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translator : andrea mcdonough reviewer : jessica ruby the world we live in is made of things , billions and billions of different things , like pickles and pianos and dump trucks and octopi . and even though these things seem totally different , they 're all made of the same stuff , just combined in different ways . to give you an idea of how this combining works , let 's take something apart . let 's start with this bowl of macaroni salad . if you were to reverse a recipe for macaroni salad , you 'll see it 's made by mixing together a bunch of ingredients , like macaroni , mayo , vinegar , vegetables , and mustard . this type of combining is called a mixture . when you make a mixture , you 're combining two or more things together without actually changing the chemical identity of those things . like mud , for example . the soil and water in mud have n't actually changed . they 're still soil and water , you 've just created a mixture of soil and water -- mud . it turns out that macaroni salad is actually a mixture of mixtures because many of the ingredients , like mayo and mustard , are already mixtures themselves , which is nice for us because if we look closely , we 'll the see the three main types of mixtures that exist . the size of the particles in a mixture determines the type of mixture . on one end of the scale is a suspension , like our muddy water example . you get this if you take big chunks of something and mix it with something else so those chunks are just floating around . take runny mustard for example . you 'll see a bunch of little particles like mustard seeds , pepper , allspice , and minced shallots all floating around in a liquid , in this case vinegar with water . this is called a suspension because you 've got particles of one thing suspended in another . now , on the other end of the spectrum is a solution . the particles in this mixture are so small , they are the actual molecules . a solution is sort of like a suspension of molecules where one type of molecule is blended or dissolved with another . vinegar is an example of a solution where the molecules of acetic acid are blended with molecules of water . the chemical properties of the molecules have n't changed , they 're just evenly mixed together now . saltwater and carbonated soda are both examples of solutions where other molecules are dissolved in water . the last type of mixture is called a colloid , which is somewhere between a suspension and a solution . it 's when you take two materials that do n't dissolve and you make the particles so small that they ca n't separate . mayo is what happens when you take oil and water , which do n't mix , and you bind them together , usually with the help of another substance called an emulsifier . in the case of mayo , it 's lecithin , found in eggs . and now you are left with really small globs of oil hanging out with really small droplets of water . whipped cream , hairspray , styrofoam , and jello are all other examples of colloids . so , let 's get back to macaroni salad . you 've call colloids like mayo , suspensions like mustard , and solutions like vinegar , but you 've also got celery , shallots , and all other vegetable chunks that are also part of the salad . these are n't mixtures , really , but we can break them up , just like a tv can be broken up into smaller and smaller complex component parts . in the case of vegetables , if you keep breaking things up , they 'll eventually end with thousands of complex organic molecules , things like atp synthase and rna transcriptase and water . so now , once we 've unblended all the solutions , unmixed all the colloids , separated all the suspensions and taken apart all of our vegetables , we 've reached the end of what we can unmix physically . what we 're left with is a whole bunch of molecules , and these molecules remain chemically the same whether they are by themselves or thrown together in a salad . if you want to separate these guys even further , we need to unmix things chemically , which means we need to start breaking some bonds .

it turns out that macaroni salad is actually a mixture of mixtures because many of the ingredients , like mayo and mustard , are already mixtures themselves , which is nice for us because if we look closely , we 'll the see the three main types of mixtures that exist . the size of the particles in a mixture determines the type of mixture . on one end of the scale is a suspension , like our muddy water example .

what is not characteristic of a mixture ?

translator : tom carter reviewer : bedirhan cinar it is the spring of 1787 . the revolutionary war has been over for only six years , and the young united states is still struggling in its infancy . uprisings , boundary disputes and the lack of a common vision all plague the newborn country . in an effort to steady this precarious ship , the confederation congress calls on states to send delegates to the grand convention , to begin on may 14 in philadelphia . the delegates must draft revisions to the articles of confederation , which would then be considered by the congress and approved by the states . under the terms of the articles , all 13 states had to agree to any changes . since the purpose of the convention is just to make recommendations , not everyone is excited about attending , and frankly , some think it 's a waste of time . as men from different parts of the country began to travel down dusty , rugged roads on the way to philadelphia , not all states send delegates . in fact , rhode island never even shows up . on may 14th , only 8 delegates -- not states , but individual delegates -- are present , so they wait . finally , on may 25th , the necessary quorum of seven states is acheived . in all , 55 delegates arrive in philadelphia over the course of the convention . they are all white males , property owners , and the average age is about 44 . some are slaveholders , some had signed the declaration of independence , [ james madison , roger sherman ] and almost all are well-educated . [ benjamin franklin ] picture the delegates , james madison and george washington among them , sitting in independence hall in hot , humid philadelphia . they 're all wearing the dress of the day : frock coats , high collars and thick pants . they vote to keep their discussions secret to encourage honest debate . but that means the windows are closed , and there is no air conditioning in 1787 , not even an electric fan . and they 'll sit in that sweltering heat , in those heavy clothes , for three months . shockingly , they all keep their vow of secrecy . that could never happen today , not even for an hour-long meeting . someone would share `` james madison thinks he 's so smart . keyword : articles are dead '' via social media , and the whole thing would be a disaster . but in 1787 , there are no leaks . not even a drip that hints at what they are doing . and what they are doing is nothing short of overthrowing the very government that sent them there . within a few days , with only a seven-state quorum , and only six of those states agreeing , a handful of men change the course of history . they vote to get rid of the articles of confederation , and write a new , more nationalistic document that becomes our constitution . the risk is immense . everyone on the outside assumes they were working on recommended revisions to the articles . it 's an incredible gamble , and even when the convention presents the signed constitution on september 17th , not all delegates endorse it . the country will argue and debate for two more years before the document is adopted by the required nine out of 13 states . but instead of punishing them for their deception , today we celebrate the wisdom and vision of those men in philadelphia .

finally , on may 25th , the necessary quorum of seven states is acheived . in all , 55 delegates arrive in philadelphia over the course of the convention . they are all white males , property owners , and the average age is about 44 .

the group of delegates that originally advocated a strong national government was a minority . how do you think were they able to achieve their objective , and achieve it relatively quickly during the initial days of the grand convention ?

if you lined up all the blood vessels in your body , they 'd be 95,000 kilometers long and everyday , they carry the equivalent of over 7,500 liters of blood , though that 's actually the same four or five liters recycled over and over , delivering oxygen , and precious nutrients like glucose and amino acids to the body 's tissues . all that blood exerts a force on the muscular walls of the blood vessels . that force is called blood pressure , and it rises and falls with the phases of the heartbeat . it 's highest during systole , when the heart contracts to force blood through the arteries . this is your systolic blood pressure . when the heart is at rest between beats , blood pressure falls to its lowest value , the diastolic pressure . a typical healthy individual produces a systolic pressure between 90 and 120 millimeters of mercury , and diastolic pressure between 60 and 80 . taken together , a normal reading is a bit less than 120 over 80 . the blood traverses the landscape of the body through the pipes of the circulatory system . in any plumbing system , several things can increase the force on the walls of the pipes : the properties of the fluid , extra fluid , or narrower pipes . so if the blood thickens , a higher pressure is needed to push it , so the heart will pump harder . a high-salt diet will lead to a similar result . the salt promotes water retention , and the extra fluid increases the blood volume and blood pressure , and stress , like the fight or flight response , releases hormones , like epinephrine and norepinephrine that constrict key vessels , increasing the resistance to flow and raising the pressure upstream . blood vessels can usually handle these fluctuations easily . elastic fibers embedded in their walls make them resilient , but if your blood pressure regularly rises above about 140 over 90 , what we call hypertension , and stays there , it can cause serious problems . that 's because the extra strain on the arterial wall can produce small tears . when the injured tissue swells up , substances that respond to the inflammation , like white blood cells , collect around the tears . fat and cholesterol floating in the blood latch on , too , eventually building up to form a plaque that stiffens and thickens the inner arterial wall . this condition is called atherosclerosis , and it can have dangerous consequences . if the plaque ruptures , a blood clot forms on top of the tear , clogging the already narrowed pipe . if the clot is big enough , it can completely block the flow of oxygen and nutrients to cells downstream . in vessels that feed the heart , that will cause a heart attack , when oxygen-deprived cardiac muscle cells start to die . if the clot cuts off blood flow to the brain , it causes a stroke . dangerously clogged blood vessels can be widened by a procedure called an angioplasty . there , doctors thread a wire through the vessel to the obstructed site , and then place a deflated balloon catheter over the wire . when the balloon is inflated , it forces the passageway open again . sometimes a rigid tube called a stent is placed in a vessel to held hold it open , letting the blood flow freely to replenish the oxygen-starved cells downstream . staying flexible under pressure is a tough job for arteries . the fluid they pump is composed of substances that can get sticky and clog them , and your typical healthy heart beats about 70 times a minute , and at least 2.5 billion times during an average lifetime . that may sound like an insurmountable amount of pressure , but do n't worry , your arteries are well suited for the challenge .

it 's highest during systole , when the heart contracts to force blood through the arteries . this is your systolic blood pressure . when the heart is at rest between beats , blood pressure falls to its lowest value , the diastolic pressure .

a 56-year-old patient comes to your clinic , presenting with a blood pressure of 142/95 mm hg . would you describe this patient as hypertensive ? if so , what three questions would you ask them in order to determine the cause of their condition ? why did you choose these questions in particular ?

this is the story of three plastic bottles , empty and discarded . their journeys are about to diverge with outcomes that impact nothing less than the fate of the planet . but they were n't always this way . to understand where these bottles end up , we must first explore their origins . the heroes of our story were conceived in this oil refinery . the plastic in their bodies was formed by chemically bonding oil and gas molecules together to make monomers . in turn , these monomers were bonded into long polymer chains to make plastic in the form of millions of pellets . those were melted at manufacturing plants and reformed in molds to create the resilient material that makes up the triplets ' bodies . machines filled the bottles with sweet bubbily liquid and they were then wrapped , shipped , bought , opened , consumed and unceremoniously discarded . and now here they lie , poised at the edge of the unknown . bottle one , like hundreds of millions of tons of his plastic brethren , ends up in a landfill . this huge dump expands each day as more trash comes in and continues to take up space . as plastics sit there being compressed amongst layers of other junk , rainwater flows through the waste and absorbs the water-soluble compounds it contains , and some of those are highly toxic . together , they create a harmful stew called leachate , which can move into groundwater , soil and streams , poisoning ecosystems and harming wildlife . it can take bottle one an agonizing 1,000 years to decompose . bottle two 's journey is stranger but , unfortunately , no happier . he floats on a trickle that reaches a stream , a stream that flows into a river , and a river that reaches the ocean . after months lost at sea , he 's slowly drawn into a massive vortex , where trash accumulates , a place known as the great pacific garbage patch . here the ocean 's currents have trapped millions of pieces of plastic debris . this is one of five plastic-filled gyres in the world 's seas . places where the pollutants turn the water into a cloudy plastic soup . some animals , like seabirds , get entangled in the mess . they , and others , mistake the brightly colored plastic bits for food . plastic makes them feel full when they 're not , so they starve to death and pass the toxins from the plastic up the food chain . for example , it 's eaten by lanternfish , the lanternfish are eaten by squid , the squid are eaten by tuna , and the tuna are eaten by us . and most plastics do n't biodegrade , which means they 're destined to break down into smaller and smaller pieces called micro plastics , which might rotate in the sea eternally . but bottle three is spared the cruel purgatories of his brothers . a truck brings him to a plant where he and his companions are squeezed flat and compressed into a block . okay , this sounds pretty bad , too , but hang in there . it gets better . the blocks are shredded into tiny pieces , which are washed and melted , so they become the raw materials that can be used again . as if by magic , bottle three is now ready to be reborn as something completely new . for this bit of plastic with such humble origins , suddenly the sky is the limit .

some animals , like seabirds , get entangled in the mess . they , and others , mistake the brightly colored plastic bits for food . plastic makes them feel full when they 're not , so they starve to death and pass the toxins from the plastic up the food chain . for example , it 's eaten by lanternfish , the lanternfish are eaten by squid , the squid are eaten by tuna , and the tuna are eaten by us .

list the ways you could help to reduce plastic waste and its environmental impact .

translator : bedirhan cinar why do we cringe when we hear `` shakespeare ? '' if you ask me , it 's usually because of his words . all those thines and thous and therefores and wherefore-art-thous can be more than a little annoying . but you have to wonder , why is he so popular ? why have his plays been made and remade more than any other playwright ? it 's because of his words . back in the late 1500s and early 1600s , that was the best tool that a person had , and there was a lot to talk about . however , most of it was pretty depressing . you know , with the black plague and all . shakespeare does use a lot of words . one of his most impressive accomplishments is his use of insults . they would unify the entire audience ; and no matter where you sat , you could laugh at what was going on onstage . words , specifically dialogue in a drama setting , are used for many different reasons : to set the mood of the scene , to give some more atmosphere to the setting , and to develop relationships between characters . insults do this in a very short and sharp way . let 's first go to `` hamlet . '' right before this dialogue , polonius is the father of ophelia , who is in love with prince hamlet . king claudius is trying to figure out why prince hamlet is acting so crazy since the king married prince hamlet 's mother . polonius offers to use his daughter to get information from prince hamlet . then we go into act ii scene 2 . polonius : `` do you know me , my lord ? '' hamlet : `` excellent well . you 're a fishmonger . '' polonius : `` not i , my lord . '' hamlet : `` then i would you were so honest a man . '' now , even if you did not know what `` fishmonger '' meant , you can use some contextual clues . one : polonius reacted in a negative way , so it must be bad . two : fish smell bad , so it must be bad . and three : `` monger '' just does n't sound like a good word . so from not even knowing the meaning , you 're beginning to construct some characterization of the relationship between hamlet and polonius , which was not good . but if you dig some more , `` fishmonger '' means a broker of some type , and in this setting , would mean like a pimp , like polonius is brokering out his daughter for money , which he is doing for the king 's favor . this allows you to see that hamlet is not as crazy as he 's claiming to be , and intensifies the animosity between these two characters . want another example ? `` romeo and juliet '' has some of the best insults of any of shakespeare 's plays . it 's a play about two gangs , and the star-crossed lovers that take their own lives . well , with any fisticuffs you know that there is some serious smack talk going on . and you are not disappointed . in act i scene 1 , right from the get-go we are shown the level of distrust and hatred the members of the two families , the capulets and montagues , meet . gregory : `` i will frown as i pass by , and let them take it as they list . '' sampson : `` nay , as they dare , i will bite my thumb at them , which is a disgrace to them , if they bear it . '' enter abraham and balthasar . abraham : `` do you bite your thumb at us , sir ? '' sampson : `` i do bite my thumb , sir . '' abraham : `` do you bite your thumb at us , sir ? '' okay , so how does this development help us understand mood or character ? well , let 's break it down to the insult . biting your thumb today may not seem like a big deal , but sampson says it is an insult to them . if they take it so , it must have been one . this begins to show us the level of animosity between even the men who work for the two houses . and you normally would not do anything to someone unless you wanted to provoke them into a fight , which is exactly what 's about to happen . looking deeper , biting your thumb in the time in which the play was written is like giving someone the finger today . a pretty strong feeling comes with that , so we now are beginning to feel the tension in the scene . later on in the scene , tybalt , from the house of the capulets , lays a good one on benvolio from the house of the montagues . tybalt : `` what , art thou drawn among these heartless hinds ? turn thee , benvolio , and look upon thy death . '' benvolio : `` i do but keep the peace ; put up thy sword , or manage it to part these men with me . '' tybalt : `` what , drawn and talk of peace ! i hate the word , as i hate hell , all montagues , and thee . have at thee , coward ! '' okay , heartless hinds . we know that once again , it 's not a good thing . both families hate each other , and this is just adding fuel to the fire . but just how bad is this stinger ? a heartless hind is a coward , and calling someone that in front of his own men , and the rival family , means there 's going to be a fight . tybalt basically calls out benvolio , and in order to keep his honor , benvolio has to fight . this dialogue gives us a good look at the characterization between these two characters . tybalt thinks that the montagues are nothing but cowardly dogs , and has no respect for them . once again , adding dramatic tension to the scene . okay , now here 's a spoiler alert . tybalt 's hotheadedness and severe hatred of the montagues is what we literature people call his hamartia , or what causes his downfall . oh , yes . he goes down at the hands of romeo . so when you 're looking at shakespeare , stop and look at the words , because they really are trying to tell you something .

and you normally would not do anything to someone unless you wanted to provoke them into a fight , which is exactly what 's about to happen . looking deeper , biting your thumb in the time in which the play was written is like giving someone the finger today . a pretty strong feeling comes with that , so we now are beginning to feel the tension in the scene .

what happens in romeo and juliet that is akin to giving someone the finger ?

`` hi , bob . '' `` morning , kelly . the tulips looks great . '' have you ever wondered how your dog experiences the world ? here 's what she sees . not terribly interesting . but what she smells , that 's a totally different story . and it begins at her wonderfully developed nose . as your dog catches the first hints of fresh air , her nose 's moist , spongy outside helps capture any scents the breeze carries . the ability to smell separately with each nostril , smelling in stereo , helps to determine the direction of the smell 's source so that within the first few moments of sniffing , the dog starts to become aware of not just what kind of things are out there but also where they 're located . as air enters the nose , a small fold of tissue divides it into two separate folds , one for breathing and one just for smelling . this second airflow enters a region filled with highly specialized olfactory receptor cells , several hundred millions of them , compaired to our five million . and unlike our clumsy way of breathing in and out through the same passage , dogs exhale through slits at the side of their nose , creating swirls of air that help draw in new odor molecules and allow odor concentration to build up over mulitple sniffs . but all that impressive nasal architecture would n't be much help without something to process the loads of information the nose scoops up . and it turns out that the olfactory system dedicated to proessing smells takes up many times more relative brain area in dogs than in humans . all of this allows dogs to distinguish and remember a staggering variety of specific scents at concentrations up to 100 million times less than what our noses can detect . if you can smell a spritz of perfume in a small room , a dog would have no trouble smelling it in an enclosed stadium and distinguishing its ingredients , to boot . and everything in the street , every passing person or car , any contents of the neighbor 's trash , each type of tree , and all the birds and insects in it has a distinct odor profile telling your dog what it is , where it is , and which direction it 's moving in . besides being much more powerful than ours , a dog 's sense of smell can pick up things that ca n't even be seen at all . a whole separate olfactory system , called the vomeronasal organ , above the roof of the mouth , detects the hormones all animals , including humans , naturally release . it lets dogs identify potential mates , or distinguish between friendly and hostile animals . it alerts them to our various emotional states , and it can even tell them when someone is pregnant or sick . because olfaction is more primal than other senses , bypassing the thalamus to connect directly to the brain structures involving emotion and instinct , we might even say a dog 's perception is more immediate and visceral than ours . but the most amazing thing about your dog 's nose is that it can traverse time . the past appears in tracks left by passersby , and by the warmth of a recently parked car where the residue of where you 've been and what you 've done recently . landmarks like fire hydrants and trees are aromatic bulletin boards carrying messages of who 's been by , what they 've been eating , and how they 're feeling . and the future is in the breeze , alerting them to something or someone approaching long before you see them . where we see and hear something at a single moment , a dog smells an entire story from start to finish . in some of the best examples of canine-human collaboration , dogs help us by sharing and reacting to those stories . they can respond with kindness to people in distress , or with aggression to threats because stress and anger manifest as a cloud of hormones recognizable to the dog 's nose . with the proper training , they can even alert us to invisible threats ranging from bombs to cancer . as it turns out , humanity 's best friend is not one who experiences the same things we do , but one whose incredible nose reveals a whole other world beyond our eyes .

but all that impressive nasal architecture would n't be much help without something to process the loads of information the nose scoops up . and it turns out that the olfactory system dedicated to proessing smells takes up many times more relative brain area in dogs than in humans . all of this allows dogs to distinguish and remember a staggering variety of specific scents at concentrations up to 100 million times less than what our noses can detect .

why would the olfactory system in a dog be so much bigger than the olfactory system in a human ?

how many times does the chorus repeat in your favorite song ? and , take a moment to think , how many times have you listened to it ? chances are you 've heard that chorus repeated dozens , if not hundreds , of times , and it 's not just popular songs in the west that repeat a lot . repetition is a feature that music from cultures around the world tends to share . so , why does music rely so heavily on repetition ? one part of the answer come from what psychologists call the mere-exposure effect . in short , people tend to prefer things they 've been exposed to before . for example , a song comes on the radio that we do n't particularly like , but then we hear the song at the grocery store , at the movie theater and again on the street corner . soon , we are tapping to the beat , singing the words , even downloading the track . this mere-exposure effect does n't just work for songs . it also works for everything from shapes to super bowl ads . so , what makes repetition so uniquely prevalent in music ? to investigate , psychologists asked people to listen to musical compositions that avoided exact repetition . they heard excerpts from these pieces in either their original form , or in a version that had been digitally altered to include repetition . although the original versions had been composed by some of the most respected 20th century composers , and the repetitive versions had been assembled by brute force audio editing , people rated the repetitive versions as more enjoyable , more interesting and more likely to have been composed by a human artist . musical repetition is deeply compelling . think about the muppets classic , `` mahna mahna . '' if you 've heard it before , it 's almost impossible after i sing , `` mahna mahna , '' not to respond , `` do doo do do do . '' repetition connects each bit of music irresistibly to the next bit of music that follows it . so when you hear a few notes , you 're already imagining what 's coming next . your mind is unconsciously singing along , and without noticing , you might start humming out loud . recent studies have shown that when people hear a segment of music repeated , they are more likely to move or tap along to it . repetition invites us into music as imagined participants , rather than as passive listeners . research has also shown that listeners shift their attention across musical repetitions , focusing on different aspects of the sound on each new listen . you might notice the melody of a phrase the first time , but when it 's repeated , your attention shifts to how the guitarist bends a pitch . this also occurs in language , with something called semantic satiation . repeating a word like atlas ad nauseam can make you stop thinking about what the word means , and instead focus on the sounds : the odd way the `` l '' follows the `` t. '' in this way , repetition can open up new worlds of sound not accessible on first hearing . the `` l '' following the `` t '' might not be aesthetically relevant to `` atlas , '' but the guitarist pitch bending might be of critical expressive importance . the speech to song illusion captures how simply repeating a sentence a number of times shifts listeners attention to the pitch and temporal aspects of the sound , so that the repeated spoken language actually begins to sound like it is being sung . a similar effect happens with random sequences of sound . people will rate random sequences they 've heard on repeated loop as more musical than a random sequence they 've only heard once . repetition gives rise to a kind of orientation to sound that we think of as distinctively musical , where we 're listening along with the sound , engaging imaginatively with the note about to happen . this mode of listening ties in with our susceptibility to musical ear worms , where segments of music burrow into our head , and play again and again , as if stuck on repeat . critics are often embarrassed by music 's repetitiveness , finding it childish or regressive , but repetition , far from an embarrassment , is actually a key feature that gives rise to the kind of experience we think about as musical .

if you 've heard it before , it 's almost impossible after i sing , `` mahna mahna , '' not to respond , `` do doo do do do . '' repetition connects each bit of music irresistibly to the next bit of music that follows it . so when you hear a few notes , you 're already imagining what 's coming next .

compare the effects of repetition in music and language .

