energy comes from . for normal ocean waves , it comes from wind . because this only affects the surface , the waves are limited in size and speed . but tsunamis are caused by energy originating underwater , from a volcanic eruption , a submarine landslide , or most commonly , an earthquake on the ocean floor caused when the tectonic plates of the earth 's surface slip , releasing a massive amount of energy into the water . this energy travels up to the surface , displacing water and raising it above the normal sea level , but gravity pulls it back down , which makes the energy ripple outwards horizontally . thus , the tsunami is born , moving at over 500 miles per hour . when it 's far from shore , a tsunami can be barely detectable since it moves through the entire depth of the water . but when it reaches shallow water , something called wave shoaling occurs . because there is less water to move through , this still massive amount of energy is compressed . the wave 's speed slows down , while its height rises to as much as 100 feet . the word tsunami , japanese for `` harbor wave , '' comes from the fact that it only seems to appear near the coast . if the trough of a tsunami reaches shore first , the water will withdraw farther than normal before the wave hits , which can be misleadingly dangerous . a tsunami will not only drown people near the coast , but level buildings and trees for a mile inland or more , especially in low-lying areas . as if that were n't enough , the water then retreats , dragging with it the newly created debris , and anything , or anyone , unfortunate enough to be caught in its path . the 2004 indian ocean tsunami was one of the deadliest natural disasters in history , killing over 200,000 people throughout south asia . so how can we protect ourselves against this destructive force of nature ? people in some areas have attempted to stop tsunamis with sea walls , flood gates , and channels to divert the water . but these are not always effective . in 2011 , a tsunami surpassed the flood wall protecting japan 's fukushima power plant , causing a nuclear disaster in addition to claiming over 18,000 lives . many scientists and policy makers are instead focusing on early detection , monitoring underwater pressure and seismic activity , and establishing global communication networks for quickly distributing alerts . when nature is too powerful to stop , the safest course is to get out of its way .

although tsunamis are commonly known as tidal waves , they 're actually unrelated to the tidal activity caused by the gravitational forces of the sun and moon . in many ways , tsunamis are just larger versions of regular waves . they have a trough and a crest , and consist not of moving water , but the movement of energy through water .

which of these is not a potential cause of tsunamis ?

so this is a sample of ruthenium sponge . so the ruthenium metal has been precipitated to form very fine particles . so here we will just open the box i am rather ashamed that i made a big mistake about the name of ruthenium . i thought it referred to somewhere in middle europe perhaps in czechoslovakia whereas ruthenium actually comes from ruthenia which is the latin translation for the country that is now called russia and , in fact , the element ruthenium was first discovered in russia in the city of kazan . why would that be a particular cause of shame for you ? well , because my father was born in russia and therefore to get something connected to russia wrong is a bit embarrassing . the ruthenium is a very , very reactive metal especially when it is formed in this very fine sponge type material . ruthenium was actually discovered relatively early in the middle of the 19th century . there is some discussion , whether in fact the swedish chemist berzelius analysed something that contained ruthenium and missed it or not , but i am not quite sure about that . but the reason why i am interested in this is because i did my doctorate with a supervisor and if you look at his supervisor and then that ö then go back one supervisor after another you eventually get to the swedish chemist berzelius who was my great , great , great , great , great , great , great supervisor and you will find that most of the chemists now working in the world were related to just a few pioneering chemists in the 18th century . so the ruthenium is very finely divided and if i tip it you can see in the bottom of the vial very fine powders but again because of the particle size this is really dark , very black , very nice sample of ruthenium very useful for catalytic chemistry . it is as a catalyst that ruthenium is particularly famous . ruthenium itself if you look at a lump of the metal is a kind of silvery colour . this is a sample of ruthenium as a catalyst . now because it is an expensive metal the ruthenium is just distributed as a very thin layer on silica . silica is like sand and you can see that this finely divided ruthenium looks black . they are very finely divided so it has a large surface area so the molecules can come in and react it . and my students were using this catalyst to react an organic compound , that is one with carbon and hydrogen and to get it to react with more hydrogen and so they lent me this catalyst so i could show it to you . there are other ruthenium catalysts which dissolve in the solution that you are trying to get the reaction to go . and there is a very famous catalyst named after the american chemist bob grubbs , who won the nobel prize about 4 years ago , and his catalyst does a reaction which most people even some chemists had not heard of called which is called metathesis in which double bonds between two carbon atoms are broken and joined together in a different way . and you can use this for all sorts of things you can make plastics out of oils ; you can make new sorts of wax ; you can make a really great sort of wax that has oxygen atoms in it ; and if you use this for candles then the oxygen atoms make fragrance molecules dissolve much better than in ordinary wax . so you can have a christmas candle which , when you light it , smells of christmas pudding or smells of alcohol or vanilla or whatever spice you want . you canít do that with an ordinary wax but this ruthenium catalyst opens up all sorts of things so that is why he got the nobel prize . he got the nobel prize because he made nice smelling candles ? no , he got the nobel prize because he invented the catalyst that opened up all sorts of reactions that otherwise could not be done . bob grubbs compound has ruthenium and his is the most widely used and it is now used in a whole series of industrial processes . this is another compound of ruthenium which you can see is a rather nice red colour and it has the rather unromantic name of ruthenium bpy three times or chemists who use it call it rubpy . and the point about this compound is that it absorbs light well and it is very stable , you can shine light on it , very intense light for a long time and the compound does not decompose , it does not change . but what it can do when you shine light is that you can move electrons around inside the compound and this compound and ones like it are being used by people to try and capture the light from the sun - capture solar energy

the ruthenium is a very , very reactive metal especially when it is formed in this very fine sponge type material . ruthenium was actually discovered relatively early in the middle of the 19th century . there is some discussion , whether in fact the swedish chemist berzelius analysed something that contained ruthenium and missed it or not , but i am not quite sure about that .

the professor tells us that in his research family tree , we can find a very important 18th through 19th century chemist . who was he ?

your rich , eccentric uncle just passed away , and you and your 99 nasty relatives have been invited to the reading of his will . he wanted to leave all of his money to you , but he knew that if he did , your relatives would pester you forever . so he is banking on the fact that he taught you everything you need to know about riddles . your uncle left the following note in his will : `` i have created a puzzle . if all 100 of you answer it together , you will share the money evenly . however , if you are the first to find the pattern and solve the problem without going through all of the leg work , you will get the entire inheritance all to yourself . good luck . '' the lawyer takes you and your 99 relatives to a secret room in the mansion that contains 100 lockers , each hiding a single word . he explains : every relative is assigned a number from 1 to 100 . heir 1 will open every locker . heir 2 will then close every second locker . heir 3 will change the status of every third locker , specifically if it 's open , she 'll close it , but if it 's closed , she 'll open it . this pattern will continue until all 100 of you have gone . the words in the lockers that remain open at the end will help you crack the code for the safe . before cousin thaddeus can even start down the line , you step forward and tell the lawyer you know which lockers will remain open . but how ? pause the video now if you want to figure it out for yourself ! answer in : 3 answer in : 2 answer in : 1 the key is realizing that the number of times a locker is touched is the same as the number of factors in the locker number . for example , in locker # 6 , person 1 will open it , person 2 will close it , person 3 will open it , and person 6 will close it . the numbers 1 , 2 , 3 , and 6 are the factors of 6 . so when a locker has an even number of factors it will remain closed , and when it has an odd number of factors , it will remain open . most of the lockers have an even number of factors , which makes sense because factors naturally pair up . in fact , the only lockers that have an odd number of factors are perfect squares because those have one factor that when multiplied by itself equals the number . for locker 9 , 1 will open it , 3 will close , and 9 will open it . 3 x 3 = 9 , but the 3 can only be counted once . therefore , every locker that is a perfect square will remain open . you know that these ten lockers are the solution , so you open them immediately and read the words inside : `` the code is the first five lockers touched only twice . '' you realize that the only lockers touched twice have to be prime numbers since each only has two factors : 1 and itself . so the code is 2-3-5-7-11 . the lawyer brings you to the safe , and you claim your inheritance . too bad your relatives were always too busy being nasty to each other to pay attention to your eccentric uncle 's riddles .

3 x 3 = 9 , but the 3 can only be counted once . therefore , every locker that is a perfect square will remain open . you know that these ten lockers are the solution , so you open them immediately and read the words inside : `` the code is the first five lockers touched only twice . ''

what is the first locker to remain open ?

some of the issues that are important if you want to have people in space for long periods of time . one is that people will tend to lose bone and muscle mass . we know this . if you have to put a cast on your leg , and you take the cast off after a few weeks , you 'll see that your muscles have shrunk in size . and if you measured the bone strength , you 'd also see that might have gone down a little bit , too . and so , it 's very interesting that our body has that ability to adapt to the loads that are put on it , so that bones and muscles are n't static , they 're always changing . while we think of bone as being a solid thing that does n't change very much , it changes too . and it turns out that in weightlessness , you lose bone . and then you also cause the muscles that work against gravity , what are called the postural muscles , they 'll start to shrink and lose strength . there are other things in the cardiovascular system , the heart and blood vessels . and if you think about it , standing up in gravity means you have to work against gravity in order to keep blood pumping to your head . so , if you could n't keep blood pumping in the head , you 'd pass out every time you stood up because when you 're lying down , you do n't have to push against gravity . but when you stand up , you got to work against gravity to keep blood flowing to your head . and your heart and blood vessels have a really nicely worked-out system to make that happen every time . but that system can also change in weightlessness . and then the other area that changes is the system that has to do with balance . again , maintaining your balance is something that you 're doing against gravity , right ? if you did n't have gravity present , you would n't have to worry about falling . but you obviously do have to worry about falling , and we have a very highly developed sense of balance to keep us upright and to prevent us from falling . and when you see what skaters do , you realize just how exquisite a system it is . but when you go into weightlessness , your balance system changes . you do n't really notice it while you are in weightlessness , but when you come back , you do notice it , that your balance has changed and you have a little bit of trouble maintaining your balance . and what it shows is that while you 're in space , your brain is trying to allow you to function in weightlessness . and so , it re-adapts you to be weightless , which you do n't notice until you come back and find out that you 're now back on earth with a balance system that 's been adapted to space . you know , all life developed here on earth with gravity being present , so life evolved under the influence of gravity , and then we grow up with gravity being present , so we learn how to walk and catch a ball and ice skate or whatever , all with gravity being present . and what if you were to grow up without gravity ? what about the systems that depend on gravity , like your muscles or your balance system or the heart and blood vessels ? would they develop normally , or would they be different in some way ? one reason why you might think that it would go down a different pathway is from an experiment that was done some time ago by two neuroscientists called hubel and wiesel . and what they did is they had a kitten , and they put a patch over the eye of the kitten . and then the kitten grew up to be a cat , and they removed the patch . and so , the question is , can the cat see out of that eye ? now , there 's nothing wrong with the eye , right ? but it just has n't seen anything , there has n't been any light coming in . and the answer is that the cat ca n't see out of that eye because what happens is that the brain goes down a different pathway when it develops and the connections that would ordinarily develop to that eye do n't develop . and that ca n't be undone , that 's a permanent change . so , the brain of that cat is fundamentally different from the brain of a cat that grew up seeing out of that eye . that cat grew up with a different brain , in essence . so , then you wonder , well , what about gravity ? what if you do n't have the forces that gravity produces ? is your balance organ going to develop in the same way , or will it be different ? if somebody grew up in space , could they come back to earth and function , or would they really be a different person ?

and it turns out that in weightlessness , you lose bone . and then you also cause the muscles that work against gravity , what are called the postural muscles , they 'll start to shrink and lose strength . there are other things in the cardiovascular system , the heart and blood vessels .

the muscles that work against gravity are called the ________ muscles .

fu manchu was one of the most notorious escape artists at the omaha zoo in the 1960s . but he was n't a performer , he was an orangutan . the keepers who locked his enclosure every night were baffled to find him outside the next day hanging out with friends in a tree , or sunning on the roof . only after installing cameras did they realize fu manchu had been picking the lock with a metal wire that he kept hidden under his cheek pouch . the keepers should n't have been surprised at fu manchu 's cunningness . along with our other great ape cousins , the gorillas , chimps , and bonobos , they belong to our hominidae family tree , which stretches back 14 million years . but it 's not just their striking red hair that makes orangutans unique among our cousins . as the only great apes from asia , orangutans have adapted to a life high in the rain forest canopies . many of the skills they learn are transmitted through the special bond they have with their mothers , the most extended in the animal kingdom next to humans . orangutan mothers usually give birth to one baby at a time , waiting up to eight years before having another . this gives the young , who begin as fully dependent infants , plenty of time to learn how to climb and distinguish the hundreds of plants and fruits that make up their diet . female orangutans even stay with their mothers into their teen years to learn child-rearing . as they grow up , orangutans also develop a complex set of cooperative social skills by interacting with their peers and siblings . much like ourselves , young orangutans involuntarily mimic the facial expressions and emotions of their playmates , with behaviors that closely parallel human smiling and laughter . once they finally venture out on their own , orangutans continue to develop their resourcefulness , putting the skills they 've learned into practice . adults build a new nest each night by carefully weaving twigs together , topping them with soft leaves , pillows , and blankets . this process requires dexterity , coordination , and an eye for design . orangutans also use a variety of tools to make their lives in the jungle easier . they turn branches into fly swatters and back scratchers , construct umbrellas when it rains , make gloves from leafy pads , and even use leaves as bandages to dress their wounds . but orangutan intelligence goes far beyond jungle survival . research in controlled environments has shown that orangutans are self-aware , being one of the few species to recognize their own reflections . they also display remarkable foresight , planning , and cognition . in one experiment , researchers taught an orangutan to use a straw to extract his favorite fruit soup from a box . that orangutan was later given the choice between the straw or a grape that could be eaten right away , and he chose the straw just in case he was given another box of soup . in another experiment , orangutans figured out how to reach peanuts at the bottom of long tubes by spitting water into them . while orangutans are able to pass cognitive tests with flying colors , there are certain problems that they need our help to solve . indonesia has the world 's highest rate of deforestation , and millions of acres of rain forest are burned annually to support the logging and palm oil industries . deforestation exposes the 30,000 orangutans remaining in the wild to poachers . they kill mothers so that baby orangutans can be sold as exotic pets . but fortunately , the story often does n't end here . orphans can be confiscated and given a second chance . at special forest schools , they recover from emotional trauma and continue to develop essential life skills . against all odds , these orphans demonstrate incredible resilience and readiness to learn . in malay , the word orangutan translates literally to `` the person of the forest , '' a reminder of our common lineage . and despite orangutans being some of the smartest animals on earth , outsmarting their extinction requires the creativity , empathy , and foresight that our species share .

but orangutan intelligence goes far beyond jungle survival . research in controlled environments has shown that orangutans are self-aware , being one of the few species to recognize their own reflections . they also display remarkable foresight , planning , and cognition . in one experiment , researchers taught an orangutan to use a straw to extract his favorite fruit soup from a box .

in controlled research experiments , orangutans have demonstrated foresight , or the ability to act on what might happen in the future . what are some examples of foresight that orangutans might demonstrate in the wild ?

if you ever find yourself gazing at falling snow , why not catch a few snowflakes on your glove and examine their shapes ? you might notice that they look symmetrical , and if you look closely , you 'll see they have six sides . you could say a snowflake is simply frozen water , but compare one with an ice cube from the freezer , and you 'll realize they 're very different things . unlike ice cubes , formed when liquid freezes into a solid , snowflakes form when water vapor turns straight into ice . but that still does n't explain why snowflakes have six sides . to understand that , we need to delve deeper into the physics of water . water is made out of two hydrogen atoms and one oxygen atom . a single water molecule thus has ten protons and ten electrons , eight from oxygen and one from each hydrogen atom . the two electrons from oxygen 's outer shell are shared with two electrons from both hydrogens as they bond together , and the remaining four outer shell electrons from oxygen form two pairs . we call the bonds between these atoms covalent bonds . the pairs of electrons are all negatively charged . similar charges repel , so they tend to stay as far away from each other as possible . the pairs form four electron clouds , two of which are where the hydrogen and oxygen share electrons . the repulsion between the unbonded pairs is even stronger than repulsion between the shared pairs , so the two hydrogens get pushed a little further to an angle of 104.5 degrees . the water molecule as a whole is electrically neutral , but oxygen gets a larger share of electrons , making it slightly negative and the hydrogens slightly positive . due to its negative charge , the oxygen in one molecule is attracted to the positive charge of the hydrogen in another molecule . and so a weak bond between the two molecules , called a hydrogen bond , is formed . when water freezes , this bonding occurs on repeat , ultimately forming a hexagonal structure due to the angle between hydrogens and oxygen within each molecule . this is the seed of a snowflake , and it retains a hexagonal shape as it grows . as the snowflake moves through the air , water vapor molecules stick to the six sharp edges and expand the snowflake outwards , bit by bit . a snowflake 's developing shape depends on atmospheric conditions , like humidity and temperature . as a snowflake falls , changes in weather conditions can affect how it grows , and even small differences in the paths two snowflakes take will differentiate their shapes . however , since conditions at the six sharp edges of one snowflake are similar , a symmetric snowflake can grow . weather conditions affect snow on the ground , as well . warmer ground temperatures produce a wetter snow that is easier to pack because liquid water molecules help snowflakes stick to each other . melted snow also plays a critical role in another wintry activity , skiing . completely dry snow is very difficult to ski on because there 's too much friction between the jagged snowflakes and the ski surface . so what 's happening is that as skis move , they rub the surface of the snow and warm it up , creating a thin layer of water , which helps them slide along . so technically , it 's not really snow skiing , but water skiing . but it is true that no matter how hard you look , you 're almost definitely not going to find two identical snowflakes , and that 's a mystery that scientists are still trying to solve , though we know that it has to do with the many possible branching points in snowflake formation , and the differences in temperature and humidity , and while we wait for the answer , we can enjoy watching these tiny fractals falling from the sky .

the two electrons from oxygen 's outer shell are shared with two electrons from both hydrogens as they bond together , and the remaining four outer shell electrons from oxygen form two pairs . we call the bonds between these atoms covalent bonds . the pairs of electrons are all negatively charged .

covalent bonds result from :

we have some good reasons to completely switch over to solar power . it 's cheaper in many cases , and definitely more sustainable than our dependance on traditional power plants that use resources like coal , which will eventually run out . so why do n't we replace these traditional plants with solar energy ? because there 's one factor that makes solar power very unpredictable : cloud cover . as the sun 's rays move towards earth , some get absorbed by the earth 's atmosphere , some are reflected back into outer space , but the rest make it to the earth 's surface . the ones that are n't deviated are called direct irradiance . the ones that are deflected by clouds are called diffuse irradiance . and those rays that first get reflected by a surface , like a nearby building , before reaching the solar energy system are called reflected irradiance . but before we can examine how clouds affect the sun 's rays and electricity production , let 's see how these solar energy systems work . first up , we have solar towers . these are made up of a central tower surrounded by a huge field of mirrors that track the sun 's path and focus only the direct rays onto a single point on the tower , kind of like an eager beachgoer . the heat generated by these rays is so immense that it can be used to boil water producing steam that drives a traditional turbine , which makes electricity . but when we say solar energy systems , we 're usually talking about photovoltaics , or solar panels , which are the systems most commonly used to generate solar power . in solar panels , photons from the sun 's rays hit the surface of a panel , and electrons are released to get an electric current going . solar panels can use all types of irradiance , while solar towers can only use direct irradiance , and this is where clouds become important because depending on their type and location relative to the sun , they can either increase or decrease the amount of electricity produced . for instance , even a few cumulus clouds in front of the sun can reduce the electricity production in solar towers to almost zero because of this dependence on direct rays . in solar panels , those clouds would decrease energy output as well , though not as much because solar panels can use all types of irradiance . however , all this depends on the clouds exact positioning . due to reflection , or a particular phenomeon called mie scattering , the sun 's rays can actually be focused forward by clouds to create a more than 50 % increase in the solar irradiance reaching a solar panel . if this potential increase is n't accounted for , it could damage the solar panel . why does this matter ? well , you would n't want this lesson to stop just because a cloud passed over the panel on your roof . in solar towers , huge tanks of molten salt or oil can be used to store any excess heat and use it when needed , so that 's how they manage the problem of fluctuating solar irradiance to smooth out electricity production . but in the case of solar panels , there currently is n't any way to affordably store extra energy . that 's where traditional power plants come in because to correct for any fluctuations in these solar powered plants , extra electricity from traditional sources always needs to be available . but then why are n't these tradtional power plants just used as a backup , instead of us humans depending on them as our main sources of energy ? because it 's impossible for an employee at a coal fired or a nuclear plant to turn a knob to produce more or less electricity depending on how many clouds there are in the sky . the response time would simply be too slow . instead , to accommodate these fluctuations , some extra electricity from traditional power plants is always being produced . on clear sky days , that extra electricity might be wasted , but when cloudy skies prevail , it 's what fills the gap . this is what we currently depend on for a constant supply of energy . for this reason , a lot of researchers are interested in forcasting the motion and formation of clouds through satellite images or cameras that look up at the sky to maximize the energy from solar power plants and minimize energy waste . if we could accomplish that , you 'd be able to enjoy this video powered solely by the sun 's rays , no matter what the weather , although if the sun is shining , you may be tempted to venture outside to go and do a different kind of cloud gazing .

and those rays that first get reflected by a surface , like a nearby building , before reaching the solar energy system are called reflected irradiance . but before we can examine how clouds affect the sun 's rays and electricity production , let 's see how these solar energy systems work . first up , we have solar towers . these are made up of a central tower surrounded by a huge field of mirrors that track the sun 's path and focus only the direct rays onto a single point on the tower , kind of like an eager beachgoer .

do solar towers that produce energy from the sun work at night ?

translator : tom carter reviewer : bedirhan cinar the first 10 amendments to the u.s. constitution -- also known as the bill of rights -- were ratified or passed over 200 years ago . but even though they 're a bit , well , old , these first 10 amendments are still the most debated and discussed section of our constitution today . so , can you remember what they are ? let 's take a look . the first amendment is the freedom of speech , press , religion , assembly and petition . this may be the most revered of the amendments . the first amendment protects our rights to say and write our opinions , worship how we please , assemble together peacefully and petition our government , if we feel the need . the second amendment is the right to bear arms . the original intent of the second amendment was to protect colonists from the invading british soldiers , but it now guarantees that you have the right to own a gun to defend yourself and your property . the third amendment is called the `` quartering '' amendment . it was written in response to the british occupation , and as a result of the colonists having to house -- or quarter -- soldiers in their homes during the american revolution . because of this amendment , our government can never force us to house soldiers in our home . the fourth amendment is the right to search and seizure . the police ca n't come into our home without a search warrant and take our personal property . today , many concerns have arisen about our rights to privacy in technology . for example , can the government track your location with your smartphone , or can social media postings such as on facebook and twitter be used without a warrant ? on to the fifth : it 's all about due process . you 've probably heard the phrase `` i plead the fifth '' in movies or on tv . they 're talking about the fifth amendment , which says that you do n't have to take the witness stand against yourself if you may end up incriminating yourself . ok , we 're halfway done . the sixth and seventh amendments are about how the legal system works . if you 're accused of a crime , you have the right to a speedy public trial and an impartial jury . you also have the right to a lawyer , and the right to take the stand if you choose . this is important because it will prevent the accused from sitting in prison forever and insists that the prosecution proceed with undue delay . the seventh says you have the right to a jury trial , where 12 impartial peers decide your innocence or guilt in the courtroom , as opposed to a judge doing it all alone . the eight amendment prohibits cruel and unusual punishment . is the death penalty cruel ? is it unusual ? it 's hard for americans to agree on the definitions of cruel and unusual . the ninth and tenth amendments are called the non-rights amendments . they say that the rights not listed in the bill of rights are retained by the people in the states . we have other rights that are not listed in the constitution , and the states have the right to make their own policies , like instituting state taxes . so now you know all 10 amendments . can you remember them all ? if not , remember this : the bill of rights is a crucial piece of american history , and though society has undergone many changes these past 200 and some years , the interpretation and application of these amendments are as vital today as they were when they were written .

the original intent of the second amendment was to protect colonists from the invading british soldiers , but it now guarantees that you have the right to own a gun to defend yourself and your property . the third amendment is called the `` quartering '' amendment . it was written in response to the british occupation , and as a result of the colonists having to house -- or quarter -- soldiers in their homes during the american revolution .

which does the first amendment not protect ?

imagine you 're on a game show , and you can choose between two prizes : a diamond or a bottle of water . it 's an easy choice . the diamonds are clearly more valuable . now imagine being given the same choice again , only this time , you 're not on a game show , but dehydrated in the desert after wandering for days . do you choose differently ? why ? are n't diamonds still more valuable ? this is the paradox of value , famously described by pioneering economist adam smith . and what it tells us is that defining value is not as simple as it seems . on the game show , you were thinking about each item 's exchange value , what you could obtain for them at a later time , but in an emergency , like the desert scenario , what matters far more is their use value , how helpful they are in your current situation . and because we only get to choose one of the options , we also have to consider its opportunity cost , or what we lose by giving up the other choice . after all , it does n't matter how much you could get from selling the diamond if you never make it out of the desert . most modern economists deal with the paradox of value by attempting to unify these considerations under the concept of utility , how well something satisfies a person 's wants or needs . utility can apply to anything from the basic need for food to the pleasure of hearing a favorite song , and will naturally vary for different people and circumstances . a market economy provides us with an easy way to track utility . put simply , the utility something has to you is reflected by how much you 'd be willing to pay for it . now , imagine yourself back in the desert , only this time , you get offered a new diamond or a fresh bottle of water every five minutes . if you 're like most people , you 'll first choose enough water to last the trip , and then as many diamonds as you can carry . this is because of something called marginal utility , and it means that when you choose between diamonds and water , you compare utility obtained from every additional bottle of water to every additional diamond . and you do this each time an offer is made . the first bottle of water is worth more to you than any amount of diamonds , but eventually , you have all the water you need . after a while , every additional bottle becomes a burden . that 's when you begin to choose diamonds over water . and it 's not just necessities like water . when it comes to most things , the more of it you acquire , the less useful or enjoyable every additional bit becomes . this is the law of diminishing marginal utility . you might gladly buy two or three helpings of your favorite food , but the fourth would make you nauseated , and the hundredth would spoil before you could even get to it . or you could pay to see the same movie over and over until you got bored of it or spent all of your money . either way , you 'd eventually reach a point where the marginal utility for buying another movie ticket became zero . utility applies not just to buying things , but to all our decisions . and the intuitive way to maximize it and avoid diminishing returns is to vary the way we spend our time and resources . after our basic needs are met , we 'd theoretically decide to invest in choices only to the point they 're useful or enjoyable . of course , how effectively any of us manage to maximize utility in real life is another matter . but it helps to remember that the ultimate source of value comes from us , the needs we share , the things we enjoy , and the choices we make .

when it comes to most things , the more of it you acquire , the less useful or enjoyable every additional bit becomes . this is the law of diminishing marginal utility . you might gladly buy two or three helpings of your favorite food , but the fourth would make you nauseated , and the hundredth would spoil before you could even get to it .

using the same scenario as above , what is the total utility of purchasing two bars of chocolate ?

you 're the realm 's greatest mathematician , but ever since you criticized the emperor 's tax laws , you 've been locked in the dungeon with only a marker to count the days . but one day , you 're suddenly brought before the emperor who looks even angrier than usual . one of his twelve governors has been convicted of paying his taxes with a counterfeit coin which has already made its way into the treasury . as the kingdom 's greatest mathematician , you 've been granted a chance to earn your freedom by identifying the fake . before you are the twelve identical looking coins and a balance scale . you know that the false coin will be very slightly lighter or heavier than the rest . but the emperor 's not a patient man . you may only use the scale three times before you 'll be thrown back into the dungeon . you look around for anything else you can use , but there 's nothing in the room - just the coins , the scale , and your trusty marker . how do you identify the counterfeit ? pause here if you want to figure it out for yourself ! answer in : 3 answer in : 2 answer in : 1 obviously you ca n't weigh each coin against all of the others , so you 'll have to weigh several coins at the same time by splitting the stack into multiple piles then narrowing down where the false coin is . start by dividing the twelve coins into three equal piles of four . placing two of these on the scale gives us two possible outcomes . if the two sides balance , all eight coins on the scale are real , and the fake must be among the remaining four . so how do you keep track of these results ? that 's where the marker comes in . mark the eight authentic coins with a zero . now , take three of them and weigh them against three unmarked coins . if they balance , the remaining unmarked coin must be the fake . if they do n't , draw a plus on the three unmarked coins if they 're heavier or a minus if they 're lighter . now , take two of the newly marked coins and weigh them against each other . if they balance , the third coin is fake . otherwise , look at their marks . if they are plus coins , the heavier one is the imposter . if they are marked with minus , it 's the lighter one . but what if the first two piles you weigh do n't balance ? mark the coins on the heavier side with a plus and those on the lighter side with a minus . you can also mark the remaining four coins with zeros since you know the fake one is already somewhere on the scale . now , you 'll need to think strategically so you can remove all remaining ambiguity in just two more weighings . to do this , you 'll need to reassemble the piles . one method is to replace three of the plus coins with three of the minus coins , and replace those with three of the zero coins . > from here , you have three possibilities . if the previously heavier side of the scale is still heavier , that means either the remaining plus coin on that side is actually the heavier one , or the remaining minus coin on the lighter side is actually the lighter one . choose either one of them , and weigh it against one of the regular coins to see which is true . if the previously heavier side became lighter , that means one of the three minus coins you moved is actually the lighter one . weigh two of them against each other . if they balance , the third is counterfeit . if not , the lighter one is . similarly , if the two sides balanced after your substitution , then one of the three plus coins you removed must be the heavier one . weigh two of them against each other . if they balance , the third one is fake . if not , then it 's the heavier one . the emperor nods approvingly at your finding , and the counterfeiting lord takes your place in the dungeon .