today i ’ m going to tell you about one of my favorite creatures to ever grace this planet . it ’ s a frog that ’ s pretty bizarre but also weirdly sweet and adorable . sadly , it went extinct just before i was born , so i thought i ’ d never get the chance to see it . but a few years ago , scientists tried to bring it back from the dead . i ’ m anna and this is gross science . gastric-brooding frogs were first found in queensland , australia in 1972 . they looked pretty normal—just your average brownish , greenish frog . but there was nothing average about how they gave birth . a female frog would lay her eggs , and a male frog would fertilize them externally . so far so normal . but then , the mother frog would swallow the eggs—around 40 of them ! you ’ d think this would be a terrible idea . after all , stomachs—whether they be frog or human—usually contain strong acid to break down your last meal . but the eggs likely contained a chemical that made the mother ’ s stomach stop producing acid . that meant the mother couldn ’ t eat during her pregnancy , which from a human perspective seems awful , but the frogs seemed to make do . eventually , tadpoles would hatch from the eggs . and the tadpoles would release mucus that contained more of that acid-blocking chemical . the babies would continue to grow in the stomach for another 6 weeks , getting so big that they ’ d compress the mother ’ s lungs . luckily , these frogs could also breathe through their skin , so the mothers didn ’ t suffocate . finally , the tadpoles would metamorphose into baby frogs , and the mother would vomit them up—usually one at a time over a few days . though , when provoked some were known to projectile vomit all their babies out at once . while barfing up your babies sounds ... horrible ... it ’ s kinda sweet when you think about it . gastric-brooding , as this strategy is called , is a way to keep your babies close to you and safe while they ’ re most vulnerable . it ’ s really a lot like human pregnancy…only the babies come out the other end… anyway , there were two species of these frogs , but both went extinct by the mid-80s . the culprit was likely an invasive fungus—one that poses a major threat to amphibians worldwide , and that humans likely helped to spread around the globe . it ’ s called chytrid fungus and it affects a frog ’ s skin . because frogs use their skin for crucial functions like breathing , staying hydrated , and regulating their temperature , the parasite can easily kill its victims . and it ’ s highly contagious—by 2013 it had put 42 % of the world ’ s frog species in danger . losing all these frogs would be , in a word , devastating . not only would it have major impacts on ecosystems worldwide , and be a loss of beautiful biodiversity , but there is so much we still have to learn from these creatures that might be beneficial to human health and well-being . take the gastric-brooding frog . if we ’ d had more time to study it , maybe we could have learned more about how it turns off stomach acid production , potentially revealing some insights that could help humans with gi problems . consequently , back in 2013 , some scientists began a project to resurrect the gastric-brooding frog . they took cells from a frozen specimen , cloned the dna into the egg of another frog species , and ended up creating a living gastric-brooding frog embryo . it only survived for about three days , but they haven ’ t given up trying . and it ’ s made some researchers hopeful that “ de-extinction ” —the process of bringing extinct species back to life—will one day be a solution for reviving at least some of the valuable biodiversity we ’ ve lost , often due to humans ’ impact on the environment . obviously , this is a controversial idea . and , i think most scientists would agree that de-extinction is a last-gasp effort in conservation . it in no way means we should stop protecting and preserving the at-risk species we have . that said , while i can ’ t speak to the ethics of the situation , i will admit that there ’ s a pretty big part of me that would love to see a gastric-brooding frog vomiting up its babies . ew .

if we ’ d had more time to study it , maybe we could have learned more about how it turns off stomach acid production , potentially revealing some insights that could help humans with gi problems . consequently , back in 2013 , some scientists began a project to resurrect the gastric-brooding frog . they took cells from a frozen specimen , cloned the dna into the egg of another frog species , and ended up creating a living gastric-brooding frog embryo .

what is the goal of the lazarus project ?

in the early hours of august 13 , 1961 , east german construction workers flanked by soldiers and police began tearing up streets and erecting barriers throughout the city of berlin and its surroundings . this night marked the beginning of one of history 's most infamous dividing lines , the berlin wall . construction on the wall continued for the next decade as it cut through neighborhoods , separated families , and divided not just germany , but the world . to understand how we got to this point , we have to go back to world war ii . america , britain , and france joined forces with the soviet union against the axis powers . after they defeated nazi germany , each of the victorious nations occupied part of the country . the division was meant to be temporary , but the former allies found themselves at odds over their visions for post-war europe . while western powers promoted liberal market economies , the soviet union sought to surround itself with obedient communist nations , including a weakened germany . as their relations deteriorated , the federal republic of germany was formed in the west while the soviets established the german democratic republic in the east . the soviet satellite countries restricted western trade and movement , so a virtually impassable border formed . it became known as the iron curtain . in the former german capital of berlin , things were particularly complicated . although the city lay fully within the east german territory of the gdr , the post-war agreement gave the allies joint administration . so america , britain , and france created a democratic enclave in berlin 's western districts . while east germans were officially banned from leaving the country , in berlin , it was simply a matter of walking , or riding a subway , streetcar or bus , to the western half , then traveling on to west germany or beyond . this open border posed a problem for the east german leadership . they had staked a claim to represent the communist resistance against hitler and portrayed western germany as a continuation of the nazi regime . while the u.s. and its allies poured money into west germany 's reconstruction , the soviet union extracted resources from the east as war reparations , making its planned economy even less competitive . life in east germany passed under the watchful eye of the stasi , the secret police whose wiretaps and informants monitored citizens for any hint of disloyalty . while there was free health care and education in the east , the west boasted higher salaries , more consumer goods , and greater personal freedom . by 1961 , about 3.5 million people , nearly 20 % of the east german population , had left , including many young professionals . to prevent further losses , east germany decided to close the border , and that 's where the berlin wall came in . extending for 43 kilometers through berlin , and a further 112 through east germany , the initial barrier consisted of barbed wire and mesh fencing . some berliners escaped by jumping over the wire or leaving from windows , but as the wall expanded , this became more difficult . by 1965 , 106 kilometers of 3.6-meter-high concrete barricades had been added topped with a smooth pipe to prevent climbing . over the coming years , the barrier was strengthened with spike strips , guard dogs , and even landmines , along with 302 watchtowers and 20 bunkers . a parallel fence in the rear set off a 100-meter area called the death strip . there , all buildings were demolished and the ground covered with sand to provide a clear line of sight for the hundreds of guards ordered to shoot anyone attempting to cross . nevertheless , nearly 5,000 people in total managed to flee east germany between 1961 and 1989 . some were diplomats or athletes who defected while abroad , but others were ordinary citizens who dug tunnels , swam across canals , flew hot air balloons , or even crashed a stolen tank through the wall . yet the risk was great . over 138 people died while attempting escape . some shot in full view of west germans powerless to help them . the wall stabilized east germany 's economy by preventing its work force from leaving , but tarnished its reputation , becoming a global symbol of communist repression . as part of reconciliation with the east , the basic treaty of 1972 recognized east germany pragmatically while west germany retained its hope for eventual reunification . although the eastern regime gradually allowed family visits , it tried to discourage people from exercising these rights with an arduous bureaucratic process and high fees . nonetheless , it was still overwhelmed by applications . by the end of the 1980 's , the liberalization of other eastern bloc regimes caused mass demonstrations for free travel and demands for democracy . on the evening of november 9 , 1989 , east germany tried to defuse tension by making travel permits easier to obtain . but the announcement brought thousands of east berliners to the border crossing points in the wall , forcing the surprised guards to open the gates immediately . rejoicing crowds poured into west berlin as people from both sides danced atop the wall . and others began to demolish it with whatever tools they could find . although the border guards initially tried to maintain order , it was soon clear that the years of division were at an end . after four decades , germany was officially reunified in october 1990 . and the soviet union fell soon after . today , parts of the wall still stand as a reminder that any barriers we put up to impede freedom , we can also break down .

but the announcement brought thousands of east berliners to the border crossing points in the wall , forcing the surprised guards to open the gates immediately . rejoicing crowds poured into west berlin as people from both sides danced atop the wall . and others began to demolish it with whatever tools they could find .

discuss some of the design strategies used by the soviet government when constructing the berlin wall . how did this change over time ? why do you think this was the case ?

`` beauty is a curse , '' psyche thought as she looked over the cliff 's edge where she 'd been abandoned by her father . she 'd been born with the physical perfection so complete that she was worshipped as a new incarnation of venus , the goddess of love . but real-life human lovers were too intimidated even to approach her . when her father asked for guidance from the oracle of apollo , the god of light , reason , and prophecy . he was told to abandon his daughter on a rocky crag where she would marry a cruel and savage serpent-like winged evil . alone on the crag , psyche felt zephyr the west wind gently lifting her into the air . it set her down before a palace . `` you are home , '' she heard an unseen voice say . `` your husband awaits you in the bedroom , if you dare to meet him . '' she was brave enough , psyche told herself . the bedroom was so dark that she could n't see her husband . but he did n't feel serpent-like at all . his skin was soft , and his voice and manner were gentle . she asked him who he was , but he told her this was the one question he could never answer . if she loved him , she would not need to know . his visits continued night after night . before long , psyche was pregnant . she rejoiced , but was also conflicted . how could she raise her baby with a man she 'd never seen ? that night , psyche approached her sleeping husband holding an oil lamp . what she found was the god cupid who sent gods and humans lusting after each other with the pinpricks of his arrows . psyche dropped her lamp , burning cupid with hot oil . he said he 'd been in love with psyche ever since his jealous mother , venus , asked him to embarrass the young woman by pricking her with an arrow . but taken with psyche 's beauty , cupid used the arrow on himself . he did n't believe , however , that gods and humans could love as equals . now that she knew his true form , their hopes for happiness were dashed , so he flew away . psyche was left in despair until the unseen voice returned and told her that it was indeed possible for her and cupid to love each other as equals . encouraged , she set out to find him . but venus intercepted psyche and said she and cupid could only wed if she completed a series of impossible tasks . first , psyche was told to sort a huge , messy pile of seeds in a single night . just as she was abandoning hope , an ant colony took pity on her and helped with the work . successfully passing the first trial , psyche next had to bring venus the fleece of the golden sheep , who had a reputation for disemboweling stray adventurers , but a river god showed her how to collect the fleece the sheep had snagged on briars , and she succeeded . finally , psyche had to travel to the underworld and convince proserpina , queen of the dead , to put a drop of her beauty in a box for venus . once again , the unseen voice came to psyche 's aide . it told her to bring barley cakes for cerberus , the guard dog to the underworld and coins to pay the boatman , charon to ferry her across the river styx . with her third and final task complete , psyche returned to the land of the living . just outside venus 's palace , she opened the box of proserpina 's beauty , hoping to keep some for herself . but the box was filled with sleep , not beauty , and psyche collapsed in the road . cupid , now recovered from his wounds , flew to his sleeping bride . he told her he 'd been wrong and foolish . her fearlessness in the face of the unknown proved that she was more than his equal . cupid gave psyche amborsia , the nectar of the gods , making her immortal . shortly after , psyche bore their daughter . they named her pleasure , and she , cupid , and psyche , whose name means soul , have been complicating people 's love lives ever since .

but taken with psyche 's beauty , cupid used the arrow on himself . he did n't believe , however , that gods and humans could love as equals . now that she knew his true form , their hopes for happiness were dashed , so he flew away .

what motivates the main characters in this myth ? love ? jealousy ? shame ? is there a single emotion driving the story ?

how many times does the chorus repeat in your favorite song ? and , take a moment to think , how many times have you listened to it ? chances are you 've heard that chorus repeated dozens , if not hundreds , of times , and it 's not just popular songs in the west that repeat a lot . repetition is a feature that music from cultures around the world tends to share . so , why does music rely so heavily on repetition ? one part of the answer come from what psychologists call the mere-exposure effect . in short , people tend to prefer things they 've been exposed to before . for example , a song comes on the radio that we do n't particularly like , but then we hear the song at the grocery store , at the movie theater and again on the street corner . soon , we are tapping to the beat , singing the words , even downloading the track . this mere-exposure effect does n't just work for songs . it also works for everything from shapes to super bowl ads . so , what makes repetition so uniquely prevalent in music ? to investigate , psychologists asked people to listen to musical compositions that avoided exact repetition . they heard excerpts from these pieces in either their original form , or in a version that had been digitally altered to include repetition . although the original versions had been composed by some of the most respected 20th century composers , and the repetitive versions had been assembled by brute force audio editing , people rated the repetitive versions as more enjoyable , more interesting and more likely to have been composed by a human artist . musical repetition is deeply compelling . think about the muppets classic , `` mahna mahna . '' if you 've heard it before , it 's almost impossible after i sing , `` mahna mahna , '' not to respond , `` do doo do do do . '' repetition connects each bit of music irresistibly to the next bit of music that follows it . so when you hear a few notes , you 're already imagining what 's coming next . your mind is unconsciously singing along , and without noticing , you might start humming out loud . recent studies have shown that when people hear a segment of music repeated , they are more likely to move or tap along to it . repetition invites us into music as imagined participants , rather than as passive listeners . research has also shown that listeners shift their attention across musical repetitions , focusing on different aspects of the sound on each new listen . you might notice the melody of a phrase the first time , but when it 's repeated , your attention shifts to how the guitarist bends a pitch . this also occurs in language , with something called semantic satiation . repeating a word like atlas ad nauseam can make you stop thinking about what the word means , and instead focus on the sounds : the odd way the `` l '' follows the `` t. '' in this way , repetition can open up new worlds of sound not accessible on first hearing . the `` l '' following the `` t '' might not be aesthetically relevant to `` atlas , '' but the guitarist pitch bending might be of critical expressive importance . the speech to song illusion captures how simply repeating a sentence a number of times shifts listeners attention to the pitch and temporal aspects of the sound , so that the repeated spoken language actually begins to sound like it is being sung . a similar effect happens with random sequences of sound . people will rate random sequences they 've heard on repeated loop as more musical than a random sequence they 've only heard once . repetition gives rise to a kind of orientation to sound that we think of as distinctively musical , where we 're listening along with the sound , engaging imaginatively with the note about to happen . this mode of listening ties in with our susceptibility to musical ear worms , where segments of music burrow into our head , and play again and again , as if stuck on repeat . critics are often embarrassed by music 's repetitiveness , finding it childish or regressive , but repetition , far from an embarrassment , is actually a key feature that gives rise to the kind of experience we think about as musical .

soon , we are tapping to the beat , singing the words , even downloading the track . this mere-exposure effect does n't just work for songs . it also works for everything from shapes to super bowl ads .

the mere exposure effect captures the intution that

i 'll begin today by sharing a poem written by my friend from malawi , eileen piri . eileen is only 13 years old , but when we were going through the collection of poetry that we wrote , i found her poem so interesting , so motivating . so i 'll read it to you . she entitled her poem `` i 'll marry when i want . '' ( laughter ) `` i 'll marry when i want . my mother ca n't force me to marry . my father can not force me to marry . my uncle , my aunt , my brother or sister , can not force me to marry . no one in the world can force me to marry . i 'll marry when i want . even if you beat me , even if you chase me away , even if you do anything bad to me , i 'll marry when i want . i 'll marry when i want , but not before i am well educated , and not before i am all grown up . i 'll marry when i want . '' this poem might seem odd , written by a 13-year-old girl , but where i and eileen come from , this poem , which i have just read to you , is a warrior 's cry . i am from malawi . malawi is one of the poorest countries , very poor , where gender equality is questionable . growing up in that country , i could n't make my own choices in life . i could n't even explore personal opportunities in life . i will tell you a story of two different girls , two beautiful girls . these girls grew up under the same roof . they were eating the same food . sometimes , they would share clothes , and even shoes . but their lives ended up differently , in two different paths . the other girl is my little sister . my little sister was only 11 years old when she got pregnant . it 's a hurtful thing . not only did it hurt her , even me . i was going through a hard time as well . as it is in my culture , once you reach puberty stage , you are supposed to go to initiation camps . in these initiation camps , you are taught how to sexually please a man . there is this special day , which they call `` very special day '' where a man who is hired by the community comes to the camp and sleeps with the little girls . imagine the trauma that these young girls go through every day . most girls end up pregnant . they even contract hiv and aids and other sexually transmitted diseases . for my little sister , she ended up being pregnant . today , she 's only 16 years old and she has three children . her first marriage did not survive , nor did her second marriage . on the other side , there is this girl . she 's amazing . ( laughter ) ( applause ) i call her amazing because she is . she 's very fabulous . that girl is me . ( laughter ) when i was 13 years old , i was told , you are grown up , you have now reached of age , you 're supposed to go to the initiation camp . i was like , `` what ? i 'm not going to go to the initiation camps . '' you know what the women said to me ? `` you are a stupid girl . stubborn . you do not respect the traditions of our society , of our community . '' i said no because i knew where i was going . i knew what i wanted in life . i had a lot of dreams as a young girl . i wanted to get well educated , to find a decent job in the future . i was imagining myself as a lawyer , seated on that big chair . those were the imaginations that were going through my mind every day . and i knew that one day , i would contribute something , a little something to my community . but every day after refusing , women would tell me , `` look at you , you 're all grown up . your little sister has a baby . what about you ? '' that was the music that i was hearing every day , and that is the music that girls hear every day when they do n't do something that the community needs them to do . when i compared the two stories between me and my sister , i said , `` why ca n't i do something ? why ca n't i change something that has happened for a long time in our community ? '' that was when i called other girls just like my sister , who have children , who have been in class but they have forgotten how to read and write . i said , `` come on , we can remind each other how to read and write again , how to hold the pen , how to read , to hold the book . '' it was a great time i had with them . nor did i just learn a little about them , but they were able to tell me their personal stories , what they were facing every day as young mothers . that was when i was like , 'why ca n't we take all these things that are happening to us and present them and tell our mothers , our traditional leaders , that these are the wrong things ? '' it was a scary thing to do , because these traditional leaders , they are already accustomed to the things that have been there for ages . a hard thing to change , but a good thing to try . so we tried . it was very hard , but we pushed . and i 'm here to say that in my community , it was the first community after girls pushed so hard to our traditional leader , and our leader stood up for us and said no girl has to be married before the age of 18 . ( applause ) in my community , that was the first time a community , they had to call the bylaws , the first bylaw that protected girls in our community . we did not stop there . we forged ahead . we were determined to fight for girls not just in my community , but even in other communities . when the child marriage bill was being presented in february , we were there at the parliament house . every day , when the members of parliament were entering , we were telling them , `` would you please support the bill ? '' and we do n't have much technology like here , but we have our small phones . so we said , `` why ca n't we get their numbers and text them ? '' so we did that . it was a good thing . ( applause ) so when the bill passed , we texted them back , `` thank you for supporting the bill . '' ( laughter ) and when the bill was signed by the president , making it into law , it was a plus . now , in malawi , 18 is the legal marriage age , from 15 to 18 . ( applause ) it 's a good thing to know that the bill passed , but let me tell you this : there are countries where 18 is the legal marriage age , but do n't we hear cries of women and girls every day ? every day , girls ' lives are being wasted away . this is high time for leaders to honor their commitment . in honoring this commitment , it means keeping girls ' issues at heart every time . we do n't have to be subjected as second , but they have to know that women , as we are in this room , we are not just women , we are not just girls , we are extraordinary . we can do more . and another thing for malawi , and not just malawi but other countries : the laws which are there , you know how a law is not a law until it is enforced ? the law which has just recently passed and the laws that in other countries have been there , they need to be publicized at the local level , at the community level , where girls ' issues are very striking . girls face issues , difficult issues , at the community level every day . so if these young girls know that there are laws that protect them , they will be able to stand up and defend themselves because they will know that there is a law that protects them . and another thing i would say is that girls ' voices and women 's voices are beautiful , they are there , but we can not do this alone . male advocates , they have to jump in , to step in and work together . it 's a collective work . what we need is what girls elsewhere need : good education , and above all , not to marry whilst 11 . and furthermore , i know that together , we can transform the legal , the cultural and political framework that denies girls of their rights . i am standing here today and declaring that we can end child marriage in a generation . this is the moment where a girl and a girl , and millions of girls worldwide , will be able to say , `` i will marry when i want . '' ( applause ) thank you . ( applause )

malawi is one of the poorest countries , very poor , where gender equality is questionable . growing up in that country , i could n't make my own choices in life . i could n't even explore personal opportunities in life .

what country is memory from ?

have you ever seen a big , red `` no running '' sign at a public pool ? for the most part , the pace on the deck reflects this statement . but while the sign accurately describes the patrons ' movements , is n't it true that people are walking because the sign tells them no running ? so , is this sign portraying the pool 's environment , or is it doing something else , something more powerful ? the difference between a statement that describes and one that commands is an idea developed by british linguist j. l. austin . he defines this distinction as two separate parts of speech : constatives and performatives . constatives are sentences that describe something as true or false , and performatives are sentences that denote an action . in other words , a constative is , and a performative does . to help us distinguish these two parts of speech , let 's start by examining constatives around the park outside the pool . the first sign we encounter says , `` the park closes at 6 p.m. '' after checking with a friendly park official that the park does , indeed , close at 6 , we can confirm that this statement is a true constative . nearby , there 's a man on a bench with a newspaper , and the headline reads , `` heatwave ! '' however , the sky is cloudy and it feels quite chilly . today 's headline is a false constative as it has proven to be incorrect . before the rain starts to fall , let 's throw away our can of soda at the blue trash bin that says , `` recycle . '' it 's a performative . performatives are sentences that are meant to inspire actions . rather than conveying a message , it acts upon the world , it does something . in this case , the performative of `` recycle '' is requesting people to put their trash into the proper receptacle . words not only bring about actions , sometimes words themselves are actions . this is what is known as speech acts . these actions include , but are not limited to , ordering , promising , apologizing , warning , sentencing , christening , and even marrying . take a look at the wedding near the gazebo . the couple says the words , `` i do . '' the speech act here are the words , `` i do . '' these words cause them to marry one another . `` i do '' has acted upon them and profoundly changed their world . however , performatives depend on context and reception . these are known as felicity conditions . imagine if the mayor showed up to the wedding and said , `` by the power vested in me as mayor of the city , i name this gazebo 'the mayor 's pizza palace . ' '' his words would be a speech act by which he named the gazebo . and because he 's the mayor , the gazebo would be known by its new name . but if someone who is n't the mayor , just a normal passerby , decides to name the gazebo after her favorite cat , the chances are the name would not change . felicity conditions are the rules under which the performative can be enacted . these are fairly logical . the performative should have proper authority , it should be understood , it should be clear , and it should be able to be executed . if the performative does n't meet these conditions , then it does n't have the power to denote action . but just because a performative meets its conditions and is clearly stated , does n't mean that it 's implicitly followed . back at the pool , a rowdy group of teenagers races to the high dive . `` no running '' does not seem to have power over them , and they 'll have to face the consequences of breaking this performative . they may even have to force out some performatives of their own , such as apologizing to the life guard and promising to never run again . maybe the life guard will respond with another performative , sentencing them to be banished from the pool for the rest of the day . after all , these teenagers must learn to respect the power of words .

if the performative does n't meet these conditions , then it does n't have the power to denote action . but just because a performative meets its conditions and is clearly stated , does n't mean that it 's implicitly followed . back at the pool , a rowdy group of teenagers races to the high dive .

just because a performative meets the felicity conditions and is clearly stated , it does n't mean it 's implicitly followed .