if they are marked with minus , it 's the lighter one . but what if the first two piles you weigh do n't balance ? mark the coins on the heavier side with a plus and those on the lighter side with a minus .

in the original problem , if the two sides don ’ t balance after the first weighing , can you think of an alternate method of splitting up the coins for the second weighing ?

with every year , machines surpass humans in more and more activities we once thought only we were capable of . today 's computers can beat us in complex board games , transcribe speech in dozens of languages , and instantly identify almost any object . but the robots of tomorrow may go futher by learning to figure out what we 're feeling . and why does that matter ? because if machines and the people who run them can accurately read our emotional states , they may be able to assist us or manipulate us at unprecedented scales . but before we get there , how can something so complex as emotion be converted into mere numbers , the only language machines understand ? essentially the same way our own brains interpret emotions , by learning how to spot them . american psychologist paul ekman identified certain universal emotions whose visual cues are understood the same way across cultures . for example , an image of a smile signals joy to modern urban dwellers and aboriginal tribesmen alike . and according to ekman , anger , disgust , fear , joy , sadness , and surprise are equally recognizable . as it turns out , computers are rapidly getting better at image recognition thanks to machine learning algorithms , such as neural networks . these consist of artificial nodes that mimic our biological neurons by forming connections and exchanging information . to train the network , sample inputs pre-classified into different categories , such as photos marked happy or sad , are fed into the system . the network then learns to classify those samples by adjusting the relative weights assigned to particular features . the more training data it 's given , the better the algorithm becomes at correctly identifying new images . this is similar to our own brains , which learn from previous experiences to shape how new stimuli are processed . recognition algorithms are n't just limited to facial expressions . our emotions manifest in many ways . there 's body language and vocal tone , changes in heart rate , complexion , and skin temperature , or even word frequency and sentence structure in our writing . you might think that training neural networks to recognize these would be a long and complicated task until you realize just how much data is out there , and how quickly modern computers can process it . from social media posts , uploaded photos and videos , and phone recordings , to heat-sensitive security cameras and wearables that monitor physiological signs , the big question is not how to collect enough data , but what we 're going to do with it . there are plenty of beneficial uses for computerized emotion recognition . robots using algorithms to identify facial expressions can help children learn or provide lonely people with a sense of companionship . social media companies are considering using algorithms to help prevent suicides by flagging posts that contain specific words or phrases . and emotion recognition software can help treat mental disorders or even provide people with low-cost automated psychotherapy . despite the potential benefits , the prospect of a massive network automatically scanning our photos , communications , and physiological signs is also quite disturbing . what are the implications for our privacy when such impersonal systems are used by corporations to exploit our emotions through advertising ? and what becomes of our rights if authorities think they can identify the people likely to commit crimes before they even make a conscious decision to act ? robots currently have a long way to go in distinguishing emotional nuances , like irony , and scales of emotions , just how happy or sad someone is . nonetheless , they may eventually be able to accurately read our emotions and respond to them . whether they can empathize with our fear of unwanted intrusion , however , that 's another story .

essentially the same way our own brains interpret emotions , by learning how to spot them . american psychologist paul ekman identified certain universal emotions whose visual cues are understood the same way across cultures . for example , an image of a smile signals joy to modern urban dwellers and aboriginal tribesmen alike .

what was the main point of paul ekman ’ s theory of universal emotions ?

what 's that sound ? depending on whom you ask , the crackle of popping joints is either the sound of sweet relief or the noxious tones of a stomach-turning habit . really , though . what 's that sound ? i mean , why does bending your joints in a certain way make them pop like that ? scientists have offered several explanations , including rapidly stretching ligaments , and in severe cases , actual bones grinding against each other . but the most common explanation for why your stretched-out joints sound like bubbles popping is that , well , there are bubbles in there . the joints in your fingers are the easiest ones to crack , but many people also crack the joints between vertebrae in their neck and back , and even their hips , wrists , shoulders and so on . all these joints are synovial joints , and they 're the most flexible ones in your body . the space between the two bones is filled with a viscous liquid , synovial fluid , which contains long , lubricating molecules , like hyaluronic acid and lubricin . synovial fluid is more or less the texture of egg yolk and its primary purpose is to cushion the bones and help them glide past each other . it also contains phagocytic cells that help clean up any bone or cartilage debris that ends up in the joint . but the reason it 's important for knuckle cracking is that , like other fluids in your body , it contains lots of dissolved gas molecules . knuckle-crackers know that to get that satisfying pop , you stretch the joint farther than it normally goes by bending your fingers backwards , for example . when you do that , the bones move away from each other . the space between bones gets bigger , but the amount of synovial fluid stays constant . that creates a low-pressure zone that pulls dissolved gases out of the synovial fluid , just like the carbon dioxide that fizzes out of soda when you twist open the cap . inside the joint , the escaping gases form a bubble with a pop . but the bubble does n't last long . the surrounding fluid presses on it until it finally collapses . the bubble 's gases scatter throughout the synovial cavity and slowly dissolve back into the fluid over the course of about twenty minutes , which is why it can take a while before you can pop the same joint again . some scientists think there may actually be two pops . one when the bubble forms , and another when it bursts . popping a joint temporarily enlarges it , which may be why dedicated knuckle- , neck- and back-crackers say the habit makes their joints feel looser and more flexible . but you may have heard from a concerned relative or annoyed officemate that cracking your joints will give you arthritis . a doctor named donald unger heard this , too . so , determined to disprove his mother 's warnings , he cracked the knuckles of his left hand repeatedly for 50 years , while the right-hand knuckles went unpopped . 36,500 cracks later , both hands were arthritis-free . for this selfless act of devotion to science , dr. unger received an ig nobel prize , a parody of the nobel prize that recognizes wacky , but weirdly fascinating , scientific accomplishments . unger wrote that his results should prompt investigation into other parental beliefs , like the importance of eating spinach . the jury 's still out on that one . as for knuckle-cracking , one study suggests that all that joint stretching and bubble bursting can cause your hands to swell and weaken your grip . but the biggest proven danger seems to be annoying those around you .

the space between bones gets bigger , but the amount of synovial fluid stays constant . that creates a low-pressure zone that pulls dissolved gases out of the synovial fluid , just like the carbon dioxide that fizzes out of soda when you twist open the cap . inside the joint , the escaping gases form a bubble with a pop .

why do the dissolved gases come out of solution ?

without a doubt , the most exciting scientific observation of 2012 was the discovery of a new particle at the cern laboratory that could be the higgs boson , a particle named after physicist peter higgs . the higgs field is thought to give mass to fundamental , subatomic particles like the quarks and leptons that make up ordinary matter . the higgs bosons are wiggles in the field , like the bump you see when you twitch a rope . but how does this field give mass to particles ? if this sounds confusing to you , you 're not alone . in 1993 , the british science minister challenged physicists to invent a simple way to understand all this higgs stuff . the prize was a bottle of quality champagne . the winning explanation went something like this : suppose there 's a large cocktail party at the cern laboratory filled with particle physics researchers . this crowd of physicists represents the higgs field . if a tax collector entered the party , nobody would want to talk to them , and they could very easily cross the room to get to the bar . the tax collector would n't interact with the crowd in much the same way that some particles do n't interact with the higgs field . the particles that do n't interact , like photons for example , are called massless . now , suppose that peter higgs entered the same room , perhaps in search of a pint . in this case , the physicists will immediately crowd around higgs to discuss with him their efforts to measure the properties of his namesake boson . because he interacts strongly with the crowd , higgs will move slowly across the room . continuing our analogy , higgs has become a massive particle through his interactions with the field . so , if that 's the higgs field , how does the higgs boson fit into all of this ? let 's pretend our crowd of party goers is uniformly spread across the room . now suppose someone pops their head in the door to report a rumor of a discovery at some distant , rival laboratory . people near the door will hear the rumor , but people far away wo n't , so they 'll move closer to the door to ask . this will create a clump in the crowd . as people have heard the rumor , they will return to their original positions to discuss its implications , but people further away will then ask what 's going on . the result will be a clump in the crowd that moves across the room . this clump is analogous to the higgs boson . it is important to remember that it is not that massive particles interact more with the higgs field . in our analogy of the party , all particles are equal until they enter the room . both peter higgs and the tax collector have zero mass . it is the interaction with the crowd that causes them to gain mass . i 'll say that again . mass comes from interactions with a field . so , let 's recap . a particle gets more or less mass depending on how it interacts with a field , just like different people will move through the crowd at different speeds depending on their popularity . and the higgs boson is just a clump in the field , like a rumor crossing the room . of course , this analogy is just that -- an analogy , but it 's the best analogy anyone has come up with so far . so , that 's it . that 's what the higgs field and the higgs boson is all about . continuing research will tell us if we found it , and the reward will probably be more than just a bottle of champagne .

without a doubt , the most exciting scientific observation of 2012 was the discovery of a new particle at the cern laboratory that could be the higgs boson , a particle named after physicist peter higgs . the higgs field is thought to give mass to fundamental , subatomic particles like the quarks and leptons that make up ordinary matter .

the higgs particle was discovered at

in this short video , we 're going to show you how we constructed and animated a pop-up book to explain earth 's tectonic plates . the supercontinent pangaea broke apart 200,000,000 years ago , but the pieces have n't stopped shifting . although with animation we can show this movement easily with drawings , we thought it 'd be more interesting to depict gigantic sliding slabs of rock using a tangible object that also moves and shifts . and the pop-up book idea was born . ( music ) to make your own pop-up book , you 'll need some basic paper tools , such as scissors , an x-acto knife , glue , double-sided scotch tape , a ruler , a bone folder or other creasing tool , and , of course , some paper . for this lesson , we first determined the visual style by making illustrations and deciding on the overall design , colors , shapes and elements we wanted on each page , or spread . you can have more detailed illustrations , but we wanted to illustrate this lesson simply by playing with shapes and colors . when you visualize your pop-up and choose a visual style , you will want to make a bunch of good old pencil sketches on paper and plan each movement for each spread . plan as much as you can : all the basic shapes and how they connect and how you want them to move , which parts you want to pop-up first . challenge yourself , and explore multiple possibilities of how your main element on the spread can pop up . for the next step , make a mock-up spread and see if your masterful paper engineering ideas translate from a sketch to the actual prototype . instead of using fancy paper , start with the cheap stuff and allow yourself to make mistakes and adjustments . this prototype lets you see how your preliminary sketches will come to life . you will want to first draw all individual parts on a single sheet , including all your main pieces , all the supporting pieces and the folds . you may be surprised that there are only two types of folds that can make your elements pop up the way you want : a step fold and a v-fold . here , you can see how we used a step fold to make each layer of the earth step out . then , cut all your individual elements and assemble using glue or double-sided scotch tape . ( music ) through trial and error , make sure that all the elements , shapes and placements are moving the way you imagined , and that they fold properly when closed and opened . ( music ) once your prototype is tested and complete , you can proceed to making the final product in color . draw or paint on your main pop-up elements as you see fit . for this lesson , we decided to just play with simple shapes in different colors to create the world of shifting continents we imagined . ( music ) when we were planning each spread , we knew we wanted some elements to move independently of the typical pop-up book using slight manipulations and animations . we had to plan well , but also use a few tricks . as always , when you 're making stop-motion , you may have to be creative and use all sorts of unusual tools and props to achieve the effect that you want . in this shot , the birds had to fly across and off the edge of the book , so we used fun-tak to move the clouds across the page . once they left the page , they had to be trimmed to get the illusion they flew off . when the pages of the book close at the end , we had to flip each page , supporting it in each position long enough to be photographed as an individual frame . we used binder clips , wedges , fun-tak , and almost every handy little thing you can think of . once all the individual frames were photographed , we put them all together and composited to make our pop-up book look like it 's moving on its own . so now , think of a special occasion where you can surprise someone with your own unique pop-up card , or an entire story that you want to tell , and start plotting the ins and outs of your pop-up book .

in this short video , we 're going to show you how we constructed and animated a pop-up book to explain earth 's tectonic plates . the supercontinent pangaea broke apart 200,000,000 years ago , but the pieces have n't stopped shifting . although with animation we can show this movement easily with drawings , we thought it 'd be more interesting to depict gigantic sliding slabs of rock using a tangible object that also moves and shifts .

the supercontinent pangaea broke up 200 million years ago and the plates :

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 .

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 .

jenkins lists a few ways the world seems to be increasingly troubled . however , she states that the desire for peace is growing ever stronger . what is the example she gives to support her argument ?

imagine you 're walking through a forest . everything might seem quiet ... but beneath your feet is a flurry of conversation . all the plants around you are actually talking to each other . the trees and the shrubs and the flowers are passing information back and forth , with serious life and death consequences . so , how are they communicating ? they ’ re using a giant network of fungi—one so pervasive and powerful that some scientists have started comparing it to the internet . they ’ re calling it the “ wood wide web. ” i ’ m anna , and this is gross science . the so-called wood wide web is made up of what are called “ mycorrhizal fungi. ” there are many different types of mycorrhizal fungi , but generally these little guys will grow on the roots of plants and provide them with water and nutrients—like nitrogen and phosphorus—in exchange for sugars from the plant . while they ’ re incredibly thin , the threads of the fungi can be up to 1000 times the length of a tree root . this allows the fungi to connect together many different plants . once connections are made , the fungi can act almost like the neurons in our brain , transporting signals from plant to plant . and these networks are everywhere . it ’ s estimated that around 90 % of land plants are connected to some kind of mycorrhizal network . so , how can plants use these networks ? well , to begin with , they can help each other out in times of stress . for example , during the fall months , when paper birch trees lose their leaves and can ’ t produce sugar , douglas-fir trees may shuttle them nutrients through the fungal network . and in the summer , when paper birch trees have lots of leaves , they send sugars to young douglas-fir saplings growing in their shadows . plants can also warn each other of danger . douglas-fir trees connected by a fungal network can alert their ponderosa pine neighbors if they ’ re attacked by budworms . in response , the neighboring ponderosa pine trees will produce insect-repelling chemicals—even though they haven ’ t been directly exposed to the insects themselves . mycorrhizal fungi can also enable parental care of among plants . some adult trees will help out their younger relatives by sending those seedlings more nutrients through the fungal network than they send to strangers . the adults may even make more room for them in the soil by reducing the number of their own roots . but not everyone is so generous . much like our internet , things can sometimes get a little nasty on the wood wide web . take black walnut trees , for example . they can spread poison through the network , hindering the growth of their neighbors . and the fungi making up the network can be just as tricky . mycorrhizal fungi tend to pick favorites . they may share resources with one species of tree , but bleed another species dry without giving anything back in return . the fungi may also judge a plant 's health . if they think it ’ s too weak or sick , they may not allow it to receive nutrients or danger signals from the network . now , we ’ re only beginning to understand how complex these relationships get . but imagine the possibilities for agriculture and forestry . if we find out certain species share well across the network , maybe we can plant them near each other to yield better harvests , or grow healthier forests . so next time you ’ re walking through the woods or the park don ’ t forget to thank the fungal web beneath your feet . ew .

and these networks are everywhere . it ’ s estimated that around 90 % of land plants are connected to some kind of mycorrhizal network . so , how can plants use these networks ?

what percentage of land plants are connected to some kind of mycorrhizal network ?

if you 've got a cold , mucus is hard to miss . but what is it , and what does it do besides making you miserable ? your body produces more than a liter of mucus every day , and all the wet surfaces of your body that are not covered by skin , like your eyes , nose , mouth , lungs , and stomach get a liberal coating . that 's why they 're known as mucus membranes . mucus plays lots of roles in your body . it keeps delicate tissues from drying out and cracking , which would expose them to infection . it lubricates your eyes so you can blink . it protects your stomach lining from acid . it neutralizes threats by removing or trapping substances that could make you sick . and finally , it houses and keeps your body 's trillions of bacterial inhabitants , your microbiota , under control . mucus contains lots of different compounds , including proteins , fats , and salts . but a key component of mucus versatility is a set of proteins called mucins . mucins are the primary large molecules in mucus and are essential for giving mucus its slippery feel . they belong to a class of proteins called glycoproteins which are built out of both amino acids and sugars . in mucin , long chains of sugars are attached to specific amino acids in the protein backbone . the hydrophilic sugar chains help mucin dissolve in your body 's watery fluids . mucus , which is up to 90 % water , stays hydrated thanks to these sugar chains . some of these mucins can interact with other mucin molecules to create a complex network that establishes a barrier against pathogens and other invaders . that 's why mucus is the body 's first line of defense against foreign objects , like bacteria and dust . it 's continuously produced to clear them from the respiratory tract , like a slimy conveyor belt . this keeps bacteria from getting a solid purchase on delicate lung tissue , or making it to the blood stream , where they could cause a major infection . many of those harmful bacteria also cause diseases when they cluster into slimy growths called biofilms . but mucus contains mucins , antimicrobial peptides , antibodies , and even bacteria-hungry viruses called bacteriophages that all work together to prevent biofilms from forming . if microbes do become harmful and you get sick , the body ramps up mucus production to try to quickly flush out the offenders , and the immune system floods your mucus with extra white blood cells . in fact , the greenish mucus often associated with infections gets its color from an enzyme produced by those white blood cells . this multi-pronged approach to bacterial management is one of the main reasons why we 're not sick all the time . even though mucus protects against the infectious bacteria , the vast majority of your body 's bacterial tenants are not harmful , and many are actually beneficial . that 's particularly true when they live in mucus , where they can perform important functions , like synthesizing vitamins , suppressing harmful inflammation , and controlling the growth of more harmful species . so even though you probably associate mucus with being ill , it 's really helping you stay healthy . sure , it might seem gross , but can you think of any other substance that can lubricate , keep your body clean , fight infection , and domesticate a teeming bacterial population ? nope , just mucus .

that 's why they 're known as mucus membranes . mucus plays lots of roles in your body . it keeps delicate tissues from drying out and cracking , which would expose them to infection .

which of the following is not a function of mucus in your body ?

each year in the united states , players of sports and recreational activities receive between 2.5 and 4 million concussions . how dangerous are all those concussions ? the answer is complicated , and lies in how the brain responds when something strikes it . the brain is made of soft fatty tissue , with a consistency something like jello . inside its protective membranes and the skull 's hard casing , this delicate organ is usually well-shielded . but a sudden jolt can make the brain shift and bump against the skull 's hard interior , and unlike jello , the brain 's tissue is n't uniform . it 's made of a vast network of 90 billion neurons , which relay signals through their long axons to communicate throughout the brain and control our bodies . this spindly structure makes them very fragile so that when impacted , neurons will stretch and even tear . that not only disrupts their ability to communicate but as destroyed axons begin to degenerate , they also release toxins causing the death of other neurons , too . this combination of events causes a concussion . the damage can manifest in many different ways including blackout , headache , blurry vision , balance problems , altered mood and behavior , problems with memory , thinking , and sleeping , and the onset of anxiety and depression . every brain is different , which explains why people 's experiences of concussions vary so widely . luckily , the majority of concussions fully heal and symptoms disappear within a matter of days or weeks . lots of rest and a gradual return to activity allows the brain to heal itself . on the subject of rest , many people have heard that you 're not supposed to sleep shortly after receiving a concussion because you might slip into a coma . that 's a myth . so long as doctors are n't concerned there may also be a more severe brain injury , like a brain bleed , there 's no documented problem with going to sleep after a concussion . sometimes , victims of concussion can experience something called post-concussion syndrome , or pcs . people with pcs may experience constant headaches , learning difficulties , and behavioral symptoms that even affect their personal relationships for months or years after the injury . trying to play through a concussion , even for only a few minutes , or returning to sports too soon after a concussion , makes it more likely to develop pcs . in some cases , a concussion can be hard to diagnose because the symptoms unfold slowly over time . that 's often true of subconcussive impacts which result from lower impact jolts to the head than those that cause concussions . this category of injury does n't cause noticable symptoms right away , but can lead to severe degenerative brain diseases over time if it happens repeatedly . take soccer players , who are known for repeatedly heading soccer balls . using a technique called diffusion tensor imaging , we 're beginning to find out what effect that has on the brain . this method allows scientists to find large axon bundles and see how milder blows might alter them structurally . in 2013 , researchers using this technique discovered that athletes who had headed the ball most , about 1,800 times a year , had damaged the structural integrity of their axon bundles . the damage was similar to how a rope will fail when the individual fibers start to fray . those players also performed worse on short-term memory tests , so even though no one suffered full-blown concussions , these subconcussive hits added up to measurable damage over time . in fact , researchers know that an overload of subconcussive hits is linked to a degenerative brain disease known as chronic traumatic encephalopathy , or cte . people with cte suffer from changes in their mood and behavior that begin appearing in their 30s or 40s followed by problems with thinking and memory that can , in some cases , even result in dementia . the culprit is a protein called tau . usually , tau proteins support tiny tubes inside our axons called microtubules . it 's thought that repeated subconcussive hits damage the microtubules , causing the tau proteins to dislodge and clump together . the clumps disrupt transport and communication along the neuron and drive the breakdown of connections within the brain . once the tau proteins start clumping together , they cause more clumps to form and continue to spread throughout the brain , even after head impacts have stopped . the data show that at least among football players , between 50 and 80 % of concussions go unreported and untreated . sometimes that 's because it 's hard to tell a concussion has occurred in the first place . but it 's also often due to pressure or a desire to keep going despite the fact that something 's wrong . this does n't just undermine recovery . it 's also dangerous . our brains are n't invincible . they still need us to shield them from harm and help them undo damage once it 's been done .

this category of injury does n't cause noticable symptoms right away , but can lead to severe degenerative brain diseases over time if it happens repeatedly . take soccer players , who are known for repeatedly heading soccer balls . using a technique called diffusion tensor imaging , we 're beginning to find out what effect that has on the brain .

what did the study in soccer players tell scientists about the cumulative effect of sub-concussive blows ?

take a look at the water in this glass . refreshing , hydrating , and invaluable to your survival . before you take a sip , though , how do you know that the water inside is free from disease-causing organisms and pollutants ? one out of ten people in the world ca n't actually be sure that their water is clean and safe to drink . why is that ? inadequate sanitation , poor protection of drinking water sources , and improper hygiene often lead to sewage and feces-contaminated water . that 's the ideal breeding ground for dangerous bacteria , viruses , and parasites . and the effects of these pathogens are staggering . diarrheal disease from unsafe water is one of the leading causes of death around the world for children under five . and according to a u.n. report from 2010 , microbial water-borne illnesses killed more people per year than war . proper treatment processes , though , can address these threats . they usually have three parts : sedimentation , filtration , and disinfection . once water has been collected in a treatment facility , it 's ready for cleaning . the first step , sedimentation , just takes time . the water sits undisturbed , allowing heavier particles to sink to the bottom . often , though , particles are just too small to be removed by sedimentation alone and need to be filtered . gravity pulls the water downward through layers of sand that catch leftover particles in their pores , prepping the water for its final treatment , a dose of disinfectant . chemicals , primarily forms of chlorine and ozone , are mixed in to kill off any pathogens and to disinfect pipes and storage systems . chlorine is highly effective in destroying water 's living organisms , but its use remains government-regulated because it has potentially harmful chemical byproducts . and if an imbalance of chlorine occurs during the disinfection process , it can trigger other chemical reactions . for example , levels of chlorine byproducts , like trihalomethanes , could skyrocket , leading to pipe corrosion and the release of iron , copper , and lead into drinking water . water contamination from these and other sources including leaching , chemical spills , and runoffs , has been linked to long-term health effects , like cancer , cardiovascular and neurological diseases , and miscarriage . unfortunately , analyzing the exact risks of chemically contaminated water is difficult . so while it 's clear that disinfectants make us safer by removing disease-causing pathogens , experts have yet to determine the full scope of how the chemical cocktail in our drinking water really impacts human health . so how can you tell whether the water you have access to , whether from a tap or otherwise , is drinkable ? firstly , too much turbidity , trace organic compounds , or high-density heavy metals like arsenic , chromium , or lead , mean that the water is unsuitable for consumption . a lot of contaminants , like lead or arsenic , wo n't be obvious without tests , but some clues , like cloudiness , brown or yellow coloration , a foul odor , or an excessive chlorine smell can indicate the need to investigate further . water testing kits can go a step further and confirm the presence of many different contaminants and chemicals . with many types of contamination , there are ways of treating water where it 's used instead of close to its source . point-of-use treatment has actually been around for thousands of years . ancient egyptians boiled away many organic contaminants with the sun 's heat . and in ancient greece , hippocrates designed a bag that trapped bad tasting sediments from water . today , point-of-use processes usually involve ionization to lower mineral content . they also use adsorption filtration , where a porous material called activated carbon strains the water to remove contaminants and chemical byproducts . while it 's not always an effective long-term solution , point-of-use treatment is portable , easy to install , and adaptable . and in regions where large-scale systems are unavailable , or where water has been contaminated further along its journey , these systems can mean the difference between life and death . clean water remains a precious and often scarce commodity . there are nearly 800 million of us who still do n't have regular access to it . the good news is that continued developments in water treatment , both on a large and small scale , can alleviate a lot of unsafe conditions . implementing proper systems where they 're needed and paying careful attention to the ones already in place will fulfill one of the most basic of our human needs .

why is that ? inadequate sanitation , poor protection of drinking water sources , and improper hygiene often lead to sewage and feces-contaminated water . that 's the ideal breeding ground for dangerous bacteria , viruses , and parasites . and the effects of these pathogens are staggering .

sewage or feces infested water is the ideal breeding ground for :

nestled in the tissues of your neck is a small unassuming organ that wields enormous power over your body . it 's called the thyroid . like the operations manager in a company , its role is to make sure that the cells in your body are working properly . it does that by using hormones to deliver messages to every single one of them . this high-ranking organ is made up of lobules that each contains smaller cells called follicles , which store the hormones the thyroid sends out into your blood . two of the most important hormones it produces are thyroxine and triiodothyronine , or t3 and t4 . as messengers , the hormone 's job is to instruct every cell in the body when to consume oxygen and nutrients . that maintains the body 's metabolism , the series of reactions our cells perform to provide us with energy . this hormonal notification from the thyroid gets the heart pumping more efficiently , and makes our cells break down nutrients faster . when you need more energy , the thyroid helps by sending out hormones to increase metabolism . ultimately , the thyroid allows our cells to use energy , grow and reproduce . the thyroid is controlled by the pituitary gland , a hormonal gland deep in the brain that oversees the thyroid 's tasks , making sure it knows when to send out its messengers . the pituitary 's role is to sense if hormone levels in the blood are too low or too high , in which case it sends out instructions in the form of the thyroid- stimulating hormone . even in this tightly controlled system , however , management sometimes slips up . certain diseases , growths in the thryoid or chemical imbalances in the body can confuse the organ and make it deaf to the pituitary 's guiding commands . the first problem this causes is hyperthyroidism , which happens when the organ sends out too many hormones . that means the cells are overloaded with instructions to consume nutrients and oxygen . they become overactive as a result , meaning a person with hyperthyroidism experiences a higher metabolism signaled by a faster heartbeat , constant hunger , and rapid weight loss . they also feel hot , sweaty , anxious , and find it difficult to sleep . the opposite problem is hypothyroidism , which happens when the thyroid sends out too few hormones , meaning the body 's cells do n't have as many messengers to guide them . in response , cells grow listless and metabolism slows . people with hypothyroidism see symptoms in weight gain , sluggishness , sensitivity to cold , swollen joints and feeling low . luckily , there are medical treatments that can help trigger the thyroid 's activities again , and bring the body back to a steady metabolic rate . for such a little organ , the thyroid wields an awful lot of power . but a healthy thyroid manages our cells so effectively that it can keep us running smoothly without us even noticing it 's there .

this hormonal notification from the thyroid gets the heart pumping more efficiently , and makes our cells break down nutrients faster . when you need more energy , the thyroid helps by sending out hormones to increase metabolism . ultimately , the thyroid allows our cells to use energy , grow and reproduce .

the thyroid secretes hormones that :

check this out : here 's a grid , nothing special , just a basic grid , very grid-y . but look closer , into this white spot at the center where the two central vertical and horizontal lines intersect . look very closely . notice anything funny about this spot ? yeah , nothing . but keep looking . get weird and stare at it . now , keeping your gaze fixed on this white spot , check what 's happening in your peripheral vision . the other spots , are they still white ? or do they show weird flashes of grey ? now look at this pan for baking muffins . oh , sorry , one of the cups is inverted . it pops up instead of dipping down . wait , no spin the pan . the other five are domed now ? whichever it is , this pan 's defective . here 's a photo of abraham lincoln , and here 's one upside down . nothing weird going on here . wait , turn that upside down one right side up . what have they done to abe ? those are just three optical illusions , images that seem to trick us . how do they work ? are magical things happening in the images themselves ? while we could certainly be sneaking flashes of grey into the peripheral white spots of our animated grid , first off , we promise we are n't . you 'll see the same effect with a grid printed on a plain old piece of paper . in reality , this grid really is just a grid . but not to your brain 's visual system . here 's how it interprets the light information you call this grid . the white intersections are surrounded by relatively more white on all four sides than any white point along a line segment . your retinal ganglion cells notice that there is more white around the intersections because they are organized to increase contrast with lateral inhibition . better contrast means it 's easier to see the edge of something . and things are what your eyes and brain have evolved to see . your retinal ganglion cells do n't respond as much at the crossings because there is more lateral inhibition for more white spots nearby compared to the lines , which are surrounded by black . this is n't just a defect in your eyes ; if you can see , then optical illusions can trick you with your glasses on or with this paper or computer screen right up in your face . what optical illusions show us is the way your photo receptors and brain assemble visual information into the three-dimensional world you see around you , where edges should get extra attention because things with edges can help you or kill you . look at that muffin pan again . you know what causes confusion here ? your brain 's visual cortex operates on assumptions about the lighting of this image . it expects light to come from a single source , shining down from above . and so these shading patterns could only have been caused by light shining down on the sloping sides of a dome , or the bottom of a hole . if we carefully recreate these clues by drawing shading patterns , even on a flat piece of paper , our brain reflexively creates the 3d concave or convex shape . now for that creepy lincoln upside down face . faces trigger activity in areas of the brain that have specifically evolved to help us recognize faces . like the fusiform face area and others in the occipital and temporal lobes . it makes sense , too , we 're very social animals with highly complex ways of interacting with each other . when we see faces , we have to recognize they are faces and figure out what they 're expressing very quickly . and what we focus on most are the eyes and mouth . that 's how we figure out if someone is mad at us or wants to be our friend . in the upside down lincoln face , the eyes and mouth were actually right side up , so you did n't notice anything was off . but when we flipped the whole image over , the most important parts of the face , the eyes and mouth , were now upside down , and you realized something fishy was up . you realized your brain had taken a short cut and missed something . but your brain was n't really being lazy , it 's just very busy . so it spends cognitive energy as efficiently as possible , using assumptions about visual information to create a tailored , edited vision of the world . imagine your brain calling out these edits on the fly : `` okay , those squares could be objects . let 's enhance that black-white contrast on the sides with lateral inhibition . darken those corners ! dark grey fading into light grey ? assume overhead sunlight falling on a sloping curve . next ! those eyes look like most eyes i 've seen before , nothing weird going on here . '' see ? our visual tricks have revealed your brain 's job as a busy director of 3d animation in a studio inside your skull , allocating cognitive energy and constructing a world on the fly with tried and mostly -- but not always -- true tricks of its own .

what have they done to abe ? those are just three optical illusions , images that seem to trick us . how do they work ?

if all these assumptions sometimes lead to mistakes , for example in these optical illusions , why do we make them ?

will winning the lottery make you happier ? imagine winning a multi-million dollar lottery tomorrow . if you 're like many of us , you 'd be ecstatic , unable to believe your good luck . but would that joy still be there a few years later ? maybe not . a famous study of 22 lottery winners showed that months after winning , their average reported levels of happiness had increased no more than that of a control group who had n't won the lottery . some were actually unhappier than they had been before winning . and later studies have confirmed that our emotional well-being , how often and how intensely we feel things like joy , sorrow , anxiety , or anger , do n't seem to improve with wealth or status beyond a certain point . this has to do with a phenomenon known as hedonic adaptation , or the hedonic treadmill . it describes our tendency to adapt to new situations to maintain a stable emotional equilibrium . when it comes to feeling happy , most of us seem to have a base level that stays more or less constant throughout our existence . of course , the novelty of better food , superior vacations , and more beautiful homes can at first make you feel like you 're walking on air , but as you get used to those things , you revert to your default emotional state . that might sound pretty gloomy , but hedonic adaptation makes us less emotionally sensitive to any kind of change , including negative ones . the study with the lottery winners also looked at people who had suffered an accident that left them paralyzed . when asked several months after their accidents how happy they were , they reported levels of happiness approaching their original baseline . so while the hedonic treadmill may inhibit our enjoyment of positive changes , it seems to also enable our resilience in recovering from adversity . there are other reasons that winning the lottery may not make us happier in the long run . it can be difficult to manage large sums of money , and some lottery winners wind up spending or losing it all quickly . it can also be socially isolating . some winners experience a deluge of unwelcome requests for money , so they wind up cutting themselves off from others . and wealth may actually make us meaner . in one study , participants played a rigged game of monopoly where the experimenters made some players rich quickly . the wealthy players started patronizing the poorer players and hogging the snacks they were meant to share . but just because a huge influx of cash is n't guaranteed to bring joy into your life does n't mean that money can never make us happier . findings show that we adapt to extrinsic and material things , like a new car or a bigger house , much faster than we do to novel experiences , like visiting a new place or learning a new skill . so by that reasoning , the more you spend money on experiences rather than things , the happier you 'd be . and there 's another way to turn your money into happiness : spend it on other people . in one study , participants were given some money and were either asked to spend it on themselves or on someone else . later that evening , researchers called up these participants and asked them how happy they were . the happiness levels of those who had spent the money on others were significantly greater than that of those who had spent it on themselves . and that seems to be true around the world . another study examined the generosity of over 200,000 people from 136 countries . in over 90 % of these countries , people who donated tended to be happier than those who did n't . but this may all be easier said than done . let 's say a million dollars falls into your lap tomorrow . what do you do with it ?

will winning the lottery make you happier ? imagine winning a multi-million dollar lottery tomorrow . if you 're like many of us , you 'd be ecstatic , unable to believe your good luck .

winning the lottery sometimes not be a wonderful event . what can happen ?

magnesium is one of the lightest elements . it ’ s right at the beginning of the period table and , in fact , it ’ s the first of the light metals that you can actually use . lithium and sodium react violently with water so you can ’ t really use them as a metal and beryllium is fantastically poisonous so unless you are using it in the lab where you can be sure that nobody is going to touch it , it ’ s useless , so magnesium is the lightest metal you can use . so , for example , if you are trying to make mobile phones that are really light , then you can make the frame of the mobile phone out of magnesium . you can use it for laptops . there is a professor in germany , who has promised to send me a laptop frame made of magnesium , but it hasn ’ t arrived yet . so another classroom classic . normally comes along in chemistry lesson number three i guess , time to combust a reactive metal in the air , so the reactive metal we are going to look at is magnesium . the other thing that is good about magnesium is that there is a lot of magnesium about in the world , so it is not an element that is difficult to get . if you look at this periodic table here , which is from barcelona so it is in catalan , the areas of these , each element are approximately the abundance in the world . some of the rarer elements have a slightly bigger squares than they should do so you can read the letters , but you see magnesium here is pretty large , so magnesium and sodium are pretty common , beryllium is much less common , and lithium is even less common than that , so there is lots of magnesium . magnesium is very light , it is very reactive , very pliable metal , it is very nice , it is easily alloyed with things like aluminium and other light metals to make very strong , very robust materials . used in construction , it ’ s used in high-performance components of cars . when i was a child when we got , had indigestion , we were given ‘ milk of magnesia ’ . magnesium oxide in water which came in these really nice blue bottles , sort of white looking liquid , didn ’ t taste very nice , but it was meant to be good for you , i am not sure if it was . it is used in the hulls of ships , you know like , warships , things like that , so incredibly strong , incredibly light but incredibly reactive if you give it enough energy . so we are going to combust it in the oxygen and see what happens . magnesium as you know , burns , and one of the ways that magnesium used to be used was for photographic flashlights , and you use bulbs like these which contain magnesium , inside a bulb filled with oxygen . and for each photograph you had to put this on the top of the camera . so i ’ ve got one here that i have taken out . so , if you look at it , so much heat has been produced by this tiny amount of magnesium , that it has melted the glass . so , let ’ s see what happens when we light it . you can see , really fierce bright white light that classical glow , everyone has seen this in the chemistry lab at school , fantastic reaction . it is one of the few metals which is meant to burn in nitrogen . in theory you can take a piece of magnesium , set fire to it in air so its burning well and then plunge it into nitrogen gas , and it should continue burning . i have tried this experiment lots of times and it ’ s never worked . in fact for 25 years i demonstrated this experiment to my lecture class when i was talking about nitrogen , and every time , it didn ’ t work , and the students thought , the poor professor , he has been made a fool of , it hasn ’ t worked and they didn ’ t know that it never worked and i would have been more surprised if it had done , but it taught them a bit about the chemistry of nitrogen and magnesium . why did you keep doing it if it never worked ? because it is a really good experiment , because it got such a good reaction from the audience . because it went wrong ? yes ! you were playing the fool on purpose ? yes ! so this is magnesium metal , but the magnesium metal here is not the ribbon which we normally see in perhaps , scientific labs or perhaps in school labs , this is a very , very fine powder of magnesium , so what we are going to do in a moment is bring on a really very powerful torch , a gas flame and we are going to see what happens when we sprinkle a little of this material into the flame . magnesium is also very important in all our lives , because magnesium is found in the green pigments in the leaves of all plants , in chlorophyll . chlorophyll is an organic molecule , carbon , hydrogen and nitrogen and in the middle there is an atom of magnesium , and it is chlorophyll which catches the sunlight and transfers it eventually to cause the reaction of carbon dioxide and water to make all the sugars and other things in the plant . if that didn ’ t happen none of us would be alive , because we all rely either directly or indirectly on plants , to give us the energy to live . i don ’ t understand completely the mechanism of photosynthesis , because the energy that is absorbed by one molecule , is transferred to another and another one as it were along a chain , but the magnesium is very important , if you don ’ t have magnesium there it is not nearly as efficient . let ’ s light it again .

in theory you can take a piece of magnesium , set fire to it in air so its burning well and then plunge it into nitrogen gas , and it should continue burning . i have tried this experiment lots of times and it ’ s never worked . in fact for 25 years i demonstrated this experiment to my lecture class when i was talking about nitrogen , and every time , it didn ’ t work , and the students thought , the poor professor , he has been made a fool of , it hasn ’ t worked and they didn ’ t know that it never worked and i would have been more surprised if it had done , but it taught them a bit about the chemistry of nitrogen and magnesium .

what is the experiment that never works in the professor´s lectures ?

imagine you 're asked to invent something new . it could be whatever you want made from anything you choose in any shape or size . that kind of creative freedom sounds so liberating , does n't it ? or does it ? if you 're like most people , you 'd probably be paralyzed by this task . without more guidance , where would you even begin ? as it turns out , boundless freedom is n't always helpful . in reality , any project is restricted by many factors , such as the cost , what materials you have at your disposal , and unbreakable laws of physics . these factors are called creative constraints , and they 're the requirements and limitations we have to address in order to accomplish a goal . creative constraints apply across professions , to architects and artists , writers , engineers , and scientists . in many fields , constraints play a special role as drivers of discovery and invention . during the scientific process in particular , constraints are an essential part of experimental design . for instance , a scientist studying a new virus would consider , `` how can i use the tools and techniques at hand to create an experiment that tells me how this virus infects the body 's cells ? and what are the limits of my knowledge that prevent me from understanding this new viral pathway ? '' in engineering , constraints have us apply our scientific discoveries to invent something new and useful . take , for example , the landers viking 1 and 2 , which relied on thrusters to arrive safely on the surface of mars . the problem ? those thrusters left foreign chemicals on the ground , contaminating soil samples . so a new constraint was introduced . how can we land a probe on mars without introducing chemicals from earth ? the next pathfinder mission used an airbag system to allow the rover to bounce and roll to a halt without burning contaminating fuel . years later , we wanted to send a much larger rover : curiosity . however , it was too large for the airbag design , so another constraint was defined . how can we land a large rover while still keeping rocket fuel away from the martian soil ? in response , engineers had a wild idea . they designed a skycrane . similar to the claw machine at toy stores , it would lower the rover from high above the surface . with each invention , the engineers demonstrated an essential habit of scientific thinking - that solutions must recognize the limitations of current technology in order to advance it . sometimes this progress is iterative , as in , `` how can i make a better parachute to land my rover ? '' and sometimes , it 's innovative , like how to reach our goal when the best possible parachute is n't going to work . in both cases , the constraints guide decision-making to ensure we reach each objective . here 's another mars problem yet to be solved . say we want to send astronauts who will need water . they 'd rely on a filtration system that keeps the water very clean and enables 100 % recovery . those are some pretty tough constraints , and we may not have the technology for it now . but in the process of trying to meet these objectives , we might discover other applications of any inventions that result . building an innovative water filtration system could provide a solution for farmers working in drought-stricken regions , or a way to clean municipal water in polluted cities . in fact , many scientific advances have occurred when serendipitous failures in one field address the constraints of another . when scientist alexander fleming mistakenly contaminated a petri dish in the lab , it led to the discovery of the first antibiotic , penicillin . the same is true of synthetic dye , plastic , and gunpowder . all were created mistakenly , but went on to address the constraints of other problems . understanding constraints guides scientific progress , and what 's true in science is also true in many other fields . constraints are n't the boundaries of creativity , but the foundation of it .

these factors are called creative constraints , and they 're the requirements and limitations we have to address in order to accomplish a goal . creative constraints apply across professions , to architects and artists , writers , engineers , and scientists . in many fields , constraints play a special role as drivers of discovery and invention .

scientists and engineers aren ’ t the only people who face creative constraints . discuss some of the constraints faced by professionals in other fields .

so my name is kakani katija , and i 'm a bioengineer . i study marine organisms in their natural environment . and what i want to point out , and at least you can see this in this visualization , is that the ocean environment is a dynamic place . what you 're seeing are the kinds of currents , as well as the whirls , that are left behind in the ocean because of tides or because of winds . and imagine a marine organism as living in this environment , and they 're trying to undergo their entire lives while dealing with currents like these . but what i also want to point out is that small organisms also create small fluid motions , as well . and it 's these fluid motions that i study . and we can think about them like being footprints . so this is my dog kieran , and take a look at her footprints . footprints provide a lot of information . not only do they tell us what kind of organism left them , they might also tell us something about when that organism was there , but also what kind of behavior , were they running or were they walking ? and so terrestrial organisms , like my cute dog kieran , might be leaving footprints behind in dirt or in sand , but marine organisms leave footprints in the form of what we call wake structures , or hydrodynamic signatures , in fluid . now imagine , it 's really hard to see these kinds of structures because fluid is transparent . however , if we add something to the fluid , we get a completely different picture . and you can see that these footprints that marine organisms create are just dynamic . they are constantly changing . and marine organisms also have the ability to sense these signatures . they can also inform decisions , like whether or not they want to continue following a signature like this to find a mate or to find food , or maybe avoid these signatures to avoid being eaten . so imagine the ability to be able to not only see or visualize these kinds of signatures , but to also measure them . this is the engineering side of what i do . and so what i 've done is i actually took a laboratory technique and miniaturized it and basically shrunk it down into the use of underwater housings to make a device that a single scuba diver can use . and so a single scuba diver can go anywhere from the surface to 40 meters , or 120 feet deep , to measure the hydrodynamic signatures that organisms create . before i begin , i want to immerse you into what these kinds of measurements require . so in order to work , we actually dive at night , and this is because we 're trying to minimize any interactions between the laser and sunlight and we 're diving in complete darkness because we do not want to scare away the organisms we 're trying to study . and then once we find the organisms we 're interested in , we turn on a green laser . and this green laser is actually illuminating a sheet of fluid , and in that fluid , it 's reflecting off of particles that are found everywhere in the ocean . and so as an animal swims through this laser sheet , you can see these particles are moving over time , and so we actually risk our lives to get this kind of data . what you 're going to see is that on the left these two particles images that shows the displacement of fluid over time , and using that data , you can actually extract what the velocity of that fluid is , and that 's indicated by the vector plots that you see in the middle . and then we can use that data to answer a variety of different questions , not only to understand the rotational sense of that fluid , which you see on the right , but also estimate something about energetics , or the kinds of forces that act on these organisms or on the fluid , and also evaluate swimming and feeding performance . we 've used this technique on a variety of different organisms , but remember , there 's an issue here . we 're only able to study organisms that a scuba diver can reach . and so before i finish , i want to tell you what the next frontier is in terms of these kinds of measurements . and with collaborators at monterey bay aquarium research institute , we 're developing instrumentation to go on remotely opperated vehicles so we can study organisms anywhere from the surface down to 4000 meters , or two and a half miles . and so we can answer really interesting questions about this organism , this is a larvacean , that creates a feeding current and forces fluids through their mucus house and extracts nutrients . and then this animal , this is a siphonophore , and they can get to lengths about half the size of a football field . and they 're able to swim vertically in the ocean by just creating jet propulsion . and then finally we can answer these questions about how swarming organisms , like krill , are able to affect mixing on larger scales . and this is actually one of the most interesting results so far that we 've collected using the scuba diving device in that organisms , especially when they 're moving in mass , are able to generate mixing at levels that are equivalent to some other physical processes that are associated with winds and tides . but before i finish , i want to leave you all with a question because i think it 's important to keep in mind that technologies today that we take for granted started somewhere . it was inspired from something . so imagine scientists and engineers were inspired by birds to create airplanes . and something we take for granted , flying from san francisco to new york , is something that was inspired by an organism . and as we 're developing these new technologies to understand marine organisms , what we want to do is answer this question : how will marine organisms inspire us ? will they allow us to develop new underwater technologies , like underwater vehicles that look like a jellyfish ? i think it 's a really exciting time in ocean exploration because now we have the tools available to answer this kind of question , and with the help of you guys at some point , you can apply these tools to answer this kind of question and also develop technologies of the future . thank you .

not only do they tell us what kind of organism left them , they might also tell us something about when that organism was there , but also what kind of behavior , were they running or were they walking ? and so terrestrial organisms , like my cute dog kieran , might be leaving footprints behind in dirt or in sand , but marine organisms leave footprints in the form of what we call wake structures , or hydrodynamic signatures , in fluid . now imagine , it 's really hard to see these kinds of structures because fluid is transparent .

all organisms create footprints in air or water ( a.k.a . fluid ) that are called hydrodynamic signatures .

translator : tom carter reviewer : bedirhan cinar we take a breath every few seconds . our life depends upon inhaling oxygen , but we never think about how we breathe . it just seems to happen automatically . how can something that seems so simple be the key to keeping us alive ? breathing starts with the environment around us . the air we breathe in , or inspire , has a mixture of gases including nitrogen , carbon dioxide and oxygen , which is the most important for our survival . it enters our body through the nose and mouth , moves down into the pharynx , trachea and bronchial tubes , and ultimately reaches the alveoli air sacs in the lungs . the alveoli use pressure to move oxygen and nutrients into the blood . the diaphragm and intercostal muscles are a pumping system that facilitates this air exchange . how you breathe affects your energy level , especially when you are under physical or emotional stress . think back to the last difficult test you had to take . it 's likely that as you became more nervous , the tension in your body increased , and your breathing quickly sped up . the shallower our breath , the less oxygen that reaches our brain , and the harder it is to focus . what 's our response to physical stress , like a fast-paced game of field hockey after school ? as we exert pressure on our bodies , the muscles require a great deal of energy and demand additional oxygen . our panting breath starts to kick in , which creates pressure to draw in more air and oxygen to the body , and regulates body temperature by allowing it to cool down naturally . these are n't the only times our breathing is affected or altered . think about the last time you got angry or emotional . anger creates a metabolic reaction in the body , which stresses it out and heats up our internal temperature . have you ever seen anyone lose their cool ? ultimately , if we 're breathing under stress over long periods of time , there are consequences . when the cells of a body are n't getting the oxygen they need , the nutrients available to the body decrease and toxins build up in the blood . it is thought that a hypoxic , or oxygen-poor environment , can increase cancerous cells . the good news is that we can control our breath much more than we realize . this means we can increase both the quality and quantity of the breath . the science of breathing has been around for thousands of years , from ancient yogis in india to respiratory therapists working with patients today . both would tell you that there are specific techniques that will help you improve your breathing . breathing is all about moving air from a higher-pressure to a lower-pressure environment . more breath means more oxygen , and ultimately a greater amount of nutrients that 's available for our cells and blood . we naturally do this when we let out a big sigh . changing the air pressure going into the lungs is one of the main ways to alter breathing . our body automatically does this when we cough , sneeze , or have the hiccups . here 's a simple experiment . close off your right nostril with your right thumb . breathe in and out just through the left nostril . notice how much harder it is to get the breath in . you have to focus your attention , and use your diaphragm and muscles much more than normal . by decreasing the surface area of the airways , you 're increasing the pressure of oxygen moving from the alveoli to the blood . yogis often practice alternate nostril breathing to slow down the breath , increase oxygen , and activate the body 's parasympathetic nervous system , which deals with the body 's operations when it 's at rest . let 's try another exercise . visualize the way a dog pants when it breathes . now try doing the same type of panting , first with your tongue out , then with your mouth closed . you will find yourself using your stomach muscles to push the air out as you exhale . place your hand under your nose , and you 'll feel the strength of the breath coming out . breathing this way is hard because it requires an active movement of our diaphragm and intercostal muscles . our body temperature changes quickly during this exercise from the amount of pressure we are exerting on our breath . it 's no surprise that you 'll find dogs doing this breath often to cool down on a hot day . when we sleep at night , the medulla center of the brain makes sure that we keep breathing . lucky for us we do n't have to think about it . during the day , our breath is much more vulnerable , especially under stressful or difficult situations . that 's why it 's helpful to pay attention to your breathing . if you can monitor and change your breath , you can improve both the quality and quantity of oxygen that enters your body . this lowers stress , increases energy , and strengthens your immune system . so the next time someone tells you to relax and take a deep breath , you 'll know exactly why .

when the cells of a body are n't getting the oxygen they need , the nutrients available to the body decrease and toxins build up in the blood . it is thought that a hypoxic , or oxygen-poor environment , can increase cancerous cells . the good news is that we can control our breath much more than we realize .

what does a ‘ hypoxic ’ cell environment mean ?

you can think of your cells as the kitchen in a busy restaurant . sometimes your body orders chicken . other times , it orders steak . your cells have to be able to crank out whatever the body needs and quickly . when an order comes in , the chef looks to the cookbook , your dna , for the recipe . she then transcribes that message onto a piece of paper called rna and brings it back to her countertop , the ribosome . there , she can translate the recipe into a meal , or for your cells , a protein , by following the directions that she 's copied down . but rna does more for the cell than just act as a messenger between a cook and her cookbook . it can move in reverse and create dna , it can direct amino acids to their targets , or it can take part in rna interference , or rnai . but wait ! why would rna want to interfere with itself ? well , sometimes a cell does n't want to turn all of the messenger rna it creates into protein , or it may need to destroy rna injected into the cell by an attacking virus . say , for example , in our cellular kitchen , that someone wanted to cancel their order or decided they wanted chips instead of fries . that 's where rnai comes in . thankfully , your cells have the perfect knives for just this kind of job . when the cell finds or produces long , double-stranded rna molecules , it chops these molecules up with a protein actually named dicer . now , these short snippets of rna are floating around in the cell , and they 're picked up by something called risc , the rna silencing complex . it 's composed of a few different proteins , the most important being slicer . this is another aptly named protein , and we 'll get to why in just a second . risc strips these small chunks of double-stranded rna in half , using the single strand to target matching mrna , looking for pieces that fit together like two halves of a sandwich . when it finds the matching piece of mrna , risc 's slicer protein slices it up . the cell then realizes there are odd , strangely sized pieces of rna floating around and destroys them , preventing the mrna from being turned into protein . so , you have double-stranded rna , you dice it up , it targets mrna , and then that gets sliced up , too . voila ! you 've prevented expression and saved yourself some unhappy diners . so , how did anybody ever figure this out ? well , the process was first discovered in petunias when botanists trying to create deep purple blooms introduced a pigment-producing gene into the flowers . but instead of darker flowers , they found flowers with white patches and no pigment at all . instead of using the rna produced by the new gene to create more pigment , the flowers were actually using it to knock down the pigment-producing pathway , destroying rna from the plant 's original genes with rnai , and leaving them with pigment-free white flowers . scientists saw a similar phenomena in tiny worms called c. elegans , and once they figured out what was happening , they realized they could use rnai to their advantage . want to see what happens when a certain gene is knocked out of a worm or a fly ? introduce an rnai construct for that gene , and bam ! no more protein expression . you can even get creative and target that effect to certain systems , knocking down genes in just the brain , or just the liver , or just the heart . figuring out what happens when you knock down a gene in a certain system can be an important step in figuring out what that gene does . but rnai is n't just for understanding how things happen . it can also be a powerful , therapeutic tool and could be a way for us to manipulate what is happening within own cells . researchers have been experimenting with using it to their advantage in medicine , including targeting rna and tumor cells in the hopes of turning off cancer-causing genes . in theory , our cellular kitchens could serve up an order of cells , hold the cancer .

this is another aptly named protein , and we 'll get to why in just a second . risc strips these small chunks of double-stranded rna in half , using the single strand to target matching mrna , looking for pieces that fit together like two halves of a sandwich . when it finds the matching piece of mrna , risc 's slicer protein slices it up . the cell then realizes there are odd , strangely sized pieces of rna floating around and destroys them , preventing the mrna from being turned into protein .

risc stands for :

in islamic culture , geometry is everywhere . you can find it in mosques , madrasas , palaces and private homes . this tradition began in the 8th century ce during the early history of islam , when craftsman took preexisting motifs from roman and persian cultures and developed them into new forms of visual expression . this period of history was a golden age of islamic culture , during which many achievements of previous civilizations were preserved and further developed , resulting in fundamental advancements in scientific study and mathematics . accompanying this was an increasingly sophisticated use of abstraction and complex geometry in islamic art , from intricate floral motifs adorning carpets and textiles , to patterns of tilework that seemed to repeat infinitely , inspiring wonder and contemplation of eternal order . despite the remarkable complexity of these designs , they can be created with just a compass to draw circles and a ruler to make lines within them , and from these simple tools emerges a kaleidoscope multiplicity of patterns . so how does that work ? well , everything starts with a circle . the first major decision is how will you divide it up ? most patterns split the circle into four , five or six equal sections . and each division gives rise to distinctive patterns . there 's an easy way to determine whether any pattern is based on fourfold , fivefold , or sixfold symmetry . most contain stars surrounded by petal shapes . counting the number of rays on a starburst , or the number of petals around it , tells us what category the pattern falls into . a star with six rays , or surrounded by six petals , belongs in the sixfold category . one with eight petals is part of the fourfold category , and so on . there 's another secret ingredient in these designs : an underlying grid . invisible , but essential to every pattern , the grid helps determine the scale of the composition before work begins , keeps the pattern accurate , and facilitates the invention of incredible new patterns . let 's look at an example of how these elements come together . we 'll start with a circle within a square , and divide it into eight equal parts . we can then draw a pair of criss-crossing lines and overlay them with another two . these lines are called construction lines , and by choosing a set of their segments , we 'll form the basis of our repeating pattern . many different designs are possible from the same construction lines just by picking different segments . and the full pattern finally emerges when we create a grid with many repetitions of this one tile in a process called tessellation . by choosing a different set of construction lines , we might have created this pattern , or this one . the possibilities are virtually endless . we can follow the same steps to create sixfold patterns by drawing construction lines over a circle divided into six parts , and then tessellating it , we can make something like this . here 's another sixfold pattern that has appeared across the centuries and all over the islamic world , including marrakesh , agra , konya and the alhambra . fourfold patterns fit in a square grid , and sixfold patterns in a hexagonal grid . fivefold patterns , however , are more challenging to tessellate because pentagons do n't neatly fill a surface , so instead of just creating a pattern in a pentagon , other shapes have to be added to make something that is repeatable , resulting in patterns that may seem confoundingly complex , but are still relatively simple to create . also , tessellation is not constrained to simple geometric shapes , as m.c . escher 's work demonstrates . and while the islamic geometric design tradition does n't tend to employ elements like fish and faces , it does sometimes make use of multiple shapes to craft complex patterns . this more than 1,000-year-old tradition has wielded basic geometry to produce works that are intricate , decorative and pleasing to the eye . and these craftsman prove just how much is possible with some artistic intuition , creativity , dedication and a great compass and ruler .