scientific breakthrough , the kind that can potentially save lives , can sometimes be lying right out in the open for us to discover , in the evolved , accumulated body of human anecdote , for example , or in the time-tested adaptations that we observe in the natural world around us . science starts with observation , but the trick is to identify the patterns and signatures that we might otherwise dismiss as myth or coincidence , isolate them , and test them with scientific rigor . and when we do , the results will often surprise . western australia has had a particular problem with shark attacks over the last three years , unfortunately and tragically culminating in five fatal shark attacks in a 10-month period during that time . but western australia is not alone in this . the incident of shark engagements on humans is escalating worldwide . and so it 's not surprising , perhaps , that in july of this year , shark attack mitigation systems in collaboration with the university of western australia oceans institute made an announcement which captured the attention of the worldwide media and of ocean users worldwide , and that was around the development of technology to mitigate or reduce the risk of shark attack based on the science of what sharks can see . and i have for you today the story of that journey , but also the notion that science can be as powerful as a translator as it can be for invention . when we began this process , we were looking , it was about three years ago , and we 'd just had the first two fatal shark attacks in western australia , and by chance , in a previous role , i happened to be having dinner with harry butler . now harry butler , who most australians would know is a famous naturalist , had spent a lot of time in the marine environment . harry butler is a precursor , if you like , to the late steve irwin . when i asked him about what the solution to the problem might be , the answer was quite surprising . he said , `` take a black wetsuit , band it in yellow stripes like a bumblebee , and you 'll be mimicking the warning systems of most marine species . '' i did n't think about that much at the time , and it was n't until the next three fatal shark attacks happened , and it caused me to think , maybe there 's some merit to this idea . and i turned to the web to see if there might be some clues . and it turns out the web is awash with this sort of evidence that supports this sort of thinking . so biologically , there are plenty of species that display banding or patterns , warning patterns , to either be cryptical in the water or warn against being attacked , not the least of which is the pilot fish which spends a big slab of its life around the business end of a shark . on the human side , walter starck , an oceanographer , has been painting his wetsuit since the 1970s , and anthropologically , pacific island tribes painted themselves in bands in a sea snake ceremony to ward off the shark god . so what 's going on here ? is this an idea lying wide out in the open for us to consider and define ? we know that sharks use a range of sensors when they engage , particularly for attack , but the sight sensor is the one that they use to identify the target , and particularly in the last number of meters before the attack . it makes sense to pay attention to the biological anecdote because that 's time-tested evolution over many millennia . but is n't human anecdote also an evolution of sorts , the idea that there 's a kernel of truth thought to be important , passed down from generation to generation , so that it actually ends up shaping human behavior ? i wanted to test this idea . i wanted to put some science to this anecdotal evidence , because if science could support this concept , then we might have at least part of the solution to shark attack right under our very nose . to do that , i needed some experts in shark vision and shark neurology , and a worldwide search , again , led to the university of w.a . on the doorstep here , with the oceans institute . and professor nathan hart and his team had just written a paper which tells us , confirms that predatory sharks see in black and white , or grayscale . so i called up nathan , a little bit sheepishly , actually , about this idea that maybe we could use these patterns and shapes to produce a wetsuit to try and mitigate the risk of shark attack , and fortunately , he thought that was a good idea . so what ensued is a collaborative bit of research supported by the west australian state government . and we did three key things . the first is that we mapped the characteristics , the physical characteristics of the eyes of the three main predatory sharks , so the great white , tiger and bull shark . we did that genetically and we did that anatomically . the next thing we did was to understand , using complex computer modeling , what that eye can see at different depths , distances , light conditions , and water clarity in the ocean . and from there , we were able to pinpoint two key characteristics : what patterns and shapes would present the wearer as hidden or hard to make out in the water , cryptic , and what patterns and shapes might provide the greatest contrast but provide the greatest breakup of profile so that that person was n't confused for shark prey or shark food . the next thing we needed to do was to convert this into wetsuits that people might actually wear , and to that end , i invited ray smith , a surfer , industrial designer , wetsuit designer , and in fact the guy that designed the original quiksilver logo , to come over and sit with the science team and interpret that science into aesthetic wetsuits that people might actually wear . and here 's an example of one of the first drawings . so this is what i call a `` do n't eat me '' wetsuit . so this takes that banding idea , takes that banding idea , it 's highly visible , provides a highly disruptive profile , and is intended to prevent the shark from considering that you would be ordinary food , and potentially even create confusion for the shark . and this one 's configured to go with a surfboard . you can see that dark , opaque panel on the front , and it 's particularly better for the surface , where being backlit and providing a silhouette is problematic . second iteration is the cryptic wetsuit , or the one which attempts to hide the wearer in the water column . there are three panels on this suit , and in any given conditions , one or more of those panels will match the reflective spectra of the water so as to disappear fully or partially , leaving the last panel or panels to create a disruptive profile in the water column . and this one 's particularly well-suited to the dive configuration , so when you 're deeper under the water . so we knew that we had some really solid science here . we knew , if you wanted to stand out , you needed to look stripy , and we knew if you wanted to be cryptic , you needed to look like this . but the acid test is always going to be , how would sharks really behave in the context of these patterns and shapes . and testing to simulate a person in a wetsuit in the water with a predatory shark in a natural environment is actually a lot harder than you might think . ( laughter ) so we have to bait the rig , because we need to get the statistical number of samples through to get the scientific evidence , and by baiting the rig , we 're obviously changing shark behavior . we ca n't put humans in the water . we 're ethically precluded from even using humanoid shapes and baiting them up in the water . but nevertheless , we started the testing process in january of this year , initially with tiger sharks and subsequently with great white sharks . the way we did that was to get a perforated drum which is full of bait , wrap it in a neoprene skin , and then run two stereo underwater cameras to watch how the shark actually engages with that rig . and because we use stereo , we can capture all the statistics on how big the shark is , what angle it comes in at , how quickly it leaves , and what its behavior is in an empirical rather than a subjective way . because we needed to preserve the scientific method , we ran a control rig which was a black neoprene rig just like a normal black wetsuit against the , what we call , sams technology rig . and the results were not just exciting , but very encouraging , and today i would like to just give you a snapshot of two of those engagements . so here we 've got a four-meter tiger shark engaging the black control rig , which it had encountered about a minute and a half before . now that exact same shark had engaged , or encountered this sams rig , which is the elude sams rig , about eight minutes before , and spent six minutes circling it , hunting for it , looking for what it could smell and sense but not see , and this was the final engagement . great white sharks are more confident than the tigers , and here you see great white shark engaging a control rig , so a black neoprene wetsuit , and going straight to the bottom , coming up and engaging . in contrast to the sams technology rig , this is the banded one , where it 's more tactile , it 's more investigative , it 's more apprehensive , and shows a reluctance to come straight in and go . ( applause ) so , it 's important for us that all the testing is done independently , and the university of w.a . is doing the testing . it 'll be an ongoing process . it 's subject to peer review and subject to publication . it 's so important that this concept is led with the science . from the perspective of shark attack mitigation systems , we 're a biotechnology licensing company , so we do n't make wetsuits ourselves . we 'll license others to do that . but i thought you might be interested in seeing what sams technology looks like embedded in a wetsuit , and to that end , for the first time , live , worldwide -- ( laughter ) — i can show you what biological adaptation , science and design looks like in real life . so i can welcome sam , the surfer , from this side . where are you , sam ? ( applause ) and eduardo . ( applause ) cheers , mate . cheers . thanks , gentlemen . ( applause ) so what have we done here ? well , to my mind , rather than take a blank sheet and use science as a tool for invention , we 've paid attention to the biological evidence , we 've put importance to the human anecdotal evidence , and we 've used science as a tool for translation , translation of something that was already there into something that we can use for the benefit of mankind . and it strikes me that this idea of science as a tool for translation rather than invention is one that we can apply much more widely than this in the pursuit of innovation . after all , did the wright brothers discover manned flight , or did they observe the biological fact of flight and translate that mechanically , replicate it in a way that humans could use ? as for the humble wetsuit , who knows what oceanwear will look like in two years ' time , in five years ' time or in 50 years ' time , but with this new thinking , i 'm guessing there 's a fair chance it wo n't be pure black . thank you . ( applause )

and when we do , the results will often surprise . western australia has had a particular problem with shark attacks over the last three years , unfortunately and tragically culminating in five fatal shark attacks in a 10-month period during that time . but western australia is not alone in this .

how many fatal shark attacks occurred in a 10 month period in australia ?

translator : tom carter reviewer : bedirhan cinar every minute of every day , you breathe without even thinking about it . your body does it on its own , from the day you 're born until the day you die . you have muscles contract to bring oxygen , a gas , into your lungs , which is then transferred by your bloodstream to every cell in your body . gases are strange . we ca n't see them , but we know they 're there because we can feel them . what we experience as wind is really trillions and trillions of gas molecules slamming into your body . and it feels good , right ? science is based on observation . unfortunately , we can not observe gases with our eyes -- they 're too small . we have to use our other senses to make observations and draw conclusions . observations are then compiled , and we create a model . no , not that kind of model . a model is a way scientists describe the properties of physical phenomena . first , gases always move in a straight line . we do n't really have anything to demonstrate this with because gravity always pulls objects down . so imagine a bullet fired from a gun , and that bullet goes on at a constant speed in a perfectly straight line . that would be like a gas molecule . second , gases are so small , they occupy no volume on their own . as a group they do , blow up any balloon and you can see how that volume changes . but single gases have no volume compared to other forms of matter . rather than calculating such a small amount of matter , we just call it zero for simplicity . third , if gas molecules collide , and they do -- remember , these are assumptions -- their energy remains constant . an easy way to demonstrate this is by dropping a soccer ball with a tennis ball balanced on top . because the soccer ball is bigger , it has more potential energy , and the energy from the larger ball is transferred to the smaller tennis ball and it flies away when that energy is transferred . the total energy stays the same . gases work the same way . if they collide , smaller particles will speed up , larger particles will slow down . the total energy is constant . fourth , gases do not attract one another , and they do n't like to touch . but remember rule three . in reality , they do collide . finally , gases have energy that is proportional to the temperature . the higher the temperature , the higher the energy the gases have . the crazy thing is that at the same temperature , all gases have the same energy . it does n't depend on the type of gas , just the temperature that gas is at . keep in mind this is a model for the way gas particles behave , and based on our observations , gases always move in straight lines . they 're so small , that they 're not measurable on their own , and they do n't interact with one another . but if they do bump into one another , that energy is transferred from one particle to another , and the total amount never changes . temperature has a major effect , and in fact , all gases at the same temperature have the same average energy . whew ! i need to go catch my breath .

you have muscles contract to bring oxygen , a gas , into your lungs , which is then transferred by your bloodstream to every cell in your body . gases are strange . we ca n't see them , but we know they 're there because we can feel them .

why do individual gases have a volume of zero ?

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 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 ?

a small change in temperature may cause a tipping point resulting in a shift in climate behavior such as :

between 2008 and 2012 , archeologists excavated the rubble of an ancient hospital in england . in the process , they uncovered a number of skeletons . one in particular belonged to a wealthy male who lived in the 11th or 12th century and died of leprosy between the ages of 18 and 25 . how do we know all this ? simply by examining some old , soil-caked bones ? even centuries after death , skeletons carry unique features that tell us about their identities . and using modern tools and techniques , we can read those features as clues . this is a branch of science known as biological anthropology . it allows researchers to piece together details about ancient individuals and identify historical events that affected whole populations . when researchers uncover a skeleton , some of the first clues they gather , like age and gender , lie in its morphology , which is the structure , appearance , and size of a skeleton . bones , like the clavicle , stop growing at age 25 , so a skeleton with a clavicle that has n't fully formed must be younger than that . similarly , the plates in the cranium can continue fusing up to age 40 , and sometimes beyond . by combining these with some microscopic skeletal clues , physical anthropologists can estimate an approximate age of death . meanwhile , pelvic bones reveal gender . biologically , female pelvises are wider , allowing women to give birth , where as males are narrower . bones also betray the signs of ancient disease . disorders like anemia leave their traces on the bones . and the condition of teeth can reveal clues to factors like diet and malnutrition , which sometimes correlate with wealth or poverty . a protein called collagen can give us even more profound details . the air we breathe , water we drink , and food we eat leaves permanent traces in our bones and teeth in the form of chemical compounds . these compounds contain measurable quantities called isotopes . stable isotopes in bone collagen and tooth enamel varies among mammals dependent on where they lived and what they ate . so by analyzing these isotopes , we can draw direct inferences regarding the diet and location of historic people . not only that , but during life , bones undergo a constant cycle of remodeling . so if someone moves from one place to another , bones synthesized after that move will also reflect the new isotopic signatures of the surrounding environment . that means that skeletons can be used like migratory maps . for instance , between 1-650 ad , the great city of teotihuacan in mexico bustled with thousands of people . researchers examined the isotope ratios in skeletons ' tooth enamel , which held details of their diets when they were young . they found evidence for significant migration into the city . a majority of the individuals were born elsewhere . with further geological and skeletal analysis , they may be able to map where those people came from . that work in teotihuacan is also an example of how bio-anthropologists study skeletons in cemeteries and mass graves , then analyze their similarities and differences . from that information , they can learn about cultural beliefs , social norms , wars , and what caused their deaths . today , we use these tools to answer big questions about how forces , like migration and disease , shape the modern world . dna analysis is even possible in some relatively well-preserved ancient remains . that 's helping us understand how diseases like tuberculosis have evolved over the centuries so we can build better treatments for people today . ancient skeletons can tell us a surprisingly great deal about the past . so if your remains are someday buried intact , what might archeologists of the distant future learn from them ?

when researchers uncover a skeleton , some of the first clues they gather , like age and gender , lie in its morphology , which is the structure , appearance , and size of a skeleton . bones , like the clavicle , stop growing at age 25 , so a skeleton with a clavicle that has n't fully formed must be younger than that . similarly , the plates in the cranium can continue fusing up to age 40 , and sometimes beyond . by combining these with some microscopic skeletal clues , physical anthropologists can estimate an approximate age of death . meanwhile , pelvic bones reveal gender .

what is the age at which cranial sutures completely fuse in the human skull ?

the idea of human rights is that each one of us , no matter who we are or where we are born , is entitled to the same basic rights and freedoms . human rights are not privileges , and they can not be granted or revoked . they are inalienable and universal . that may sound straighforward enough , but it gets incredibly complicated as soon as anyone tries to put the idea into practice . what exactly are the basic human rights ? who gets to pick them ? who enforces them , and how ? the history behind the concept of human rights is a long one . throughout the centuries and across societies , religions , and cultures we have struggled with defining notions of rightfulness , justice , and rights . but one of the most modern affirmations of universal human rights emerged from the ruins of world war ii with the creation of the united nations . the treaty that established the un gives as one of its purposes to reaffirm faith in fundamental human rights . and with the same spirit , in 1948 , the un general assembly adopted the universal declaration of human rights . this document , written by an international committee chaired by eleanor roosevelt , lays the basis for modern international human rights law . the declaration is based on the principle that all human beings are born free and equal in dignity and rights . it lists 30 articles recognizing , among other things , the principle of nondiscrimination and the right to life and liberty . it refers to negative freedoms , like the freedom from torture or slavery , as well as positive freedoms , such as the freedom of movement and residence . it encompasses basic civil and political rights , such as freedom of expression , religion , or peaceful assembly , as well as social , economic , and cultural rights , such as the right to education and the right to freely choose one 's occupation and be paid and treated fairly . the declaration takes no sides as to which rights are more important , insisting on their universality , indivisibility , and interdependence . and in the past decades , international human rights law has grown , deepening and expanding our understanding of what human rights are , and how to better protect them . so if these principles are so well-developed , then why are human rights abused and ignored time and time again all over the world ? the problem in general is that it is not at all easy to universally enforce these rights or to punish transgressors . the udhr itself , despite being highly authoritative and respected , is a declaration , not a hard law . so when individual countries violate it , the mechanisms to address those violations are weak . for example , the main bodies within the un in charge of protecting human rights mostly monitor and investigate violations , but they can not force states to , say , change a policy or compensate a victim . that 's why some critics say it 's naive to consider human rights a given in a world where state interests wield so much power . critics also question the universality of human rights and emphasize that their development has been heavily guided by a small number of mostly western nations to the detriment of inclusiveness . the result ? a general bias in favor of civil policital liberties over sociopolitical rights and of individual over collective or groups rights . others defend universal human rights laws and point at the positive role they have on setting international standards and helping activists in their campaigns . they also point out that not all international human rights instruments are powerless . for example , the european convention on human rights establishes a court where the 47 member countries and their citizens can bring cases . the court issues binding decisions that each member state must comply with . human rights law is constantly evolving as are our views and definitions of what the basic human rights should be . for example , how basic or important is the right to democracy or to development ? and as our lives are increasingly digital , should there be a right to access the internet ? a right to digital privacy ? what do you think ?

a general bias in favor of civil policital liberties over sociopolitical rights and of individual over collective or groups rights . others defend universal human rights laws and point at the positive role they have on setting international standards and helping activists in their campaigns . they also point out that not all international human rights instruments are powerless . for example , the european convention on human rights establishes a court where the 47 member countries and their citizens can bring cases .

within the international system , the main body tasked with protecting human rights is :

dating back at least to the time of socrates , some early societies decided that certain disputes , such as whether a person committed a particular crime , should be heard by a group of citizens . several centuries later , trial by jury was introduced to england , where it became a fundamental feature of the legal system , checking the government and involving citizens in decision-making . juries decided whether defendants would be tried on crimes , determined whether the accused defendants were guilty , and resolved monetary disputes . while the american colonies eventually cast off england 's rule , its legal tradition of the jury persisted . the united states constitution instructed a grand jury to decide whether criminal cases proceeded , required a jury to try all crimes , except impeachment , and provided for juries in civil cases as well . yet , in the us today , grand juries often are not convened , and juries decide less than 4 % of criminal cases and less than 1 % of civil cases filed in court . that 's at the same time as jury systems in other countries are growing . so what happened in the u.s. ? part of the story lies in how the supreme court has interpreted the constitution . it 's permitted plea bargaining , which now occurs in almost every criminal case . the way it works is the prosecutor presents the accused with a decision of whether to plead guilty . if they accept the plea , the case wo n't go in front of a jury , but they 'll receive a shorter prison sentence than they 'd get if a jury did convict them . the risk of a much greater prison sentence after a trial can frighten even an innocent defendant into taking a plea . between the 19th century and the 21st century , the proportion of guilty pleas has increased from around 20 % to 90 % , and the numbers continue to grow . the supreme court has permitted the use of another procedure that interferes with the jury called summary judgement . using summary judgement , judges can decide that civil trials are unnecessary if the people who sue have insufficient evidence . this is intended only for cases where no reasonable jury would disagree . that 's a difficult thing to determine , yet usage of summary judgement has stretched to the point where some would argue it 's being abused . for instance , judges grant fully , or in part , over 70 % of employers ' requests to dismiss employment discrimination cases . in other cases , both the person who sues and the person who defends forgo their right to go to court , instead resolving their dispute through a professional arbitrator . these are generally lawyers , professors , or former judges . arbitration can be a smart decision by both parties to avoid the requirements of a trial in court , but it 's often agreed to unwittingly when people sign contracts like employment applications and consumer agreements . that can become a problem . for example , some arbitrators may be biased towards the companies that give them cases . these are just some of the ways in which juries have disappeared . but could the disappearance of juries be a good thing ? well , juries are n't perfect . they 're costly , time-consuming , and may make errors . and they 're not always necessary , like when people can simply agree to settle their disputes . but juries have their advantages . when properly selected , jurors are more representative of the general population and do n't have the same incentives as prosecutors , legislators , or judges seeking reelection or promotion . the founders of the united states trusted in the wisdom of impartial groups of citizens to check the power of all three branches of government . and the jury trial itself has given ordinary citizens a central role in upholding the social fabric . so will the jury system in the u.s. survive into the future ?

while the american colonies eventually cast off england 's rule , its legal tradition of the jury persisted . the united states constitution instructed a grand jury to decide whether criminal cases proceeded , required a jury to try all crimes , except impeachment , and provided for juries in civil cases as well . yet , in the us today , grand juries often are not convened , and juries decide less than 4 % of criminal cases and less than 1 % of civil cases filed in court . that 's at the same time as jury systems in other countries are growing .

juries decide less than __ percent of civil cases and less than __ percent of criminal cases .

imagine as a thought experiment that you live in a small village and depend on the local fish pond for food . you share the pond with three other villagers . the pond starts off with a dozen fish , and the fish reproduce . for every two fish , there will be one baby added each night . so , in order to maximize your supply of food , how many fish should you catch each day ? take a moment to think about it . assume baby fish grow to full size immediately and that the pond begins at full capacity , and ignore factors like the sex of the fish you catch . the answer ? one , and it 's not just you . the best way to maximize every villager 's food supply is for each fisherman to take just one fish each day . here 's how the math works . if each villager takes one fish , there will be eight fish left over night . each pair of fish produces one baby , and the next day , the pond will be fully restocked with twelve fish . if anyone takes more than one , the number of reproductive pairs drops , and the population wo n't be able to bounce back . eventually , the fish in the lake will be gone , leaving all four villagers to starve . this fish pond is just one example of a classic problem called the tragedy of the commons . the phenomenon was first described in a pamphlet by economist william forster lloyd in 1833 in a discussion of the overgrazing of cattle on village common areas . more than 100 years later , ecologist garrett hardin revived the concept to describe what happens when many individuals all share a limited resource , like grazing land , fishing areas , living space , even clean air . hardin argued that these situations pit short-term self-interest against the common good , and they end badly for everyone , resulting in overgrazing , overfishing , overpopulation , pollution , and other social and environmental problems . the key feature of a tragedy of the commons is that it provides an opportunity for an individual to benefit him or herself while spreading out any negative effects across the larger population . to see what that means , let 's revisit our fish pond . each individual fisherman is motivated to take as many fish as he can for himself . meanwhile , any decline in fish reproduction is shared by the entire village . anxious to avoid losing out to his neighbors , a fisherman will conclude that it 's in his best interest to take an extra fish , or two , or three . unfortunately , this is the same conclusion reached by the other fisherman , and that 's the tragedy . optimizing for the self in the short term is n't optimal for anyone in the long term . that 's a simplified example , but the tragedy of the commons plays out in the more complex systems of real life , too . the overuse of antibiotics has led to short-term gains in livestock production and in treating common illnesses , but it 's also resulted in the evolution of antibiotic-resistant bacteria , which threaten the entire population . a coal-fired power plant produces cheap electricity for its customers and profits for its owners . these local benefits are helpful in the short term , but pollution from mining and burning coal is spread across the entire atmosphere and sticks around for thousands of years . there are other examples , too . littering , water shortages , deforestation , traffic jams , even the purchase of bottled water . but human civilization has proven it 's capable of doing something remarkable . we form social contracts , we make communal agreements , we elect governments , and we pass laws . all this to save our collective selves from our own individual impulses . it is n't easy , and we certainly do n't get it right nearly all of the time . but humans at our best have shown that we can solve these problems and we can continue to do so if we remember hardin 's lesson . when the tragedy of the commons applies , what 's good for all of us is good for each of us .

eventually , the fish in the lake will be gone , leaving all four villagers to starve . this fish pond is just one example of a classic problem called the tragedy of the commons . the phenomenon was first described in a pamphlet by economist william forster lloyd in 1833 in a discussion of the overgrazing of cattle on village common areas .

what is the definition of the tragedy of the commons ?

translator : tom carter reviewer : bedirhan cinar optics , or the enhancement of our natural vision , has been one of the biggest catalysts for science over the past 500 years , interestingly , it was n't scientific interest , but more practical matters that led to the initial advancements in optics , starting around 1440 when johannes gutenberg invented his printing press . in short order , books , which had been a rarity , were now becoming a widespread phenomenon . all that new reading material meant more knowledge was circulating , but it also meant that more people were straining their eyes , likely as they read by candlelight . and while spectacles had been invented in italy around 1286 , the need for reading glasses increased substantially . now that people could use lenses to see things more clearly , they started wondering if vision could be enhanced to see things the human eye could n't perceive by its own devices . robert hooke pursued microscopy , and 1665 he published his findings of worlds inside worlds , which he called `` cells '' in the book `` micrographia . '' at the other end of the spectrum , galileo innovated with telescopic lenses , and in 1609 , he had refined a telescope until he had an instrument powerful enough to see distant objects in the sky with an accuracy no one had before him . he found that the moon had craters and mountains , that jupiter had moons of its own , and the whole system governing the earth and space was brought into question . not everyone was thrilled with all the things galileo saw though . for instance , it was taught at the time that the moon was a perfectly smooth sphere . yet here was visual proof that was awfully hard to discount . upon finding moons around jupiter , he also verified what johannes kepler had surmised : that the earth was not the center of the universe , dispelling another central dogma of galileo 's day . then almost exactly a year after galileo died , isaac newton was born . a lot that had been unknown was visible by now , but much of it was simply the foundation for further questions . what was light anyway ? and color , for that matter ? what were the laws that governed the earth , and the heavens ? and could we capture them through keen observation ? newton experimented extensively with optics , and came to understand light as something of substance , and colors as components of light at different frequencies . before newton , people widely believed that the color was due to different amounts of light , with red being lots of light , and blue being mostly dark . newton 's prism experiments showed that white light could not only be broken into its component colors with one prism , but that a second lens could recompose those colors back into white light again , thus showing that color was a matter of light 's refraction rather than how light or dark it was . newton 's studies of optics led to the development of the reflecting telescope . this , together with his study of planetary motion , led to his theory of gravitation , one of the world 's greatest examples of learning to see something invisible by observing its effect on things that are visible . so fast forward a few hundred years , and here we stand . we 've evolved from a single lens to optics that reveal the birth of a star in another galaxy , or a child developing in the womb , or an electron whirling around an atom . at a time when so much is visible , how we see the world around us matters even more than what we see . will we see a world where everything important has already been discovered ? or will we see one in which yesterday 's discoveries are but a doorway to the breakthroughs of tomorrow ?

robert hooke pursued microscopy , and 1665 he published his findings of worlds inside worlds , which he called `` cells '' in the book `` micrographia . '' at the other end of the spectrum , galileo innovated with telescopic lenses , and in 1609 , he had refined a telescope until he had an instrument powerful enough to see distant objects in the sky with an accuracy no one had before him . he found that the moon had craters and mountains , that jupiter had moons of its own , and the whole system governing the earth and space was brought into question .

what year did galileo innovate telescopic lenses which led to an instrument powerful enough to see jupiter 's moons ?

so when i was taught as a student , i was taught by a chemist at cambridge school alfie maddock . who during the second world war was working in canada on plutonium chemistry . and one night he managed to spill the entire uk 's supply of plutonium . which was only 10 milligrams onto the bench in the lab . and so rather then saying 'oh dear i have spilt it ' , he went and got a saw and sawed a large chunk out of the bench , and burned the wood , and got back 9.5 of the 10 mg that he spilled . and nobody would have known except at that point , he was too tired to repair the bench . so they came down in the morning , and there was a large hole in the bench , to show what he had done . ok so plutonium . i think plutonium is quite well known for the fact its been used in certain types of nuclear bombs . it 's a fairly interesting element , it 's incredibly dense . if you hold a golf ball size shape of plutonium in your hand , it would weigh in excess of half a kilogram . which is one heavy golf ball . and if you were holding it , you would have to be holding it through several layers of gloves , at least one of which would be lead lined . and as you held it , it would be like having a really hot cup of tea in your hand . and that 's from the radioactivity coming out . just the shear heat of the radioactivity which you would be feeling . i also had an interesting experience with ... at a conference , i was sitting next to a lady , who i asked her why she was at the conference , which was about super critical fluids . high pressure gases , solvents . and i asked her why she was there and she said she worked with weapons grade plutonium . what is used in making atom bombs . and she said she was worried about the environmental effects of using chlorinated solvents . there are compounds of carbon and chlorine , for removing the greace from the plutonium that we are using to make the bombs . so she was at the conference to see whether you could use high pressure carbon dioxide or as an alternative to make the making of atomic bombs environmentally friendly . that was slightly macabre . worrying about the environment . i like that , wanting to make more environmentaly friendly bombs . i have not seen any because the sort of facilities you need to be able to handle it are way beyond what you find in a normal university . i 've had some fascinating stories about it , it 's incredibly dense . and a few people at the atomic weapons agency wanted to cut a little piece off , it took three of them with a hacksaw several hours , and several hacksaw blades , before they got a tiny little chip off . so it 's incredibly dense and hard . hence the high weight for its size . plutonium is quite a poisonous element , and there have been a number of cases . particularly the famous case in america , with karen silkwood , who was poisoned , or had traces of poisonous plutonium found in her refrigerator , and all through her flat . which in fact inspired my brother to write a play called `` stronger then the sun '' in the early 1970s . one of his first successful television films . perhaps a little known thing about plutonium , 'cause obviously it has a pretty bad image in terms of its use in nuclear weapons , is that it is what helped power the astronauts on the moon landings in the 60s and 70s . captions by www.subply.com

so they came down in the morning , and there was a large hole in the bench , to show what he had done . ok so plutonium . i think plutonium is quite well known for the fact its been used in certain types of nuclear bombs .

why did the professor find it quite macabre when he met a woman at a conference who was worried about the impact of her plutonium research on the environment ?