here 's another sixfold pattern that has appeared across the centuries and all over the islamic world , including marrakesh , agra , konya and the alhambra . fourfold patterns fit in a square grid , and sixfold patterns in a hexagonal grid . fivefold patterns , however , are more challenging to tessellate because pentagons do n't neatly fill a surface , so instead of just creating a pattern in a pentagon , other shapes have to be added to make something that is repeatable , resulting in patterns that may seem confoundingly complex , but are still relatively simple to create .

which of the following statements are true ? a grid _____ .

the story of the buddha ’ s life , like all of buddhism , is a story about confronting suffering . he was born between the sixth and fourth century b.c. , the son of a wealthy king in the himalayan foothills of nepal . it was prophesied that the young buddha — then called siddhartha gautama — would either become the emperor of india or a very holy man . since siddhartha ’ s father desperately wanted him to become the former , he kept the child isolated in a palace . young gautama had every imaginable luxury : jewels , servants , lotus ponds , even beautiful dancing women . for 29 years , gautama lived in bliss , protected from the smallest misfortunes of the outside world but then , he left the palace for short excursions . what he saw amazed him : first he met a sick man , then an aging man , and then a dying man . show these kind of people in india—add them to the same image one by one he was astounded to discover that these unfortunate people represented normal—indeed , inevitable—parts of the human condition that would one day touch him , too . horrified and fascinated , gautama made a fourth trip outside the palace walls—and encountered a holy man , who had learned to seek spiritual life in the midst of the vastness of human suffering . inspired by the holy man , gautama left the palace for good . he tried to learn from other holy men . he almost starved himself to death by avoiding all physical comforts and pleasures , as they did . perhaps unsurprisingly , it did not bring him solace from suffering . then he thought of a moment when he was a small boy : sitting by the river , he ’ d noticed that when the grass was cut , the insects and their eggs were trampled and destroyed . as a child , he ’ d felt a deep compassion for the tiny insects . reflecting on his childhood compassion , gautama felt a profound sense of peace . he ate , meditated , and finally reached the highest state of enlightenment : nirvana it refers to the “ blowing out ” of the flames of desire . with this , gautama had become the buddha , “ the awakened one ” . the buddha awoke by recognising that all of creation , from distraught ants to dying human beings , is unified by suffering . recognising this , the buddha discovered how to best approach suffering . first , one shouldn ’ t bathe in luxury , nor abstain from food and comforts altogether . instead , one ought to live in moderation . the buddha called this the middle way this allows for maximal concentration on cultivating compassion for others and seeking enlightenment next , the buddha described a path to transcending suffering called the four noble truths the first noble truth is the realisation that first prompted the buddha ’ s journey : that there is suffering and constant dissatisfaction in the world . the second is that this suffering is caused by our desires . as the buddha said , “ attachment is the root of all suffering. ” the third truth is that we can transcend suffering by removing or managing these desires . the buddha thus made the remarkable claim that we must change our outlook , not our circumstances . we are unhappy not because we don ’ t have enough money , love or status but because we are greedy , vain , and insecure . by re-orienting our mind we can grow to be content . the people become happier—superimpose smiles or use a second image of their face with the correct behaviour and what we now term a mindful attitude , we can also become better people . we can invert negative emotions and states of mind , turning ignorance into wisdom , anger into compassion , and greed into generosity . the fourth and final noble truth the buddha uncovered is that we can learn to move beyond suffering through what he termed the noble eightfold path . the eightfold path involves a series of aspects of behaving “ right ” and wisely : right view , right intention , right speech , right action , right livelihood , right effort , right mindfulness , and right concentration . what strikes the western observer is the notion that wisdom is a habit , not merely an intellectual realisation . one must exercise one ’ s nobler impulses on a regular basis , as one would train a limb . the moment of understanding is only one part of becoming a better person . after his death , the buddha ’ s followers collected his “ sutras ” ( sermons or sayings ) into scripture , and developed texts to guide followers in meditation , ethics , and mindful living . the monasteries that had developed during the buddha ’ s lifetime grew and multiplied , throughout china and east asia . for a time , buddhism was particularly uncommon in india itself , and only a few quiet groups of yellow-clad monks and nuns roamed the countryside , meditating quietly in nature . but then , in the 3rd century b.c. , an indian king named ashoka grew troubled by the wars he had fought and converted to buddhism . he sent monks and nuns far and wide to spread the practice . buddhist spiritual tradition spread across asia and eventually throughout the world . buddha ’ s followers divided into two main schools : theravada buddhism which colonised southeast asia , and mahayana buddhism which took hold in china and northeast asia . today , there are between a half and one and a half billion buddhists in both east and west following the buddha ’ s teachings and seeking a more enlightened and compassionate state of mind . intriguingly , the buddha ’ s teachings are important regardless of our spiritual identification . like the buddha , we are all born into the world not realising how much suffering it contains , and unable to fully comprehend that misfortune , sickness , and death will come to us too . as we grow older , this reality often feels overwhelming , and we may seek to avoid it altogether . but the buddha ’ s teachings remind us of the importance of facing suffering directly . we must do our best to liberate ourselves from the grip of our own desires , and recognise that suffering can be viewed as part of our common connection with others , spurring us to compassion and gentleness .

he was born between the sixth and fourth century b.c. , the son of a wealthy king in the himalayan foothills of nepal . it was prophesied that the young buddha — then called siddhartha gautama — would either become the emperor of india or a very holy man . since siddhartha ’ s father desperately wanted him to become the former , he kept the child isolated in a palace .

according to buddhism , a prophecy foretold that when he grew up , the buddha would become either a holy man , or ...

take a look at the water in this glass . refreshing , hydrating , and invaluable to your survival . before you take a sip , though , how do you know that the water inside is free from disease-causing organisms and pollutants ? one out of ten people in the world ca n't actually be sure that their water is clean and safe to drink . why is that ? inadequate sanitation , poor protection of drinking water sources , and improper hygiene often lead to sewage and feces-contaminated water . that 's the ideal breeding ground for dangerous bacteria , viruses , and parasites . and the effects of these pathogens are staggering . diarrheal disease from unsafe water is one of the leading causes of death around the world for children under five . and according to a u.n. report from 2010 , microbial water-borne illnesses killed more people per year than war . proper treatment processes , though , can address these threats . they usually have three parts : sedimentation , filtration , and disinfection . once water has been collected in a treatment facility , it 's ready for cleaning . the first step , sedimentation , just takes time . the water sits undisturbed , allowing heavier particles to sink to the bottom . often , though , particles are just too small to be removed by sedimentation alone and need to be filtered . gravity pulls the water downward through layers of sand that catch leftover particles in their pores , prepping the water for its final treatment , a dose of disinfectant . chemicals , primarily forms of chlorine and ozone , are mixed in to kill off any pathogens and to disinfect pipes and storage systems . chlorine is highly effective in destroying water 's living organisms , but its use remains government-regulated because it has potentially harmful chemical byproducts . and if an imbalance of chlorine occurs during the disinfection process , it can trigger other chemical reactions . for example , levels of chlorine byproducts , like trihalomethanes , could skyrocket , leading to pipe corrosion and the release of iron , copper , and lead into drinking water . water contamination from these and other sources including leaching , chemical spills , and runoffs , has been linked to long-term health effects , like cancer , cardiovascular and neurological diseases , and miscarriage . unfortunately , analyzing the exact risks of chemically contaminated water is difficult . so while it 's clear that disinfectants make us safer by removing disease-causing pathogens , experts have yet to determine the full scope of how the chemical cocktail in our drinking water really impacts human health . so how can you tell whether the water you have access to , whether from a tap or otherwise , is drinkable ? firstly , too much turbidity , trace organic compounds , or high-density heavy metals like arsenic , chromium , or lead , mean that the water is unsuitable for consumption . a lot of contaminants , like lead or arsenic , wo n't be obvious without tests , but some clues , like cloudiness , brown or yellow coloration , a foul odor , or an excessive chlorine smell can indicate the need to investigate further . water testing kits can go a step further and confirm the presence of many different contaminants and chemicals . with many types of contamination , there are ways of treating water where it 's used instead of close to its source . point-of-use treatment has actually been around for thousands of years . ancient egyptians boiled away many organic contaminants with the sun 's heat . and in ancient greece , hippocrates designed a bag that trapped bad tasting sediments from water . today , point-of-use processes usually involve ionization to lower mineral content . they also use adsorption filtration , where a porous material called activated carbon strains the water to remove contaminants and chemical byproducts . while it 's not always an effective long-term solution , point-of-use treatment is portable , easy to install , and adaptable . and in regions where large-scale systems are unavailable , or where water has been contaminated further along its journey , these systems can mean the difference between life and death . clean water remains a precious and often scarce commodity . there are nearly 800 million of us who still do n't have regular access to it . the good news is that continued developments in water treatment , both on a large and small scale , can alleviate a lot of unsafe conditions . implementing proper systems where they 're needed and paying careful attention to the ones already in place will fulfill one of the most basic of our human needs .

a lot of contaminants , like lead or arsenic , wo n't be obvious without tests , but some clues , like cloudiness , brown or yellow coloration , a foul odor , or an excessive chlorine smell can indicate the need to investigate further . water testing kits can go a step further and confirm the presence of many different contaminants and chemicals . with many types of contamination , there are ways of treating water where it 's used instead of close to its source .

which two chemicals are commonly used to disinfect water ?

spray-painted subway cars , tagged bridges , mural-covered walls . graffiti pops up boldly throughout our cities . it can make statements about identity , art , empowerment , and politics , while simultaneously being associated with destruction . and , it turns out , it 's nothing new . graffiti , or the act of writing or scribbling on public property , has been around for thousands of years . and across that span of time , it 's raised the same questions we debate now : is it art ? is it vandalism ? in the 1st century bce , romans regularly inscribed messages on public walls , while oceans away , mayans were prolifically scratching drawings onto their surfaces . and it was n't always a subversive act . in pompeii , ordinary citizens regularly marked public walls with magic spells , prose about unrequited love , political campaign slogans , and even messages to champion their favorite gladiators . some , including the greek philosopher plutarch , pushed back , deeming graffiti ridiculous and pointless . but it was n't until the 5th century that the roots of the modern concept of vandalism were planted . at that time , a barbaric tribe known as the vandals swept through rome , pillaging and destroying the city . but it was n't until centuries later that the term vandalism was actually coined in an outcry against the defacing of art during the french revolution . and as graffiti became increasingly associated with deliberate rebellion and provocativeness , it took on its vandalist label . that 's part of the reason why , today , many graffiti artists stay underground . some assume alternate identities to avoid retribution , while others do so to establish comradery and make claim to territory . beginning with the tags of the 1960s , a novel overlap of celebrity and anonymity hit the streets of new york city and philadelphia . taggers used coded labels to trace their movements around cities while often alluding to their origins . and the very illegality of graffiti-making that forced it into the shadows also added to its intrigue and growing base of followers . the question of space and ownership is central to graffiti 's history . its contemporary evolution has gone hand in hand with counterculture scenes . while these movements raised their anti-establishment voices , graffiti artists likewise challenged established boundaries of public property . they reclaimed subway cars , billboards , and even once went so far as to paint an elephant in the city zoo . political movements , too , have used wall writing to visually spread their messages . during world war ii , both the nazi party and resistance groups covered walls with propaganda . and the berlin wall 's one-sided graffiti can be seen as a striking symbol of repression versus relatively unrestricted public access . as the counterculture movements associated with graffiti become mainstream , does graffiti , too , become accepted ? since the creation of so-called graffiti unions in the 1970s and the admission of select graffiti artists into art galleries a decade later , graffiti has straddled the line between being outside and inside the mainstream . and the appropriation of graffiti styles by marketers and typographers has made this definition even more unclear . the once unlikely partnerships of graffiti artists with traditional museums and brands , have brought these artists out of the underground and into the spotlight . although graffiti is linked to destruction , it 's also a medium of unrestricted artistic expression . today , the debate about the boundary between defacing and beautifying continues . meanwhile , graffiti artists challenge common consensus about the value of art and the degree to which any space can be owned . whether spraying , scrawling , or scratching , graffiti brings these questions of ownership , art , and acceptability to the surface .

in pompeii , ordinary citizens regularly marked public walls with magic spells , prose about unrequited love , political campaign slogans , and even messages to champion their favorite gladiators . some , including the greek philosopher plutarch , pushed back , deeming graffiti ridiculous and pointless . but it was n't until the 5th century that the roots of the modern concept of vandalism were planted .

the greek philosopher plutarch :

i 'm mckenna pope . i 'm 14 years old . and when i was 13 , i convinced one of the largest toy companies , toy makers in the world , hasbro , to change the way that they marketed one of their best-selling products . so , allow me to tell you about it . so , i have a brother , gavin . when this whole shebang happened , he was four . he loved to cook . he was always getting ingredients out of the fridge and mixing them into these , needless to say , uneatable concoctions or making invisible macaroni and cheese . he wanted to be a chef really badly . and , so what better gift for someone , for a kid who wanted to be a chef , than an easy bake oven , right ? i mean , we all had those when we were little . and he wanted one so badly . but then , he started to realize something . in the commercials and on the boxes for the easy bake oven , hasbro marketed them specifically to girls . and the way that they did this was they would only feature girls on the boxes or in the commercials , and there would be flowery prints all over the ovens , and it would be in bright pink and purple . very gender-specific colors to females , right ? so , it kind of was sending a message that only girls are supposed to cook . boys are n't . and this discouraged my brother a lot . he thought that he was n't supposed to want to be a chef . because that was something girls did . girls cooked , boys did n't . or so , the message that hasbro was sending . and this got me thinking , `` god , i wish there was a way i could change this , that i could have my voice heard by hasbro , so i could ask them and tell them what they were doing wrong and ask them to change it . '' and that got me thinking about a website that i had learned about a few months prior called change.org . change.org is an online petition-sharing platform , where you can create a petition and share it across all these social media networks , through facebook , through twitter , through youtube , through reddit , through tumblr , through whatever you can think of . and so , i created a petition , along with a youtube video that i added to the petition , basically asking hasbro to change the way that they marketed it , in featuring boys in the commercials and on the boxes , and most of all creating them in less gender-specific colors . so , this petititon started to take off , like humongously fast , you have no idea . i was getting interviewed by all these national news outlets and press outlets , and it was amazing . in three weeks , maybe three and a half , i had 46,000 signatures on this petition . ( applause ) thank you . so , needless to say , it was crazy . eventually , hasbro themselves invited me to their headquarters so they could go and unveil their new easy bake oven product to me , in black , silver and blue . it was literally one of the best moments of my life . it was like `` willy wonka and the chocolate factory . '' that thing was amazing . what i did n't realize at the time , however , was that i had become an activist . i could change something that , even as a kid , or maybe even especially as a kid , my voice mattered . and your voice matters , too ! i want to let you know that it 's not going to be easy , and it was n't easy for me because i faced a lot of obstacles . people online , and sometimes even in real life , were disrespectful to me and my family and talked about how the whole thing was a waste of time , and it really discouraged me . and actually , i have some examples because what 's better revenge than displaying their idiocy ? so , let 's see . from username liquidsword29 , interesting usernames we have here , `` disgusting liberal moms making their son 's gay . '' liquidsword29 , really ? really ? okay , how about from whiteboy77ags , `` people always need something to 'female dog ' about . '' from jeffrey gutierrez , `` omg shut up ! you just want money and attention . '' so , it was comments like these that really discouraged me from wanting to make change in the future because i thought , `` people do n't care . people think it 's a waste of time . and people are going to be disrespectful to me and my family . '' it hurt me . and it made me think , `` what 's the point in making change in the future ? '' but then i started to realize something . haters gon na hate . come on , say it with me ! one , two , three , haters gon na hate ! so let your haters hate , you know what ! and make your change because i know you can . i look out into this crowd , and i see 400 people who came out because they wanted to know how they could make a change . and i know that you can , and all of you watching at home can , too , because you have so much that you can do and that you believe in . and you can trade it across all the social media , through facebook , through twitter , through youtube , through reddit , through tumblr , through whatever else you can think of . and you can make that change . you can take what you believe in and turn it into a cause and change it . and that spark that you 've been hearing about all day today you can use that spark that you have within you and turn it into a fire . thank you . ( applause )

and you can trade it across all the social media , through facebook , through twitter , through youtube , through reddit , through tumblr , through whatever else you can think of . and you can make that change . you can take what you believe in and turn it into a cause and change it .

how many social networking sites are available to try and start change in america ?

when we hear the word radiation , it 's tempting to picture huge explosions and frightening mutations , but that 's not the full story . radiation also applies to rainbows and a doctor examining an x-ray . so what is radiation really , and how much should we worry about its effects ? the answer begins with understanding that the word radiation describes two very different scientific phenomena : electromagnetic radiation and nuclear radiation . electromagnetic radiation is pure energy consisting of interacting electrical and magnetic waves oscillating through space . as these waves oscillate faster , they scale up in energy . at the lower end of the spectrum , there 's radio , infrared , and visible light . at the higher end are ultraviolet , x-ray , and gamma rays . modern society is shaped by sending and detecting electromagnetic radiation . we might download an email to our phone via radio waves to open an image of an x-ray print , which we can see because our screen emits visible light . nuclear radiation , on the other hand , originates in the atomic nucleus , where protons repel each other due to their mutually positive charges . a phenomenon known as the strong nuclear force struggles to overcome this repulsion and keep the nucleus intact . however , some combinations of protons and neutrons , known as isotopes , remain unstable , or radioactive . they will randomly eject matter and/or energy , known as nuclear radiation , to achieve greater stability . nuclear radiation comes from natural sources , like radon , a gas which seeps up from the ground . we also refine naturally occurring radioactive ores to fuel nuclear power plants . even bananas contain trace amounts of a radioactive potassium isotope . so if we live in a world of radiation , how can we escape its dangerous effects ? to start , not all radiation is hazardous . radiation becomes risky when it rips atoms ' electrons away upon impact , a process that can damage dna . this is known as ionizing radiation because an atom that has lost or gained electrons is called an ion . all nuclear radiation is ionizing , while only the highest energy electromagnetic radiation is . that includes gamma rays , x-rays , and the high-energy end of ultraviolet . that 's why as an extra precaution during x-rays , doctors shield body parts they do n't need to examine , and why beach-goers use sunscreen . in comparison , cell phones and microwaves operate at the lower end of the spectrum , so there is no risk of ionizing radiation from their use . the biggest health risk occurs when lots of ionizing radiation hits us in a short time period , also known as an acute exposure . acute exposures overwhelm the body 's natural ability to repair the damage . this can trigger cancers , cellular dysfunction , and potentially even death . fortunately , acute exposures are rare , but we are exposed daily to lower levels of ionizing radiation from both natural and man-made sources . scientists have a harder time quantifying these risks . your body often repairs damage from small amounts ionizing radiation , and if it ca n't , the results of damage may not manifest for a decade or more . one way scientists compare ionizing radiation exposure is a unit called the sievert . an acute exposure to one sievert will probably cause nausea within hours , and four sieverts could be fatal . however , our normal daily exposures are far lower . the average person receives 6.2 millisieverts of radiation from all sources annually , around a third due to radon . at only five microsieverts each , you 'd need to get more than 1200 dental x-rays to rack up your annual dosage . and remember that banana ? if you could absorb all the banana 's radiation , you 'd need around 170 a day to hit your annual dosage . we live in a world of radiation . however , much of that radiation is non-ionizing . for the remainder that is ionizing , our exposures are usually low , and choices like getting your home tested for radon and wearing sunscreen can help reduce the associated health risks . marie curie , one of the early radiation pioneers , summed up the challenge as follows : `` nothing in life is to be feared , it is only to be understood . now is the time to understand more , so that we may fear less . ''

so what is radiation really , and how much should we worry about its effects ? the answer begins with understanding that the word radiation describes two very different scientific phenomena : electromagnetic radiation and nuclear radiation . electromagnetic radiation is pure energy consisting of interacting electrical and magnetic waves oscillating through space .

the reason why we have nuclear radiation is because of :

steel and plastic . these two materials are essential to so much of our infrastructure and technology , and they have a complementary set of strengths and weaknesses . steel is strong and hard , but difficult to shape intricately . while plastic can take on just about any form , it 's weak and soft . so would n't it be nice if there were one material as strong as the strongest steel and as shapeable as plastic ? well , a lot of scientists and technologists are getting excited about a relatively recent invention called metallic glass with both of those properties , and more . metallic glasses look shiny and opaque , like metals , and also like metals , they conduct heat and electricity . but they 're way stronger than most metals , which means they can withstand a lot of force without getting bent or dented , making ultrasharp scalpels , and ultrastrong electronics cases , hinges , screws ; the list goes on . metallic glasses also have an incredible ability to store and release elastic energy , which makes them perfect for sports equipment , like tennis racquets , golf clubs , and skis . they 're resistant to corrosion , and can be cast into complex shapes with mirror-like surfaces in a single molding step . despite their strength at room temperature , if you go up a few hundred degrees celsius , they soften significantly , and can be deformed into any shape you like . cool them back down , and they regain the strength . so where do all of these wondrous attributes come from ? in essence , they have to do with metallic glass ' unique atomic structure . most metals are crystalline as solids . that means that if you zoomed in close enough to see the individual atoms , they 'd be neatly lined up in an orderly , repeating pattern that extends throughout the whole material . ice is crystalline , and so are diamonds , and salt . if you heat these materials up enough and melt them , the atoms can jiggle freely and move randomly , but when you cool them back down , the atoms reorganize themselves , reestablishing the crystal . but what if you could cool a molten metal so fast that the atoms could n't find their places again , so that the material was solid , but with the chaotic , amorphous internal structure of a liquid ? that 's metallic glass . this structure has the added benefit of lacking the grain boundaries that most metals have . those are weak spots where the material is more susceptible to scratches or corrosion . the first metallic glass was made in 1960 from gold and silicon . it was n't easy to make . because metal atoms crystallize so rapidly , scientists had to cool the alloy down incredibly fast , a million degrees kelvin per second , by shooting tiny droplets at cold copper plates , or spinning ultrathin ribbons . at that time , metallic glasses could only be tens or hundreds of microns thick , which was too thin for most practical applications . but since then , scientists have figured out that if you blend several metals that mix with each other freely , but ca n't easily crystallize together , usually because they have very different atomic sizes , the mixture crystallizes much more slowly . that means you do n't have to cool it down as fast , so the material can be thicker , centimeters instead of micrometers . these materials are called bulk metallic glasses , or bmgs . now there are hundreds of different bmgs , so why are n't all of our bridges and cars made out of them ? many of the bmgs currently available are made from expensive metals , like palladium and zirconium , and they have to be really pure because any impurities can cause crystallization . so a bmg skyscraper or space shuttle would be astronomically expensive . and despite their strength , they 're not yet tough enough for load-bearing applications . when the stresses get high , they can fracture without warning , which is n't ideal for , say , a bridge . but when engineers figure out how to make bmgs from cheaper metals , and how to make them even tougher , for these super materials , the sky 's the limit .

well , a lot of scientists and technologists are getting excited about a relatively recent invention called metallic glass with both of those properties , and more . metallic glasses look shiny and opaque , like metals , and also like metals , they conduct heat and electricity . but they 're way stronger than most metals , which means they can withstand a lot of force without getting bent or dented , making ultrasharp scalpels , and ultrastrong electronics cases , hinges , screws ; the list goes on .

what are some of the similarities between metallic glasses and metals ?

translator : tom carter reviewer : bedirhan cinar you step into an elevator . it starts going down , fast . what would happen if you jumped right when it started going down ? would the ceiling hit your head ? ouch ! do you stay suspended in the air while the elevator plummets down ? let 's examine the elevator problem one step at a time . first , consider a scale . you know , the kind of scale you weigh yourself on . when you step on a scale to weigh yourself , there are two forces involved . one , gravity pulls you down . two , the scale pushes you up . what ? you did n't know a scale could push ? of course it can ! if it did n't push up on you , you would go crashing through the floor . this upward push is called the normal force and yes , it is normally there . since you 're just standing there on the scale , you 're not moving . therefore , you 're not accelerating . newton 's second law of motion -- net force equals mass times acceleration -- tells us that if the acceleration equals zero , the net force must equal zero . which means that the force of gravity pulling you down must be equal to the force of the scale pushing you up . now let 's suppose you 're standing on that scale in an elevator . at first , the elevator is standing still , so you and the scale are standing still . the two forces on you are equal and opposite . you can read how hard the scale is pushing by looking at it . we call that your weight . then , the elevator starts falling down . you and the scale are in the elevator , so you are falling down too , faster and faster . that means you are accelerating downward . now there is a net force in the same direction as the acceleration -- down . since gravity has n't changed , that must mean the scale is n't pushing up as hard . so the scale is reading a smaller number . the faster the elevator accelerates , the less the scale pushes up . what if you jumped ? would you stop falling ? would the elevator hit your head ? well , what 's pulling the elevator down ? gravity . is gravity pulling on you ? of course . so your relative position in the elevator will stay the same . the ceiling will only hit you if you can jump up to the ceiling . now consider : what would happen if the elevator accelerated upward and , even more frightening , if someone snuck in and cut the cable holding the elevator , what would happen then ? think about it .

what if you jumped ? would you stop falling ? would the elevator hit your head ? well , what 's pulling the elevator down ?

physics is a natural science that involves the study of matter and its motion through space and time , along with related concepts such as energy and force . more broadly , it is the general analysis of nature , conducted in order to understand how the universe behaves . along with `` would you weight less in an elevator , '' what are some other interesting questions that a physicist might study ?

have you ever had someone try to explain something to you a dozen times with no luck – but , then , when you see a picture , the idea finally clicks ? if that sounds familiar , maybe you might consider yourself a visual learner . or , if reading or listening does the trick , maybe you feel like you ’ re a verbal learner . we call these labels learning styles , but is there /really/ a way to categorize different types of students ? well , it actually seems like /multiple/ presentation formats , especially if one of them is visual , help most people learn . when psychologists and educators test for learning styles , they ’ re trying to figure out whether these are inherent traits that affect how well students learn , instead of just a preference . usually , they start by giving a survey to figure out what style a student favors , like visual or verbal learning . then , they try to teach the students something with a specific presentation style , like using visual aids , and do a follow-up test to see how much they learned . that way , the researchers can see if the self-identified verbal learners really learned better when the information was just spoken aloud , for example . but , according to a 2008 review , only /one/ study that followed this design found that students actually learned best with their preferred style… and it had some pretty big flaws . the researchers excluded two-thirds of the original participants because they did n't seem to have /any/ clear learning style from the survey at the beginning . plus , they removed outliers from the data if they thought they were “ extreme , ” without defining exactly what that meant . and , they did n't even report the actual test scores in the final paper . so ... it doesn ’ t really seem like learning styles are an inherent trait that we all have . but , that does n't mean that all students will do amazingly if they just spend all their time reading from a textbook . instead , /most people/ seem to learn better if they ’ re taught in several ways – especially if one is visual . in one study , researchers tested whether students remembered lists of words better if they heard them , saw them , or both . and everyone seemed to do better if they got to see the words in print , even the self-identified auditory learners . that preference did n't seem to matter . similar studies tested whether students learned basic physics and chemistry concepts better by reading plain text or viewing pictures , too . and everyone did better with the help of pictures . so the question of whether or not you 're a visual learner could best be answered with : `` well , yeah , kinda . but so are most people . '' thanks for asking , and thanks especially to all of our patrons on patreon who keep these answers coming . if you ’ d like to submit questions to be answered , or get some videos a few days early , go to patreon.com/scishow . and don ’ t forget to go to youtube.com/scishow and subscribe !

have you ever had someone try to explain something to you a dozen times with no luck – but , then , when you see a picture , the idea finally clicks ? if that sounds familiar , maybe you might consider yourself a visual learner . or , if reading or listening does the trick , maybe you feel like you ’ re a verbal learner .

if someone claims they are a visual learner , what might you say to them , according to this video ?