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 marginal utility of purchasing the second bar of chocolate ?

have you ever been floating in a swimming pool , all comfy and warm , thinking , `` man , it 'd be cool to be an astronaut ! you could float out in outer space , look down at the earth and everything . it 'd be so neat ! '' only that 's not how it is at all . if you are in outer space , you are orbiting the earth : it 's called free fall . you 're actually falling towards the earth . think about this for a moment : that 's the feeling you get if you 're going over the top of a roller coaster , going , like , `` whoa ! '' only you 're doing this the whole time you 're orbiting the earth , for two , three , four hours , days . whatever it takes , right ? so , how does orbiting work ? let 's take a page from isaac newton . he had this idea , a little mental experiment : you take a cannon , you put it on top of a hill . if you shoot the cannonball , it goes a little bit away . but if you shoot it harder , it goes far enough so that it lands a little bit past the curvature of earth . well , you can imagine if you shot it really , really , hard , it would go all the way around the earth and come back -- boom ! -- and hit you in the backside or something . let 's zoom way back and put you in a little satellite over the north pole of the earth and consider north to be up . you 're going to fall down and hit the earth . but you are actually moving sideways really fast . so when you fall down , you 're going to miss . you 're going to end up on the side of the earth , falling down , and now the earth is pulling you back in sideways . so it 's pulling you back in and you fall down , and so you miss the earth again , and now you 're under the earth . the earth is going to pull you up , but you 're moving sideways still . so you 're going to miss the earth again . now you 're on the other side of the earth , moving upward , and the earth 's pulling you sideways . so you 're going to fall sideways , but you 're going to be moving up and so you 'll miss . now you 're back on top of the earth again , over the north pole , going sideways and falling down , and yep -- you guessed it . you 'll keep missing because you 're moving so fast . in this way , astronauts orbit the earth . they 're always falling towards the earth , but they 're always missing , and therefore , they 're falling all the time . they feel like they 're falling , so you just have to get over it . so technically , if you ran fast enough and tripped , you could miss the earth . but there 's a big problem . first , you have to be going eight kilometers a second . that 's 18,000 miles an hour , just over mach 23 ! the second problem : if you 're going that fast , yes , you would orbit the earth and come back where you came from , but there 's a lot of air in the way , much less people and things . so you would burn up due to atmospheric friction . so , i do not recommend this .

only that 's not how it is at all . if you are in outer space , you are orbiting the earth : it 's called free fall . you 're actually falling towards the earth .

if an astronaut orbiting the earth lets go of a rock , what will happen to the rock ? describe the path of the rock and why it follows that path .

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

that is completely false . if you experience math anxiety , it may not help to just know that math anxiety exists . or perhaps it 's reassuring to put a name to the problem .

why is it important to reduce the number of math anxious people in western society ? why is it important to reduce math anxiety in one 's own life ?

three and a half thousand years ago in egypt , a noble pharaoh was the victim of a violent attack . but the attack was not physical . this royal had been dead for 20 years . the attack was historical , an act of damnatio memoriae , the damnation of memory . somebody smashed the pharaoh 's statues , took a chisel and attempted to erase the pharaoh 's name and image from history . who was this pharaoh , and what was behind the attack ? here 's the key : the pharaoh hatshepsut was a woman . in the normal course of things , she should never have been pharaoh . although it was legal for a woman to be a monarch , it disturbed some essential egyptian beliefs . firstly , the pharaoh was known as the living embodiment of the male god horus . secondly , disturbance to the tradition of rule by men was a serious challenge to maat , a word for `` truth , '' expressing a belief in order and justice , vital to the egyptians . hatshepsut had perhaps tried to adapt to this belief in the link between order and patriarchy through her titles . she took the name maatkare , and sometimes referred to herself as hatshepsu , with a masculine word ending . but apparently , these efforts did n't convince everyone , and perhaps someone erased hatshepsut 's image so that the world would forget the disturbance to maat , and egypt could be balanced again . hatshepsut , moreover , was not the legitimate heir to the thrown , but a regent , a kind of stand-in co-monarch . the egyptian kingship traditionally passed from father to son . it passed from thutmose i to his son thutmose ii , hatshepsut 's husband . it should have passed from thutmose ii directly to his son thutmose iii , but thutmose iii was a little boy when his father died . hatshepsut , the dead pharaoh 's chief wife and widow , stepped in to help as her stepson 's regent but ended up ruling beside him as a fully fledged pharaoh . perhaps thutmose iii was angry about this . perhaps he was the one who erased her images . it 's also possible that someone wanted to dishonor hatshepsut because she was a bad pharaoh . but the evidence suggests she was actually pretty good . she competently fulfilled the traditional roles of the office . she was a great builder . her mortuary temple , djeser-djeseru , was an architectural phenomenon at the time and is still admired today . she enhanced the economy of egypt , conducting a very successful trade mission to the distant land of punt . she had strong religious connections . she even claimed to be the daughter of the state god , amun . and she had a successful military career , with a nubian campaign , and claims she fought alongside her soldiers in battle . of course , we have to be careful when we assess the success of hatshepsut 's career , since most of the evidence was written by hatshepsut herself . she tells her own story in pictures and writing on the walls of her mortuary temple and the red chapel she built for amun . so who committed the crimes against hatshepsut 's memory ? the most popular suspect is her stepson , nephew and co-ruler , thutmose iii . did he do it out of anger because she stole his throne ? this is unlikely since the damage was n't done until 20 years after hatshepsut died . that 's a long time to hang onto anger and then act in a rage . maybe thutmose iii did it to make his own reign look stronger . but it is most likely that he or someone else erased the images so that people would forget that a woman ever sat on egypt 's throne . this gender anomaly was simply too much of a threat to maat and had to be obliterated from history . happily , the ancient censors were not quite thorough enough . enough evidence survived for us to piece together what happened , so the story of this unique powerful woman can now be told .

she tells her own story in pictures and writing on the walls of her mortuary temple and the red chapel she built for amun . so who committed the crimes against hatshepsut 's memory ? the most popular suspect is her stepson , nephew and co-ruler , thutmose iii .

why were hatshepsut 's monuments destroyed ?

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

we can pump air into someone 's lungs , but it wo n't do much good if the many other processes involved in the respiratory cycle are no longer functioning . similarly , the electric shock from a defibrillator does n't jump-start an inanimate heart , but resynchronizes the muscle cells in an abnormally beating heart so they regain their normal rhythm . this can prevent a person from dying , but it wo n't raise a dead body , or a monster sewn together from dead bodies .

how does a defibrillator work ?

at pixar , we 're all about telling stories , but one story that has n't been told very much is the huge degree to which math is used in the production of our films . the math that you 're learning in middle school and high school is used all the time at pixar . so , let 's start with a very simple example . anybody recognize this guy ? ( cheers ) yeah , so this is woody from toy story , and let 's ask woody to , say , walk across the stage from , say , left to right , just like that . so , believe it or not , you just saw a ton of mathematics . where is it ? well , to explain that , it 's important to understand that artists and designers think in terms of shape and images but computers think in terms of numbers and equations . so , to bridge those two worlds we use a mathematical concept called coordinate geometry , right ? that is , we lay down a coordinate system with x describing how far something is to the right and y describing how high something is . so , with these coordinates we can describe where woody is at any instant in time . for instance , if we know the coordinates of the lower left corner of that image , then we know where the rest of the image is . and in that little sliding animation we saw a second ago , that motion we call translation , the x coordinate started with a value of one , and it ended with a value of about five . so , if we want to write that in mathematics , we see that the x at the end is four bigger than x at the start . so , in other words , the mathematics of translation is addition . alright ? how about scaling ? that is making something bigger or smaller . any guesses as to what the mathematics of scaling might be ? dilation , multiplication , exactly . if you 're going to make something twice as big , you need to mulitply the x and the y coordinates all by two . so , this shows us that the mathematics of scaling is mulitiplication . okay ? how about this one ? how about rotation ? alright , spinning around . the mathematics of rotation is trigonometry . so , here 's an equation that expresses that . it looks a little scary at first . you 'll probably get this in eighth or ninth grade . if you find yourselves sitting in trigonometry class wondering when you 're ever going to need this stuff , just remember that any time you see anything rotate in one of our films , there 's trigonometry at work underneath . i first fell in love with mathematics in seventh grade . any seventh graders ? a few of you ? yeah . my seventh grade science teacher showed me how to use trigonometry to compute how high the rockets that i was building was going . i just thought that was amazing , and i 've been enamored with math ever since . so , this is kind of old mathematics . mathematics that 's been known and , you know , developed by the old dead greek guys . and there 's a myth out there that all the interesting mathematics has already been figured out , in fact all of mathematics has been figured out . but the real story is that new mathematics is being created all the time . and some of it is being created at pixar . so , i 'd like to give you an example of that . so , here are some characters from some of our early films : finding nemo , monsters inc. and toy story 2 . anybody know who the blue character in the upper left is ? it 's dory . okay , that was easy . here 's a little harder one . anybody know who 's the character in the lower right ? al mcwhiggin from al 's toy barn , exactly . the thing to notice about these characters is they 're really complicated . those shapes are really complicated . in fact , the toy cleaner , i have an example , the toy cleaner there in the middle , here 's his hand . you can imagine how fun it was to bring this through airport security . his hand is a really complicated shape . it 's not just a bunch of spheres and cylinders stuck together , right ? and not only is it complicated , but it has to move in complicated ways . so , i 'd like to tell you how we do that , and to do that i need to tell you about midpoints . so , here 's a couple of points , a and b , and the line segment between them . we 're going to start out first in two dimensions . the midpoint , m , is the point that splits that line segment in the middle , right ? so , that 's the geometry . to make equations and numbers , we again introduce a coordinate system , and if we know the coordinates of a and b , we can easily compute the coordinates of m just by averaging . you now know enough to work at pixar . let me show you . so , i 'm going to do something slightly terrifying and move to a live demo here . so , what i have is a four-point polygon here , and it 's going to be my job to make a smooth curve out of this thing . and i 'm going to do it just using the idea of midpoints . so , the first thing i 'm going to do is an operation i 'll call split , which adds midpoints to all those edges . so , i went from four points to eight points , but it 's no smoother . i 'm going to make it a little bit smoother by moving all of these points from where they are now to the midpoint of their clockwise neighbor . so , let me animate that for you . i 'm going to call that the averaging step . so , now i 've got eight points , they 're a little bit smoother , my job is to make a smooth curve , so what do i do ? do it again . split and average . so , now i 've got sixteen points . i 'm going to put those two steps , split and average , together into something i 'll call subdivide , which just means split and then average . so , now i 've got 32 points . if that 's not smooth enough , i 'll do more . i 'll get 64 points . do you see a smooth curve appearing here from those original points ? and that 's how we create the shapes of our charcters . but remember , i said a moment ago it 's not enough just to know the static shape , the fixed shape . we need to animate it . and to animate these curves , the cool thing about subdivision . did you see the aliens in toy story ? you know that sound they make , `` ooh '' ? ready ? so , the way we animate these curves is simply by animating the original four points . `` ooh . '' alright , i think that 's pretty cool , and if you do n't , the door is there , it does n't get any better than that , so . this idea of splitting and averaging also holds for surfaces . so , i 'll split , and i 'll average . i 'll split , and i 'll average . put those together into subdivide , and this how we actually create the shapes of all of our surface characters in three dimensions . so , this idea of subdivision was first used in a short film in 1997 called geri 's game . and geri actually made a cameo apperance in toy story 2 as the toy cleaner . each of his hands was the first time we ever used subdivision . so , each hand was a subdivision surface , his face was a subdivision surface , so was his jacket . here 's geri 's hand before subdivision , and here 's geri 's hand after subdivision , so subdivision just goes in and smooths out all those facets , and creates the beautiful surfaces that you see on the screen and in the theaters . since that time , we 've built all of our characters this way . so , here 's merida , the lead character from brave . her dress was a subdivision surface , her hands , her face . the faces and hands of all the clansman were subdivision surfaces . today we 've seen how addition , multiplication , trigonometry and geometry play a roll in our films . given a little more time , i could show you how linear algebra , differential calculus , integral calculus also play a roll . the main thing i want you to go away with today is to just remember that all the math that you 're learning in high school and actually up through sophomore college we use all the time , everyday , at pixar . thanks .

so , that 's the geometry . to make equations and numbers , we again introduce a coordinate system , and if we know the coordinates of a and b , we can easily compute the coordinates of m just by averaging . you now know enough to work at pixar .

if point a has coordinates ( 1,2 ) and b has coordinates ( 3,4 ) , then the midpoint of the line segment ab has coordinates :

`` war and peace , '' a tome , a slog , the sort of book you should n't read in bed because if you fall asleep , it could give you a concussion , right ? only partly . `` war and peace '' is a long book , sure , but it 's also a thrilling examination of history , populated with some of the deepest , most realistic characters you 'll find anywhere . and if its length intimidates you , just image how poor tolstoy felt . in 1863 , he set out to write a short novel about a political dissident returning from exile in siberia . five years later , he had produced a 1,200 page epic featuring love stories , battlefields , bankruptcies , firing squads , religious visions , the burning of moscow , and a semi-domesticated bear , but no exile and no political dissidents . here 's how it happened . tolstoy , a volcanic soul , was born to a famously eccentric aristocratic family in 1828 . by the time he was 30 , he had already dropped out of kazan university , gambled away the family fortune , joined the army , written memoirs , and rejected the literary establishment to travel europe . he then settled into yasnaya polyana , his ancestral mansion , to write about the return of the decembrists , a band of well-born revolutionaries pardoned in 1856 after 30 years in exile . but , tolstoy thought , how could he tell the story of the decembrists return from exile without telling the story of 1825 , when they revolted against the conservative tsar nicholas i ? and how could he do that without telling the story of 1812 , when napoleon 's disastrous invasion of russia helped trigger the authoritarianism the decembrists were rebelling against ? and how could he tell the story of 1812 without talking about 1805 , when the russians first learned of the threat napoleon posed after their defeat at the battle of austerlitz ? so tolstoy began writing , both about the big events of history and the small lives that inhabit those events . he focused on aristocrats , the class he knew best . the book only occasionally touches on the lives of the vast majority of the russian population , who were peasants , or even serfs , farmers bound to serve the owners of the land on which they lived . `` war and peace '' opens on the eve of war between france and russia . aristocrats at a cocktail party fret about the looming violence , but then change the topic to those things aristocrats always seem to care about : money , sex , and death . this first scene is indicative of the way the book bounces between the political and personal over an ever-widening canvas . there are no main characters in `` war and peace . '' instead , readers enter a vast interlocking web of relationships and questions . will the hapless and illegitimate son of a count marry a beautiful but conniving princess ? will his only friend survive the battlefields of austria ? and what about that nice young girl falling in love with both men at once ? real historical figures mix and mingle with all these fictional folk , napoleon appears several times , and even one of tolstoy 's ancestors plays a background part . but while the characters and their psychologies are gripping , tolstoy is not afraid to interrupt the narrative to pose insightful questions about history . why do wars start ? what are good battlefield tactics ? do nations rise and fall on the actions of so-called great men like napoleon , or are there larger cultural and economic forces at play ? these extended digressions are part of what make `` war and peace '' so panoramic in scope . but for some 19th century critics , this meant `` war and peace '' barely felt like a novel at all . it was a `` large , loose , baggy monster , '' in the words of henry james . tolstoy , in fact , agreed . to him , novels were a western european form . russian writers had to write differently because russian people lived differently . `` what is 'war and peace ' ? '' he asked . `` it is not a novel . still less an epic poem . still less a historical chronicle . 'war and peace ' is what the author wanted and was able to express in the form in which it was expressed . '' it is , in other words , the sum total of tolstoy 's imaginative powers , and nothing less . by the time `` war and peace '' ends , tolstoy has brought his characters to the year 1820 , 36 years before the events he originally hoped to write about . in trying to understand his own times , he had become immersed in the years piled up behind him . the result is a grand interrogation into history , culture , philosophy , psychology , and the human response to war .

russian writers had to write differently because russian people lived differently . `` what is 'war and peace ' ? '' he asked .

tolstoy ’ s life before he wrote `` war and peace '' was filled with :

[ goproject films ] [ traffic sounds ] [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] [ ♪ orchestral music ♪ ] i discovered working with tea really by accident . [ ♪ orchestral music ♪ ] i spilled the tea on a drawing . [ ♪ orchestral music ♪ ] i look at them , and i read them like somebody would read coffee beans . [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] [ silent crescendo ] [ ♪ orchestral music ♪ ] a drink this beautiful of chinese pu-ehr tea . [ ♪ orchestral music ♪ ] the element of slowing down . [ ♪ orchestral music ♪ ] the tea allows us to breathe , to move . [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] the whole things starts with big splashes of tea . [ ♪ orchestral music ♪ ] it 's like some empty space inside the mind . [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] [ ♪ orchestral music ♪ ] i start with the pen , [ ♪ orchestral music ♪ ] and then i look at the markings . [ ♪ orchestral music ♪ ] it 's almost like a little oracle . i am not drawing it to be holy , to be out of this world . i just allow myself a little space , a little , a little moment . [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] [ ♪ orchestral music continues ♪ ] there is no attempt to be original . originality 's totally irrelevant . if they look like something else , why not ? [ ♪ orchestral music ♪ ] there is some deep , internal intelligence . some almost non-verbal narrative which nourishes us , which has its own natural wellspring . and so these drawings try to , you know , touch the rim of that . [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] [ ♪ orchestral music continues ♪ ] [ directed by emmanuel vaughan-lee ] [ produced by dorothée royal-hedinger ] [ filmed & amp ; amp ; edited by elias koch ] [ sound recording by emmanuel vaughan-lee ] [ music by h. scott salinas ] [ sound mix by d. chris smith ] [ www.globalonenessproject.org ]

[ ♪ orchestral music ♪ ] the tea allows us to breathe , to move . [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] the whole things starts with big splashes of tea . [ ♪ orchestral music ♪ ] it 's like some empty space inside the mind . [ ♪ orchestral music ♪ ] [ ♪ orchestral music continues ♪ ] [ ♪ orchestral music ♪ ] i start with the pen , [ ♪ orchestral music ♪ ] and then i look at the markings .

“ the whole thing starts with big splashes of tea . it ’ s like some empty space inside the mountain. ” what do you think he means by this ?

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 .

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 .

what is the most straightforward way to determine into which category a pattern falls ?

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 .

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 .

what is meant by the term “ authorial intent ” ?

on july 26 , 1943 , los angeles was blanketed by a thick gas that stung people 's eyes and blocked out the sun . panicked residents believed their city had been attacked using chemical warfare . but the cloud was n't an act of war . it was smog . a portmanteau of smoke and fog , the word smog was coined at the beginning of the 20th century to describe the thick gray haze that covered cities such as london , glasgow , and edinburgh . this industrial smog was known to form when smoke from coal-burning home stoves and factories combined with moisture in the air . but the smog behind the la panic was different . it was yellowish with a chemical odor . since the city did n't burn much coal , its cause would remain a mystery until a chemist named arie haagen-smit identified two culprits , volatile organic compounds , or vocs , and nitrous oxides . vocs are compounds that easily become vapors and may contain elements , such as carbon , oxygen , hydrogen , chlorine , and sulfur . some are naturally produced by plants and animals , but others come from manmade sources , like solvents , paints , glues , and petroleum . meanwhile , the incomplete combustion of gas in motor vehicles releases nitrous oxide . that 's what gives this type of smog its yellowish color . vocs and nitrous oxide react with sunlight to produce secondary pollutants called pans and tropospheric , or ground level , ozone . pans and ozone cause eye irritation and damage lung tissue . both are key ingredients in photochemical smog , which is what had been plaguing la . so why does smog affect some cities but not others ? both industrial and photochemical smog combine manmade pollution with local weather and geography . london 's high humidity made it a prime location for industrial smog . photochemical smog is strongest in urban areas with calm winds and dry , warm , sunny weather . the ultraviolet radiation from sunlight provides the energy necessary to breakdown molecules that contribute to smog formation . cities surrounded by mountains , like la , or lying in a basin , like beijing , are also especially vulnerable to smog since there 's nowhere for it to dissipate . that 's also partially due to a phenomenon known as temperature inversion , where instead of warm air continuously rising upward , a pollution-filled layer of air remains trapped near the earth 's surface by a slightly warmer layer above . smog is n't just an aesthetic eyesore . both forms of smog irritate the eyes , nose , and throat , exacerbate conditions like asthma and emphysema , and increase the risk of respiratory infections like bronchitis . smog can be especially harmful to young children and older people and exposure in pregnant women has been linked to low birth weight and potential birth defects . secondary pollutants found in photochemical smog can damage and weaken crops and decrease yield , making them more susceptible to insects . yet for decades , smog was seen as the inevitable price of civilization . londoners had become accustomed to the notorious pea soup fog swirling over their streets until 1952 , when the great smog of london shut down all transportation in the city for days and caused more than 4,000 respiratory deaths . as a result , the clean air act of 1956 banned burning coal in certain areas of the city , leading to a massive reduction in smog . similarly , regulations on vehicle emissions and gas content in the us reduced the volatile compounds in the air and smog levels along with them . smog remains a major problem around the world . countries like china and poland that depend on coal for energy experience high levels of industrial smog . photochemical smog and airborne particles from vehicle emissions affect many rapidly developing cities , from mexico city and santiago to new delhi and tehran . governments have tried many methods to tackle it , such as banning cars from driving for days at a time . as more than half of the world 's population crowds into cities , considering a shift to mass transit and away from fossil fuels may allow us to breathe easier .

vocs and nitrous oxide react with sunlight to produce secondary pollutants called pans and tropospheric , or ground level , ozone . pans and ozone cause eye irritation and damage lung tissue . both are key ingredients in photochemical smog , which is what had been plaguing la .

the two secondary pollutants associated with photochemical smog that cause both eye irritation and potential lung damage are :

all animals communicate . crabs wave their claws at each other to signal that they 're healthy and ready to mate . cuttlefish use pigmented skin cells called chromatophores to create patterns on their skin that act as camouflage or warnings to rivals . honeybees perform complex dances to let other bees know the location and quality of a food source . all of these animals have impressive communication systems , but do they have language ? to answer that question , we can look at four specific qualities that are often associated with language : discreteness , grammar , productivity , and displacement . discreteness means that there is a set of individual units , such as sounds or words , that can be combined to communicate new ideas , like a set of refrigerator poetry magnets you can rearrange to create different phrases . grammar provides a system of rules that tells you how to combine those individual units . productivity is the ability to use language to create an infinite number of messages . and displacement is the ability to talk about things that are n't right in front of you , such as past , future , or fictional events . so , does animal communication exhibit any of these qualities ? for crabs and cuttlefish , the answer is no . they do n't combine their signals in creative ways . those signals also do n't have to be in a grammatical order , and they only communicate current conditions , like , `` i am healthy , '' or `` i am poisonous . '' but some animals actually do display some of these properties . bees use the moves , angle , duration , and intensity of their waggle dance to describe the location and richness of a food source . that source is outside the hive , so they exhibit the property of displacement . they share that language trait with prairie dogs , which live in towns of thousands , and are hunted by coyotes , hawks , badgers , snakes , and humans . their alarms calls indicate the predator 's size , shape , speed , and , even for human predators , what the person is wearing and if he 's carrying a gun . great apes , like chimps and gorillas , are great communicators , too . some have even learned a modified sign language . a chimpanzee named washoe demonstrated discreteness by combining multiple signs into original phrases , like , `` please open . hurry . '' coco , a female gorilla who understands more than 1000 signs , and around 2000 words of spoken english referred to a beloved kitten that had died . in doing so , she displayed displacement , though it 's worth noting that the apes in both of these examples were using a human communication system , not one that appeared naturally in the wild . there are many other examples of sophisticated animal communication , such as in dolphins , which use whistles to identify age , location , names , and gender . they can also understand some grammar in a gestural language researchers use to communicate with them . however , grammar is not seen in the dolphin 's natural communication . while these communication systems may have some of the qualities of language we 've identified , none display all four . even washoe and coco 's impressive abilities are still outpaced by the language skills of most three-year-old humans . and animals ' topics of conversation are usually limited . bees talk about food , prairie dogs talk about predators , and crabs talk about themselves . human language stands alone due to the powerful combination of grammar and productivity , on top of discreteness and displacement . the human brain can take a finite number of elements and create an infinite number of messages . we can craft and understand complex sentences , as well as words that have never been spoken before . we can use language to communicate about an endless range of subjects , talk about imaginary things , and even lie . research continues to reveal more and more about animal communication . it may turn out that human language and animal communication are n't entirely different but exist on a continuum . after all , we are all animals .

all animals communicate . crabs wave their claws at each other to signal that they 're healthy and ready to mate .

how are the communications systems of humans and animals similar ?

your body is a temple , but it ’ s also a museum of natural history . look closely and you ’ ll see parts that aren ’ t there because you need them but because your animal ancestors did . no longer serving their previous function but not costly enough to have disappeared , these remnants of our deep history only make sense within the framework of evolution by natural selection . with your arm on a flat surface , push your thumb against your pinky and tip your hand slightly up . if you see a raised band in the middle of the wrist , you ’ ve got a vestigial muscle in your forearm . that tendon you see connects to the palmaris longus , a muscle that around 10-15 % of people are missing on one or both of their arms . it doesn ’ t make them any weaker though . there ’ s no difference in grip strength . in fact , it ’ s one of the first tendons that surgeons will take out so they can use it in reconstructive and cosmetic surgeries . you can find the palmaris longus across mammal species , but it ’ s most developed among those that use their forelimbs to move around . in primates , that means the muscle is longer in lemurs and monkeys and shorter in chimps , gorillas , and other apes that don ’ t do a lot of scrambling through trees . it ’ s not the only leftover muscle that we 've got . look at the three that are attached to our outer ear . we can ’ t get much movement out of these muscles , especially compared to some of our mammal relatives who use them to locate the sources of sounds . presumably this would have been quite helpful for early nocturnal mammals . in humans , you can still detect the remnants of this adaptation with electrodes . in one study researchers recorded a spike of activity in the ear muscle cells in response to a sudden sound . not enough to move the ear , but detectable . and you can probably guess the location of the sound based on the results - it came from a speaker to the left of the study subjects . so this is their left ear subconsciously trying ( and failing ) to pivot toward the sound . you can see another futile effort by our vestigial body parts when you get goosebumps . when we ’ re cold , tiny muscles attached to our body hairs contract , pulling the hair upright which causes the surrounding skin to form a bump . for our furry mammal relatives , the raised hair increases the amount of space for insulation , helping them stay warm . birds can do this too . you ’ ve probably seen a puffy pigeon on a cold day . adrenaline is one of the hormones involved in the body ’ s response to cold temperatures , and it ’ s also part of the fight or flight response . so it helps some animals appear larger when they ’ re threatened . and it may be why surprising and emotional turns in music can give some people goosebumps . and then there ’ s our tail . at the end of our spine are a set of fused vertebrae - some people have 3 , some have 5 . we call it the tailbone . it now serves as an anchor for some pelvic muscles but it ’ s also what ’ s left of our ancestors ’ tails . every one of us actually had a tail at one point . when the basic body plan is being laid out at around 4 weeks of gestation , humans embryos closely resemble embryos of other vertebrates . and that includes a tail with 10-12 developing vertebrae . in many other animals it continues to develop into a proper tail . but in humans and other apes , the cells in the tail are programmed to die a few weeks after they appear . vary rarely though , a mutation allows the ancestral blueprint to prevail and a human baby will be born with a true vestigial tail . the most adorable vestigial behavior is the palmar grasp reflex , where infants up until they ’ re about 6 months old have this incredible grasp on whatever you put in their hand . there ’ s a similar reflex for their feet . i wanted to show you this great piece of footage from the 1930s where they demonstrated this behavior . these babies are only 1 month old and you can see that their inner monkey can support their entire weight .

so this is their left ear subconsciously trying ( and failing ) to pivot toward the sound . you can see another futile effort by our vestigial body parts when you get goosebumps . when we ’ re cold , tiny muscles attached to our body hairs contract , pulling the hair upright which causes the surrounding skin to form a bump .

what does the word `` vestigial '' mean with regard to the physical traits described in this video ?

to understand what 's happening with greece and the eurozone , think about a dinner party . if you 're cooking just for yourself and your spouse , it 's easy : you make something you both like . but if you 've got guests , things get harder . if you need to accommodate a vegetarian , and someone who is gluten free , and someone with a soy allergy , your options get really limited . and that 's the problem with europe 's idea of having a whole bunch of countries all use the same currency . so greece 's economy is in a disaster . a quarter of the population is unemployed , and it has this very high debt burden . normally , if you 've got really high unemployment , what happens is that a country makes its currency cheaper by printing extra money . that makes its products cheaper on world markets , it makes it a more attractive tourist destination , and it means that foreign investors can get great bargains . but if unemployment is really low , a country likes to have an expensive currency . that increases people 's purchasing power and it keeps prices down . and in europe , you have a bunch of economies that are really different . a price of euros that 's appropriate for greece , where they have a 25 % unemployment rate is way too low for germany , where the unemployment rate is below 5 % . and greece 's problem is that it 's small , poor , and geographically isolated from the rest of the eurozone . it 's like the only vegetarian at a barbeque , except when it comes to currencies , there 's no side dishes . and so there 's plenty of specific decisions we can second-guess , plenty of things greece did and various banks did that we can question , but fundamentally having all these countries come to a dinner party with only one dish on the menu was a mistake . the euro was a project that europe set about on for really political reasons . it was a symbol of their determination to have peace on the continent , but they did n't really take the economics of it seriously . so greece joins the euro in 2001 and initially , it works out great for greece because all of a sudden everyone was like 'yeah , sure , let 's lend them money . ' so they borrowed lots and lots and lots of euros , except that did n't change the fact that their economy is a lot weaker than some of the other european countries . so to really work , you would need a much , much , much closer union , where you had big financial transfers coming from the richer places to the poorer places all the time . in the united states , the poor states like kentucky , mississippi , alabama , they 're constantly getting money from the richer states like massachusetts , california , new york , through the welfare system , through social security , through medicare , through medicaid . and you know , people may complain about this or that program , but we do n't dispute the idea that it 's all one country so money is going to circulate around . europeans , you know , they just do n't feel that way . germans are willing to support poor german people , but they do n't want to support greek people with their tax dollars . so they 're kind of like half-way integrated in a way that does n't really work .

so greece 's economy is in a disaster . a quarter of the population is unemployed , and it has this very high debt burden . normally , if you 've got really high unemployment , what happens is that a country makes its currency cheaper by printing extra money .

according to the video , how much of the greek population is unemployed ?

how high can you count on your fingers ? it seems like a question with an obvious answer . after all , most of us have ten fingers , or to be more precise , eight fingers and two thumbs . this gives us a total of ten digits on our two hands , which we use to count to ten . it 's no coincidence that the ten symbols we use in our modern numbering system are called digits as well . but that 's not the only way to count . in some places , it 's customary to go up to twelve on just one hand . how ? well , each finger is divided into three sections , and we have a natural pointer to indicate each one , the thumb . that gives us an easy to way to count to twelve on one hand . and if we want to count higher , we can use the digits on our other hand to keep track of each time we get to twelve , up to five groups of twelve , or 60 . better yet , let 's use the sections on the second hand to count twelve groups of twelve , up to 144 . that 's a pretty big improvement , but we can go higher by finding more countable parts on each hand . for example , each finger has three sections and three creases for a total of six things to count . now we 're up to 24 on each hand , and using our other hand to mark groups of 24 gets us all the way to 576 . can we go any higher ? it looks like we 've reached the limit of how many different finger parts we can count with any precision . so let 's think of something different . one of our greatest mathematical inventions is the system of positional notation , where the placement of symbols allows for different magnitudes of value , as in the number 999 . even though the same symbol is used three times , each position indicates a different order of magnitude . so we can use positional value on our fingers to beat our previous record . let 's forget about finger sections for a moment and look at the simplest case of having just two options per finger , up and down . this wo n't allow us to represent powers of ten , but it 's perfect for the counting system that uses powers of two , otherwise known as binary . in binary , each position has double the value of the previous one , so we can assign our fingers values of one , two , four , eight , all the way up to 512 . and any positive integer , up to a certain limit , can be expressed as a sum of these numbers . for example , the number seven is 4+2+1 . so we can represent it by having just these three fingers raised . meanwhile , 250 is 128+64+32+16+8+2 . how high an we go now ? that would be the number with all ten fingers raised , or 1,023 . is it possible to go even higher ? it depends on how dexterous you feel . if you can bend each finger just halfway , that gives us three different states - down , half bent , and raised . now , we can count using a base-three positional system , up to 59,048 . and if you can bend your fingers into four different states or more , you can get even higher . that limit is up to you , and your own flexibility and ingenuity . even with our fingers in just two possible states , we 're already working pretty efficiently . in fact , our computers are based on the same principle . each microchip consists of tiny electrical switches that can be either on or off , meaning that base-two is the default way they represent numbers . and just as we can use this system to count past 1,000 using only our fingers , computers can perform billions of operations just by counting off 1 's and 0 's .

and any positive integer , up to a certain limit , can be expressed as a sum of these numbers . for example , the number seven is 4+2+1 . so we can represent it by having just these three fingers raised .

the doubling numbers ( that is , the powers of two ) begin 1 , 2 , 4 , 8 , 16 , 32 ... do any of these numbers ever begin with a seven ?

translator : andrea mcdonough reviewer : bedirhan cinar this is zeno of elea , an ancient greek philosopher famous for inventing a number of paradoxes , arguments that seem logical , but whose conclusion is absurd or contradictory . for more than 2,000 years , zeno 's mind-bending riddles have inspired mathematicians and philosophers to better understand the nature of infinity . one of the best known of zeno 's problems is called the dichotomy paradox , which means , `` the paradox of cutting in two '' in ancient greek . it goes something like this : after a long day of sitting around , thinking , zeno decides to walk from his house to the park . the fresh air clears his mind and help him think better . in order to get to the park , he first has to get half way to the park . this portion of his journey takes some finite amount of time . once he gets to the halfway point , he needs to walk half the remaining distance . again , this takes a finite amount of time . once he gets there , he still needs to walk half the distance that 's left , which takes another finite amount of time . this happens again and again and again . you can see that we can keep going like this forever , dividing whatever distance is left into smaller and smaller pieces , each of which takes some finite time to traverse . so , how long does it take zeno to get to the park ? well , to find out , you need to add the times of each of the pieces of the journey . the problem is , there are infinitely many of these finite-sized pieces . so , should n't the total time be infinity ? this argument , by the way , is completely general . it says that traveling from any location to any other location should take an infinite amount of time . in other words , it says that all motion is impossible . this conclusion is clearly absurd , but where is the flaw in the logic ? to resolve the paradox , it helps to turn the story into a math problem . let 's supposed that zeno 's house is one mile from the park and that zeno walks at one mile per hour . common sense tells us that the time for the journey should be one hour . but , let 's look at things from zeno 's point of view and divide up the journey into pieces . the first half of the journey takes half an hour , the next part takes quarter of an hour , the third part takes an eighth of an hour , and so on . summing up all these times , we get a series that looks like this . `` now '' , zeno might say , `` since there are infinitely many of terms on the right side of the equation , and each individual term is finite , the sum should equal infinity , right ? '' this is the problem with zeno 's argument . as mathematicians have since realized , it is possible to add up infinitely many finite-sized terms and still get a finite answer . `` how ? '' you ask . well , let 's think of it this way . let 's start with a square that has area of one meter . now let 's chop the square in half , and then chop the remaining half in half , and so on . while we 're doing this , let 's keep track of the areas of the pieces . the first slice makes two parts , each with an area of one-half the next slice divides one of those halves in half , and so on . but , no matter how many times we slice up the boxes , the total area is still the sum of the areas of all the pieces . now you can see why we choose this particular way of cutting up the square . we 've obtained the same infinite series as we had for the time of zeno 's journey . as we construct more and more blue pieces , to use the math jargon , as we take the limit as n tends to infinity , the entire square becomes covered with blue . but the area of the square is just one unit , and so the infinite sum must equal one . going back to zeno 's journey , we can now see how how the paradox is resolved . not only does the infinite series sum to a finite answer , but that finite answer is the same one that common sense tells us is true . zeno 's journey takes one hour .

we 've obtained the same infinite series as we had for the time of zeno 's journey . as we construct more and more blue pieces , to use the math jargon , as we take the limit as n tends to infinity , the entire square becomes covered with blue . but the area of the square is just one unit , and so the infinite sum must equal one .

at which step of the argument did we “ take the limit as it tends to infinity ” ?

translator : andrea mcdonough reviewer : jessica ruby what 's an algorithm ? in computer science , an algorithm is a set of instructions for solving some problem , step-by-step . typically , algorithms are executed by computers , but we humans have algorithms as well . for instance , how would you go about counting the number of people in a room ? well , if you 're like me , you probably point at each person , one at a time , and count up from 0 : 1 , 2 , 3 , 4 and so forth . well , that 's an algorithm . in fact , let 's try to express it a bit more formally in pseudocode , english-like syntax that resembles a programming language . let n equal 0 . for each person in room , set n = n + 1 . how to interpret this pseudocode ? well , line 1 declares , so to speak , a variable called n and initializes its value to zero . this just means that at the beginning of our algorithm , the thing with which we 're counting has a value of zero . after all , before we start counting , we have n't counted anything yet . calling this variable n is just a convention . i could have called it almost anything . now , line 2 demarks the start of loop , a sequence of steps that will repeat some number of times . so , in our example , the step we 're taking is counting people in the room . beneath line 2 is line 3 , which describes exactly how we 'll go about counting . the indentation implies that it 's line 3 that will repeat . so , what the pseudocode is saying is that after starting at zero , for each person in the room , we 'll increase n by 1 . now , is this algorithm correct ? well , let 's bang on it a bit . does it work if there are 2 people in the room ? let 's see . in line 1 , we initialize n to zero . for each of these two people , we then increment n by 1 . so , in the first trip through the loop , we update n from zero to 1 , on the second trip through that same loop , we update n from 1 to 2 . and so , by this algorithm 's end , n is 2 , which indeed matches the number of people in the room . so far , so good . how about a corner case , though ? suppose that there are zero people in the room , besides me , who 's doing the counting . in line 1 , we again initialize n to zero . this time , though , line 3 does n't execute at all since there is n't a person in the room , and so , n remains zero , which indeed matches the number of people in the room . pretty simple , right ? but counting people one a time is pretty inefficient , too , no ? surely , we can do better ! why not count two people at a time ? instead of counting 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , and so forth , why not count 2 , 4 , 6 , 8 , and so on ? it even sounds faster , and it surely is . let 's express this optimization in pseudocode . let n equal zero . for each pair of people in room , set n = n + 2 . pretty simple change , right ? rather than count people one at a time , we instead count them two at a time . this algorithm 's thus twice as fast as the last . but is it correct ? let 's see . does it work if there are 2 people in the room ? in line 1 , we initialize n to zero . for that one pair of people , we then increment n by 2 . and so , by this algorithm 's end , n is 2 , which indeed matches the number of people in the room . suppose next that there are zero people in the room . in line 1 , we initialize n to zero . as before , line 3 does n't execute at all since there are n't any pairs of people in the room , and so , n remains zero , which indeed matches the number of people in the room . but what if there are 3 people in the room ? how does this algorithm fair ? let 's see . in line 1 , we initialize n to zero . for a pair of those people , we then increment n by 2 , but then what ? there is n't another full pair of people in the room , so line 2 no longer applies . and so , by this algorithm 's end , n is still 2 , which is n't correct . indeed this algorithm is said to be buggy because it has a mistake . let 's redress with some new pseudocode . let n equal zero . for each pair of people in room , set n = n + 2 . if 1 person remains unpaired , set n = n + 1 . to solve this particular problem , we 've introduced in line 4 a condition , otherwise known as a branch , that only executes if there is one person we could not pair with another . so now , whether there 's 1 or 3 or any odd number of people in the room , this algorithm will now count them . can we do even better ? well , we could count in 3 's or 4 's or even 5 's and 10 's , but beyond that it 's going to get a little bit difficult to point . at the end of the day , whether executed by computers or humans , algorithms are just a set of instructions with which to solve problems . these were just three . what problem would you solve with an algorithm ?

as before , line 3 does n't execute at all since there are n't any pairs of people in the room , and so , n remains zero , which indeed matches the number of people in the room . but what if there are 3 people in the room ? how does this algorithm fair ? let 's see .

if there are 3 people in the room , how many times does line 3 of our first algorithm execute ?

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 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 .

you have to be famous or be a celebrity to start and successfully win with an online petition .

translator : bedirhan cinar my wife is pregnant right now with our first child , and when people see her with her big baby bump , the first question people ask , almost without fail , is , `` is it a boy or is it a girl ? '' now , there are some assumptions behind that question that we take for granted because of our familiarity with our own human biology . for human babies , we take it for granted that there 's a 50/50 chance of either answer , boy or girl . but why is it that way ? well , the answer depends on the sex determination system that has evolved for our species . you see , for most mammals , the sex of a baby is determined genetically with the xy chromosome system . mammals have a pair of sex chromosomes , one passed down from mom , and one from dad . a pair of x 's gives us a girl , and an x and a y together gives us a boy . since females only have x 's to pass on in their egg cells , and males can give either an x or a y in their sperm cells , the sex is determined by the father and the chance of producing a male or a female is 50/50 . this system has worked well for mammals , but throughout the tree of life , we can see other systems that have worked just as well for other animals . there are other groups of animals that also have genetic sex determination , but their systems can be pretty different from ours . birds and some reptiles have their sex genetically determined , but instead of the sex being determined by dad , their sex is determined by mom . in those groups , a pair of z sex chromosomes produces a male , so these males only have z 's to give . however , in these animals , one z and one w chromosome together , as a pair , produces a female . in this system , the chance of a male or a female is still 50/50 , it just depends on whether mom puts a z or a w into her egg . certain groups have taken genetic sex determination in completely other directions . ants , for example , have one of the most interesting systems for determining sex , and because of it , if you are a male ant , you do not have a father . in an ant colony , there are dramatic divisions of labor . there are soldiers that defend the colony , there are workers that collect food , clean the nest and care for the young , and there 's a queen and a small group of male reproductives . now , the queen will mate and then store sperm from the males . and this is where the system gets really interesting . if the queen uses the stored sperm to fertilize an egg , then that egg will grow up to become female . however , if she lays an egg without fertilizing it , then that egg will still grow up to be an ant , but it will always be a male . so you see , it 's impossible for male ants to have fathers . and male ants live their life like this , with only one copy of every gene , much like a walking sex cell . this system is called a haplodiploid system , and we see it not only in ants , but also in other highly social insects like bees and wasps . since our own sex is determined by genes , and we do know of these other animals that have their sex determined by genes , it 's easy to assume that for all animals the sex of their babies still must be determined by genetics . however , for some animals , the question of whether it will be a boy or a girl has nothing to do with genes at all , and it can depend on something like the weather . these are animals like alligators and most turtles . in these animals , the sex of an embryo in a developing egg is determined by the temperature . in these species , the sex of the baby is not yet determined when the egg is laid , and it remains undetermined until sometime in the middle of the overall development period , when a critical time is reached . and during this time , the sex is completely determined by temperature in the nest . in painted turtles , for example , warm temperatures above the critical temperature will produce females within the eggs , and cool temperatures will produce a male . i 'm not sure who came up with this mnemonic , but you can remember that when it comes to painted turtles , they are all hot chicks and cool dudes . for some tropical fish , the question of will it be a boy or will it be a girl is n't settled until even later in life . you see , clownfish all start out their lives as males , however , as they mature , they become female . they also spend their lives in small groups with a strict dominance hierarchy where only the most dominant male and female reproduce . and amazingly , if the dominant female in the group dies , the largest and most dominant male will then quickly become female and take her place , and all of the other males will move up one rank in the hierarchy . in another very different ocean animal , the green spoonworm , the sex of the babies is determined by a completely different aspect of the environment . for this species , it is simply a matter of where a larva happens to randomly fall on the sea floor . if a larva lands on the open sea floor , then it will become a female . but if it lands on top of a female , then it will become a male . so for some species , the question of boy or girl is answered by genetics . for others , it 's answered by the environment . and for others still , they do n't even bother with the question at all . take whiptail lizards , for example . for those desert lizards , the answer is easy . it 's a girl . it 's always a girl . they are a nearly all-female species , and although they still lay eggs , these eggs hatch out female clones of themselves . so will it be a girl or will it be a boy ? throughout the entire animal kingdom , it does really all depend on the system of sex determination . for humans , that system is a genetic xy system . and for me and my wife , we found out it 's going to be a baby boy . ( kiss )

in these species , the sex of the baby is not yet determined when the egg is laid , and it remains undetermined until sometime in the middle of the overall development period , when a critical time is reached . and during this time , the sex is completely determined by temperature in the nest . in painted turtles , for example , warm temperatures above the critical temperature will produce females within the eggs , and cool temperatures will produce a male .

for species with temperature dependent sex determination , like the painted turtle , global climate change is a serious concern . in what ways would you expect that female painted turtles will respond behaviorally when choosing nest sites in a warming climate ?

translator : andrea mcdonough reviewer : bedirhan cinar i would like to introduce you to my favorite parasite . there are millions that i could choose from and this is it : it 's called the jewel wasp . you can find it in parts of africa and asia . it 's a little under an inch long , and it is a beautiful looking parasite . now , you may be saying to yourself , `` this is not a parasite . it 's not a tapeworm , it 's not a virus , how could a wasp be a parasite ? '' you are probably thinking about regular wasps , you know , the ones that build paper nests as their house . well , the thing is that the jewel wasp makes its house inside a living cockroach . here 's how it happens . a jewel wasp is flying around , looking for a cockroach . when it sees one , it lands and bites on its wing . so , i 'll be the cockroach . be-wha ! bewha ! and the cockroach starts shaking it off , `` get away from me ! '' the wasp very quickly starts stinging the cockroach . all of a sudden , the cockroach ca n't move , for about a minute . and then it recovers and stands up . it could run away now , but it does n't . it just does n't want to . it just stays there . it 's become a zombie slave . again , i 'm not making this up . the wasp goes off , it walks away and finds a hole and digs it out , makes it into a burrow . it walks back . this can take up to half an hour . the cockroach is still there . what do we do now ? the wasps grabs onto one of the antenna , bites down on it , of the cockroach , and pulls the cockroach . and the cockroach says , `` alright , '' and walks like a dog on a leash . the wasp takes it all the way down into the burrow . the cockroach says , `` nice place . '' the wasp takes care of some business and then goes and leaves the burrow and seals it shut , leaving the cockroach entombed in darkness , still alive . the cockroach says , `` alright , i 'll stay here if you want . '' now , i mentioned that the cockroach took care , ah , the wasp took care of a little business before it left the burrow . the business was laying an egg on the underside of the cockroach . the egg hatches . out comes a wasp larva . it looks kind of like a maggot with big , nasty jaws . it chews a hole into the cockroach and starts to feed from the outside . it gets bigger , like you can see over here . and then when it gets big enough , it decides to crawl into the hole , into the cockroach . so now it 's inside the still-living cockroach and the cockroach does n't mind much . this goes on for about a month . the larva grows and grows and grows , then makes a pupa , kind of like a cocoon . inside there it grows eyes , it grows wings , it grows legs , the cockroach is still alive , still waiting . finally the wasp is ready to leave , and that 's when the cockroach finally dies because the fullly-formed adult wasp crawls out of the cockroach 's dying body . the wasp shakes itself off , climbs out of the burrow , goes and finds another wasp to mate with to start this whole , crazy cycle again . so , this is not science fiction , this happens every day , all over the world . and scientists are totally fascinated by this . they 're just starting to figure out how all this happens . and , when you really start to look at the science of it , you start to kind of respect this very creepy wasp . you see , the thing is that when it attacks the cockroach , it 's not just stinging wildly , it delivers two precise stings . it knows this cockroach 's nervous system like you know the back of your hand . the first sting goes to that spot there , called the `` walking rhythm generators , '' and , as you can guess , those are the neurons that send signals to the legs to move . it blocks the channels that the neurons use to send these signals . so the cockroach wants to go , it wants to run away , but it ca n't because it ca n't move its legs . and that lasted for about a minute . this is really sophisticated pharmacology . we actually use the same method , a drug called ivermectin , to cure river blindness , which is caused by a parasitic worm that gets into your eye . if you take ivermectin , you paralyze the worm using the same strategy . now , we discovered this in the 1970s , the wasp has been doing this for millions of years . then comes the second sting . now the second sting actually hits two places along the way . and to try to imagine how this can happen , i want you to picture yourself with a friend who 's got a very long , very , very scary looking needle . and your friend , or at least you thought he was your friend , sticks it in your neck , goes into your skull , stops off at one part of your brain and injects some drugs , then keeps going in your brain and injects some more . these are two particular spots , marked here , `` seg '' , and you can see the tip of it in the brain , marked `` br '' . now , we can do this , but it 's really hard for us . it 's called stereotactic drug delivery . you have to put a patient in a big metal frame to hold them still , you need cat scans to know where you 're going , so you look at the picture and say , `` are we going the right way ? '' the jewel wasp has sensors on its stinger and scientists think that it can actually feel its way through the cockroach 's brain until it gets to the exact , right place , and then penetrates an individual neuron and then delivers the goods . so , this is quite amazing stuff , and what seems to happen then is that the wasp is taking away the control that the cockroach has over its own body . it 's taking away the cockroach 's free will . we did n't really appreciate that cockroaches have free will until this wasp showed us . and , we have no idea how it 's doing this , we do n't know yet what the venom has in it and we do n't know which circuits it 's hitting in the cockroach 's brain , and i think that 's why this is , most of all , my favorite parasite because we have so much left to learn from it . thank you very much .