what 's the definition of comedy ? thinkers and philosophers from plato and aristotle to hobbes , freud , and beyond , including anyone misguided enough to try to explain a joke , have pondered it , and no one has settled it . you 're lucky you found this video to sort it out . to define comedy , you should first ask why it seems comedy defies definition . the answer 's simple . comedy is the defiance of definition because definitions sometimes need defiance . consider definition itself . when we define , we use language to set borders around a thing that we 've perceived in the whirling chaos of existence . we say what the thing means and fit that in a system of meanings . chaos becomes cosmos . the universe is translated into a cosmological construct of knowledge . and let 's be honest , we need some logical cosmic order , otherwise we 'd have pure chaos . chaos can be rough , so we build a thing that we call reality . now think about logic and logos , that tight knot connecting a word and truth . and let 's jump back to thinking about what 's funny , because some people say it 's real simple : truth is funny . it 's funny because it 's true . but that 's simplistic . plenty of lies are funny . comedic fiction can be funny . made-up nonsense jibberish is frequently hilarious . for instance , florp -- hysterical ! and plenty of truths are n't funny . two plus two truly equals four , but i 'm not laughing just because that 's the case . you can tell a true anecdote , but your date may not laugh . so , why are some untruths and only some truths funny ? how do these laughable truths and untruths relate to that capital-t truth , the cosmological reality of facts and definitions ? and what makes any of them funny ? there 's a frenchman who can help , another thinker who did n't define comedy because he expressly did n't want to . henri bergson 's a french philosopher who prefaced his essay on laughter by saying he would n't define `` the comic '' because it 's a living thing . he argued laughter has a social function to destroy mechanical inelasticity in people 's attitudes and behavior . someone doing the same thing over and over , or building up a false image of themself and the world , or not adapting to reality by just noticing the banana peel on the ground -- this is automatism , ignorance of one 's own mindless rigidity , and it 's dangerous but also laughable and comic ridicule helps correct it . the comic is a kinetic , vital force , or elan vital , that helps us adapt . bergson elaborates on this idea to study what 's funny about all sorts of things . but let 's stay on this . at the base of this concept of comedy is contradiction between vital , adaptive humanity and dehumanized automatism . a set system that claims to define reality might be one of those dehumanizing forces that comedy tends to destroy . now , let 's go back to aristotle . not poetics , where he drops a few thoughts on comedy , no , metaphysics , the fundamental law of non-contradiction , the bedrock of logic . contradictory statements are not at the same time true . if a is an axiomatic statement , it ca n't be the case that a and the opposite of a are both true . comedy seems to live here , to subsist on the illogic of logical contradiction and its derivatives . we laugh when the order we project on the world is disrupted and disproven , like when the way we all act contradicts truths we do n't like talking about , or when strange observations we all make in the silent darkness of private thought are dragged into public by a good stand-up , and when cats play piano , because cats that are also somehow humans disrupt our reality . so , we do n't just laugh at truth , we laugh at the pleasurable , edifying revelation of flaws , incongruities , overlaps , and outright conflicts in the supposedly ordered system of truths we use to define the world and ourselves . when we think too highly of our thinking , when we think things are true just because we all say they 're logos and stop adapting , we become the butt of jokes played on us by that wacky little trickster , chaos . comedy conveys that destructive , instructive playfulness , but has no logical definition because it acts upon our logic paralogically from outside its finite borders . far from having a definite definition , it has an infinite infinition . and the infinition of comedy is that anything can be mined for comedy . thus , all definitions of reality , especially those that claim to be universal , logical , cosmic , capital-t truth become laughable .

there 's a frenchman who can help , another thinker who did n't define comedy because he expressly did n't want to . henri bergson 's a french philosopher who prefaced his essay on laughter by saying he would n't define `` the comic '' because it 's a living thing . he argued laughter has a social function to destroy mechanical inelasticity in people 's attitudes and behavior . someone doing the same thing over and over , or building up a false image of themself and the world , or not adapting to reality by just noticing the banana peel on the ground -- this is automatism , ignorance of one 's own mindless rigidity , and it 's dangerous but also laughable and comic ridicule helps correct it .

imagine an ideal society where everything ’ s working out great , and a terrible society where everything ’ s falling apart : which one has more laughter in it ?

translator : tom carter reviewer : bedirhan cinar the first 10 amendments to the u.s. constitution -- also known as the bill of rights -- were ratified or passed over 200 years ago . but even though they 're a bit , well , old , these first 10 amendments are still the most debated and discussed section of our constitution today . so , can you remember what they are ? let 's take a look . the first amendment is the freedom of speech , press , religion , assembly and petition . this may be the most revered of the amendments . the first amendment protects our rights to say and write our opinions , worship how we please , assemble together peacefully and petition our government , if we feel the need . the second amendment is the right to bear arms . the original intent of the second amendment was to protect colonists from the invading british soldiers , but it now guarantees that you have the right to own a gun to defend yourself and your property . the third amendment is called the `` quartering '' amendment . it was written in response to the british occupation , and as a result of the colonists having to house -- or quarter -- soldiers in their homes during the american revolution . because of this amendment , our government can never force us to house soldiers in our home . the fourth amendment is the right to search and seizure . the police ca n't come into our home without a search warrant and take our personal property . today , many concerns have arisen about our rights to privacy in technology . for example , can the government track your location with your smartphone , or can social media postings such as on facebook and twitter be used without a warrant ? on to the fifth : it 's all about due process . you 've probably heard the phrase `` i plead the fifth '' in movies or on tv . they 're talking about the fifth amendment , which says that you do n't have to take the witness stand against yourself if you may end up incriminating yourself . ok , we 're halfway done . the sixth and seventh amendments are about how the legal system works . if you 're accused of a crime , you have the right to a speedy public trial and an impartial jury . you also have the right to a lawyer , and the right to take the stand if you choose . this is important because it will prevent the accused from sitting in prison forever and insists that the prosecution proceed with undue delay . the seventh says you have the right to a jury trial , where 12 impartial peers decide your innocence or guilt in the courtroom , as opposed to a judge doing it all alone . the eight amendment prohibits cruel and unusual punishment . is the death penalty cruel ? is it unusual ? it 's hard for americans to agree on the definitions of cruel and unusual . the ninth and tenth amendments are called the non-rights amendments . they say that the rights not listed in the bill of rights are retained by the people in the states . we have other rights that are not listed in the constitution , and the states have the right to make their own policies , like instituting state taxes . so now you know all 10 amendments . can you remember them all ? if not , remember this : the bill of rights is a crucial piece of american history , and though society has undergone many changes these past 200 and some years , the interpretation and application of these amendments are as vital today as they were when they were written .

the original intent of the second amendment was to protect colonists from the invading british soldiers , but it now guarantees that you have the right to own a gun to defend yourself and your property . the third amendment is called the `` quartering '' amendment . it was written in response to the british occupation , and as a result of the colonists having to house -- or quarter -- soldiers in their homes during the american revolution .

if you had to add another amendment , what would it be ? do you think the bill of rights is antiquated ? what needs to be updated ?

translator : andrea mcdonough reviewer : bedirhan cinar you look down and see a yellow pencil lying on your desk . your eyes , and then your brain , are collecting all sorts of information about the pencil : its size , color , shape , distance , and more . but , how exactly does this happen ? the ancient greeks were the first to think more or less scientifically about what light is and how vision works . some greek philosophers , including plato and pythagoras , thought that light originated in our eyes and that vision happened when little , invisible probes were sent to gather information about far-away objects . it took over a thousand years before the arab scientist , alhazen , figured out that the old , greek theory of light could n't be right . in alhazen 's picture , your eyes do n't send out invisible , intelligence-gathering probes , they simply collect the light that falls into them . alhazen 's theory accounts for a fact that the greek 's could n't easily explain : why it gets dark sometimes . the idea is that very few objects actually emit their own light . the special , light-emitting objects , like the sun or a lightbulb , are known as sources of light . most of the things we see , like that pencil on your desk , are simply reflecting light from a source rather than producing their own . so , when you look at your pencil , the light that hits your eye actually originated at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye , which is pretty cool when you think about it . but , what exactly is the stuff that is emitted from the sun and how do we see it ? is it a particle , like atoms , or is it a wave , like ripples on the surface of a pond ? scientists in the modern era would spend a couple of hundred years figuring out the answer to this question . isaac newton was one of the earliest . newton believed that light is made up of tiny , atom-like particles , which he called corpuscles . using this assumption , he was able to explain some properties of light . for example , refraction , which is how a beam of light appears to bend as it passes from air into water . but , in science , even geniuses sometimes get things wrong . in the 19th century , long after newton died , scientists did a series of experiments that clearly showed that light ca n't be made up of tiny , atom-like particles . for one thing , two beams of light that cross paths do n't interact with each other at all . if light were made of tiny , solid balls , then you would expect that some of the particles from beam a would crash into some of the particles from beam b . if that happened , the two particles involved in the collision would bounce off in random directions . but , that does n't happen . the beams of light pass right through each other as you can check for yourself with two laser pointers and some chalk dust . for another thing , light makes interference patterns . interference patterns are the complicated undulations that happen when two wave patterns occupy the same space . they can be seen when two objects disturb the surface of a still pond , and also when two point-like sources of light are placed near each other . only waves make interference patterns , particles do n't . and , as a bonus , understanding that light acts like a wave leads naturally to an explanation of what color is and why that pencil looks yellow . so , it 's settled then , light is a wave , right ? not so fast ! in the 20th century , scientists did experiments that appear to show light acting like a particle . for instance , when you shine light on a metal , the light transfers its energy to the atoms in the metal in discrete packets called quanta . but , we ca n't just forget about properties like interference , either . so these quanta of light are n't at all like the tiny , hard spheres newton imagined . this result , that light sometimes behaves like a particle and sometimes behaves like a wave , led to a revolutionary new physics theory called quantum mechanics . so , after all that , let 's go back to the question , `` what is light ? '' well , light is n't really like anything we 're used to dealing with in our everyday lives . sometimes it behaves like a particle and other times it behaves like a wave , but it is n't exactly like either .

but , how exactly does this happen ? the ancient greeks were the first to think more or less scientifically about what light is and how vision works . some greek philosophers , including plato and pythagoras , thought that light originated in our eyes and that vision happened when little , invisible probes were sent to gather information about far-away objects .

who were the first to think ( more or less scientifically ) about what light is ?

element 118 , ununoctium or uuo , is the last element in the periodic table , and it 's in the group which contains the noble gases , going from helium right down to radioactive radon , so it is going to be radioactive . so far , only 3 atoms , have been observed . first one atom then another two . so it 's more than ununquadium , is it more ? it 's more than ununquadium , where we had , only one atom , but it 's still not very many atoms . it 's still arguable whether it will be a gass-like radon , or it may be a solid , just like some of the other elements , perhaps a solid that 's rather volatile . so that it would evaporate easily . but nobody knows . how can you know 118 is the last element , on the periodic table ? -well formally , they could be heavier elements than 118 , but the electrons , the negatively charged particles , that surround , the positively charged nucleus , are in shells , which gradually go outwards . rather like the skins , of an onion . so that element 118 , represents the whole of a shell , being filled . so we know that there are no more electrons , that can be easily accommodated and if we make element 119 , which would be an alkali metal like sodium or cesium , then we would have to put a single electron , a lot further away , from the nucleus . and as soon as you start adding electrons , that are further away , the whole system , is expected to become very much less stable . so if we can only make 3 atoms of element 118 , something that 's going to be very much less stable , is not likely to be found in the short time . though one of the exciting things about science , is that the unexpected often happens . so , it might be that before we 've started updating , some of these videos , element 119 will be announced . and nobody will be more excited than me . www.periodicvideos.com university of nottingham captions by www.subply.com

so it 's more than ununquadium , is it more ? it 's more than ununquadium , where we had , only one atom , but it 's still not very many atoms . it 's still arguable whether it will be a gass-like radon , or it may be a solid , just like some of the other elements , perhaps a solid that 's rather volatile .

how many electrons are there in the outer shell of the ununoctium atom ?

without a doubt , the most exciting scientific observation of 2012 was the discovery of a new particle at the cern laboratory that could be the higgs boson , a particle named after physicist peter higgs . the higgs field is thought to give mass to fundamental , subatomic particles like the quarks and leptons that make up ordinary matter . the higgs bosons are wiggles in the field , like the bump you see when you twitch a rope . but how does this field give mass to particles ? if this sounds confusing to you , you 're not alone . in 1993 , the british science minister challenged physicists to invent a simple way to understand all this higgs stuff . the prize was a bottle of quality champagne . the winning explanation went something like this : suppose there 's a large cocktail party at the cern laboratory filled with particle physics researchers . this crowd of physicists represents the higgs field . if a tax collector entered the party , nobody would want to talk to them , and they could very easily cross the room to get to the bar . the tax collector would n't interact with the crowd in much the same way that some particles do n't interact with the higgs field . the particles that do n't interact , like photons for example , are called massless . now , suppose that peter higgs entered the same room , perhaps in search of a pint . in this case , the physicists will immediately crowd around higgs to discuss with him their efforts to measure the properties of his namesake boson . because he interacts strongly with the crowd , higgs will move slowly across the room . continuing our analogy , higgs has become a massive particle through his interactions with the field . so , if that 's the higgs field , how does the higgs boson fit into all of this ? let 's pretend our crowd of party goers is uniformly spread across the room . now suppose someone pops their head in the door to report a rumor of a discovery at some distant , rival laboratory . people near the door will hear the rumor , but people far away wo n't , so they 'll move closer to the door to ask . this will create a clump in the crowd . as people have heard the rumor , they will return to their original positions to discuss its implications , but people further away will then ask what 's going on . the result will be a clump in the crowd that moves across the room . this clump is analogous to the higgs boson . it is important to remember that it is not that massive particles interact more with the higgs field . in our analogy of the party , all particles are equal until they enter the room . both peter higgs and the tax collector have zero mass . it is the interaction with the crowd that causes them to gain mass . i 'll say that again . mass comes from interactions with a field . so , let 's recap . a particle gets more or less mass depending on how it interacts with a field , just like different people will move through the crowd at different speeds depending on their popularity . and the higgs boson is just a clump in the field , like a rumor crossing the room . of course , this analogy is just that -- an analogy , but it 's the best analogy anyone has come up with so far . so , that 's it . that 's what the higgs field and the higgs boson is all about . continuing research will tell us if we found it , and the reward will probably be more than just a bottle of champagne .

without a doubt , the most exciting scientific observation of 2012 was the discovery of a new particle at the cern laboratory that could be the higgs boson , a particle named after physicist peter higgs . the higgs field is thought to give mass to fundamental , subatomic particles like the quarks and leptons that make up ordinary matter . the higgs bosons are wiggles in the field , like the bump you see when you twitch a rope .

how does the higgs boson , which is thought to be a particle , differ from other familiar subatomic particles , like electrons and quarks ?

if you live on the east coast of the united states , you 've spent the last 17 years of your life walking , eating and sleeping above a dormant army of insects . these are the cicadas . every 17 years , billions of them emerge from the ground to do three things : molt , mate and die . there are 15 different broods of cicadas out there , grouped by when they 'll emerge from the ground . some of these broods are on a 13-year cycle , others are on a 17-year clock . either way , the cicadas live underground for most of their lives , feeding on the juices of plant roots . when it 's time to emerge , the adults begin to burrow their way out of the ground and up to the surface , where they 'll live for just a few weeks . during these weeks , though , everybody will know the cicadas have arrived . there will be billions of them . and they 're loud . male cicadas band together to call for female mates , and their collective chorus can reach up to 100 decibels -- as loud as a chain saw . in fact , if you happen to be using a chain saw or a lawn mower , male cicadas will flock to you , thinking that you 're one of them . now , like most things in nature , the cicadas do n't arrive without a posse . there are all sort of awesome and gross predators and parasites that come along with the buzzing bugs . take the fungus massospora for example . this little white fungus buries itself in the cicada 's abdomen and eats the bug alive , leaving behind its spores . when those spores rupture , they burst out of the still-alive cicada , turning the bug into a flying saltshaker of death , raining spores down upon its unsuspecting cicada neighbors . but while we know pretty precisely when the cicadas will arrive and fade away , we 're still not totally certain of why . there are certain advantages to having your entire species emerge at once , of course . the sheer number of cicadas coming out of the ground is so overwhelming to predators , it is essentially guaranteed that a few bugs will survive and reproduce . and since cicadas emerge every 13 or 17 years , longer than the lifespan of many of their predators , the animals that eat them do n't learn to depend on their availability . but why 13 and 17 years , instead of 16 or 18 or 12 ? well , that part no one really knows . it 's possible the number just happened by chance , or , perhaps , cicadas really love prime numbers . eventually , the cicadas will mate and slowly die off , their call fading into the distance . the eggs they lay will begin the cycle again , their cicada babies burrowing into the earth , feeding on plant juice , and waiting for their turn to darken the skies and fill the air with their songs . in 17 years , they 'll be ready . will you ?

if you live on the east coast of the united states , you 've spent the last 17 years of your life walking , eating and sleeping above a dormant army of insects . these are the cicadas . every 17 years , billions of them emerge from the ground to do three things : molt , mate and die .

what eats cicadas ?

translator : tom carter reviewer : bedirhan cinar we take a breath every few seconds . our life depends upon inhaling oxygen , but we never think about how we breathe . it just seems to happen automatically . how can something that seems so simple be the key to keeping us alive ? breathing starts with the environment around us . the air we breathe in , or inspire , has a mixture of gases including nitrogen , carbon dioxide and oxygen , which is the most important for our survival . it enters our body through the nose and mouth , moves down into the pharynx , trachea and bronchial tubes , and ultimately reaches the alveoli air sacs in the lungs . the alveoli use pressure to move oxygen and nutrients into the blood . the diaphragm and intercostal muscles are a pumping system that facilitates this air exchange . how you breathe affects your energy level , especially when you are under physical or emotional stress . think back to the last difficult test you had to take . it 's likely that as you became more nervous , the tension in your body increased , and your breathing quickly sped up . the shallower our breath , the less oxygen that reaches our brain , and the harder it is to focus . what 's our response to physical stress , like a fast-paced game of field hockey after school ? as we exert pressure on our bodies , the muscles require a great deal of energy and demand additional oxygen . our panting breath starts to kick in , which creates pressure to draw in more air and oxygen to the body , and regulates body temperature by allowing it to cool down naturally . these are n't the only times our breathing is affected or altered . think about the last time you got angry or emotional . anger creates a metabolic reaction in the body , which stresses it out and heats up our internal temperature . have you ever seen anyone lose their cool ? ultimately , if we 're breathing under stress over long periods of time , there are consequences . when the cells of a body are n't getting the oxygen they need , the nutrients available to the body decrease and toxins build up in the blood . it is thought that a hypoxic , or oxygen-poor environment , can increase cancerous cells . the good news is that we can control our breath much more than we realize . this means we can increase both the quality and quantity of the breath . the science of breathing has been around for thousands of years , from ancient yogis in india to respiratory therapists working with patients today . both would tell you that there are specific techniques that will help you improve your breathing . breathing is all about moving air from a higher-pressure to a lower-pressure environment . more breath means more oxygen , and ultimately a greater amount of nutrients that 's available for our cells and blood . we naturally do this when we let out a big sigh . changing the air pressure going into the lungs is one of the main ways to alter breathing . our body automatically does this when we cough , sneeze , or have the hiccups . here 's a simple experiment . close off your right nostril with your right thumb . breathe in and out just through the left nostril . notice how much harder it is to get the breath in . you have to focus your attention , and use your diaphragm and muscles much more than normal . by decreasing the surface area of the airways , you 're increasing the pressure of oxygen moving from the alveoli to the blood . yogis often practice alternate nostril breathing to slow down the breath , increase oxygen , and activate the body 's parasympathetic nervous system , which deals with the body 's operations when it 's at rest . let 's try another exercise . visualize the way a dog pants when it breathes . now try doing the same type of panting , first with your tongue out , then with your mouth closed . you will find yourself using your stomach muscles to push the air out as you exhale . place your hand under your nose , and you 'll feel the strength of the breath coming out . breathing this way is hard because it requires an active movement of our diaphragm and intercostal muscles . our body temperature changes quickly during this exercise from the amount of pressure we are exerting on our breath . it 's no surprise that you 'll find dogs doing this breath often to cool down on a hot day . when we sleep at night , the medulla center of the brain makes sure that we keep breathing . lucky for us we do n't have to think about it . during the day , our breath is much more vulnerable , especially under stressful or difficult situations . that 's why it 's helpful to pay attention to your breathing . if you can monitor and change your breath , you can improve both the quality and quantity of oxygen that enters your body . this lowers stress , increases energy , and strengthens your immune system . so the next time someone tells you to relax and take a deep breath , you 'll know exactly why .

breathing starts with the environment around us . the air we breathe in , or inspire , has a mixture of gases including nitrogen , carbon dioxide and oxygen , which is the most important for our survival . it enters our body through the nose and mouth , moves down into the pharynx , trachea and bronchial tubes , and ultimately reaches the alveoli air sacs in the lungs .

there is a lot of talk in the news about the earth ’ s atmosphere , and increases in carbon dioxide that may be causing global warming . how does the amount of carbon dioxide or oxygen in the air affect humans , or even animals and plants ? what are the health effects of breathing polluted air , and who is most vulnerable ?

the politics of 19th century europe were messy . ( what 's changed ? ) it was made up of various empires spreading across the world , trying to show each other who was the biggest power . they each built up massive armies to stave off war , thinking that everyone else would be too scared to fight against them , or so they thought ... things all changed when a gang of yugoslav nationalists who did n't like being part of austria-hungary shot the austro-hungarian archduke franz ferdinand while he was in sarajevo . swiftly the austro-hungarian empire declared war on serbia . russia came in to aid serbia , so germany decided to declare war on russia ! knowing that france would go to war with germany , germany decided to attack france quickly and invaded via neutral belgium and luxembourg and because of this , great britain stepped in to stop the germans getting any closer . it was a mess of allegiances and old rivalries with two sides forming the allies and the central powers . and so began what became known at the time as the great war ; the war to end all wars ! a new form of warfare evolved as these fully industrialized armies with engines , machine guns , airplanes and new chemical gas weapons fought against each other . it was the dawn of modern warfare . at the time , national pride was at an all-time high and men were proud to go off and fight for their country . it was seen as a romantic idea to go off and be a hero ! boys as young as 12 managed to lie their way into the army ranks only to discover that it was not such a sweet and honourable thing to die for one 's country ! germany marched on paris but was stopped by the french and both sides dug themselves into trenches in what became known as the western front . on the eastern front , the russians invaded austria-hungary but were stopped in eastern prussia by the germans . the ottoman empire joined in on the site of the central powers in 1914 . more and more nations from all over the world joined the fight as the war spread across europe . trench warfare was quite terrible . each army would dig a long network of trenches in the ground , fortifying the front with barbed wire and sandbags . i was a long stalemate where neither side dared advance on the other . machine guns were a new and very effective weapon . when the time was right , the army would climb up over the top and charge across no-man 's land to the enemy trench and capture it , thus gaining more land and taking another step towards their goal ! at least that was the plan ... spirits were high at least when the first christmas came by . both forces climbed out of their trenches to celebrate christmas together , talk , share stories and play football . when christmas ended , they would climb back into their trenches to become enemies once again . conditions in the trenches were dreadful . soldiers in france and belgium found their feet rotting away from the constant damp . in contrast , australian , new zealand and ottoman soldiers fighting in gallipoli had blisteringly hot trenches where rain and cold were replaced with dehydration and overheating . disease was everywhere in the trenches . 1916 saw a renewed push on the western front from both sides . thousands of french died at verdun as the germans unleashed their chlorine gas . the infamous battle of the somme was a long and grueling battle that lasted from july to november . the first day alone saw over 80,000 men wounded or killed ; mostly british , due to disastrous attacks . fundamental errors and contradictions from the high command led to confusion and unclear plans . in places , soldiers were n't organized in time to charge so by the time that they got going , the artillery had stopped firing on the germans , allowing them to easily fire upon their attackers . planes and artillery were supposed to clear the german barbed wire , but the shrapnel was ineffective against the wire . when the order came to go over the top , thousands of men ran out to their death to be caught on the barbed wire and picked off one by one by the german machine guns . this battle saw the first use of tanks by the british . ultimately , france and britain pushed against germany and gained much ground . by christmas 1916 , no man wanted good cheer wished upon their faceless enemy . during 1916 also , before the somme , irish republicans staged an uprising in dublin in the hopes to catch britain while they were distracted by the war . it was crushed by britain but after executing the rebel leaders irish support for britain and the war dropped , at least in the south of ireland . most irish troops after that came from the protestant north . on the sea britain mined many patches of international water to stop movement of german ships . germany was blockaded . after many naval battles , britain tried to stay in control of the seas , above the water at least ! germany were on the attack with the u-boat submarines adding a new dimension to naval warfare ; they could attack without warning ! they sank many ships including the ship the lusitania and because this broke loads of war rules , it ultimately influenced the united states of america to enter the war ... two years later ! the british pushed up through the arabian peninsula with t.e . lawrence aka lawrence of arabia helping to organize the arab revolt against the ottoman empire . in 1917 , the russians had a series of revolutions . in the february revolution , the tsars were gotten rid of , but russia remained in the war , and the october revolution , the bolsheviks took control and brought power to the people and sowed the seeds for communism in russia . the russians signed a treaty with germany and pulled out of the war causing an initial difficulty for the enemies of the central powers . the allies however became refreshed with reinforcements from the united states of america who eventually decided to enter the war in 1917 after germany tried to convince mexico to attack them . germany made a fierce and effective push before the allies could use their advantage . however , american troops continued to arrive in such great numbers that germany 's army could n't last any longer . the allies pushed up from italy , the balkans , and the middle east putting austria-hungary , bulgaria and the ottoman empire out of the war . as the allies advanced the western front , germany called for an armistice to stop the fighting , bringing victory to the allies and an end to the war . the fighting stopped on the 11th hour of the 11th day of the 11th month , 1918 . it took six months to negotiate terms and it was ultimately decided that the central powers were to pay for the damages they had caused in the war . germany only fully paid off this debt in 2010 . the map of europe was redrawn . soldiers who made it home again were changed men . they were haunted by the horrors which they had seen in the trenches . gas attacks , friends dying by their side , and the constant shelling of enemy artillery ; they were shell-shocked and so many found it impossible to go back to normal life after the trenches . many great poets and writers were inspired by their hell in the trenches such as wilfred owen , jrr tolkien and ernest hemingway of the so-called lost generation ? some survived , many did not . the world was a changed place after the world war . people had seen the death and destruction that could be dealt by mankind . the men who left to become heroes came back scarred , or worse never returned at all . the poppy is used to remember the millions who died in this war as it was just about the only flower to grow in the carnage-ridden wasteland between the trenches . the world was now a darker place . people hoped that it would indeed be the war to end all wars ! unfortunately , they were mistaken ... if you liked this video , please subscribe and you can follow me on twitter at @ johndruddy or find me on facebook through manny man comic and john d ruddy artisty actory guy and if you want to find out more about world war one and also the easter rising of 1916 i 'll be doing an irish tour of the play the rising by joe o ' byrne where we tell the story of the easter rising through the eyes of two friendly foes . billy mckeague , a loyalist from belfast and paddy o'brien , a republican from dublin . the dates are up here and you can find out more on facebook . thanks so much for the support glad you enjoy it !

germany marched on paris but was stopped by the french and both sides dug themselves into trenches in what became known as the western front . on the eastern front , the russians invaded austria-hungary but were stopped in eastern prussia by the germans . the ottoman empire joined in on the site of the central powers in 1914 .

name the man from austria-hungary who was assassinated , marking the beginning of wwi .

in 1997 , in a game between france and brazil , a young brazilian player named roberto carlos set up for a 35 meter free kick . with no direct line to the goal , carlos decided to attempt the seemingly impossible . his kick sent the ball flying wide of the players , but just before going out of bounds , it hooked to the left and soared into the goal . according to newton 's first law of motion , an object will move in the same direction and velocity until a force is applied on it . when carlos kicked the ball , he gave it direction and velocity , but what force made the ball swerve and score one of the most magnificent goals in the history of the sport ? the trick was in the spin . carlos placed his kick at the lower right corner of the ball , sending it high and to the right , but also rotating around its axis . the ball started its flight in an apparently direct route , with air flowing on both sides and slowing it down . on one side , the air moved in the opposite direction to the ball 's spin , causing increased pressure , while on the other side , the air moved in the same direction as the spin , creating an area of lower pressure . that difference made the ball curve towards the lower pressure zone . this phenomenon is called the magnus effect . this type of kick , often referred to as a banana kick , is attempted regularly , and it is one of the elements that makes the beautiful game beautiful . but curving the ball with the precision needed to both bend around the wall and back into the goal is difficult . too high and it soars over the goal . too low and it hits the ground before curving . too wide and it never reaches the goal . not wide enough and the defenders intercept it . too slow and it hooks too early , or not at all . too fast and it hooks too late . the same physics make it possible to score another apparently impossible goal , an unassisted corner kick . the magnus effect was first documented by sir isaac newton after he noticed it while playing a game of tennis back in 1670 . it also applies to golf balls , frisbees and baseballs . in every case , the same thing happens . the ball 's spin creates a pressure differential in the surrounding air flow that curves it in the direction of the spin . and here 's a question . could you theoretically kick a ball hard enough to make it boomerang all the way around back to you ? sadly , no . even if the ball did n't disintegrate on impact , or hit any obstacles , as the air slowed it , the angle of its deflection would increase , causing it to spiral into smaller and smaller circles until finally stopping . and just to get that spiral , you 'd have to make the ball spin over 15 times faster than carlos 's immortal kick . so good luck with that .