it just stays there . it 's become a zombie slave . again , i 'm not making this up .

what do you think of when you hear the word zombie ? can you find other examples of zombies in the natural world ?

after witnessing the violent rage shown by babies whenever deprived of an item they considered their own , jean piaget , a founding father of child psychology , observed something profound about human nature . our sense of ownership emerges incredibly early . why are we so clingy ? there 's a well-established phenomenon in psychology known as the endowment effect where we value items much more highly just as soon as we own them . in one famous demonstration , students were given a choice between a coffee mug or a swiss chocolate bar as a reward for helping out with research . half chose the mug , and half chose the chocolate . that is , they seemed to value the two rewards similarly . other students were given a mug first and then a surprise chance to swap it for a chocolate bar , but only 11 % wanted to . yet another group started out with chocolate , and most preferred to keep it rather than swap . in other words , the students nearly always put greater value on whichever reward they started out with . part of this has to do with how quickly we form connections between our sense of self and the things we consider ours . that can even be seen at the neural level . in one experiment , neuroscientists scanned participants ' brains while they allocated various objects either to a basket labeled `` mine , '' or another labeled , `` alex 's . '' when participants subsequently looked at their new things , their brains showed more activity in a region that usually flickers into life whenever we think about ourselves . another reason we 're so fond of our possessions is that from a young age we believe they have a unique essence . psychologists showed us this by using an illusion to convince three to six-year-olds they built a copying machine , a device that could create perfect replicas of any item . when offered a choice between their favorite toy or an apparently exact copy , the majority of the children favored the original . in fact , they were often horrified at the prospect of taking home a copy . this magical thinking about objects is n't something we grow out of . rather it persists into adulthood while becoming ever more elaborate . for example , consider the huge value placed on items that have been owned by celebrities . it 's as if the buyers believed the objects they 'd purchased were somehow imbued with the essence of their former celebrity owners . for similar reasons , many of us are reluctant to part with family heirlooms which help us feel connected to lost loved ones . these beliefs can even alter our perception of the physical world and change our athletic abilities . participants in a recent study were told they were using a golf putter once owned by the champion ben curtis . during the experiment , they perceived the hole as being about a centimeter larger than controlled participants using a standard putter and they sank slightly more putts . although feelings of ownership emerge early in life , culture also plays a part . for example , it was recently discovered that hadza people of northern tanzania who are isolated from modern culture do n't exhibit the endowment effect . that 's possibly because they live in an egalitarian society where almost everything is shared . at the other extreme , sometimes our attachment to our things can go too far . part of the cause of hoarding disorder is an exaggerated sense of responsibility and protectiveness toward one 's belongings . that 's why people with this condition find it so difficult to throw anything away . what remains to be seen today is how the nature of our relationship with our possessions will change with the rise of digital technologies . many have forecast the demise of physical books and music , but for now , at least , this seems premature . perhaps there will always be something uniquely satisfying about holding an object in our hands and calling it our own .

in fact , they were often horrified at the prospect of taking home a copy . this magical thinking about objects is n't something we grow out of . rather it persists into adulthood while becoming ever more elaborate .

what are some of the almost magical ways that we think about the connection between objects and their owners ?

translator : andrea mcdonough reviewer : bedirhan cinar the development and spread of railroads across the united states brought a wave of changes to american life . during the railroad boom , thousands of jobs were created , new towns were born , trade increased , transportation was faster , and the overall landscape of the nation transformed . but , perhaps the most interesting change of all is the least known : the establishment of standard time . today , we know if it is 6:28 a.m. in los angeles , it is 9:28 a.m. in new york , 2:28 p.m. in london , 5:28 p.m. in moscow , and 10:28 p.m in tokyo . no matter where you are , the minute and second are the exact same . but , before the railroads , there was no need for a national or global clock , and each town kept its own local time . so when it was 12 noon in chicago , it was 12:07 p.m. in indianapolis , 11:50 a.m. in st. louis , and 11:27 a.m. in omaha . this worked just fine when the only modes of travel were horses or steamboats , but it became incredibly problematic when railroads came along . how can you keep a train schedule when each town has its own time ? and how do you prevent collisions or accidents on the tracks if train conductors are using different clocks ? it does n't really make sense to leave a station at 12:14 p.m. , travel for 22 minutes , and arrive at 12:31 p.m . in order to eliminate that confusion , the railroads of the united states and canada instituted standard time zones on november 18 , 1883 at noon . it allowed the railroad companies to operate more effectively and reduce deadly accidents . the american public , however , was not so quick to embrace this new change , as many cities continued to use their own local time . resistance was so strong that , in some towns , clocks would show both the local time and the railway time . imagine this conversation : `` pardon me , sir . do you have the time ? '' `` why yes , which do you need ? it 's 12:13 local time and 12:16 railway time . '' ultimately , the logic of keeping a standard time prevailed , and the united states government made time zones a matter of law with the standard time act of march 19 , 1918 . since then , there have been numerous changes to the time zones , but the concept of standard time has remained . but , the united states was actually not the first to develop standard time . the first company to implement the use of standard time was the great western railway in 1840 in britain , and by 1847 , most british railways were using greenwich mean time , or g.m.t . the british government made it official on august 2 , 1880 with the statutes , or definition of time , act . but , while britain may have been the first to establish standard time , it is asia and the islands of the south pacific that enjoyed the first hour of each new day . the international date line passes through the pacific ocean on the opposite side of the earth from the prime meridian in greenwich where , thanks to trains , standard time was first used . trains have evolved over the years and remain a prominent form of transportation and trade throughout the world . and , from the new york city subways to the freight trains traveling across the great plains , to the trolleys in san francisco , they all know exactly what time it is . and , thanks to them , we do too !

it allowed the railroad companies to operate more effectively and reduce deadly accidents . the american public , however , was not so quick to embrace this new change , as many cities continued to use their own local time . resistance was so strong that , in some towns , clocks would show both the local time and the railway time . imagine this conversation : `` pardon me , sir .

just like local towns were resistant to adopt standardized time , what are other instances when the general population has been resistant to change that has been overall beneficial ?

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

so why would you think to combine them ? physicists did n't just decide to mash these things together out of no where . rather , they were led to the dual nature of the universe through a process of small steps , fitting together lots of bits of evidence , like pieces in a puzzle . the first person to seriously suggest the dual nature of light was albert einstein in 1905 , but he was picking up an earlier idea from max planck .

the idea that everything in the universe has both particle and wave characteristics was pieced together by many scientists , each with a different bit of evidence . describe another example ( in physics or another subject ) where an important discovery was made by piecing together lots of small clues .

if you visit a museum with a collection of modern and contemporary art , you 're likely to see works that sometimes elicit the response , `` my cat could make that , so how is it art ? '' a movement called abstract expressionism , also known as the new york school , gets this reaction particularly often . abstract expressionism started in 1943 and developed after the end of world war ii . it 's characterized by large , primarily abstract paintings , all-over compositions without clear focal points , and sweeping swaths of paint embodying and eliciting emotions . the group of artists who are considered abstract expressionists includes barnett newman with his existential zips , willem de kooning , famous for his travestied women , helen frankenthaler , who created soak-stains , and others . but perhaps the most famous , influential , and head-scratching one was jackson pollock . most of his paintings are immediately recognizable . they feature tangled messes of lines of paint bouncing around in every direction on the canvas . and sure , these fields of chaos are big and impressive , but what 's so great about them ? did n't he just drip the paint at random ? ca n't anyone do that ? well , the answer to these questions is both yes and no . while pollock implemented a technique anyone is technically capable of regardless of artistic training , only he could have made his paintings . this paradox relates to his work 's roots in the surrealist automatic drawings of andré masson and others . these surrealists supposedly drew directly from the unconscious to reveal truths hidden within their minds . occasionally , instead of picturing something and then drawing it , they let their hands move automatically and would later tease out familiar figures that appeared in the scribbles . and after pollock moved away from representation , he made drip , or action , paintings following a similar premise , though he developed a signature technique and never looked for images or messages hidden in the works . first , he took the canvas off of the easel and laid it on the floor , a subversive act in itself . then , in a controlled dance , he stepped all around the canvas , dripping industrial paint onto it from stirrers and other tools , changing speed and direction to control how the paint made contact with the surface . these movements , like the surrealist scribbles , were supposedly born out of pollock 's subconscious . but unlike the surrealists , whose pictures represented the mind 's hidden contents , pollock 's supposedly made physical manifestations of his psyche . his paintings are themselves signatures of his mind . in theory , anyone could make a painting that is an imprint of their mind . so why is pollock so special ? well , it 's important to remember that while anyone could have done what he did , he and the rest of the new york school were the ones who actually did it . they destroyed conventions of painting that had stood for centuries , forcing the art world to rethink them entirely . but one last reason why jackson pollock 's work has stayed prominent stems from the specific objects he made , which embody fascinating contradictions . for instance , while pollock 's process resulted in radically flat painted surfaces , the web of painted lines can create the illusion of an infinite layered depth when examined up close . and the chaos of this tangled mess seems to defy all control , but it 's actually the product of a deliberate , though not pre-planned , process . these characteristics made pollock into a celebrity , and within art history , they also elevated him to the mythified status of the genius artist as hero . so rather than evening the playing field for all creative minds , his work unfortunately reinforced a long-standing elitist aspect of art . elitist , innovative , whatever you choose to call it , the history embedded in abstract expressionism is one that no cat , however talented , can claim .

if you visit a museum with a collection of modern and contemporary art , you 're likely to see works that sometimes elicit the response , `` my cat could make that , so how is it art ? '' a movement called abstract expressionism , also known as the new york school , gets this reaction particularly often . abstract expressionism started in 1943 and developed after the end of world war ii . it 's characterized by large , primarily abstract paintings , all-over compositions without clear focal points , and sweeping swaths of paint embodying and eliciting emotions .

what characterizes abstract expressionism ?

translator : andrea mcdonough reviewer : bedirhan cinar what does `` going viral '' on the internet really mean , and why does it happen so quickly ? why is a financial institution too big to fail ? how does a virus in africa end up in the united states in a matter of hours ? why are facebook and google such powerful companies at creating global connections ? well , in a word : networks . but what are networks ? everyone knows about their social network , but there are all different kinds of networks you probably have n't thought about . networks are collections of links which combine by specific rules and behaviors if they are alive . we say that networks are alive because they are in constant change . over time , the connections within a network migrate and concentrate in new places , forming evolving structures . how the evolution and concentration of constantly changing connections occurs is the subject of a whole discipline called network theory . we can think of networks as neighborhoods . neighborhoods are defined by maps . a google map demonstrates the relationship between locations in exactly the same fashion a network connects hubs and nodes , using streets as links to connect neighborhoods . the reason a network can expand and evolve so quickly is based upon a mathematical concept called power functions . a power function is a mathematical amplification mechanism , which over specific and very small ranges , accelerates changes logarithmically . that is , a very small change in one parameter produces a huge change in another over a very specific range of values . an example of how network structure emerges is the algorithm used by google . as the number of links around a search term , say `` friends '' , increases , connections begin to form among millions of different searches using the term `` friend '' . what google has cleverly accomplished is a real-time mathematical model for how to predict the emergence of growing connections among billions of search terms . the algorithm google derived collects the number of references to any search object . as references to a search object increase , the number of links also increases , creating a node . as the node increases in size , it eventually becomes a hub , which links to many nodes . networks will continue to emerge as new ways of connecting and creating neighborhoods are defined . perhaps you can begin to see why networks are so powerful . as google continues to collect the billions of daily searches , new clusters of links will rapidly emerge , forming additional and growing networks . despite the logarithmic expansion of your network , the laws of six degrees of separation still apply . therefore , if you explore a close friend or acquaintances in you facebook network , everyone on average will be separated by six individuals or less and a map of your social network will create neighborhoods linked by common connections among friends .

as references to a search object increase , the number of links also increases , creating a node . as the node increases in size , it eventually becomes a hub , which links to many nodes . networks will continue to emerge as new ways of connecting and creating neighborhoods are defined .

as a node increases in size , it eventually becomes a ______ .

beneath your ribs , you 'll find , among other things , the pancreas , an organ that works a lot like a personal health coach . this organ controls your sugar levels and produces a special juice that releases the nutrients from your food to help keep you in the best possible shape . the pancreas sits just behind your stomach , an appropriate home , as one of its jobs is to break down the food you eat . it aids digestion by producing a special tonic made of water , sodium bicarbonate , and digestive enzymes . sodium bicarbonate neutralizes the stomach 's natural acidity , so these digestive enzymes can perform their jobs . lipase breaks down fatty substances , protease splits up proteins , and amylase divides carbohydrates to create energy-rich sugars . most of those nutrients then get absorbed into the blood stream , and go on to enrich the body . while all this is happening , the pancreas works on another critical task , controlling the amount of sugar in your blood . it achieves this with the hormones insulin and glucagon , which are produced in special cells called the islets of langerhans . having too much or too little sugar can be life threatening , so the pancreas must stay on constant alert . after a big meal , the blood often becomes flushed with sugar . to bring us back to normal , the pancreas releases insulin , which makes the excess sugar move into cells , where it 's either used as an energy source , or stored for later . insulin also tells the liver to shut down sugar production . on the other hand , if blood sugar is low , the pancreas releases a hormone called glucagon that tells the body 's cells and liver to release stored sugars back into the bloodstream . the interplay between insulin and glucagon is what keeps our sugar levels balanced . but a faulty pancreas can no longer coach us like this , meaning that this healthy balance is destroyed . if it 's weakened by disease , the organ 's ability to produce insulin may be reduced , or even extinguished , which can trigger the condition known as diabetes . without regular insulin release , sugar steadily builds up in the blood , eventually hardening the blood vessels and causing heart attacks , kidney failure , and strokes . the same lack of insulin deprives cells of the energy-rich sugar they need to grow and function . people with diabetes also tend to have higher levels of glucagon , which makes even more sugar circulate . without this internal health coach , our sugar levels would go haywire , and we would n't be able to digest important nutrients . but like any coach , it 's not the pancreas ' job alone to keep us healthy . it needs our conscious participation , too .

on the other hand , if blood sugar is low , the pancreas releases a hormone called glucagon that tells the body 's cells and liver to release stored sugars back into the bloodstream . the interplay between insulin and glucagon is what keeps our sugar levels balanced . but a faulty pancreas can no longer coach us like this , meaning that this healthy balance is destroyed .

what condition results when the body 's sugar levels are n't balanced ?

imagine two people are listening to music . what are the odds that they are listening to the exact same playlist ? probably pretty low . after all , everyone has very different tastes in music . now , what are the odds that your body will need the exact same medical care and treatment as another person 's body ? even lower . as we go through our lives , each of us will have very different needs for our own healthcare . scientists and doctors are constantly researching ways to make medicine more personalized . one way they are doing this is by researching stem cells . stem cells are cells that are undifferentiated , meaning they do not have a specific job or function . while skin cells protect your body , muscle cells contract , and nerve cells send signals , stem cells do not have any specific structures or functions . stem cells do have the potential to become all other kinds of cells in your body . your body uses stem cells to replace worn-out cells when they die . for example , you completely replace the lining of your intestines every four days . stem cells beneath the lining of your intestines replace these cells as they wear out . scientists hope that stem cells could be used to create a very special kind of personalized medicine in which we could replace your own body parts with , well , your own body parts . stem cell researchers are working hard to find ways in which to use stem cells to create new tissue to replace the parts of organs that are damaged by injury or disease . using stem cells to replace damaged bodily tissue is called regenerative medicine . for example , scientists currently use stem cells to treat patients with blood diseases such as leukemia . leukemia is a form of cancer that affects your bone marrow . bone marrow is the spongy tissue inside your bones where your blood cells are created . in leukemia , some of the cells inside your bone marrow grow uncontrollably , crowding out the healthy stem cells that form your blood cells . some leukemia patients can receive a stem cell transplant . these new stem cells will create the blood cells needed by the patient 's body . there are actually multiple kinds of stem cells that scientists can use for medical treatments and research . adult stem cells or tissue-specific stem cells are found in small numbers in most of your body 's tissues . tissue-specific stem cells replace the existing cells in your organs as they wear out and die . embryonic stem cells are created from leftover embryos that are willingly donated by patients from fertility clinics . unlike tissue-specific stem cells , embryonic stem cells are pluripotent . this means that they can be grown into any kind of tissue in the body . a third kind of stem cells is called induced pluripotent stem cells . these are regular skin , fat , liver , or other cells that scientists have changed to behave like embryonic stem cells . like embryonic stem cells , they , too , can become any kind of cell in the body . while scientists and doctors hope to use all of these kinds of stem cells to create new tissue to heal your body , they can also use stem cells to help understand how the body works . scientists can watch stem cells develop into tissue to understand the mechnanisms that the body uses to create new tissue in a controlled and regulated way . scientists hope that with more research , they can not only develop specialized medicine that is specific to your body but also better understand how your body functions , both when it 's healthy and when it 's not .

embryonic stem cells are created from leftover embryos that are willingly donated by patients from fertility clinics . unlike tissue-specific stem cells , embryonic stem cells are pluripotent . this means that they can be grown into any kind of tissue in the body .

what is the source of embryos used for embryonic stem cell research ? what would have been the outcome for these cells had they not been used for research ? why do some people consider this to be unethical while others do not ?

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

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

math anxiety _______ the resources of working memory .

you 're in line at the grocery store when , uh oh , someone sneezes on you . the cold virus is sucked inside your lungs and lands on a cell on your airway lining . every living thing on earth is made of cells , from the smallest one-celled bacteria to the giant blue whale to you . each cell in your body is surrounded by a cell membrane , a thick flexible layer made of fats and proteins , that surrounds and protects the inner components . it 's semipermeable , meaning that it lets some thing pass in and out but blocks others . the cell membrane is covered with tiny projections . they all have functions , like helping cells adhere to their neighbors or binding to nutrients the cell will need . animal and plant cells have cell membranes . only plant cells have a cell wall , which is made of rigid cellulose that gives the plant structure . the virus cell that was sneezed into your lungs is sneaky . pretending to be a friend , it attaches to a projection on the cell membrane , and the cell brings it through the cell membrane and inside . when the virus gets through , the cell recognizes its mistake . an enemy is inside ! special enzymes arrive at the scene and chop the virus to pieces . they then send one of the pieces back through the cell membrane , where the cell displays it to warn neighboring cells about the invader . a nearby cell sees the warning and immediately goes into action . it needs to make antibodies , proteins that will attack and kill the invading virus . this process starts in the nucleus . the nucleus contains our dna , the blueprint that tells our cells how to make everything our bodies need to function . a certain section of our dna contains instructions that tell our cells how to make antibodies . enzymes in the nucleus find the right section of dna , then create a copy of these instructions , called messenger rna . the messenger rna leaves the nucleus to carry out its orders . the messenger rna travels to a ribosome . there can be as many as 10 million ribosomes in a human cell , all studded along a ribbon-like structure called the endoplasmic reticulum . this ribosome reads the instructions from the nucleus . it takes amino acids and links them together one by one creating an antibody protein that will go fight the virus . but before it can do that , the antibody needs to leave the cell . the antibody heads to the golgi apparatus . here , it 's packed up for delivery outside the cell . enclosed in a bubble made of the same material as the cell membrane , the golgi apparatus also gives the antibody directions , telling it how to get to the edge of the cell . when it gets there , the bubble surrounding the antibody fuses to the cell membrane . the cell ejects the antibody , and it heads out to track down the virus . the leftover bubble will be broken down by the cell 's lysosomes and its pieces recycled over and over again . where did the cell get the energy to do all this ? that 's the roll of the mitochondria . to make energy , the mitochondria takes oxygen , this is the only reason we breathe it , and adds electrons from the food we eat to make water molecules . that process also creates a high energy molecule , called atp which the cell uses to power all of its parts . plant cells make energy a different way . they have chloroplasts that combine carbon dioxide and water with light energy from the sun to create oxygen and sugar , a form of chemical energy . all the parts of a cell have to work together to keep things running smoothly , and all the cells of your body have to work together to keep you running smoothly . that 's a whole lot of cells . scientists think there are about 37 trillion of them .

that process also creates a high energy molecule , called atp which the cell uses to power all of its parts . plant cells make energy a different way . they have chloroplasts that combine carbon dioxide and water with light energy from the sun to create oxygen and sugar , a form of chemical energy .

cells need energy to perform all of their functions . where in the cell is energy made ?

albert einstein . the icon of genius . why ? because he figured out e equals m c squared ? because he did n't like socks ? nope ! because he came up with the most powerful idea in science.. general relativity his masterpiece is now 100 years old . and while the physicists are partying , the rest of us are left wondering what the bleep it ’ s all about ! well here goes . at 26 he figured out nothing less than a new theory of space and time . it led to a nifty way of simplifying physics – by treating space and time as one thing ... spacetime ! but albert was just warming up . he wasn ’ t happy with isaac newton ’ s mysterious force of gravity . naturally , he started work on his own theory . and sure enough , he cracked it . mass causes spacetime to curve ! the natural motion of things is to follow the simplest path through spacetime . but since objects with mass curve spacetime , stuff moves towards the most massive objects . that ’ s what you feel as gravity . it ’ s warped space and time that ’ s keeping your feet on the ground . “ warped space ” might sound too sci-fi to be true . but we can measure the bending of starlight as is passes through the warped space around the sun . warped time sounds even more ridiculous . but take an accurate clock to the top of a building and you ’ ll see it runs slightly quicker than one on the ground ! that ’ s because as you move away from the centre of the planet space and time are less warped . most amazing of all , einstein ’ s theory told us that our universe has a beginning . everything is expanding out from a hot dense origin 13.8 billion years ago . but here ’ s the catch : we ’ ve spotted that the universe is expanding faster than albert ’ s theory predicts . could the old genius be wrong ? to stick with his idea we ’ ve had to invent a made up energy - ‘ dark energy ’ - to account for the speedy expansion . and we ’ ve had to assume there ’ s an exotic form of ‘ dark matter ' we haven ’ t detected yet either . these two unknowns should make up 95 % of the universe – yet we ’ ve never detected them . that ’ s the sort of thing that keeps physicists awake at night . so they ’ re plotting some seriously big experiments to put albert ’ s theory to the ultimate test . for the last 100 years , uncle albert ’ s great theory has passed every test possible . if it succeeds again physicists will party . if they find its limits and it finally fails they ’ ll party too . physicists are funny like that .

albert einstein . the icon of genius .

according to einstein 's theory of relativity what causes gravity ?

somewhere right now , people are lining up to scare themselves , maybe with a thrill ride or horror movie . in fact , in october of 2015 alone , about 28 million people visited a haunted house in the u.s . but many consider this behavior perplexing , asking the question , `` what could possibly be fun about being scared ? '' fear has a bad rap , but it 's not all bad . for starters , fear can actually feel pretty good . when a threat triggers our fight or flight response , our bodies prepare for danger by releasing chemicals that change how our brains and bodies function . this automatic response jumpstarts systems that can aid in survival . they do this by making sure we have enough energy and are protected from feeling pain , while shutting down nonessential systems , like critical thought . feeling pain-free and energized , while not getting caught up in worrisome thoughts that normally occupy our brains , that all sounds great , and it can be because this response is similar , though not exactly the same to what we experience in positive , high-arousal states , like excitement , happiness , and even during sex . the difference lays in the context . if we 're in real danger , we 're focused on survival , not fun . but when we trigger this high arousal response in a safe place , we can switch over to enjoying the natural high of being scared . it 's why people on roller coasters can go from screaming to laughing within moments . your body is already in a euphoric state . you 're just relabeling the experience . and though the threat response is universal , research shows differences between individuals in how the chemicals associated with the threat response work . this explains why some are more prone to thrill-seeking than others . other normal physical differences explain why some may love the dizziness associated with a loop-de-loop , while loathing the stomach-drop sensation of a steep roller coaster , or why some squeal with delight inside a haunted house , but retreat in terror if taken to an actual cemetery . fear brings more than just a fun , natural high . doing things that we 're afraid of can give us a nice boost of self-esteem . like any personal challenge , whether it 's running a race or finishing a long book , when we make it through to the end , we feel a sense of accomplishment . this is true even if we know we 're not really in any danger . our thinking brains may know the zombies are n't real , but our bodies tell us otherwise . the fear feels real , so when we make it through alive , the satisfaction and sense of accomplishment also feel real . this is a great evolutionary adaptation . those who had the right balance of bravery and wit to know when to push through the fear and when to retreat were rewarded with survival , new food , and new lands . finally , fear can bring people together . emotions can be contagious , and when you see your friend scream and laugh , you feel compelled to do the same . this is because we make sense of what our friends are experiencing by recreating the experience ourselves . in fact , the parts of the brain that are active when our friend screams are active in us when we watch them . this not only intensifies our own emotional experience , but makes us feel closer to those we 're with . the feeling of closeness during times of fear is aided by the hormone oxytocin released during fight or flight . fear is a powerful emotional experience , and anything that triggers a strong reaction is going to be stored in our memory really well . you do n't want to forget what can hurt you . so if your memory of watching a horror film with your friends is positive and left you with a sense of satisfaction , then you 'll want to do it over and over again .

you 're just relabeling the experience . and though the threat response is universal , research shows differences between individuals in how the chemicals associated with the threat response work . this explains why some are more prone to thrill-seeking than others .

the threat response ( fight or flight ) is universal , but how individuals experience and interpret the response can very from person to person .

to human eyes , the world at night is a formless canvas of grey . many nocturnal animals , on the other hand , experience a rich and varied world bursting with details , shapes , and colors . what is it , then , that separates moths from men ? moths and many other nocturnal animals see at night because their eyes are adapted to compensate for the lack of light . all eyes , whether nocturnal or not , depend on photoreceptors in the retina to detect light particles , known as photons . photoreceptors then report information about these photons to other cells in the retina and brain . the brain sifts through that information and uses it to build up an image of the environment the eye perceives . the brighter the light is , the more photons hit the eye . on a sunny day , upwards of 100 million times more photons are available to the eye than on a cloudy , moonless night . photons are n't just less numerous in darkness , but they also hit the eye in a less reliable way . this means the information that photoreceptors collect will vary over time , as will the quality of the image . in darkness , trying to detect the sparse scattering of randomly arriving photons is too difficult for the eyes of most daytime animals . but for night creatures , it 's just a matter of adaptation . one of these adaptations is size . take the tarsier , whose eyeballs are each as big as its brain , giving it the biggest eyes compared to head size of all mammals . if humans had the same brain to eye ratio , our eyes would be the size of grapefruits . the tarsier 's enlarged orbs have n't evolved to make it cuter , however , but to gather as much light as possible . bigger eyes can have larger openings , called pupils , and larger lenses , allowing for more light to be focused on the receptors . while tarsiers scan the nocturnal scene with their enormous peepers , cats use gleaming eyes to do the same . cats ' eyes get their shine from a structure called the tapetum lucidum that sits behind the photoreceptors . this structure is made from layers of mirror-like cells containing crystals that send incoming light bouncing back towards the photoreceptors and out of the eye . this results in an eerie glow , and it also gives the photoreceptors a second chance to detect photons . in fact , this system has inspired the artificial cats ' eyes we use on our roads . toads , on the other hand , have adapted to take it slow . they can form an image even when just a single photon hits each photoreceptor per second . they accomplish this with photoreceptors that are more than 25 times slower than human ones . this means toads can collect photons for up to four seconds , allowing them to gather many more than our eyes do at each visual time interval . the downside is that this causes toads to react very slowly because they 're only receiving an updated image every four seconds . fortunately , they 're accustomed to targeting sluggish prey . meanwhile , the night is also buzzing with insects , such as hawk moths , which can see their favorite flowers in color , even on a starlit night . they achieve this by a surprising move - getting rid of details in their visual perception . information from neighboring photoreceptors is grouped in their brains , so the photon catch of each group is higher compared to individual receptors . however , grouping photoreceptors loses details in the image , as fine details require a fine grid of photoreceptors , each detecting photons from one small point in space . the trick is to balance the need for photons with the loss of detail to still find their flowers . whether eyes are slow , enormous , shiny , or coarse , it 's the combination of these biological adaptations that gives nocturnal animals their unique visual powers . imagine what it might be like to witness through their eyes the world that wakes up when the sun goes down .

however , grouping photoreceptors loses details in the image , as fine details require a fine grid of photoreceptors , each detecting photons from one small point in space . the trick is to balance the need for photons with the loss of detail to still find their flowers . whether eyes are slow , enormous , shiny , or coarse , it 's the combination of these biological adaptations that gives nocturnal animals their unique visual powers .

what other senses could animals use to support a night active lifestyle ( where they need to find food , find mates , hide or escape from predators , and navigate their environment ) ?

jean-paul sartre made thinking and philosophy glamorous . he was born in paris in 1905 . his father , a navy captain , died when he was a baby – and he grew up extremely close to his mother until she remarried , much to his regret , when he was twelve . sartre spent most of his life in paris , where he often went to cafes on the left bank . he had a strabismus , a wandering eye , and wore distinctive , heavy glasses . he was very short ( five feet three inches ) and frequently described himself as ugly . by the 60 ’ s sartre was a household name in both europe and the united states , and so was his chosen philosophy , existentialism . sartre is famous principally for his book being and nothingness ( 1943 ) , which enhanced his reputation not so much because people could understand his ideas but because they could n't quite . existentialism was built around a number of key insights : one : things are weirder than we think sartre is acutely attentive to moments when the world reveals itself as far stranger and more uncanny than we normally admit ; moments when the logic we ascribe to it day-to-day becomes unavailable , showing things to be highly contingent and even absurd and frightening . sartre ’ s first novel – nausea , published in 1938 – is full of evocations of such moments . at one point , the hero , roquentin , a 30-year-old writer living in a fictional french seaside town , is on a tram . he puts his hand on the seat , but then pulls it back rapidly . instead of being the most basic and obvious piece of design , scarcely worth a moment ’ s notice , the seat promptly strikes him as deeply strange ; the word ‘ seat ’ comes loose from its moorings , the object it refers to shines forth in all its primordial oddity , as if he ’ s never seen one before . roquentin has to force himself to remember that this thing beside him is something for people to sit on . for a terrifying moment , roquentin has peered into what sartre calls the ‘ absurdity of the world. ’ such a moment goes to the heart of sartre ’ s philosophy . to be sartrean is to be aware of existence as it is when it has been stripped of any of the prejudices and stabilising assumptions lent to us by our day-to-day routines . we can try out a sartrean perspective on many aspects of our own lives . think of what you know as ‘ the evening meal with your partner ’ . under such a description , it all seems fairly logical , but a sartrean would strip away the surface normality to show the radical strangeness lurking beneath . dinner really means that : when your part of the planet has spun away from the energy of a distant hydrogen and helium explosion , you slide your knees under strips of a chopped-up tree and put sections of dead animals and plants in your mouth and chew , while next to you , another mammal whose genitals you sometimes touch is doing the same . two : we are free such weird moments are certainly disorienting and rather scary , but sartre wants to draw our attention to them for one central reason : because of their liberating dimensions . life is a lot odder than we think , but it ’ s also as a consequence far richer in possibilities . things don ’ t have to be quite the way they are . in the course of fully realising our freedom , we will come up against what sartre calls the ‘ angoisse ’ or ‘ anguish ’ of existence . everything is ( terrifyingly ) possible because nothing has any pre-ordained , god-given sense or purpose . humans are just making it up as they go along , and are free to cast aside the shackles at any moment . three : we shouldn ’ t live in ‘ bad faith ’ sartre gave a term to the phenomenon of living without taking freedom properly on board . he called it bad faith . we are in bad faith whenever we tell ourselves that things have to be a certain way and shut our eyes to other options . it is bad faith to insist that we have to do a particular kind of work or live with a specific person or make our home in a given place . the most famous description of ‘ bad faith ’ comes in being and nothingness , when sartre notices a waiter who strikes him as overly devoted to his role , as if he were first and foremost a waiter rather than a free human being . his movement is quick and forward , a little too precise , a little too rapid . he comes towards the patrons with a step that is a little too quick . he bends forward a little too eagerly : his voice , his eyes express an interest a little too solicitous for the order of the customer… ’ the man ( he was probably modelled on someone in saint-germain ’ s café de flore ) has convinced himself that he is essentially , necessarily a waiter rather than a free creature who could be a jazz pianist or a fisherman on a north sea trawler . four : we 're free to dismantle capitalism . the one factor that most discourages people from experiencing themselves as free is money . most of us will shut down a range of possible options ( moving abroad , trying out a new career , leaving a partner ) by saying , ‘ that ’ s if i didn ’ t have to worry about money . ' this passivity in the face of money enraged sartre at a political level . he thought of capitalism as a giant machine designed to create a sense of necessity which doesn ’ t in fact exist in reality : it makes us tell ourselves we have to work a certain number of hours , buy a particular product or service , and so on . but in this , there is only the denial of freedom – and a refusal to take as seriously as we should the possibility of living in other ways . it was because of these views that sartre had a life long interest in marxism . marxism seemed in theory to allow people to explore their freedom , by reducing the role played in their lives by material considerations . sartre took part in many protests in the streets of paris in the 60s . arrested yet again in 1968 , president charles de gaulle had him pardoned , saying , “ you don ’ t arrest voltaire. ” sartre also visited fidel castro and che guevara and admired them both deeply . as a result of these connections and his radical politics , the fbi kept a large file on sartre trying to deduce what his suspicious philosophy might really mean . sartre is inspiring in his insistence that things do not have to be the way they are . he is hugely alive to our unfulfilled potential , as individuals and as a species . he urges us to accept the fluidity of existence and to create new institutions , habits , outlooks and ideas . the admission that life doesn ’ t have some preordained logic and is not inherently meaningful can be a source of immense relief when we feel oppressed by the weight of tradition and the status quo .

roquentin has to force himself to remember that this thing beside him is something for people to sit on . for a terrifying moment , roquentin has peered into what sartre calls the ‘ absurdity of the world. ’ such a moment goes to the heart of sartre ’ s philosophy . to be sartrean is to be aware of existence as it is when it has been stripped of any of the prejudices and stabilising assumptions lent to us by our day-to-day routines .

how do we see `` the absurdity of the world ? ''

where does bread get its fluffiness ? swiss cheese its holes ? and what makes vinegar so sour ? these foods may taste completely different , but all of these phenomena come from tiny organisms chowing down on sugar and belching up some culinary byproducts . let 's start with yeast . yeast are single-celled fungi used to make bread , beer , and wine , among other products . yeast break down carbohydrates , like sugar , to get energy and the molecules they need to function . they have two different ways to do this : the oxygen-dependent , or aerobic , pathway , and the oxygen-independent , anaerobic pathway , which is also called fermentation . when you bake bread , yeast can use both pathways , but they normally prefer to start with the anaerobic process of fermentation . in this process , ethanol is produced in addition to co2 . no , bread is n't alcoholic . small amounts of alcohol that are secreted evaporate during baking . in the aerobic , or oxygen-dependent pathway , the yeast consume some of the sugar and produce carbon dioxide gas , or co2 , and water . in both processes , the co2 accumulates and creates tiny bubbles . these bubbles get trapped by gluten and create a sponge-like structure that gives the bread its soft texture . wine also relies on yeast . but a wine-making set-up keeps the oxygen levels low so that yeast consume sugar using fermentation , the anaerobic pathway . the process often starts with wild yeasts already hanging out on the grapes . but to get consistent results , most winemakers also add carefully selected strains of yeast that can tolerate high levels of alcohol . the yeast consume the sugar in the grape juice , and as the sugar level drops , the alcohol level rises . this does n't necessarily mean that sweeter wines have less alcohol . different types of grapes start with different amounts of sugar , and sugar can also be added . what happens to the carbon dioxide ? it just bubbles away through a vent . in carbonated alcoholic beverages , like champagne and beer , sealed containers are used in primary or secondary fermentation to keep the carbon dioxide in the bottle . wine also introduces us to our second type of food-producing microorganism : bacteria . a special strain of bacteria turns a tart compound in grape juice into softer tasting ones that are responsible for some of the flavors in red wines and chardonnays . another type of bacteria , called acetic acid bacteria , is n't so desirable in wine , but they have their function , too . if there 's oxygen around , these bacteria convert the ethanol in wine into , well , acetic acid . let this process continue and you 'll eventually get vinegar . bacteria are the key for cheese , too . to make cheese , milk is inoculated with bacteria . the bacteria gobble up the lactose , a kind of sugar , and produce lactic acid , along with many other chemicals . as the milk gets more and more acidic , its proteins start to aggregate and curdle . that 's why spoiled milk is clumpy . cheesemakers usually add an enzyme called rennet , naturally found inside of cows , goats , and some other mammals to help this process along . eventually , those little curdles turn into bigger curds , which are pressed to squeeze out the water , and create a firm cheese . different strains of bacteria make different kinds of cheese . for example , a species of bacteria that emits carbon dioxide is what gives swiss cheese its characteristic holes . some cheeses , brie and camembert , use another kind of microorganism , too : mold . so your kitchen functions as a sort of biotechnology lab manned by microorganisms that culture your cuisine . yogurt , soy sauce , sour cream , sauerkraut , kefir , kimchi , kombucha , cheddar , challah , pita , and naan . but maybe not all at the same dinner .

no , bread is n't alcoholic . small amounts of alcohol that are secreted evaporate during baking . in the aerobic , or oxygen-dependent pathway , the yeast consume some of the sugar and produce carbon dioxide gas , or co2 , and water .

all the dishes described involve metabolism -- breaking down of substances and secretion of byproducts . try to think of another byproduct secreted due to metabolic activity .

translator : andrea mcdonough reviewer : bedirhan cinar let me guess , you 've got facebook albums full of photos . you have photos on your computer desktop , on your mobile phone , on your bedroom wall . you see photos in magazines and newspapers , on the side of buses , and of course , in your family albums . we take photos for granted in a major way . but , creating a picture that looked exactly like the person or thing that you were photographing was n't always obvious . in fact , in the past , it was a big mystery . how could you , in essence , take your reflection in the mirror and freeze it in there ? in the 9th century , the arab scientist alhazen had come up with the idea of using the camera obscura , which was literally a dark room , or box , with a single , small hole in one side that let light through . this would project the image outside into the wall inside . during the renaissance , artists like leonardo davinci used this method to introduce 3-d scenes onto a flat plane so that they could copy things , like perspective , more easily . in 1724 , johann heinrich schultz discovered that exposing certain silver compounds to light altered their appearance and left marks wherever the light touched . essentially , schultz found a way to record the images that alhazen was able to project , but only for a little while . schultz 's images disappeared soon after he had made them . it was n't until 1839 that people figured out how to project images onto light-sensitive surfaces that would retain the image after exposure , and thus , photography was born . at that point , it was mostly two inventors who fought for the best way to make photos . one was british scientist henry fox talbot , whose calotype process used paper and allowed many copies to be made from a single negative . the other inventor , louis daguerre , was an artist and chemist in france . he developed something called a daguerreotype , which used a silvered plate and which produced a sharper image . but the daguerreotype could only make positive images so copies had to be made by taking another photo . in the end , the daguerreotype won out as the first commercially successful photographic process mostly because the government made it freely available to the public . so now that photography was available , getting a picture of yourself would be a snap , right ? well , not exactly ! this process still required a whole dark room at the location of the photograph , which was a big hassle . picture the early photographers lugging enormous trailers with all their equipment wherever they wanted to take a picture . not only that , but the early processes had extremely long exposure times . to get a good photo , you would have to stand perfectly still for up to two minutes ! this led to development of inventions like the head holder , a wire frame that would hide behind you while supporting your head . it 's also why you do n't see people smiling in early photographs . it 's not that life was that bad , it was just hard to keep a steady grin for more than a few seconds , so people opted for a straight-faced look . and then george eastman came along . eastman believed that everyone should have access to photography , and he spent many late nights mixing chemicals in his mother 's kitchen to try to achieve a dry plate photographic process . this would allow exposed negatives to be stored and developed later at a more convenient place instead of carting those dark rooms , necessary for wet plates , around . after starting a business , which initially made dry plates , eastman eventually discovered plastic roll film that would fit in hand-held , inexpensive cameras . these cameras sold by the millions under the tag line , `` you push the button , we do the rest . '' while eastman was largely responsible for making photography a universal pastime , even he could not have dreamed of the ways photography had since shaped the world . it 's now estimated that over 380 billion photographs are taken each year . that 's more photographs each day than were taken in the first hundred years after photography was invented . say cheese !

this led to development of inventions like the head holder , a wire frame that would hide behind you while supporting your head . it 's also why you do n't see people smiling in early photographs . it 's not that life was that bad , it was just hard to keep a steady grin for more than a few seconds , so people opted for a straight-faced look .

why do n't people smile in early photographs ?

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

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 ?

psychology question : reflect on this line from the song : “ why did i have to learn this stuff ? it has never come in handy , never used it for nothing. ” on a scale from 1 ( not at all ) to 7 ( completely agree ) , how much do you agree with the singer ’ s sentiment ? why or why not ?

statistics are persuasive . so much so that people , organizations , and whole countries base some of their most important decisions on organized data . but there 's a problem with that . any set of statistics might have something lurking inside it , something that can turn the results completely upside down . for example , imagine you need to choose between two hospitals for an elderly relative 's surgery . out of each hospital 's last 1000 patient 's , 900 survived at hospital a , while only 800 survived at hospital b . so it looks like hospital a is the better choice . but before you make your decision , remember that not all patients arrive at the hospital with the same level of health . and if we divide each hospital 's last 1000 patients into those who arrived in good health and those who arrived in poor health , the picture starts to look very different . hospital a had only 100 patients who arrived in poor health , of which 30 survived . but hospital b had 400 , and they were able to save 210 . so hospital b is the better choice for patients who arrive at hospital in poor health , with a survival rate of 52.5 % . and what if your relative 's health is good when she arrives at the hospital ? strangely enough , hospital b is still the better choice , with a survival rate of over 98 % . so how can hospital a have a better overall survival rate if hospital b has better survival rates for patients in each of the two groups ? what we 've stumbled upon is a case of simpson 's paradox , where the same set of data can appear to show opposite trends depending on how it 's grouped . this often occurs when aggregated data hides a conditional variable , sometimes known as a lurking variable , which is a hidden additional factor that significantly influences results . here , the hidden factor is the relative proportion of patients who arrive in good or poor health . simpson 's paradox is n't just a hypothetical scenario . it pops up from time to time in the real world , sometimes in important contexts . one study in the uk appeared to show that smokers had a higher survival rate than nonsmokers over a twenty-year time period . that is , until dividing the participants by age group showed that the nonsmokers were significantly older on average , and thus , more likely to die during the trial period , precisely because they were living longer in general . here , the age groups are the lurking variable , and are vital to correctly interpret the data . in another example , an analysis of florida 's death penalty cases seemed to reveal no racial disparity in sentencing between black and white defendants convicted of murder . but dividing the cases by the race of the victim told a different story . in either situation , black defendants were more likely to be sentenced to death . the slightly higher overall sentencing rate for white defendants was due to the fact that cases with white victims were more likely to elicit a death sentence than cases where the victim was black , and most murders occurred between people of the same race . so how do we avoid falling for the paradox ? unfortunately , there 's no one-size-fits-all answer . data can be grouped and divided in any number of ways , and overall numbers may sometimes give a more accurate picture than data divided into misleading or arbitrary categories . all we can do is carefully study the actual situations the statistics describe and consider whether lurking variables may be present . otherwise , we leave ourselves vulnerable to those who would use data to manipulate others and promote their own agendas .

but there 's a problem with that . any set of statistics might have something lurking inside it , something that can turn the results completely upside down . for example , imagine you need to choose between two hospitals for an elderly relative 's surgery .

what is the name of the paradox that can turn the results upside down ?