on one side , the air moved in the opposite direction to the ball 's spin , causing increased pressure , while on the other side , the air moved in the same direction as the spin , creating an area of lower pressure . that difference made the ball curve towards the lower pressure zone . this phenomenon is called the magnus effect .

what causes the ball to curve ?

most people will take a pill , receive an injection , or otherwise take some kind of medicine during their lives , but most of us do n't know anything about how these substances actually work . how can various compounds impact the way we physically feel , think , and even behave ? for the most part , this depends on how a drug alters the communication between cells in the brain . there are a number of different ways that can happen . but before it gets into the brain , any drug must first reach the bloodstream on a journey that can take anywhere from seconds to hours , depending on factors like how it 's administered . the slowest method is to take a drug orally because it must be absorbed by our digestive system before it takes effect . inhaling a drug gets it into the bloodstream faster . and injecting a drug intravenously works quickly too because it pumps the chemicals directly into the blood . once there , the drug quickly reaches the gates of its destination , the brain . the entrance to this organ is guarded by the blood-brain barrier , which separates blood from the nervous system to keep potentially dangerous substances out . so all drugs must have a specific chemical composition which gives them the key to unlock this barrier and pass through . once inside , drugs start to interfere with the brain 's normal functioning by targeting its web of neurons and synapses . neurons are brain cells that have a nucleus , dendrites , and an axon . synapses are structures placed along the dendrites or the axon which allow the exchange of electrochemical signals between neurons . those signals take the form of chemicals called neurotransmitters . each neurotransmitter plays different roles in regulating our behaviors , emotions , and cognition . but they all work in one of two ways . they can either inhibit the receiving neuron , limiting its activity , or excite it , creating a new electrochemical signal that spreads throughout the network . any leftover neurotransmitter usually gets degraded or reabsorbed into the transmitting neuron . a drug 's effectiveness stems from its ability to manipulate these synaptic transmissions at different phases of the process . that results in an increase or a decrease in the amount of neurotransmitters being spread . for instance , common antidepressants , like ssris , stop the reabsorption of serotonin , a neurotransmitter that modulates our moods . this effectively pushes more of it into the neural network . meanwhile , painkillers , like morphine , raise levels of serotonin and noradrenaline , which regulate energy , arousal , alertness , and pleasure . those same neurotransmitters also affect endorphin receptors , reducing pain perception . and tranquilizers works by increasing the production of gaba to inhibit neural activity putting the person in a relaxed or sedated state . what about illegal or elicit drugs ? these have powerful impacts on the brain that we 're still trying to understand . crystal meth , an amphetamine , induces a long-lasting release of dopamine , a neurotransmitter linked with the perception of reward and pleasure . it also activates noradrenaline receptors , which increases the heart rate , dilates pupils , and triggers the body 's fight or flight response . cocaine blocks the reuptake of dopamine and serotonin , pushing more into the network where they boost energy , create feelings of euphoria , and suppress appetites . and hallucinogenic drugs have some of the most puzzling effects . substances like lsd , mescaline , and dmt all block the release of serotonin , which regulates mood and impulsivity . they also have an impact on the neural circuits involved in perception , learning , and behavioral regulation , which may explain why these drugs have such powerful impacts . even if some of these effects sound exciting , there are reasons why some of these drugs are highly controlled and often illegal . drugs have the power to alter the brain 's chemistry , and repeated use can permanently rewire the neural networks that support our ability to think , make decisions , learn , and remember things . there 's a lot we still do n't know about drugs and their effects , both the good and the bad . but those we do know about are the ones we 've studied closely , and turned into effective medicines . as our knowledge grows about drugs and the brain , the possibilities will also increase for treating the many medical problems that puzzle researchers today .

the slowest method is to take a drug orally because it must be absorbed by our digestive system before it takes effect . inhaling a drug gets it into the bloodstream faster . and injecting a drug intravenously works quickly too because it pumps the chemicals directly into the blood .

which of the following is the quickest way for a drug to reach the bloodstream ?

so here we have a sample of cobalt . now i have got lots and lots of different samples of cobalt in my drawer , so this is cobalt sponge . cobalt is , in many ways , similar to iron . it can form magnets . so this cobalt has been generated from a solution and it ’ s been made in very , very finely dispersed so it has a very large surface area . it ’ s very good for doing catalytic reactions . the magnets that you use in colour televisions , for the loud speakers , contain cobalt . you need to use cobalt in the magnets in the colour television or the old sort of colour television not the ones with lcd screens because the magnetic fields from larger magnets could affect the electron guns and so spoil the colours so you need a very small magnet on your loud speaker or the colours all go funny . cobalt sponge absorbs lots and lots of gas for perhaps hydrogenation . many years ago , in the 1970s , when there was a civil war in africa in the region katanga where cobalt is mined , there was a shortage of cobalt and the production of colour televisions stopped for some considerable time until the production restarted . so you can see it flows in the bottle . so i have another sample of cobalt and that is simply a foil . so again that is a very nice malleable tin-type foil ; very , very good structures .

cobalt sponge absorbs lots and lots of gas for perhaps hydrogenation . many years ago , in the 1970s , when there was a civil war in africa in the region katanga where cobalt is mined , there was a shortage of cobalt and the production of colour televisions stopped for some considerable time until the production restarted . so you can see it flows in the bottle .

why did a civil war in the area of katanga ( africa ) affect the world production of televisions in the 1970s ?

translator : jenny zurawell one of the funny things about owning a brain is that you have no control over the things that it gathers and holds onto , the facts and the stories . and as you get older , it only gets worse . things stick around for years sometimes before you understand why you 're interested in them , before you understand their import to you . here 's three of mine . when richard feynman was a young boy in queens , he went for a walk with his dad and his wagon and a ball . he noticed that when he pulled the wagon , the ball went to the back of the wagon . he asked his dad , `` why does the ball go to the back of the wagon ? '' and his dad said , `` that 's inertia . '' he said , `` what 's inertia ? '' and his dad said , `` ah . inertia is the name that scientists give to the phenomenon of the ball going to the back of the wagon . '' ( laughter ) `` but in truth , nobody really knows . '' feynman went on to earn degrees at mit , princeton , he solved the challenger disaster , he ended up winning the nobel prize in physics for his feynman diagrams , describing the movement of subatomic particles . and he credits that conversation with his father as giving him a sense that the simplest questions could carry you out to the edge of human knowledge , and that that 's where he wanted to play . and play he did . eratosthenes was the third librarian at the great library of alexandria , and he made many contributions to science . but the one he is most remembered for began in a letter that he received as the librarian , from the town of swenet , which was south of alexandria . the letter included this fact that stuck in eratosthenes ' mind , and the fact was that the writer said , at noon on the solstice , when he looked down this deep well , he could see his reflection at the bottom , and he could also see that his head was blocking the sun . i should tell you -- the idea that christopher columbus discovered that the world is spherical is total bull . it 's not true at all . in fact , everyone who was educated understood that the world was spherical since aristotle 's time . aristotle had proved it with a simple observation . he noticed that every time you saw the earth 's shadow on the moon , it was circular , and the only shape that constantly creates a circular shadow is a sphere , q.e.d . the earth is round . but nobody knew how big it was until eratosthenes got this letter with this fact . so he understood that the sun was directly above the city of swenet , because looking down a well , it was a straight line all the way down the well , right past the guy 's head up to the sun . eratosthenes knew another fact . he knew that a stick stuck in the ground in alexandria at the same time and the same day , at noon , the sun 's zenith , on the solstice , the sun cast a shadow that showed that it was 7.2 degrees off-axis . if you know the circumference of a circle , and you have two points on it , all you need to know is the distance between those two points , and you can extrapolate the circumference . 360 degrees divided by 7.2 equals 50 . i know it 's a little bit of a round number , and it makes me suspicious of this story too , but it 's a good story , so we 'll continue with it . he needed to know the distance between swenet and alexandria , which is good because eratosthenes was good at geography . in fact , he invented the word geography . ( laughter ) the road between swenet and alexandria was a road of commerce , and commerce needed to know how long it took to get there . it needed to know the exact distance , so he knew very precisely that the distance between the two cities was 500 miles . multiply that times 50 , you get 25,000 , which is within one percent of the actual diameter of the earth . he did this 2,200 years ago . now , we live in an age where multi-billion-dollar pieces of machinery are looking for the higgs boson . we 're discovering particles that may travel faster than the speed of light , and all of these discoveries are made possible by technology that 's been developed in the last few decades . but for most of human history , we had to discover these things using our eyes and our ears and our minds . armand fizeau was an experimental physicist in paris . his specialty was actually refining and confirming other people 's results , and this might sound like a bit of an also-ran , but in fact , this is the soul of science , because there is no such thing as a fact that can not be independently corroborated . and he was familiar with galileo 's experiments in trying to determine whether or not light had a speed . galileo had worked out this really wonderful experiment where he and his assistant had a lamp , each one of them was holding a lamp . galileo would open his lamp , and his assistant would open his . they got the timing down really good . they just knew their timing . and then they stood at two hilltops , two miles distant , and they did the same thing , on the assumption from galileo that if light had a discernible speed , he 'd notice a delay in the light coming back from his assistant 's lamp . but light was too fast for galileo . he was off by several orders of magnitude when he assumed that light was roughly ten times as fast as the speed of sound . fizeau was aware of this experiment . he lived in paris , and he set up two experimental stations , roughly 5.5 miles distant , in paris . and he solved this problem of galileo 's , and he did it with a really relatively trivial piece of equipment . he did it with one of these . i 'm going to put away the clicker for a second because i want to engage your brains in this . so this is a toothed wheel . it 's got a bunch of notches and it 's got a bunch of teeth . this was fizeau 's solution to sending discrete pulses of light . he put a beam behind one of these notches . if i point a beam through this notch at a mirror , five miles away , that beam is bouncing off the mirror and coming back to me through this notch . but something interesting happens as he spins the wheel faster . he notices that it seems like a door is starting to close on the light beam that 's coming back to his eye . why is that ? it 's because the pulse of light is not coming back through the same notch . it 's actually hitting a tooth . and he spins the wheel fast enough and he fully occludes the light . and then , based on the distance between the two stations and the speed of his wheel and the number of notches in the wheel , he calculates the speed of light to within two percent of its actual value . and he does this in 1849 . this is what really gets me going about science . whenever i 'm having trouble understanding a concept , i go back and i research the people that discovered that concept . i look at the story of how they came to understand it . what happens when you look at what the discoverers were thinking about when they made their discoveries , is you understand that they are not so different from us . we are all bags of meat and water . we all start with the same tools . i love the idea that different branches of science are called fields of study . most people think of science as a closed , black box , when in fact it is an open field . and we are all explorers . the people that made these discoveries just thought a little bit harder about what they were looking at , and they were a little bit more curious . and their curiosity changed the way people thought about the world , and thus it changed the world . they changed the world , and so can you . thank you . ( applause )

what happens when you look at what the discoverers were thinking about when they made their discoveries , is you understand that they are not so different from us . we are all bags of meat and water . we all start with the same tools .

savage says , “ we ’ re all bags of meat and water ” and that “ we all start with the same tools. ” scientists like feynman , eratosthenes and fizeau , he argues , just think a little harder about a question and are a little more curious . do you agree with savage that scientists are basically the same as anybody else ? what other personality traits or habits of mind would be helpful to a scientist , in your opinion ?

hi , i ’ m john green , and this is crash course world history . let ’ s begin today with a question . why am i alive ? also , why don ’ t i have any eyes ? ah , that ’ s better . the way we answer that question ends up organizing all kinds of other thoughts , like what we should value , and how we should behave , and if we should eat meat , and whether we should dump that boy who is very nice , but insanely clingy , in a way that he can not possibly think is attractive . all of which adds up- uh , mr. green , mr. green , uh , are you talking about me ? yes , i ’ m talking about you , me from the past . i ’ m telling you that one of the reasons we study history is so that you can be a less terrible boyfriend , but more on that momentarily . [ theme music ] today we ’ re going to talk about civilizations , but in order to do that , we have to talk about talking about civilizations , because it ’ s a problematic word . so problematic , in fact , that i have to turn to camera 2 to discuss it . certain conglomerations of humans are seen as civilizations , whereas , say , nomadic cultures generally aren ’ t , unless , you are -- say it with me -- the mongols by calling some groups civilizations , you imply that all other social orders are uncivilized , which is basically just another way of saying that they ’ re savages or barbarians . side note : originally greek , the word barbarian denoted anyone who did not speak ancient greek , because to the greeks , all other languages sounded like bar bar bar bar bar bar . so , that is to say that we are all essentially barbarians , except for the classics majors , which is worth remembering when we ’ re discussing civilizations . civilizations are like most of the things we like to study , they ’ re intellectual constructs . no one woke up in the city of thebe ’ s in egypt one morning and said , “ what a beautiful morning , i sure am living at the height of egyptian civilization. ” still , they ’ re useful constructs , particularly when you ’ re comparing one civilization to another . they ’ re less useful when you ’ re comparing a civilization to a non-civilization type social order , which is why we will try to avoid that . and yes , i am getting to the good boyfriend stuff . patience , grasshopper . so what is a civilization ? well , diagnosing a civilization is a little like like diagnosing an illness . if you have four or more of the following symptoms , you might be a civilization . surplus production . once one person can make enough food to feed several people , it becomes possible to build a city , another symptom of civilization . it also leads to the specialization of labor , which in turn leads to trade . like , if everybody picks berries for a living , there ’ s no reason to trade , because i have berries , and you have berries , but if i pick berries for a living and you make hammers , suddenly , we have cause to trade . civilizations are also usually associated with social stratification , centralized government , shared values , generally in the form of religion , and writing . and at least in the early days , they were almost always associated with rivers . these days you can just bisect a segment of land horizontally and vertically , and boom , build a city . but 5000 years ago , civilizations were almost always associated with rivers . whether that ’ s the tigris and euphrates , the yellow river , the nile , the amazon basin , the coatzacoalcos - gaaah ! i was doing so good until i got to coatzacoalcos ! ( computer says : coatzacoalcos ) coatzacoalcos . maybe . why river valleys ? they ’ re flat , they ’ re well watered , and when they flood , they deposit nutrient-rich silt . we ’ ll have more to say about most of these civilizations later , but let ’ s talk about this guy , the indus valley civilization , ‘ cause it ’ s my all time favorite . the indus valley civilization was located in the flood plain of the indus and sarawati rivers , and it was about the best place in the world to have an ancient civilization because the rivers flooded very reliably twice a year , which meant that it had the most available calories per acre of pretty much anywhere on the planet . we know the indus valley civilization flourished a long time ago . probably around 3000 bce . why is that question literally hanging over my head ? but people of the indus valley were trading with mesopotamians as early as 3500 bce . we also know that it was the largest of the ancient civilizations . archaeologists have discovered more than 1500 sites . so what do we know about this civilization ? let ’ s go to the thought bubble . everything we know about the indus valley civilization comes from archaeology , because while they did use written language , we don ’ t know how to read it , and no rosetta stone has thus appeared to help us learn it . i meant the other rosetta stone , thought bubble , yeah . although , come to think of it , either would be acceptable . so here ’ s what we know , they had amazing cities . harappa and mohenjo daro are the best known , with dense , multi-story homes constructed out of uniformly sized bricks along perpendicular streets . i mean this wasn ’ t some ancient world version of houston , more like chicago . this means they must have had some form of government and zoning , but we don ’ t know what gave this government its authority . cities were oriented to catch the wind and provide a natural form of air conditioning . and they were clean . most homes were connected to a centralized drainage system that used gravity to carry waste and water out of the city in big sewer ditches that ran under the main avenues , a plumbing system that would have been the envy of many 18th century european cities . also , in mohenjo daro , the largest public building was not a temple or a palace , but a public bath , which historians call the great bath . we don ’ t know what the great bath was used for , but since later indian culture placed a huge emphasis on ritual purity , which is the basis for the caste system , some historians have speculated that the bath might have been like a giant baptismal pool . also , they traded . one of the coolest things that the indus valley civilization produced were seals used as identification markers on goods and clay tablets . these seals contained the writing that we still can ’ t decipher , and a number of fantastic designs , many featuring animals and monsters . one of the most famous and frightening is of a man with what looks like water buffalo horns on his head , sitting cross-legged between a tiger and a bull . we don ’ t know what ’ s really going on here , but it ’ s safe to say that this was a powerful dude , because he seems to be able to control the tiger . how do these seals let us know that they traded ? well , because we found them in mesopotamia , not the indus valley . plus , archaeologists have found stuff like bronze in the indus valley that is not native to the region . so what did they trade ? cotton cloth . still such a fascinating export , incidentally that it will be the subject of the 40th and final video in this very series . but here ’ s the most amazing thing about the indus valley people . they were peaceful . despite archaeologists finding 1500 sites , they have found very little evidence of warfare , almost no weapons . thanks thought bubble . ok , before we talk about the fascinating demise of the indus valley civilization . it ’ s time for the open letter . magic ! i wonder what the secret compartment has for me today ? oh ! fancy clothes . i guess the secret compartment didn ’ t think i was dressed up enough for the occasion . an open letter to historians . dear historians , the great bath ? really ? the great bath ? i ’ m trying to make history fascinating , and you give me a term that evokes scented candles , bath salts and frederic fekkai hair products ? i know sometimes the crushingly boring names of history aren ’ t your fault . you didn ’ t name the federalist papers or the austro-hungarian empire or adam smith . but when you do get a chance to name something , you go with the great bath ? not the epic bath of mohenjo daro , or the bath to end all baths , or the pool that ruled , or the moist mystery of mohenjo daro or the wet wonder ? the great bath ? really ? you can do better . best wishes , john green . so what happened to these people ? well , here ’ s what didn ’ t happen to them . they didn ’ t morph into the current residents of that area of the world , hindu indians or muslim pakistanis . those people probably came from the caucasus . instead , sometime around 1750 bce , the indus valley civilization declined until it faded into obscurity . why ? historians have three theories . one : conquest ! turns out to be a terrible military strategy not to have any weapons , and it ’ s possible people from the indus valley were completely overrun by people from the caucasus . two : environmental disaster ! it ’ s possible they brought about their own end by destroying their environment . three : earthquake ! the most interesting theory is that a massive earthquake changed the course of the rivers so much that a lot of the tributaries dried up . without adequate water supplies for irrigation , the cities couldn ’ t sustain themselves , so people literally picked up and headed for greener pastures . well , probably not pastures , it ’ s unlikely they became nomads . they probably just moved to a different plain an continued their agricultural ways . i am already boring you and i haven ’ t even told you yet how to be a better boyfriend and/or girlfriend . i ’ m going to do that now . so we don ’ t know why the indus valley civilization ended , but we also don ’ t really know why it started . why did these people build cities , and dig swimming pools , and make unnecessarily ornate seals ? were they motivated by hunger , fear , a desire for companionship , the need to be near their sacred spaces , or a general feeling that city life was just more awesome than foraging ? thinking about what motivated them to structure their life as they did helps us to think about how we structure our own lives . in short , you ’ re clingy because you ’ re motivated by fear and a need for companionship , and she finds it annoying because it ’ s enough work having to be responsible for herself without having to also be responsible for you . also , you ’ re not really helping her by clinging , and from the indus valley in the bronze age , to school life today , human life is all about collaboration . trading cloth for bronze , building cities together , and collaborating to make sure that human lives are tilted to catch the wind . next week we will travel here to discuss the hot mess o ’ potamia , but in the meantime , if you have any questions , leave them in comments , and our team of semi-trained semi-professionals will do their best to answer them . also , you ’ ll find some suggested resources in the video info below , he said , pointing at his pants . thanks for watching , and we ’ ll see you next week !

best wishes , john green . so what happened to these people ? well , here ’ s what didn ’ t happen to them .

except for the coast , there are only a few narrow passes through the mountains , such as the khyber pass , that have allowed people to enter this land . in which mountain range was this pass located ?

when the infamous fictional character , carrie white , left her high school prom hall ablaze , and brought terror upon her town , she relied on her powers of telekinesis , the ability to manipulate physical objects using the power of the mind alone . but while carrie is just a fictional film based upon a fictional book , belief in telekinesis is n't fictional at all . for centuries , humans have claimed they really do have the power to control the motion of objects using only their minds . levitation , opening doors at will and spoon bending are all intriguing examples . it happens in the matrix when neo freezes bullets midair , and it 's a skill that yoda has honed to a t. but is telekinesis real , or just as fictional as carrie , yoda and neo combined ? to investigate , we need to evaluate telekinetic claims through a scientific lens using the scientific method . telekinesis is part of the discipline called parapsychology , in which researchers study psychic phenomena . parapsychologists regard what they do as a science , but other scientists disagree . let 's start with a few basic observations . observation # 1 : while there are loads of anecdotes out there about telekinesis , there 's no scientific proof that it exists ; no studies conducted according to the scientific method and repeated under lab conditions can show that its real . in the 1930s , the so-called father of parapsychology , joseph banks rhine , tested in the lab whether people could use telekinesis to make a dice roll the way they wanted it to . but afterwards , scientists could n't replicate his results , and since replication is key to proving an idea , that was a problem . aside from scientists , there are also countless self-proclaimed telekinetics , but all have been exposed as tricksters , or ca n't perform under conditions where they 're not totally in control , suggesting that they manipulate the situation to get the results they want . today , there 's even a huge stash of prize money available from lots of organizations for anyone who can prove that psychic abilities , like telekinesis , are real . but these riches remain unclaimed . observation # 2 : when we investigate telekinesis , there 's no consensus about what exactly is being measured . are powerful , yoda-like brainwaves at work perhaps ? since nobody agrees , it 's difficult to apply a research standard , something required in all other types of science to test the validity of ideas . observation # 3 : the point of science is to discover the unknown , and in the history of scientific investigation , it 's definitely happened that new discoveries have gone against established science , and even overturned whole branches of science . such discoveries must be proven extra carefully to withstand skepticism . in the case of telekinesis , the idea goes against established science , but lacks the powerful evidence in favor of it . our universe is controlled and explained by the laws of physics , and one of these laws tells us that brain waves ca n't control objects because they 're neither strong nor far-reaching enough to influence anything outside of our skulls . physics also tells us that the only forces that can influence objects from afar are magnetic and gravitational . probably the closest thing to telekinesis that science can explain is the use of thoughts to control a robotic arm . in the brains of stroke patients who ca n't move , researchers can implant tiny wires into the region that controls movement , and then train the patient to concentrate on moving a robotic arm , which acts like an extension of their minds , and it works . it 's amazing , but it is n't telekinesis . the patients thoughts are n't just vague , undetectable things . they 're measurable brain signals , translated through wires into a robot . science can measure , test and explain the motion , and that 's how we 've shown that this kind of mind control is real . science is a slow process of accumulating the evidence that either stands for or against an idea . when we stack up evidence , we can see which tower grows tallest , and in the case of telekinesis , it 's not the tower showing that it exists . some say this mystical phenomenon ca n't fit within the confines of science , and that 's okay . but then telekinesis becomes purely a matter of personal conviction . if something ca n't be assessed scientifically , then it ca n't be described as scientific either . so the results of our investigation reveal that however much we may want to believe that the force really is within us , the case for telekinesis remains weak . sorry neo , carrie and yoda . your skills are mind-blowing , but for now , they belong in the movies .

observation # 1 : while there are loads of anecdotes out there about telekinesis , there 's no scientific proof that it exists ; no studies conducted according to the scientific method and repeated under lab conditions can show that its real . in the 1930s , the so-called father of parapsychology , joseph banks rhine , tested in the lab whether people could use telekinesis to make a dice roll the way they wanted it to . but afterwards , scientists could n't replicate his results , and since replication is key to proving an idea , that was a problem .

to make telekinesis happen , telekinetics say they use :

deep inside yale university 's beinecke rare book and manuscript library lies the only copy of a 240-page tome . recently carbon dated to around 1420 , its vellum pages features looping handwriting and hand-drawn images seemingly stolen from a dream . real and imaginary plants , floating castles , bathing women , astrology diagrams , zodiac rings , and suns and moons with faces accompany the text . this 24x16 centimeter book is called the voynich manuscript , and its one of history 's biggest unsolved mysteries . the reason why ? no one can figure out what it says . the name comes from wilfrid voynich , a polish bookseller who came across the document at a jesuit college in italy in 1912 . he was puzzled . who wrote it ? where was it made ? what do these bizarre words and vibrant drawings represent ? what secrets do its pages contain ? he purchased the manuscript from the cash-strapped priest at the college , and eventually brought it to the u.s. , where experts have continued to puzzle over it for more than a century . cryptologists say the writing has all the characteristics of a real language , just one that no one 's ever seen before . what makes it seem real is that in actual languages , letters and groups of letters appear with consistent frequencies , and the language in the voynich manuscript has patterns you would n't find from a random letter generator . other than that , we know little more than what we can see . the letters are varied in style and height . some are borrowed from other scripts , but many are unique . the taller letters have been named gallows characters . the manuscript is highly decorated throughout with scroll-like embellishments . it appears to be written by two or more hands , with the painting done by yet another party . over the years , three main theories about the manuscript 's text have emerged . the first is that it 's written in cypher , a secret code deliberately designed to hide secret meaning . the second is that the document is a hoax written in gibberish to make money off a gullible buyer . some speculate the author was a medieval con man . others , that it was voynich himself . the third theory is that the manuscript is written in an actual language , but in an unknown script . perhaps medieval scholars were attempting to create an alphabet for a language that was spoken but not yet written . in that case , the voynich manuscript might be like the rongorongo script invented on easter island , now unreadable after the culture that made it collapsed . though no one can read the voynich manuscript , that has n't stopped people from guessing what it might say . those who believe the manuscript was an attempt to create a new form of written language speculate that it might be an encyclopedia containing the knowledge of the culture that produced it . others believe it was written by the 13th century philosopher roger bacon , who attempted to understand the universal laws of grammar , or in the 16th century by the elizabethan mystic john dee , who practiced alchemy and divination . more fringe theories that the book was written by a coven of italian witches , or even by martians . after 100 years of frustration , scientists have recently shed a little light on the mystery . the first breakthrough was the carbon dating . also , contemporary historians have traced the provenance of the manuscript back through rome and prague to as early as 1612 , when it was perhaps passed from holy roman emperor rudolf ii to his physician , jacobus sinapius . in addition to these historical breakthroughs , linguistic researchers recently proposed the provisional identification of a few of the manuscript 's words . could the letters beside these seven stars spell tauran , a name for taurus , a constellation that includes the seven stars called the pleiades ? could this word be centaurun for the centaurea plant in the picture ? perhaps , but progress is slow . if we can crack its code , what might we find ? the dream journal of a 15th-century illustrator ? a bunch of nonsense ? or the lost knowledge of a forgotten culture ? what do you think it is ?

real and imaginary plants , floating castles , bathing women , astrology diagrams , zodiac rings , and suns and moons with faces accompany the text . this 24x16 centimeter book is called the voynich manuscript , and its one of history 's biggest unsolved mysteries . the reason why ?

what do you think was the original purpose of the voynich manuscript ?

translator : andrea mcdonough reviewer : bedirhan cinar deep in the jungles of vietnam , soldiers from both sides battled heat exhaustion and each other for nearly 20 long years . but the key to communist victory was n't weapons or stamina , it was a dirt road . the ho chi minh trail , winding through vietnam , laos , and cambodia , started as a simple network of dirt roads and blossomed into the centerpiece of the winning north vietnamese strategy during the vietnam war , supplying weapons , troops , and psychological support to the south . the trail was a network of tracks , dirt roads , and river crossings that threaded west out of north vietnam and south along the truong son mountain range between vietnam and laos . the journey to the south originally took six months . but , with engineering and ingenuity , the vietnamese expanded and improved the trail . towards the end of war , as the main roads detoured through laos , it only took one week . here is how it happened . in 1959 , as relations deteriorated between the north and the south , a system of trails was constructed in order to infiltrate soldiers , weapons , and supplies into south vietnam . the first troops moved in single-file along routes used by local ethnic groups , and broken tree branches at dusty crossroads were often all that indicated the direction . initially , most of the communist cadres who came down the trail were southerners by birth who had trained in north vietnam . they dressed like civilian peasants in black , silk pajamas with a checkered scarf . they wore ho chi minh sandals on their feet , cut from truck tires , and carried their ration of cooked rice in elephants ' intestines , a linen tube hung around the body . the conditions were harsh and many deaths were caused by exposure , malaria , and amoebic dysentery . getting lost , starving to death , and the possibility of attacks by wild tigers or bears were constant threats . meals were invariably just rice and salt , and it was easy to run out . fear , boredom , and homesickness were the dominant emotions . and soldiers occupied their spare time by writing letters , drawing sketches , and drinking and smoking with local villagers . the first troops down the trail did not engage in much fighting . and after an exhausting six month trip , arriving in the south was a real highlight , often celebrated by bursting into song . by 1965 , the trip down the trail could be made by truck . thousands of trucks supplied by china and russia took up the task amidst ferocious b-52 bombing and truck drivers became known as pilots of the ground . as traffic down the trail increased , so did the u.s. bombing . they drove at night or in the early morning to avoid air strikes , and watchmen were ready to warn drivers of enemy aircraft . villages along the trail organized teams to guarantee traffic flow and to help drivers repair damage caused by air attacks . their catch cries were , `` everything for our southern brothers ! '' and , `` we will not worry about our houses if the vehicles have not yet gotten through . '' some families donated their doors and wooden beds to repair roads . vietnamese forces even used deception to get the u.s. aircraft to bomb mountainsides in order to make gravel for use in building and maintaining roads . the all-pervading red dust seeped into every nook and cranny . the ho chi minh trail had a profound impact on the vietnam war and it was the key to hanoi 's success . north vietnamese victory was not determined by the battlefields , but by the trail , which was the political , strategic , and economic lynchpin . americans recognized its achievement , calling the trail , `` one of the great achievements in military engineering of the 20th century . '' the trail is a testimony to the strength of will of the vietnamese people , and the men and women who used the trail have become folk heros .

the all-pervading red dust seeped into every nook and cranny . the ho chi minh trail had a profound impact on the vietnam war and it was the key to hanoi 's success . north vietnamese victory was not determined by the battlefields , but by the trail , which was the political , strategic , and economic lynchpin .

from bombs to homesickness , travelers on the ho chi minh trail had to face many challenges . which do you think was the most difficult ? why ?

[ pbs intro ] this episode is supported by 23 and me a long time ago a guy built a tomb out of rocks so he could live in it after he died and not be dead . his son was like “ hey that ’ s cool ” so he built one too.. then his son was like “ me too ” so he made a third and they were all buried there . and that ’ s how we got this . the pyramids of giza . how did people who hadn ’ t even invented the wheel build these things , and… why ? they ’ re so big ! they ’ re so precise ! they ’ re so directionally oriented ! they ’ re so mysterrrrrrious . at first glance they really do look out-of-this world . thing is , the pyramids are much older than you probably think . they were already ancient history to people in ancient history , which led to some pretty wild theories about how they came to be . but pyramid technology didn ’ t just show up out of nowhere . it was the end product of centuries of scientific and cultural evolution , of people… figuring it out . and it definitely wasn ’ t aliens . [ open ] early on , egyptians buried their dead like we do . the desert naturally mummified some corpses , which influenced their religious beliefs : you need to preserve the body to reach the afterlife , and when you get there you ’ ll need all your stuff . rich people ’ s graves had nicer stuff , and they needed to protect their afterlife investment . first with simple mounds , and later with mud brick “ eternal houses ” . then a king named djoser was like “ why have one little mud mastaba when i can have six stone mastabas in a stack ? ” so he stacked six stone mastabas like a mastaba boss and the age of the pyramids had begun . this was literally the first time humans had piled stone this high . egyptians knew totally vertical walls got less stable as they got taller , so djoser ’ s architect stacked bricks at an incline and let gravity do the work . step pyramid achieved ! why pyramids and not other shapes ? if you want to make a big pile of blocks , a pyramid gets you the most stability for the least material . a third of the way up , you ’ ve already laid two-thirds of your stone . halfway , you ’ ve placed more than 80 % . next comes sneferu , mr. pyramid . he built his own step pyramid , but then decided he wanted a smooth one instead , so they started on a second . no one had ever built one of those before , so they made some mistakes . for starters , they built it on sand , which is soft , they laid blocks carelessly , and it was too steep , so halfway through they changed the slope and ended up with this . sneferu was like “ you ’ re not burying me in that ” , so he ordered a third pyramid ! only this time they built a solid foundation , laid the stones in horizontal rows , and precision cut the edges . sneferu ’ s motto ? if at first you don ’ t succeed , try again , and then try again one more time . sneferu had experimented his way to a blueprint for building awesome pyramids the great pyramid at giza , built by his son khufu , took that blueprint to the next level . khufu ’ s pyramid remained the tallest structure on earth for almost 4000 years , until some church tower in the year 1311 , which fell down , so it was tallest again until this radio antenna was finished in 1889 . khufu ’ s son khafre built his pyramid right next to dad ’ s , and he didn ’ t stop innovating . instead of leveling the entire 46,000 square meter footprint , he built his pyramid over a natural stone mound and only leveled the outer edge , which was less work , duh ! it ’ s 3 meters shorter than his dad ’ s , but this higher ground creates the illusion that khafre ’ s pyramid is taller . kids , amirite ? but even these seemingly perfect pyramids weren ’ t without mistakes . khafre ’ s had a slight twist near the top in order to make the edges line up evenly . what ’ s remarkable is egypt ’ s biggest stone pyramids were the product of just three human generations , but those were generations full of trial and error . pyramid building continued for nearly 700 years , and like any product , efficiency started to win out over quality . precision-cut cores were replaced by rough-cut blocks . kings still wrapped their pyramids in fine white limestone , but over the next thousand years that was removed by stone stealers and rock robbers , leaving the cheaply-produced cores to collapse into rubble , which is probably why you ’ ve never heard of them . ironically , the kings were probably disappointed by the whole afterlife thing , but the pyramids themselves have proven to be surprisingly resilient . ancient is not a synonym for stupid . the world ’ s first skyscrapers were tombs , and just like our own buildings , they didn ’ t spring up out of nowhere , they were the product of centuries of engineering trial and error . go back 500 years and show someone a smartphone and they ’ d probably think you were a wizard . but when we look back from the present at the ideas and failures along the way , we see that it ’ s not magic at all ! it ’ s science . and if you still think aliens did it , you ’ re in de-nile . you know , the river . stay curious .

if at first you don ’ t succeed , try again , and then try again one more time . sneferu had experimented his way to a blueprint for building awesome pyramids the great pyramid at giza , built by his son khufu , took that blueprint to the next level . khufu ’ s pyramid remained the tallest structure on earth for almost 4000 years , until some church tower in the year 1311 , which fell down , so it was tallest again until this radio antenna was finished in 1889 . khufu ’ s son khafre built his pyramid right next to dad ’ s , and he didn ’ t stop innovating . instead of leveling the entire 46,000 square meter footprint , he built his pyramid over a natural stone mound and only leveled the outer edge , which was less work , duh !

for how many years was khufu 's pyramid the largest man-made structure in the world ?

to someone first encountering the works of william shakespeare , the language may seem strange . but there is a secret to appreciating it . although he was famous for his plays , shakespeare was first and foremost a poet . one of the most important things in shakespeare 's language is his use of stress . not that kind of stress , but the way we emphasize certain syllables in words more than others . we 're so used to doing this that we may not notice it at first . but if you say the word slowly , you can easily identify them . playwright , computer , telephone . poets are very aware of these stresses , having long experimented with the number and order of stressed and unstressed syllables , and combined them in different ways to create rhythm in their poems . like songwriters , poets often express their ideas through a recognizable repetition of these rhythms or poetic meter . and like music , poetry has its own set of terms for describing this . in a line of verse , a foot is a certain number of stressed and unstressed syllables forming a distinct unit , just as a musical measure consists of a certain number of beats . one line of verse is usually made up of several feet . for example , a dactyl is a metrical foot of three syllables with the first stressed , and the second and third unstressed . dactyls can create lines that move swiftly and gather force , as in robert browning 's poem , `` the lost leader . '' `` just for a handful of silver he left us . just for a rib and to stick in his coat . '' another kind of foot is the two-syllable long trochee , a stressed syllable followed by an unstressed one . the trochees in these lines from shakespeare 's `` macbeth '' lend an ominous and spooky tone to the witches ' chant . `` double , double , toil and trouble ; fire burn and cauldron bubble . '' but with shakespeare , it 's all about the iamb . this two-syllable foot is like a reverse trochee , so the first syllable is unstressed and the second is stressed , as in , `` to be , or not to be . '' shakespeare 's favorite meter , in particular , was iambic pentameter , where each line of verse is made up of five two-syllable iambs , for a total of ten syllables . and it 's used for many of shakespeare 's most famous lines : `` shall i compare thee to a summer 's day ? '' `` arise fair sun , and kill the envious moon . '' notice how the iambs cut across both punctuation and word separation . meter is all about sound , not spelling . iambic pentameter may sound technical , but there 's an easy way to remember what it means . the word iamb is pronounced just like the phrase , `` i am . '' now , let 's expand that to a sentence that just happens to be in iambic pentameter . `` i am a pirate with a wooden leg . '' the pirate can only walk in iambs , a living reminder of shakespeare 's favorite meter . iambic pentameter is when he takes ten steps . our pirate friend can even help us remember how to properly mark it if we image the footprints he leaves walking along a deserted island beach : a curve for unstressed syllables , and a shoe outline for stressed ones . `` if music be the food of love , play on . '' of course , most lines of shakespeare 's plays are written in regular prose . but if you read carefully , you 'll notice that shakespeare 's characters turn to poetry , and iambic pentameter in particular , for many of the same reasons that we look to poetry in our own lives . feeling passionate , introspective , or momentous . whether it 's hamlet pondering his existence , or romeo professing his love , the characters switch to iambic pentameter when speaking about their emotions and their place in the world . which leaves just one last question . why did shakespeare choose iambic pentameter for these moments , rather than , say , trochaic hexameter or dactylic tetrameter ? it 's been said that iambic pentameter was easy for his actors to memorize and for the audience to understand because it 's naturally suited to the english language . but there might be another reason . the next time you 're in a heightened emotional situation , like the ones that make shakespeare 's characters burst into verse , put your hand over the left side of your chest . what do you feel ? that 's your heart beating in iambs . da duhm , da duhm , da duhm , da duhm , da duhm . shakespeare 's most poetic lines do n't just talk about matters of the heart . they follow its rhythm .

one line of verse is usually made up of several feet . for example , a dactyl is a metrical foot of three syllables with the first stressed , and the second and third unstressed . dactyls can create lines that move swiftly and gather force , as in robert browning 's poem , `` the lost leader . ''

which of these is not a type of metrical foot ?

how do nerves work ? are nerves simply the wires in the body that conduct electricity , like the wires in the walls of your home or in your computer ? this is an analogy often made , but the reality is that nerves have a much more complex job in the body . they are not just the wires , but the cells that are the sensors , detectors of the external and internal world , the transducers that convert information to electrical impulses , the wires that transmit these impulses , the transistors that gate the information and turn up or down the volume- and finally , the activators that take that information and cause it to have an effect on other organs . consider this . your mother gently strokes your forearm and you react with pleasure . or a spider crawls on your forearm and you startle and slap it off . or you brush your forearm against a hot rack while removing a cake from the oven and you immediately recoil . light touch produced pleasure , fear , or pain . how can one kind of cell have so many functions ? nerves are in fact bundles of cells called neurons and each of these neurons is highly specialized to carry nerve impulses , their form of electricity , in response to only one kind of stimulus , and in only one direction . the nerve impulse starts with a receptor , a specialized part of each nerve , where the electrical impulse begins . one nerve 's receptor might be a thermal receptor , designed only to respond to a rapid increase in temperature . another receptor type is attached to the hairs of the forearm , detecting movement of those hairs , such as when a spider crawls on your skin . yet another kind of neuron is low-threshold mechanoreceptor , activated by light touch . each of these neurons then carry their specific information : pain , warning , pleasure . and that information is projected to specific areas of the brain and that is the electrical impulse . the inside of a nerve is a fluid that is very rich in the ion potassium . it is 20 times higher than in the fluid outside the nerve while that outside fluid has 10 times more sodium than the inside of a nerve . this imbalance between sodium outside and potassium inside the cell results in the inside of the nerve having a negative electrical charge relative to the outside of the nerve , about equal to -70 or -80 millivolts . this is called the nerve 's resting potential . but in response to that stimulus the nerve is designed to detect , pores in the cell wall near the receptor of the cell open . these pores are specialized protein channels that are designed to let sodium rush into the nerve . the sodium ions rush down their concentration gradient , and when they do , the inside of the nerve becomes more positively charged- about +40 millivolts . while this happens , initially in the nerve right around the receptor , if the change in the nerve 's electrical charge is great enough , if it reaches what is called threshold , the nearby sodium ion channels open , and then the ones nearby those , and so on , and so forth , so that the positivity spreads along the nerve 's membrane to the nerve 's cell body and then along the nerve 's long , thread-like extension , the axon . meanwhile , potassium ion channels open , potassium rushes out of the nerve , and the membrane voltage returns to normal . actually , overshooting it a bit . and during this overshoot , the nerve is resistant to further depolarization-it is refractory , which prevents the nerve electrical impulse from traveling backwards . then , ion pumps pump the sodium back back out of the nerve , and the potassium back into the nerve , restoring the nerve to its normal resting state . the end of the nerve , the end of the axon , communicates with the nerve 's target . this target will be other nerves in a specialized area of the spinal cord , to be processed and then transmitted up to the brain . or the nerve 's target may be another organ , such as a muscle . when the electrical impulse reaches the end of the nerve , small vesicles , or packets , containing chemical neurotransmitters , are released by the nerve and rapidly interact with the nerve 's target . this process is called synaptic transmission , because the connection between the nerve and the next object in the chain is called a synapse . and it is here , in this synapse , that the neuron 's electrical information can be modulated , amplified , blocked altogether or translated to another informational process .

are nerves simply the wires in the body that conduct electricity , like the wires in the walls of your home or in your computer ? this is an analogy often made , but the reality is that nerves have a much more complex job in the body . they are not just the wires , but the cells that are the sensors , detectors of the external and internal world , the transducers that convert information to electrical impulses , the wires that transmit these impulses , the transistors that gate the information and turn up or down the volume- and finally , the activators that take that information and cause it to have an effect on other organs .

nerves are often compared to the wiring of computers or homes . why is this a good analogy ? why is it incomplete ?

stretched across a tree-peppered expanse in southern africa lies the magnificent ruins of great zimbabwe , a medieval stone city of astounding wealth and prestige . located in the present-day country of zimbabwe , it 's the sight of the largest known settlement ruins in sub-saharan africa , second on the continent only to the pyramids of egypt . but the history of this city is shrouded in controversy , defined by decades of dispute about who built it and why . its name comes from the shona word madzimbabwe , meaning big house of stone for its unscalable stone walls that reach heights of nearly ten meters and run for a length of about 250 meters . for its grandeur and historical significance , it was named a unesco world heritage site in 1986 . back in the 14th and 15th centuries , it was a thriving city . spread across nearly eight square-kilometers , great zimbabwe was defined by three main areas : the hill complex , where the king lived ; the great enclosure , reserved for members of the royal family ; and the valley complex , where regular citizens lived . rulers were both powerful economic and religious leaders for the region . at its highest point , the city had a bustling urban population of 18,000 people and was one of the major african trade centers at the time . what enabled this growth was great zimbabwe 's influential role in an intercontinental trade network . connected to several key city-states along the east african swahili coast , it was part of the larger indian ocean trade routes . the city generated its riches by controlling the sources and trade of the most prized items : gold , ivory , and copper . with this mercantile power , it was able to extend its sphere of influence across continents , fostering a strong arab and indian trader presence throughout its zenith . archaeologists have since pieced together the details of this history through artifacts discovered on site . there were pottery shards and glassworks from asia , as well as coins minted in the coastal trading city of kilwa kisiwani over 1,500 miles away . they also found soapstone bird figures , which are thought to represent each of the city 's rulers , and young calf bones , only unearthed near the royal residence , show how the diet of the elite differed from the general population . these clues have also led to theories about the city 's decline . by the mid-15th century , the buildings at great zimbabwe were almost all that remained . archaeological evidence points to overcrowding and sanitation issues as the cause , compounded by soil depletion triggered by overuse . eventually , as crops withered and conditions in the city worsened , the population of great zimbabwe is thought to have dispersed and formed the nearby mutapa and torwa states . centuries later , a new phase of great zimbabwe 's influence began to play out in the political realm as people debated who had built the famous city of stone . during the european colonization of africa , racist colonial officials claimed the ruins could n't be of african origin . so , without a detailed written record on hand , they instead relied on myths to explain the magnificence of great zimbabwe . some claimed it proved the bible story of the queen of sheba who lived in a city of riches . others argued it was built by the ancient greeks . then , in the early 20th century after extensive excavation at the site , the archaeologist david randall-maciver presented clear evidence that great zimbabwe was built by indigenous peoples . yet , at the time , the country 's white minority colonial government sought to discredit this theory because it challenged the legitimacy of their rule . in fact , the government actively encouraged historians to produce accounts that disputed the city 's african origins . over time , however , an overwhelming body of evidence mounted , identifying great zimbabwe as an african city built by africans . during the 1960s and 70s , great zimbabwe became an important symbol for the african nationalist movement that was spreading across the continent . today , the ruins at great zimbabwe , alluded to on the zimbabwean flag by a soapstone bird , still stand as a source of national pride and cultural value .

in fact , the government actively encouraged historians to produce accounts that disputed the city 's african origins . over time , however , an overwhelming body of evidence mounted , identifying great zimbabwe as an african city built by africans . during the 1960s and 70s , great zimbabwe became an important symbol for the african nationalist movement that was spreading across the continent .

who built great zimbabwe ?

as you can see , i was born without fingers on my right hand . and also my right leg was several inches shorter than my left one . they broke the bones in the leg , then they screwed metal spikes into the bone . it has not only spikes , but wires that go all the way through the leg to stabilize it . i have to walk on it . i have to stretch it out so that my muscles do n't just get all atrophied . people always ask me , `` does it hurt ? '' yes , it does , but i focus on what i can do , not on what i can not do . i want to talk with you guys about overcoming obstacles . everybody has obstacles , a disability , a hurdle . we face a choice : let the obstacle overcome you or overcome the obstacle . maybe some of you have heard of jim abbott . he was a major league baseball player . he won a gold metal in the olympics . he played for the yankees , the angels . but he threw a no-hitter , and he only had one arm . when he was a kid , he came home mad one time and told his dad , `` the kids wo n't let me play baseball because i only have one hand . '' his dad replied , `` no , the kids wo n't let you play baseball because you stink at baseball . you ca n't change the fact that you only have one hand , but you can change the fact that you stink . '' so , his dad began to practice with him , and he got good . he overcame obstacles . teams would try to exploit his weak side . they would try to bunt to the side that he had a missing arm . but they never succeeded because he practiced and practiced fielding bunts to that side . there 's no dishonor in having a disability , and i wo n't let anyone diss my ability , but i do n't want anyone 's pity either . i will not use the obstacles i face as an excuse for having a pity party . i will practice harder , play harder , and push myself harder to keep getting better . last season i started on my varsity high school basketball team as a freshman , and i won rookie of the year . i was one of the top scorers on the team . one of the things that i find funny is that people judge me by appearance . they say , `` oh , look at this one-handed whitey with the limp . i do n't want him on my team ! '' but what they do n't know is that i do n't just have a disability , i have an ability . one of my favorite moments from this last season was we played a team that we had never played before . and when the game started , you could tell that they were dissing my disability . i mean , they double-teamed our tallest player . they just were playing really soft on me , and they just , you could tell they thought , `` what can this guy with one hand do ? '' so , they left me open for a three . i made that one . they left me open for another one . i made that one . then , they started to get frustrated , so they actually fouled me . i made both free throws . and they called time out . and as we were in the huddle , i could hear the other coach yelling at his players about me . they went from not covering me at all to double-teaming me . it 's all about overcoming obstacles . it 's true , i have a disability , but so do you . i also have an ability , so do you . everyone has obstacles to overcome . some are visible like mine . some are less visible . maybe your obstacle is that you come from a poor neighborhood . maybe people say you 'll never amount to anything . prove them wrong . maybe your obstacle is that you have a learning disability , and people think that you 're dumb . prove them wrong . maybe people judge you because of the color of your skin or your family background . prove them wrong . i know a lot of people who take one look at me and judge me . they say , `` oh , that kid ca n't be any good at basketball . one leg , one hand . '' if someone things you ca n't overcome the obstacles , prove them wrong .

as you can see , i was born without fingers on my right hand . and also my right leg was several inches shorter than my left one .

which professional athlete did steven mention ?

humans have been fascinated with speed for ages . the history of human progress is one of ever-increasing velocity , and one of the most important achievements in this historical race was the breaking of the sound barrier . not long after the first successful airplane flights , pilots were eager to push their planes to go faster and faster . but as they did so , increased turbulence and large forces on the plane prevented them from accelerating further . some tried to circumvent the problem through risky dives , often with tragic results . finally , in 1947 , design improvements , such as a movable horizontal stabilizer , the all-moving tail , allowed an american military pilot named chuck yeager to fly the bell x-1 aircraft at 1127 km/h , becoming the first person to break the sound barrier and travel faster than the speed of sound . the bell x-1 was the first of many supersonic aircraft to follow , with later designs reaching speeds over mach 3 . aircraft traveling at supersonic speed create a shock wave with a thunder-like noise known as a sonic boom , which can cause distress to people and animals below or even damage buildings . for this reason , scientists around the world have been looking at sonic booms , trying to predict their path in the atmosphere , where they will land , and how loud they will be . to better understand how scientists study sonic booms , let 's start with some basics of sound . imagine throwing a small stone in a still pond . what do you see ? the stone causes waves to travel in the water at the same speed in every direction . these circles that keep growing in radius are called wave fronts . similarly , even though we can not see it , a stationary sound source , like a home stereo , creates sound waves traveling outward . the speed of the waves depends on factors like the altitude and temperature of the air they move through . at sea level , sound travels at about 1225 km/h . but instead of circles on a two-dimensional surface , the wave fronts are now concentric spheres , with the sound traveling along rays perpendicular to these waves . now imagine a moving sound source , such as a train whistle . as the source keeps moving in a certain direction , the successive waves in front of it will become bunched closer together . this greater wave frequency is the cause of the famous doppler effect , where approaching objects sound higher pitched . but as long as the source is moving slower than the sound waves themselves , they will remain nested within each other . it 's when an object goes supersonic , moving faster than the sound it makes , that the picture changes dramatically . as it overtakes sound waves it has emitted , while generating new ones from its current position , the waves are forced together , forming a mach cone . no sound is heard as it approaches an observer because the object is traveling faster than the sound it produces . only after the object has passed will the observer hear the sonic boom . where the mach cone meets the ground , it forms a hyperbola , leaving a trail known as the boom carpet as it travels forward . this makes it possible to determine the area affected by a sonic boom . what about figuring out how strong a sonic boom will be ? this involves solving the famous navier-stokes equations to find the variation of pressure in the air due to the supersonic aircraft flying through it . this results in the pressure signature known as the n-wave . what does this shape mean ? well , the sonic boom occurs when there is a sudden change in pressure , and the n-wave involves two booms : one for the initial pressure rise at the aircraft 's nose , and another for when the tail passes , and the pressure suddenly returns to normal . this causes a double boom , but it is usually heard as a single boom by human ears . in practice , computer models using these principles can often predict the location and intensity of sonic booms for given atmospheric conditions and flight trajectories , and there is ongoing research to mitigate their effects . in the meantime , supersonic flight over land remains prohibited . so , are sonic booms a recent creation ? not exactly . while we try to find ways to silence them , a few other animals have been using sonic booms to their advantage . the gigantic diplodocus may have been capable of cracking its tail faster than sound , at over 1200 km/h , possibly to deter predators . some types of shrimp can also create a similar shock wave underwater , stunning or even killing pray at a distance with just a snap of their oversized claw . so while we humans have made great progress in our relentless pursuit of speed , it turns out that nature was there first .

no sound is heard as it approaches an observer because the object is traveling faster than the sound it produces . only after the object has passed will the observer hear the sonic boom . where the mach cone meets the ground , it forms a hyperbola , leaving a trail known as the boom carpet as it travels forward .

when would you hear a sonic boom ?

ah , romantic love - beautiful and intoxicating , heartbreaking and soul-crushing , often all at the same time . why do we choose to put ourselves through its emotional wringer ? does love make our lives meaningful , or is it an escape from our loneliness and suffering ? is love a disguise for our sexual desire , or a trick of biology to make us procreate ? is it all we need ? do we need it at all ? if romantic love has a purpose , neither science nor psychology has discovered it yet . but over the course of history , some of our most respected philosophers have put forward some intriguing theories . love makes us whole , again . the ancient greek philosopher plato explored the idea that we love in order to become complete . in his `` symposium '' , he wrote about a dinner party , at which aristophanes , a comic playwright , regales the guests with the following story : humans were once creatures with four arms , four legs , and two faces . one day , they angered the gods , and zeus sliced them all in two . since then , every person has been missing half of him or herself . love is the longing to find a soulmate who 'll make us feel whole again , or , at least , that 's what plato believed a drunken comedian would say at a party . love tricks us into having babies . much , much later , german philosopher arthur schopenhauer maintained that love based in sexual desire was a voluptuous illusion . he suggested that we love because our desires lead us to believe that another person will make us happy , but we are sorely mistaken . nature is tricking us into procreating , and the loving fusion we seek is consummated in our children . when our sexual desires are satisfied , we are thrown back into our tormented existences , and we succeed only in maintaining the species and perpetuating the cycle of human drudgery . sounds like somebody needs a hug . love is escape from our loneliness . according to the nobel prize-winning british philosopher bertrand russell , we love in order to quench our physical and psychological desires . humans are designed to procreate , but without the ecstasy of passionate love , sex is unsatisfying . our fear of the cold , cruel world tempts us to build hard shells to protect and isolate ourselves . love 's delight , intimacy , and warmth helps us overcome our fear of the world , escape our lonely shells , and engage more abundantly in life . love enriches our whole being , making it the best thing in life . love is a misleading affliction . siddhārtha gautama , who became known as the buddha , or the enlightened one , probably would have had some interesting arguments with russell . buddha proposed that we love because we are trying to satisfy our base desires . yet , our passionate cravings are defects , and attachments , even romantic love , are a great source of suffering . luckily , buddha discovered the eight-fold path , a sort of program for extinguishing the fires of desire so that we can reach nirvana , an enlightened state of peace , clarity , wisdom , and compassion . the novelist cao xueqin illustrated this buddhist sentiment that romantic love is folly in one of china 's greatest classical novels , `` dream of the red chamber . '' in a subplot , jia rui falls in love with xi-feng who tricks and humiliates him . conflicting emotions of love and hate tear him apart , so a taoist gives him a magic mirror that can cure him as long as he does n't look at the front of it . but of course , he looks at the front of it . he sees xi-feng . his soul enters the mirror and he is dragged away in iron chains to die . not all buddhists think this way about romantic and erotic love , but the moral of this story is that such attachments spell tragedy , and should , along with magic mirrors , be avoided . love lets us reach beyond ourselves . let 's end on a slightly more positive note . the french philosopher simone de beauvoir proposed that love is the desire to integrate with another and that it infuses our lives with meaning . however , she was less concerned with why we love and more interested in how we can love better . she saw that the problem with traditional romantic love is it can be so captivating , that we are tempted to make it our only reason for being . yet , dependence on another to justify our existence easily leads to boredom and power games . to avoid this trap , beauvoir advised loving authentically , which is more like a great friendship . lovers support each other in discovering themselves , reaching beyond themselves , and enriching their lives and the world together . though we might never know why we fall in love , we can be certain that it will be an emotional rollercoaster ride . it 's scary and exhilarating . it makes us suffer and makes us soar . maybe we lose ourselves . maybe we find ourselves . it might be heartbreaking , or it might just be the best thing in life . will you dare to find out ?

buddha proposed that we love because we are trying to satisfy our base desires . yet , our passionate cravings are defects , and attachments , even romantic love , are a great source of suffering . luckily , buddha discovered the eight-fold path , a sort of program for extinguishing the fires of desire so that we can reach nirvana , an enlightened state of peace , clarity , wisdom , and compassion .

romantic attachments are a great source of what , according to the buddha ?

translator : andrea mcdonough reviewer : jessica ruby one of the reasons that i 'm fascinated by the ocean is that it 's really an alien world on our own planet . from our perspective , sitting on the shoreline or even out on a boat , we 're given only the tiniest glimpses at the real action that 's happening beneath the surface of the waves . and even if you were able to go down there , you would n't see very much because light does n't travel very far in the ocean . so , to answer questions about how the ocean works , in my research , we use sound . we use sonars that send out pulses of sound made up of a number of different frequencies , or pitches , that are shown with different colors . that sound bounces off things in the habitat and comes back to us . if it were to bounce off this dolphin , the signal we got back would look very much like the one we sent out where all the colors are represented pretty evenly . however , if we were to bounce that same sound off of a squid , which in this case is about the same size as that dolphin , we 'd instead only get the lowest frequencies back strongly , shown here in the red . and if we were to look at the prey of that squid , the tiny little krill that they 're eating , we would instead only get the highest frequencies back . and so by looking at this , we can tell what kinds of animals are in the ocean , we can look at how dense they are , where they are distributed , look at their interactions and even their behavior to start to study the ecology of the ocean . when we do that , we come up with something sort of surprising : on average , there is n't very much food in the ocean . so even in places which we think of as rich , the coasts , we 're talking about two parts of every million contain food . so what does that mean ? well , that means that in the volume of this theater , there would be one tub of movie theater popcorn available to be eaten . but of course , it would n't be collected for you neatly in this bucket . instead , you 'd actually have to be swimming through this entire volume willy wonka style , picking off individual kernels of popcorn , or perhaps if you were lucky , getting a hold of a few small clumps . but , of course , if you were in the ocean , this popcorn would n't be sitting here waiting for you to eat it . it would , instead , be trying to avoid becoming your dinner . so i want to know how do animals solve this challenge ? we 're going to talk about animals in the bering sea . this is where you may have see `` deadliest catch '' framed , in the northernmost part of the pacific ocean . we 've been looking specifically at krill , one of the most important food items in this habitat . these half-inch long shrimp-like critters are about the caloric equivalent of a heavily buttered kernel of popcorn . and they 're eaten by everything from birds and fur seals that pick them up one at a time to large whales that engulf them in huge mouthfuls . so i 'm going to focus in the area around three breeding colonies for birds and fur seals in the southeastern bering sea . and this is a map of that habitat that we made making maps of food the way we 've always made maps of food . this is how many krill are in this area of the ocean . red areas represent lots of krill and purple basically none . and you can see that around the northern two most islands , which are highlighted with white circles because they are so tiny , it looks like there 's a lot of food to be eaten . and yet , the fur seals and birds on these islands are crashing . their populations are declining despite decades of protection . and while on that southern island at the very bottom of the screen it does n't look like there 's anything to eat , those populations are doing incredibly well . so this left us with a dilemma . our observations of food do n't make any sense in the context of our observations of these animals . so we started to think about how we could do this differently . and this map shows not how many krill there are , but how many clumps of krill there are , how aggregated are they . and what you get is a very different picture of the landscape . now that southern island looks like a pretty good place to be , and when we combine this with other information about prey , it starts to explain the population observations . but we can also ask that question differently . we can have the animals tell us what 's important . by tagging and tracking these animals and looking at how they use this habitat , we are able to say , `` what matters to you ? '' about the prey . and what they 've told us is that how many krill there are really is n't important . it is how closely spaced those krill are because that 's how they are able to make a living . we see the same pattern when we look in very different ocean , further south in the pacific , in the warm waters around the hawaiian islands . so a very different habitat , and yet the same story . under some conditions , the physics and the nutrients , the fertilizer , set up aggregations in the plants , the phytoplankton . and when that happens , these very dense aggregations of phytoplankton attract their predators , which themselves form very dense layers . that changes the behavior and distribution of their predators as well , starting to set up how this entire ecosystem functions . finally , the predators that eat these small fish , shrimp , and squid , we 're talking about two- to three-inch long prey here , changes how they use their habitat and how they forage . and so we see changes in the spinner dolphins that are related to the changes we 're seeing in the plant life . and just by measuring the plants , we can actually predict very well what 's going to happen in the top predator three steps away in the food web . but what 's interesting is that even the densest aggregations of their prey are n't enough for spinner dolphins to make it . it 's a pretty tough life there in the ocean . so these animals actually work together to herd their prey into even denser aggregations , starting with patches that they find in the first place . and that 's what you 're going to see in this visualization . we have a group of 20 dolphins , you notice they 're all set up in pairs , that are working together to basically bulldoze prey to accumulate it on top of itself . and once they do that , they form a circle around that prey to maintain that really dense patch that is a couple thousand times higher density than the background that they started with before individual pairs of dolphins start to take turns feeding inside this circle of prey that they 've created . and so , this work is showing us that animals can first give us the answers that aggregation is critical to how they make their living . and by looking more deeply at the ocean , we 're starting to understand our interactions with it and finding more effective ways of conserving it . thank you .

this is where you may have see `` deadliest catch '' framed , in the northernmost part of the pacific ocean . we 've been looking specifically at krill , one of the most important food items in this habitat . these half-inch long shrimp-like critters are about the caloric equivalent of a heavily buttered kernel of popcorn . and they 're eaten by everything from birds and fur seals that pick them up one at a time to large whales that engulf them in huge mouthfuls .

what is the caloric equivalent of a single krill ?

ah , spring . grass growing , flowers blooming , trees growing new leaves , but if you get allergies , this explosion of new life probably inspires more dread than joy . step outside , and within minutes , you 're sneezing and congested . your nose is running , your eyes are swollen and watery , your throat is itchy . for you and millions of others , it 's seasonal allergy time . so what 's behind this onslaught of mucus ? the answer lies within you . it 's your immune system . seasonal allergies , also called hay fever , or allergic rhinitis , are a hypersensitive immune response to something that 's not actually harmful . pollen from trees and grass , and mold spores from tiny fungi find their way into your mucous membranes and your body attacks these innocuous travelers the same way it would infectious bacteria . the immune system has a memory . when a foreign substance gets tagged as threatening , white blood cells produce customized antibodies that will recognize the offender the next time around . they then promptly recruit the body 's defense team . but sometimes , the immune system accidentally discriminates against harmless substances , like pollen . when it wafts in again , antibodies on the surface of white blood cells recognize it and latch on . this triggers the cell to release inflammatory chemicals , like histamine , which stimulate nerve cells , and cause blood vessels in the mucous membranes to swell and leak fluid . in other words , itchiness , sneezing , congestion , and a runny nose . allergies usually , but not always , show up for the first time during childhood . but why do some people get allergies and others do n't ? allergies tend to run in families , so genetics may be one culprit . in fact , errors in a gene that helps regulate the immune system are associated with higher rates of allergies . the environment you grow up in matters , too . being exposed to an allergen as a baby makes you less likely to actually develop an allergy to it . people who grow up on farms , in big families , and in the developing world also tend to have fewer allergies , although there are plenty of exceptions , partly thanks to genetics . one theory is that as children , they encounter more of the microbes and parasites that co-evolved with traditional hunter-gatherer societies . called the hygiene hypothesis , the idea is that when the immune system is n't exposed to the familiar cast of microbes , it 'll keep itself busy mounting defenses against harmless substances , like pollen . another theory is that an immune system toughened up by a barrage of pathogens is less likely to overreact to allergens . pollen is a common offender , just because we encounter so much of it , but there 's a long list of substances : dust , animal dander , insect venom , medications , certain foods , that can send your immune system into overdrive . some of these reactions can be scary . an allergy can develop into full-blown anaphylaxis , which typically brings on severe swelling , shortness of breath , and very low blood pressure . it can be deadly . the body can even have an allergic reaction to itself causing auto-immune disorders , like multiple sclerosis , lupus , and type 1 diabetes . but even non-life threatening allergy symptoms can make you miserable , so what can you do about it ? medications can help reduce the symptoms . the most common ones keep histamines from binding to your cells . these antihistamines stop the inflammation response . steroids can help dial down the immune system . another more permanent option is immunotherapy . deliberate , controlled exposure to gradually increasing amounts of an allergen can teach the immune system that it is n't dangerous after all . and if you 're really adventurous , there 's a less traditional option : intestinal parasites . when hookworms sink their teeth into the intestinal wall , they secrete chemicals that blunt the immune system . some studies suggest that hookworms can treat allergies , which may be another reason allergies are more common in industrialized countries where hookworms are few and far between . of course , you can always just wait your seasonal allergies out . the spring pollen onslaught dwindles by mid-summer , just in time for ragweed season .

but sometimes , the immune system accidentally discriminates against harmless substances , like pollen . when it wafts in again , antibodies on the surface of white blood cells recognize it and latch on . this triggers the cell to release inflammatory chemicals , like histamine , which stimulate nerve cells , and cause blood vessels in the mucous membranes to swell and leak fluid . in other words , itchiness , sneezing , congestion , and a runny nose .

when these cells recognize an allergen , they release chemicals . these include :

some of the best opportunities to learn are the moments in which we are perplexed . those moments in which you begin to wonder and question . these moments have happened throughout history . and have led to some truly amazing discoveries . take this story , for example . there once was a fellow named archimedes . he was born in 287 b.c . in the city of syracuse in sicily . he was a greek mathematician , physicist , engineer , inventor , and astronomer . one day , archimedes was summoned by the king of sicily to investigate if he had been cheated by a goldsmith . the king said he had given a goldsmith the exact amount of gold needed to make a crown . however , when the crown was ready , the king suspected that the goldsmith cheated and slipped some silver into the crown , keeping some of the gold for himself . the king asked archimedes to solve the problem . but there was a catch : he could n't do any damage to the crown . one day , while taking his bath , archimedes noticed that the water level in the bathtub rose and overflowed as he immersed himself into the tub . he suddenly realized that how much water was displaced depended on how much of his body was immersed . this discovery excited him so much that he jumped out of the tub and ran through the streets naked , shouting `` eureka ! '' which comes from the ancient greek meaning `` i found it . '' what did he find ? well , he found a way to solve the king 's problem . you see , archimedes needed to check the crown 's density to see if it was the same as the density of pure gold . density is a measure of an object 's mass divided by its volume . pure gold is very dense , while silver is less dense . so if there was silver in the crown , it would be less dense than if it were made of pure gold . but no matter what it was made of , the crown would be the same shape , which means the same volume . so if archimedes could measure the mass of the crown first , and then measure its volume , he could find out how dense it was . but it is not easy to measure a crown 's volume - it has an irregular shape , that 's different from a simple box or ball . you ca n't measure its size and multiply like you might for other shapes . the solution , archimedes realized , was to give the crown a bath . by placing it in water and seeing how much water was displaced , he could measure the volume , and he 'd calculate the density of the crown . if the crown was less dense than pure gold , then the goldsmith most definitely cheated the king . when archimedes went back to the king and did his test , the story says , he found that the goldsmith had indeed cheated the king , and slipped some silver in . these days , using the way an object displaces water to measure volume is called archimedes ' principle . the next time you take a bath , you can see archimedes ' principle in action , and maybe you 'll have a genius idea of your own .

however , when the crown was ready , the king suspected that the goldsmith cheated and slipped some silver into the crown , keeping some of the gold for himself . the king asked archimedes to solve the problem . but there was a catch : he could n't do any damage to the crown .

what property did archimedes need to determine in order to solve the king 's mystery ?

translator : andrea mcdonough reviewer : bedirhan cinar a couple of years ago i started using twitter , and one of the things that really charmed me about twitter is that people would wake up in the morning and they would say , `` good morning ! '' which i thought , i 'm a canadian , so i was a little bit , i liked that politeness . and so , i 'm also a giant nerd , and so i wrote a computer program that would record 24 hours of everybody on twitter saying , `` good morning ! '' and then i asked myself my favorite question , `` what would that look like ? '' well , as it turns out , i think it would look something like this . right , so we 'd see this wave of people saying , `` good morning ! '' across the world as they wake up . now the green people , these are people that wake up at around 8 o'clock in the morning , who wakes up at 8 o'clock or says , `` good morning ! '' at 8 ? and the orange people , they say , `` good morning ! '' around 9 . and the red people , they say , `` good morning ! '' around 10 . yeah , more at 10 's than , more at 10 's than 8 's . and actually if you look at this map , we can learn a little bit about how people wake up in different parts of the world . people on the west coast , for example , they wake up a little bit later than those people on the east coast . but that 's not all that people say on twitter , right ? we also get these really important tweets , like , `` i just landed in orlando ! ! [ plane sign , plane sign ] '' or , or , `` i just landed in texas [ exclamation point ] ! '' or `` i just landed in honduras ! '' these lists , they go on and on and on , all these people , right ? so , on the outside , these people are just telling us something about how they 're traveling . but we know the truth , do n't we ? these people are show-offs ! they are showing off that they 're in cape town and i 'm not . so i thought , how can we take this vanity and turn it into utility ? so using a similar approach that i did with `` good morning , '' i mapped all those people 's trips because i know where they 're landing , they just told me , and i know where they live because they share that information on their twitter profile . so what i 'm able to do with 36 hours of twitter is create a model of how people are traveling around the world during that 36 hours . and this is kind of a prototype because i think if we listen to everybody on twitter and facebook and the rest of our social media , we 'd actually get a pretty clear picture of how people are traveling from one place to the other , which is actually turns out to be a very useful thing for scientists , particularly those who are studying how disease is spread . so , i work upstairs in the new york times , and for the last two years , we 've been working on a project called , `` cascade , '' which in some ways is kind of similar to this one . but instead of modeling how people move , we 're modeling how people talk . we 're looking at what does a discussion look like . well , here 's an example . this is a discussion around an article called , `` the island where people forget to die '' . it 's about an island in greece where people live a really , really , really , really , really , really long time . and what we 're seeing here is we 're seeing a conversation that 's stemming from that first tweet down in the bottom , left-hand corner . so we get to see the scope of this conversation over about 9 hours right now , we 're going to creep up to 12 hours here in a second . but , we can also see what that conversation looks like in three dimensions . and that three-dimensional view is actually much more useful for us . as humans , we are really used to things that are structured as three dimensions . so , we can look at those little off-shoots of conversation , we can find out what exactly happened . and this is an interactive , exploratory tool so we can go through every step in the conversation . we can look at who the people were , what they said , how old they are , where they live , who follows them , and so on , and so on , and so on . so , the times creates about 6,500 pieces of content every month , and we can model every single one of the conversations that happen around them . and they look somewhat different . depending on the story and depending on how fast people are talking about it and how far the conversation spreads , these structures , which i call these conversational architectures , end up looking different . so , these projects that i 've shown you , i think they all involve the same thing : we can take small pieces of data and by putting them together , we can generate more value , we can do more exciting things with them . but so far we 've only talked about twitter , right ? and twitter is n't all the data . we learned a moment ago that there is tons and tons , tons more data out there . and specifically , i want you to think about one type of data because all of you guys , everybody in this audience , we , we , me as well , are data-making machines . we are producing data all the time . every single one of us , we 're producing data . somebody else , though , is storing that data . usually we put our trust into companies to store that data , but what i want to suggest here is that rather than putting our trust in companies to store that data , we should put the trust in ourselves because we actually own that data . right , that is something we should remember . everything that someone else measures about you , you actually own . so , it 's my hope , maybe because i 'm a canadian , that all of us can come together with this really valuable data that we 've been storing , and we can collectively launch that data toward some of the world 's most difficulty problems because big data can solve big problems , but i think it can do it the best if it 's all of us who are in control . thank you .

but so far we 've only talked about twitter , right ? and twitter is n't all the data . we learned a moment ago that there is tons and tons , tons more data out there .

list a few other ways you think data captured from twitter can be used .

for most of us , two degrees celsius is a tiny difference in temperature , not even enough to make you crack a window . but scientists have warned that as co2 levels in the atmosphere rise , an increase in the earth 's temperature by even this amount can lead to catastrophic effects all over the world . how can such a small measurable change in one factor lead to massive and unpredictable changes in other factors ? the answer lies in the concept of a mathematical tipping point , which we can understand through the familiar game of billiards . the basic rule of billiard motion is that a ball will go straight until it hits a wall , then bounce off at an angle equal to its incoming angle . for simplicity 's sake , we 'll assume that there is no friction , so balls can keep moving indefinitely . and to simplify the situation further , let 's look at what happens with only one ball on a perfectly circular table . as the ball is struck and begins to move according to the rules , it follows a neat star-shaped pattern . if we start the ball at different locations , or strike it at different angles , some details of the pattern change , but its overall form remains the same . with a few test runs , and some basic mathematical modeling , we can even predict a ball 's path before it starts moving , simply based on its starting conditions . but what would happen if we made a minor change in the table 's shape by pulling it apart a bit , and inserting two small straight edges along the top and bottom ? we can see that as the ball bounces off the flat sides , it begins to move all over the table . the ball is still obeying the same rules of billiard motion , but the resulting movement no longer follows any recognizable pattern . with only a small change to the constraints under which the system operates , we have shifted the billiard motion from behaving in a stable and predictable fashion , to fluctuating wildly , thus creating what mathematicians call chaotic motion . inserting the straight edges into the table acts as a tipping point , switching the systems behavior from one type of behavior ( regular ) , to another type of behavior ( chaotic ) . so what implications does this simple example have for the much more complicated reality of the earth 's climate ? we can think of the shape of the table as being analogous to the co2 level and earth 's average temperature : constraints that impact the system 's performance in the form of the ball 's motion or the climate 's behavior . during the past 10,000 years , the fairly constant co2 atmospheric concentration of 270 parts per million kept the climate within a self-stabilizing pattern , fairly regular and hospitable to human life . but with co2 levels now at 400 parts per million , and predicted to rise to between 500 and 800 parts per million over the coming century , we may reach a tipping point where even a small additional change in the global average temperature would have the same effect as changing the shape of the table , leading to a dangerous shift in the climate 's behavior , with more extreme and intense weather events , less predictability , and most importantly , less hospitably to human life . the hypothetical models that mathematicians study in detail may not always look like actual situations , but they can provide a framework and a way of thinking that can be applied to help understand the more complex problems of the real world . in this case , understanding how slight changes in the constraints impacting a system can have massive impacts gives us a greater appreciation for predicting the dangers that we can not immediately percieve with our own senses . because once the results do become visible , it may already be too late .

with a few test runs , and some basic mathematical modeling , we can even predict a ball 's path before it starts moving , simply based on its starting conditions . but what would happen if we made a minor change in the table 's shape by pulling it apart a bit , and inserting two small straight edges along the top and bottom ? we can see that as the ball bounces off the flat sides , it begins to move all over the table .

the shape of a billiard table is altered by adding small straight edges ( one on the top and one on the bottom ) . choose the best description of what occurs when a billiard ball is hit :

this just in : `` thief robs town with world 's largest chocolate bunny . '' wait , so are we talking about this , or this ? that 's a classic case of a misplaced modifier , a common grammatical mistake that can dramatically change the meaning of a sentence . and lest you think this is a bit far-fetched , confusing headlines like this appear all the time . modifiers are words , phrases , and clauses that add information about other parts of a sentence , which is usually helpful . but when modifiers are n't linked clearly enough to the words they 're actually referring to , they can create unintentional ambiguity . that happens because the modifying words , in this case , `` with world 's largest chocolate bunny , '' modify the wrong thing , the robber 's actions instead of the town . to correct this particular sentence , we simply rephrase to make it clearer what the modifying phrase is talking about . `` town with world 's largest chocolate bunny robbed by thief . '' now , at least it 's clear that the thief was n't armed with a giant chocolate animal . sometimes , modifying words , phrases , or clauses do n't appear to be modifying anything at all . that 's called a dangling modifier . `` having robbed the bank in record time , it was possible to make off with the town 's chocolate rabbit as well . '' the modifying phrase in this sentence seems unrelated to anything else , and so we 're clueless about who the chocolate-loving criminal could possibly be . giving the modifier something to modify will solve the problem . then there 's another group called the squinting modifiers because they 're stuck between two things and could feasibly refer to either . often , these modifiers are adverbs , like the one in this sentence : `` robbers who steal chocolate bunnies rapidly attract the outrage of onlookers . '' `` rapidly '' is the modifier , here , but what 's not clear is whether it 's referring to the speed of the chocolate thievery , or how quickly it alerts the furious onlookers . to clarify , we can either put the modifier closer to its intended phrase , which works in some cases , or we can entirely reword the sentence so that the modifier no longer squints , but clearly applies to only one part . `` chocolate bunny-thieving robbers rapidly attract the outrage of onlookers . '' justice will eventually come to the chocolate thief , but in the meantime , our task is to avoid verbal ambiguity by making it clear which parts of the sentences modifiers belong to . that way , we can at least maintain grammatical law and order .

giving the modifier something to modify will solve the problem . then there 's another group called the squinting modifiers because they 're stuck between two things and could feasibly refer to either . often , these modifiers are adverbs , like the one in this sentence : `` robbers who steal chocolate bunnies rapidly attract the outrage of onlookers . ''

briefly explain the difference between squinting and dangling modifiers .

translator : ido dekkers reviewer : ariana bleau lugo say you 're at the beach , and you get sand in your eyes . how do you know the sand is there ? you obviously ca n't see it , but if you are a normal , healthy human , you can feel it , that sensation of extreme discomfort , also known as pain . now , pain makes you do something , in this case , rinse your eyes until the sand is gone . and how do you know the sand is gone ? exactly . because there 's no more pain . there are people who do n't feel pain . now , that might sound cool , but it 's not . if you ca n't feel pain , you could get hurt , or even hurt yourself and never know it . pain is your body 's early warning system . it protects you from the world around you , and from yourself . as we grow , we install pain detectors in most areas of our body . these detectors are specialized nerve cells called nociceptors that stretch from your spinal cord to your skin , your muscles , your joints , your teeth and some of your internal organs . just like all nerve cells , they conduct electrical signals , sending information from wherever they 're located back to your brain . but , unlike other nerve cells , nociceptors only fire if something happens that could cause or is causing damage . so , gently touch the tip of a needle . you 'll feel the metal , and those are your regular nerve cells . but you wo n't feel any pain . now , the harder you push against the needle , the closer you get to the nociceptor threshold . push hard enough , and you 'll cross that threshold and the nociceptors fire , telling your body to stop doing whatever you 're doing . but the pain threshold is n't set in stone . certain chemicals can tune nociceptors , lowering their threshold for pain . when cells are damaged , they and other nearby cells start producing these tuning chemicals like crazy , lowering the nociceptors ' threshold to the point where just touch can cause pain . and this is where over-the-counter painkillers come in . aspirin and ibuprofen block production of one class of these tuning chemicals , called prostaglandins . let 's take a look at how they do that . when cells are damaged , they release a chemical called arachidonic acid . and two enzymes called cox-1 and cox-2 convert this arachidonic acid into prostaglandin h2 , which is then converted into a bunch of other chemicals that do a bunch of things , including raise your body temperature , cause inflammation and lower the pain threshold . now , all enzymes have an active site . that 's the place in the enzyme where the reaction happens . the active sites of cox-1 and cox-2 fit arachidonic acid very cozily . as you can see , there is no room to spare . now , it 's in this active site that aspirin and ibuprofen do their work . so , they work differently . aspirin acts like a spine from a porcupine . it enters the active site and then breaks off , leaving half of itself in there , totally blocking that channel and making it impossible for the arachidonic acid to fit . this permanently deactivates cox-1 and cox-2 . ibuprofen , on the other hand , enters the active site , but does n't break apart or change the enzyme . cox-1 and cox-2 are free to spit it out again , but for the time that that ibuprofen is in there , the enzyme ca n't bind arachidonic acid , and ca n't do its normal chemistry . but how do aspirin and ibuprofen know where the pain is ? well , they do n't . once the drugs are in your bloodstream , they are carried throughout your body , and they go to painful areas just the same as normal ones . so that 's how aspirin and ibuprofen work . but there are other dimensions to pain . neuropathic pain , for example , is pain caused by damage to our nervous system itself ; there does n't need to be any sort of outside stimulus . and scientists are discovering that the brain controls how we respond to pain signals . for example , how much pain you feel can depend on whether you 're paying attention to the pain , or even your mood . pain is an area of active research . if we can understand it better , maybe we can help people manage it better .

push hard enough , and you 'll cross that threshold and the nociceptors fire , telling your body to stop doing whatever you 're doing . but the pain threshold is n't set in stone . certain chemicals can tune nociceptors , lowering their threshold for pain . when cells are damaged , they and other nearby cells start producing these tuning chemicals like crazy , lowering the nociceptors ' threshold to the point where just touch can cause pain . and this is where over-the-counter painkillers come in .

why do nociceptors cells have a threshold ( think about what would happen if they didn ’ t ) ? and why is that threshold changeable ? think about situations in which your body might want to “ turn up the pain volume ” ( or turn it down ) .

translator : tom carter reviewer : bedirhan cinar most people have heard the word `` gerrymandering '' once or twice , probably during a presidential election . what exactly is gerrymandering ? essentially , it 's the process of giving one political party an advantage over another political party by redrawing district lines . it 's like democrats trying to gain an advantage over republicans , or republicans trying to gain an advantage over democrats . you see , each party wants to gain as many districts as possible so they can do things like control the state budget , or set themselves up to win even more districts in the future . so to understand how this process began , and how it continues today , we must go back to 1812 in massachusetts . elbridge gerry , the governor of massachusetts , supported and signed a bill to allow redistricting . that is , redrawing the boundaries that separate districts . the catch ? the new lines would favor gerry 's own political party , the democratic-republican party , which no longer exists . you see , gerry wanted his party to win as many state senate seats as possible . the more members of your party who vote , the more likely you are to win an election . the new lines were drawn to include loads of areas that would help governor gerry in the future . they were so strange looking that someone said the new districts looked like a salamander . the boston gazette added gerry 's name to the word salamander , and voilà ! gerrymandering , the process of dividing up and redrawing districts to give your political party an advantage . so how exactly does someone go about protecting their own political party , and actually gerrymandering a district ? there are two successful practices . packing a district , and cracking a district . packing is the process of drawing district lines and packing in your opponents like cattle , into as few districts as possible . if more districts equals more votes , the fewer the districts there are , the fewer votes the opposition party will get . packing , then , decreases the opponent 's voter strength and influence . cracking is the opposite : taking one district and cracking it into several pieces . this is usually done in districts where your opponent has many supporters . cracking spreads these supporters out among many districts , denying your opponent a lot of votes . when you have a large number of people who would generally vote for one type of party , those folks are known as a voting bloc . cracking is a way to break that all up . so when would a party choose to pack their opponent 's districts rather than crack them ? well , that really depends on what the party needs . to dilute your opponent 's voters , you could pack them into one district and leave the surrounding districts filled with voters of your own party . or , if you and your party are in power when it 's time to redraw district lines , you could redraw districts and crack up a powerful district and spread your opponent 's voters out across several neighboring districts . so , governor gerry in 1812 wanted to gain an advantage for his party , and redrew district lines in his state in such a crazy way we have a whole new word and way of thinking about how political parties can gain advantages over their opponents . politicians think of creative ways to draw districts every few years . so the next time an election comes around , and politicians ask people to vote , be sure to look up the shape of your district and the districts that surround it . how wide does your district stretch across your state ? are all of the districts in your state relatively the same shape ? how many other districts does your district touch ? but always be sure to ask yourself , does my district look like a salamander ?

so how exactly does someone go about protecting their own political party , and actually gerrymandering a district ? there are two successful practices . packing a district , and cracking a district .

what are the two successful practices for effective gerrymandering ?

`` hey , another atom . i 'm hydrogen , nice to meet you . how are you feeling about the jump ? '' `` hi there , i 'm antihydrogen , your antiatom , and to be honest , i 'm feeling kind of neutral . my positron and antiproton balance out , just like your electron and proton , right ? '' `` hey , yeah ! you look just like me , but different somehow . '' `` whoa , be careful ! if we get too close , we 'll disappear in a spark of energy . i 'd like to stay in one piece . '' `` oh wow , sorry . '' `` it 's okay . i was just thinking , it 's kind of weird for us to be chatting like this before our jump above cern . '' `` why 's that ? '' `` well , for starters , how do we know we 'll both fall ? '' `` of course we 'll fall . it 's gravity , you know , the force of attraction between masses . i even know how fast we should fall . galileo showed in that tower experiment that all falling objects accelerate at the same rate , regardless of mass . '' `` that 's for bigger objects . it 's a different story for small particles like us . our mass is so tiny that the gravitational force we experience is miniscule , and if the particles are charged , like my antiproton or your proton , then it becomes impossible to detect compared to the much greater electromagnetic force acting on them . '' `` but that 's only for charged particles . you and i are both neutral . our charges balance out , so the electromagnetic force is small and the gravitational force should be detectable . i know mine 's been measured . '' `` because you 're everywhere , but i 'm kind of hard to find . '' `` why is that , anyway ? should n't there have been an equal amount of matter and antimatter created in the big bang ? '' `` you 'd think so , but then all of those particles would have annihilated each other into energy , remember ? and the universe is obviously full of matter . no one knows why there is more matter than antimatter , which is why scientists are so interested in studying me . '' `` so where do they find you anyway ? '' `` actually , i was made in that lab down there . they needed an accelerator to make my antiproton because it 's so heavy , just as heavy as your proton . getting my positron was easier . it 's much lighter , like your electron , and there are materials that naturally decay by emitting one . then they just had to put the two together and they got me . but it 's only recently that they 've been able to keep me around long enough to study my properties . '' `` and now they 've sent you on this jump with me . hey , wait a minute . '' `` that 's right . we 're reenacting galileo 's experiment , but with matter and antimatter instead of two objects made of matter . '' `` so what 's going to happen ? are you going to fall upwards or something ? '' `` only one way to find out ! ''

`` hi there , i 'm antihydrogen , your antiatom , and to be honest , i 'm feeling kind of neutral . my positron and antiproton balance out , just like your electron and proton , right ? '' `` hey , yeah !

what is the charge of an antiproton ?