translator : nadja nathan reviewer : denise rq hello . i 'm chetan bhatt and when i give my name , i 'm often asked , `` where are you from ? '' i normally say , `` london . '' ( laughter ) and then i 'm asked , `` where are you originally from ? '' and if i happen to be particularly cheeky that day , i say , `` well , originally , i am from my mummy 's warm and cosy tummy . '' as we all are . obviously not my mum 's , but our own mothers . ( laughter ) but of course , i know what they 're really asking , so i say something like : `` well , my grandparents and my mum were born in india . my dad and i were born in kenya . and i was brought up in london . '' then they got me mapped : `` ah , you 're a kenyan asian . i have worked with one of those . '' and from my name they probably assume that i 'm a hindu . and this sort of fixes me for them . but what about the christians , and the muslims , and the atheists that i grew up with ? or the socialists , and the liberals , even the occasional tory , indeed all kinds of women and men , vegetable sellers , factory workers , cooks , car mechanics , living in my working class area . in some profoundly important way , they 're also a part of me , and are here with me . maybe that 's why i find it hard to respond to questions about identity and about origin . and it 's not just a sort of teenager refusal to be labelled . that 's not where i am coming from . it 's about our own most identities , the ones we put our hands up to , the ones that we cheer for , the ones that we fight for , the ones that we love or hate . it 's about how we apprehend ourselves as well as others . it is about identities we just assume that we have without thinking too much about them . but our responses to questions of identity and origin have substantial social and political importance . we see the wars , the rages of identity , going on all around us . we see violent religious , national , and ethnic disputes , and often the conflict is based on old stories of identity , and belonging , and origins . and these identities are based on myths , typically about ancient primordial origins . and these could be about adam and eve , or about the supremacy of a caste or gender , or about the vitality of a supposed race , or about the past glories of an empire or civilization , or about a piece of land that some imagined deity has gifted . people say that origin stories and identity myths make us feel secure . what 's wrong with that ? they give us a sense of belonging . identity is your cultural clothing , and it can make you feel warm and fuzzy inside . but does it really ? do we really need identity myths to feel safe ? because i see , religious , national , ethnic disputes adding to human misery . can i dare you to refuse every origin myth that claims you ? if you consider yourself to be human - and i 'm assuming that everybody here does – then humanity is your mirror . how then are you going to be at ease with the complexity of humanity that faces you ? what 's your feeling towards the person that others consider to be your enemy in the world ? what if we reject every single primordial origin myth and develop a deeper sense of personhood , one responsible to humanity as a whole rather than to a particular tribe ? or a radically different idea of humanity that exposes how origin myths mystify , disguise global power , rapacious exploitation , poverty , the worldwide oppression of women and girls , and of course massive , accelerating inequalities . origin myths are closely linked to tradition . the word 'tradition ' points to something old and permanent , almost natural . and people assume tradition is just history , simply the past condensed into a nice story . but let 's not confuse tradition with history , the two are often in severe conflict . origin stories are usually recently created fictions of ancient belonging , and they are absurd given the complexity of humanity and our vastly interconnected even if very unequal world . and today , we see claims to tradition that claim to be ancient changing rapidly in front of our eyes . i was brought up in the 1970s , near wembley , with asian , english , caribbean , irish families living in our streets . and the neo-nazi national front was massive then , with regular marches and attacks on us , and a permanent threat , and often a frequent reality of violence against us , on the streets , in our homes ; typically by neo-nazis and other racists . and i remember during a general election , a leaflet came through our letterbox with a picture of the national front candidate for our area . and the picture was of our next door neighbour . he threatened to shoot me once , when i played in the garden as a kid . and many weekends , shaven headed national front activists arrived at his house and emerged with scores of placards screaming that they wanted us to `` go back home '' . but today , he 's one of my mum 's best mates , he is a very lovely , gentle , and kind man . and at some point in his political journey out of fascism , he embraced a broader idea of humanity . there was a hindu family that we got to know well , and you have to understand that life in our street was a little bit like a setting for an asian soap opera , everyone knew everyone else 's business , even if they did not want it to be known by anyone at all . you really had no choice in this matter . but in this family there was a quiet little boy who went to the same school as i did . and after i left school , i did n't hear much more about him except that he 'd gone off to india . around 2000 , i remember seeing this short book . the book was unusual because it was written by a british supporter of al qaeda . and in it , the author calls for attacks in britain . this is in 1999 . so , 9/11 and the invasion of iraq was still in the future . and he helped scout new york bombing targets . he taught others how to make a dirty bomb to use on the london underground . and he plotted a massive bombing campaign in london shopping areas . he 's a very high risk security prisoner in the uk , and one of the most important al qaeda figures to be arrested in britain . the author of that book was that very same quiet little boy who went to my school . so a hindu boy from britain became an al qaeda fighter and a most wanted international terrorist . and he rejected what people would call his hindu , or indian , or british identity . and he became someone else . he refused to be who he was . he recreated himself . and this kind of journey is very common for young men and women who become involved in al qaeda , or islamic state , or other transnational armed groups . al qaeda 's media spokesman is a white american from a jewish and catholic mixed background . neither he nor the boy from my school were from muslim backgrounds . there is no point asking them where they are from . a more important question is , `` where are they going ? '' and i would also put it to you that exactly the same journey occurs for those young men and women who were brought up in muslim family backgrounds . most of those who join al qaeda , and other salafi-jihadi groups from europe , asia , north america , even in many cases the middle east are those who have comprehensively rejected their backgrounds to become , in essence , new people . they spend an enormous amount of time attacking their parents ' backgrounds as profane , impure , blasphemous , the wrong type of islam . and their vision instead is a fantastical view of cosmic apocalypse . it 's a born again vision . discard your past , your society , your family , and friends since they are all impure . instead , become someone else , your true self . your authentic self . this is n't about a return to the past , it is about using a forgery of the past to envision an appalling future which begins today , at year zero . this is why over an 80 % of the victims of al qaeda and the islamic state are people from muslim backgrounds . the first act by salafi-jihadi groups when they take over an area is to destroy existing muslim institutions , including mosques , shrines , preachers , practices . their main purpose is to control and punish people internally , to dictate the spaces that women may go , their clothing , family relations , beliefs , even the minute detail of how one prays . and you get the impression in the news that 'they ' are after 'us ' in the west , but they are actually mainly after people from other muslim backgrounds . in their view , no other muslim can ever be pure enough . so , ordinary beliefs and practices that have existed for centuries are attacked as impure by teenagers from birmingham or london who know nothing about the histories that they so joyously obliterate . here , their claim to tradition is at war with history but they 're nevertheless , very certain about their purity and about the impurity of others . purity , certainty , the return to authentic tradition ; the quest for these can lead to lethal visions of perfect societies and perfected people . this is what the main hindu fundamentalist organization in india looks like today at its mass rally . maybe it reminds you of the 1930s in italy or germany . and this movement 's roots are indeed in fascism . it was a member of this same hindu fundamentalist movement who shot dead mahatma gandhi . hindu fundamentalists today view this murderer as a national hero , and they want to put up statues of him throughout india . they have been involved for decades in large scale mass violence against minorities . they ban books , art , films , they attack romantic couples on valentine 's day , christians on christmas day . they do n't like others talking critically about what they see as their ancient culture or using its images , or caricaturing it , or drawing cartoons about it . but the people making the strongest possible claims about ancient timeless hindu religion are dressed in brown shorts and white shirts , while claiming , oddly , to be the original aryan race , just like the violent salafi-jihadis who make their claims , about their primordial religion , while dressed in black military uniforms and wearing balaclavas . these people are manufacturing pure , pristine identities of conviction , and of certainty . fundamentalists see religion and culture as their sole property , their property . but religions and cultures are processes , they are not things . they are impermanent , they are messy , they are impure . look at any religion and you will see disputes and arguments going all the way down . any criticism of religion , in any form , has to therefore be part of the expansive sense of humanity we should aspire to . i respect your right to have and to express your religion , or your culture , or your opinion , but i do n't necessarily have to respect the content . i might like some of it , and i like how an old church looks for example , but this is n't the same thing . similarly , i have a human right to say something that you may find offensive , but you do not have a human right not to be offended . in a genuine democracy we are constantly offended since people express different views all the time . they also change their views , so their views are impermanent . you can not fix someone 's political views based on their religious , or national , or cultural background . these points about religious purity also apply to nationalism and to racism . i 'm always puzzled to have pride in your national or ethnic identity . pride in the accident of birth from a woman 's cosy womb ? belief in your superiority because of the accident of birth ? these people have very firm ideas about what belongs and what does n't belong inside the cosy national cultures that they imagine . and i 'm going to caricature a bit here , but only a little bit . i want you to imagine the supporter of some little englander or british nationalist political party , and he 's sitting at home . and he is screaming about foreigners invading his country , while watching fox news , an american cable channel owned by an australian , on his south korean television set which was bought by his spanish credit card , which is paid off monthly by his high street british bank which has its headquarters in hong kong . he supports a british football team owned by a russian . his favourite brand of fish and chips is owned by a swedish venture capitalist firm . the church he sometimes goes to has its creed decided in meetings in ghana . his union jack underpants were made in india . ( laughter ) ( applause ) thank you . and they 're laundered regularly by a very nice polish lady . there is no pure ethnicity , nation , or culture . and the ethical choices we have today are far wider than being forced to choose between racist right and religious right visions ; dismal visions of culture . culture is n't just about language , food , clothing , and music , but gender relations , ancient monuments , a heritage of sacred texts . but culture can also be what 's been decided to be culture by those who have a political stake in pounding culture into the shape of a prison . big political identity claims are elite bids for power . they 're not answers to social or economic or political injustices , they often obscure them . what about the large number of people across the globe who ca n't point to a monument from their past who do n't possess a sacred written text , who ca n't hark back to the past glories of a civilization or empire ? are these people lesser parts of humanity ? what about you now listening to this ? what about you and your identity ? because you stitch your experiences and your thoughts into a continuous person moving forward in time . and this is what you are when you say 'i am ' or 'me ' . but this also includes all of your hopes and dreams all of the 'yous ' that you could have been , and it includes all the other people and the things that are in the biography of who you are . they , the others , are also a part of you , moving forward with you . your authentic self , if such a thing exists , is a complex , messy , and uncertain self . and that is a very good thing . why not value those impurities and uncertainties ? maybe clinging to pure identities is a sign of immaturity , and ethnic , nationalist , and religious traditions are bad for you . why not be skeptical about every primordial origin claim made on your behalf ? why not reject the identity myths that call on you to belong , that politicians and community leaders , so-called community leaders , place on you ? if we do n't need origin stories and fixed identities , we can challenge ourselves to think creatively about each other and our future . and here culture always takes care of itself . i 'm not worried about culture . cultures are creative , dynamic processes , not imposed laws and boundaries . i 'd be the first to admit that some cultural innovations can seem , a little [ haggis curry ] ( laughter ) a little bit unusual . but so what if they are ? because the same dynamism of cultures can bring us unexpected gifts . i want to end with the story of two muslims from two very different times . in the late 1980s , when the protests against salman rushdie book `` the satanic verses '' were emerging in britain , dr. ghayasuddin siddiqui was at the absolute heart of the muslim fundamentalist movement in britain and internationally . he went as part of a group from britain - a delegation - to persuade ayatollah khomeini , in iran , to denounce rushdie 's book as a blasphemy and khomeini , of course , as we know , said that rushdie had to be put to death . at the very same time , i was involved in a tiny little group that was defending rushdie 's right to free expression . now , a few years later , dr. siddiqui was with some other fundamentalist activists and they had heard news about a young girl in pakistan and she had been raped , and then she had been killed for adultery . and his friends around him said the killing was unfortunate , but then again , she 's only a girl . and dr. siddiqui told me , many years later , that at that moment , something shattered in his heart . he decided to refuse to be who he was . like my former national front neighbour , his was a flight away from these ideas of primordial purity , he instead became a tireless , deeply courageous fighter for women and children 's rights , and human rights , and against religious fundamentalism of all kinds , and racism , and extreme nationalism . he staunchly opposed the fundamentalists he previously worked with and he worked with youngsters to pull them away , wean them away from salafi-jihadi ideas and he continues this work to this day aged 75 . and part of his inspiration and his energy comes from this man , in whose name dr. siddiqui initiated an annual lecture . this is abu walid muhammad ibn rushd , a very senior muslim judge and thinker in cordoba in the 12th century . and his writings were considered deeply blasphemous , heretical , and evil . long after he died , followers of his work were ruthlessly hunted down , banished , and killed over several centuries by the most powerful religious institution of the medieval period . that institution was the roman catholic church . why ? because ibn rushd said that something true in religion may conflict with something that your reason finds to be true on earth . but the latter is still true . there are two distinct worlds of truth , one based on our reason and evidence , and one that is divine . and the state , political power , social law are in the realm of reason . religious life is a different realm . they should be kept separated . social and political life should be governed by our reason not by religion . and you can see why the church was upset by his writings as indeed were some muslims during his lifetime , because he gives us a strong statement of secularism of a kind which is normal in europe today . history plays many tricks on us . it undermines our fixed truths and what we believe to be 'our culture ' and 'their culture ' . ibn rushd , someone who happens to be a muslim is considered one of the key influences in the introduction and spread of secularism in europe . so against religious nationalist and racial purists of all kinds , can you make his story a part of your own ? not because he happened to be a muslim , not because he happened to be an arab , but because he was a human being with some very good ideas that shook his world and ours . thank you . ( applause )

or a radically different idea of humanity that exposes how origin myths mystify , disguise global power , rapacious exploitation , poverty , the worldwide oppression of women and girls , and of course massive , accelerating inequalities . origin myths are closely linked to tradition . the word 'tradition ' points to something old and permanent , almost natural .

how does bhatt suggest we deal with our origin myths ?

massive vines that blanket the southern united states , climbing as high as 100 feet as they uproot trees and swallow buildings . a ravenous snake that is capable of devouring an alligator . rabbit populations that eat themselves into starvation . these are n't horror movie concepts . they 're real stories , but how could such situations exist in nature ? all three are examples of invasive species , organisms harmful not because of what they are , but where they happen to be . the kudzu vine , for example , had grown quality in its native east asia , eaten by various insects and dying off during the cold winters . but its fortunes changed when it was imported into the southeastern united states for porch decoration and cattle feed . its planting was even subsidized by the government to fight soil erosion . with sunny fields , a mild climate , and no natural predators in its new home , the vine grew uncontrollably until it became known as the plant that ate the south . meanwhile in florida 's everglades , burmese pythons , thought to have been released by pet owners , are the cause of decreasing populations of organisms . they 're successfully outcompeting top predators , such as the alligator and panther , causing a significant reduction in their food sources . they 're not a problem in their native asia because diseases , parasites , and predators help to control their population size . and in australia , european rabbits eat so many plants that they wipe out the food supply for themselves and other herbivores . they 're a pretty recent addition , intentionally introduced to the continent because one man enjoyed hunting them . like the burmese pythons , various factors in their native habitat keep their numbers in control . but in australia , the lack of predators and a climate perfect for year-long reproduction allows their populations to skyrocket . so why does this keep happening ? most of the world 's ecosystems are the result of millennia of coevolution by organisms , adapting to their environment and each other until a stable balance is reached . healthy ecosystems maintain this balance via limiting factors , environmental conditions that restrict the size or range of a species . these include things like natural geography and climate , food availability , and the presence or absence of predators . for example , plant growth depends on levels of sunlight and soil nutrients . the amount of edible plants affects the population of herbivores , which in turn impacts the carnivores that feed on them . and a healthy predator population keeps the herbivores from becoming too numerous and devouring all the plants . but even minor changes in one factor can upset this balance , and the sudden introduction of non-native organisms can be a pretty major change . a species that is evolved in a separate habitat will be susceptible to different limiting factors , different predators , different energy sources , and different climates . if the new habitat 's limiting factors fail to restrict the species growth , it will continue to multiply , out-competing native organisms for resources and disrupting the entire ecosystem . species are sometimes introduced into new habitats through natural factors , like storms , ocean currents , or climate shifts . the majority of invasive species , though , are introduced by humans . often this happens unintentionally , as when the zebra mussel was accidentally brought to lake erie by cargo ships . but as people migrate around the world , we have also deliberately brought our plants and animals along , rarely considering the consequences . but now that we 're learning more about the effects of invasive species on ecosystems , many governments closely monitor the transport of plants and animals , and ban the imports of certain organisms . but could the species with the most drastic environmental impact be a group of primates who emerged from africa to cover most of the world ? are we an invasive species ?

all three are examples of invasive species , organisms harmful not because of what they are , but where they happen to be . the kudzu vine , for example , had grown quality in its native east asia , eaten by various insects and dying off during the cold winters . but its fortunes changed when it was imported into the southeastern united states for porch decoration and cattle feed .

the kudzu vine was able to spread rapidly due to the region 's lack of :

translator : andrea mcdonough reviewer : bedirhan cinar once upon a time in the magical and very round land of pi , there lived six swashbuckling musketeers . there names were parentheses , exponents , multiplication , division , addition , and subtraction . but each was known best by his or her mark : the two hands ready to catch a fly of parentheses , the small and raised digits of exponents , the mighty x of multiplication , slash of division , plus of addition , and , well , you can guess the symbol by which little subtraction was best known . the land of pi was not necessarily the most peaceful place , and that 's why the numbers of the kingdom needed the musketeers . the land of pi had been ruled by the numbers as anarcho-syndicalist commune , each number with a vote , but , one powerful number from what we 'll call the imperial senate , engineered a war between some robot things and the knights of the kingdom , and then installed himself as supreme emperor , and then puff the magic digit dragon ate him , and a princess or two , and , well , all the other numbers in the land of pi actually . it was kind of a big day . anyway , the musketeers were called to action to save the land of pi from the voracious dragon . they rode towards him on their valiant steeds and attacked . first multiplication , then parentheses , but that did n't work . the dragon continued eating people . so addition tried , but was thrown aside . exponents leaped at the beast and was quickly squashed . nothing was working . the musketeers huddled and formulated a plan . they would attack in sequence , but who should go first ? they bickered for a while , the dragon ate a few more princesses , and then they finally agreed . they jumped into the first , smallest parentheses inside the great puff the digit dragon . parentheses pointed out where to work first and protected exponents , multiplication , division , addition , and subtraction while they diced and sliced . first here , then , move over there , then there . look out ! there 's another set ! parentheses pointed and exponents took the lead . then , it was multiplication , division , addition , and subtraction , each in turn , always the same order . p-e-m-d-a-s when they finished that set , they went to another , and another , always working inside the parentheses in pemdas order . pop ! pop ! pop ! pop ! pop ! pemdas , there is another spot ! do n't forget , there can be parentheses inside parentheses . there 's one ! and that tricky exponent . there we go ! finally , the pemdas musketeers had whittled puff down to his last fearsome roar . but , having vanquished puff the magic digit dragon , all the empire 's numbers sprang again from this tiny little number one , and they all lived happily ever after . except for the emperor number , which they threw into the mouth of an ancient nesting creature in the desert . the end .

parentheses pointed and exponents took the lead . then , it was multiplication , division , addition , and subtraction , each in turn , always the same order . p-e-m-d-a-s when they finished that set , they went to another , and another , always working inside the parentheses in pemdas order .

tell us how you remember the order of operations ? perhaps it 's some sort of mnemonic device .

cloudy climate change : how clouds affect earth 's temperature . earth 's average surface temperature has warmed by .8 celsius since 1750 . when carbon dioxide concentrations in the atmosphere have doubled , which is expected before the end of the 21st century , researchers project global temperatures will have risen by 1.5 to 4.5 degrees celsius . if the increase is near the low end , 1.5 celsius , then we 're already halfway there , and we should be more able to adapt with some regions becoming drier and less productive , but others becoming warmer , wetter and more productive . on the other hand , a rise of 4.5 degrees celsius would be similar in magnitude to the warming that 's occurred since the last glacial maximum 22,000 years ago , when most of north america was under an ice sheet two kilometers thick . so that would represent a dramatic change of climate . so it 's vitally important for scientists to predict the change in temperature with as much precision as possible so that society can plan for the future . the present range of uncertainty is simply too large to be confident of how best to respond to climate change . but this estimate of 1.5 to 4.5 celsius for a doubling of carbon dioxide has n't changed in 35 years . why have n't we been able to narrow it down ? the answer is that we do n't yet understand aerosols and clouds well enough . but a new experiment at cern is tackling the problem . in order to predict how the temperature will change , scientists need to know something called earth 's climate sensitivity , the temperature change in response to a radiative forcing . a radiative forcing is a temporary imbalance between the energy received from the sun and the energy radiated back out to space , like the imbalance caused by an increase of greenhouse gases . to correct the imbalance , earth warms up or cools down . we can determine earth 's climate sensitivity from the experiment that we 've already performed in the industrial age since 1750 and then use this number to determine how much more it will warm for various projected radiative forcings in the 21st century . to do this , we need to know two things : first , the global temperature rise since 1750 , and second , the radiative forcing of the present day climate relative to the pre-industrial climate . for the radiative forcings , we know that human activities have increased greenhouse gases in the atmosphere , which have warmed the planet . but our activities have at the same time increased the amount of aerosol particles in clouds , which have cooled the planet . pre-industrial greenhouse gas concentrations are well measured from bubbles trapped in ice cores obtained in greenland and antarctica . so the greenhouse gas forcings are precisely known . but we have no way of directly measuring how cloudy it was in 1750 . and that 's the main source of uncertainty in earth 's climate sensitivity . to understand pre-industrial cloudiness , we must use computer models that reliably simulate the processes responsible for forming aerosols in clouds . now to most people , aerosols are the thing that make your hair stick , but that 's only one type of aerosol . atmospheric aerosols are tiny liquid or solid particles suspended in the air . they are either primary , from dust , sea spray salt or burning biomass , or secondary , formed by gas to particle conversion in the atmosphere , also known as particle nucleation . aerosols are everywhere in the atmosphere , and they can block out the sun in polluted urban environments , or bathe distant mountains in a blue haze . more importantly , a cloud droplet can not form without an aerosol particle seed . so without aerosol particles , there 'd be no clouds , and without clouds , there 'd be no fresh water . the climate would be much hotter , and there would be no life . so we owe our existence to aerosol particles . however , despite their importance , how aerosol particles form in the atmosphere and their effect on clouds are poorly understood . even the vapors responsible for aerosol particle formation are not well established because they 're present in only minute amounts , near one molecule per million million molecules of air . this lack of understanding is the main reason for the large uncertainty in climate sensitivity , and the corresponding wide range of future climate projections . however , an experiment underway at cern , named , perhaps unsurprisingly , `` cloud '' has managed to build a steel vessel that 's large enough and has a low enough contamination , that aerosol formation can , for the first time , be measured under tightly controlled atmospheric conditions in the laboratory . in its first five years of operation , cloud has identified the vapors responsible for aerosol particle formation in the atmosphere , which include sulfuric acid , ammonia , amines , and biogenic vapors from trees . using an ionizing particle beam from the cern proton synchrotron , cloud is also investigating if galactic cosmic rays enhance the formation of aerosols in clouds . this has been suggested as a possible unaccounted natural climate forcing agent since the flux of cosmic rays raining down on the atmosphere varies with solar activity . so cloud is addressing two big questions : firstly , how cloudy was the pre-industrial climate ? and , hence , how much have clouds changed due to human activities ? that knowledge will help sharpen climate projections in the 21st century . and secondly , could the puzzling observations of solar climate variability in the pre-industrial climate be explained by an influence of galactic cosmic rays on clouds ? ambitious but realistic goals when your head 's in the clouds .

earth 's average surface temperature has warmed by .8 celsius since 1750 . when carbon dioxide concentrations in the atmosphere have doubled , which is expected before the end of the 21st century , researchers project global temperatures will have risen by 1.5 to 4.5 degrees celsius . if the increase is near the low end , 1.5 celsius , then we 're already halfway there , and we should be more able to adapt with some regions becoming drier and less productive , but others becoming warmer , wetter and more productive .

what is the current expected increase of global mean temperature for a doubling of carbon dioxide in the atmosphere , which is expected to occur before the end of the 21st century ?

some of the world 's most recognizable symbols exist to sell products , others to steer traffic or advance political causes . but there 's one whose main purpose is to help people . you may know it as the wheelchair symbol , or a sign for people with disabilities , but its formal title as maintained by the iso is the international symbol of access . but despite its familiarity , many people are unclear as to what the symbol actually means , which has a lot to do with the symbol itself and the way it came about . in 1968 , the international commission on technology and accessibility held a design contest . they were looking for a symbol that would be readily identifiable from a reasonable distance , self-descriptive , simple , practical , and could n't be confused with existing signage . the winning design , which did n't have a head , was created by a danish designer named susanne koefed . the addition of a head a year later gave it a more human form , and within ten years , it was endorsed by both the united nations and the iso . with minimal cost and minimal fuss , a global icon was born . there have been a few tweaks over the decades . the graphic artists guild added more rounded , human-like features , and in 2012 , the accessible icon project produced a more dynamic version . but what does it really represent ? what 's its purpose ? put simply , it 's a sign to identify where there are accessible facilities . the strength of such an internationally recognized image is that wherever you travel , you do n't need to speak the language or have in-depth cultural knowledge . if you require an accessible toilet , the sign shows the way . but the confusion comes from the term accessibility and what that actually means . many people assume that because the symbol depicts a wheelchair , that accessible facilities are meant only for people who use wheelchairs , or those , at the very least , who have a visible physical condition . but accessibility is a broad concept that applies to many , many different conditions . that includes people with autism , visual impairments , and autoimmune diseases , like lupus , which can cause pain and fatigue , along with many other conditions . in fact , the world health organization estimates that there are approximately 1 billion people who experience some form of disability , which means that this group is very likely to include yourself , or a family member , a classmate , a friend , or a work colleague . and people who use wheelchairs only make up about 65 million , or 15 % of the total . the vast majority have non-visible disabilities . accessible parking spaces , facilities , and entrances are designed with that entire group in mind . so it 's easy to see why in recent years people have begun to raise questions about whether the symbol is really appropriate for what it 's meant to do . and it 's not just about accuracy . it 's common for people to become indignant , sometimes abusive , when they see people without visible disabilities using accessible facilities . the symbol is unfortunately creating widespread issues for the very people and families it 's meant to help . the recent redesigns have attempted with some success to acknowledge concerns over the current symbol . but some think that a complete redesign is in order . it 's a difficult task , though . how do you replace a symbol that 's familiar the world over ? and what do you replace it with ?

but there 's one whose main purpose is to help people . you may know it as the wheelchair symbol , or a sign for people with disabilities , but its formal title as maintained by the iso is the international symbol of access . but despite its familiarity , many people are unclear as to what the symbol actually means , which has a lot to do with the symbol itself and the way it came about .

what does the acronym iso stand for ?

you 'd have a hard time finding königsberg on any modern maps , but one particular quirk in its geography has made it one of the most famous cities in mathematics . the medieval german city lay on both sides of the pregel river . at the center were two large islands . the two islands were connected to each other and to the river banks by seven bridges . carl gottlieb ehler , a mathematician who later became the mayor of a nearby town , grew obsessed with these islands and bridges . he kept coming back to a single question : which route would allow someone to cross all seven bridges without crossing any of them more than once ? think about it for a moment . 7 6 5 4 3 2 1 give up ? you should . it 's not possible . but attempting to explain why led famous mathematician leonhard euler to invent a new field of mathematics . carl wrote to euler for help with the problem . euler first dismissed the question as having nothing to do with math . but the more he wrestled with it , the more it seemed there might be something there after all . the answer he came up with had to do with a type of geometry that did not quite exist yet , what he called the geometry of position , now known as graph theory . euler 's first insight was that the route taken between entering an island or a riverbank and leaving it did n't actually matter . thus , the map could be simplified with each of the four landmasses represented as a single point , what we now call a node , with lines , or edges , between them to represent the bridges . and this simplified graph allows us to easily count the degrees of each node . that 's the number of bridges each land mass touches . why do the degrees matter ? well , according to the rules of the challenge , once travelers arrive onto a landmass by one bridge , they would have to leave it via a different bridge . in other words , the bridges leading to and from each node on any route must occur in distinct pairs , meaning that the number of bridges touching each landmass visited must be even . the only possible exceptions would be the locations of the beginning and end of the walk . looking at the graph , it becomes apparent that all four nodes have an odd degree . so no matter which path is chosen , at some point , a bridge will have to be crossed twice . euler used this proof to formulate a general theory that applies to all graphs with two or more nodes . a eulerian path that visits each edge only once is only possible in one of two scenarios . the first is when there are exactly two nodes of odd degree , meaning all the rest are even . there , the starting point is one of the odd nodes , and the end point is the other . the second is when all the nodes are of even degree . then , the eulerian path will start and stop in the same location , which also makes it something called a eulerian circuit . so how might you create a eulerian path in königsberg ? it 's simple . just remove any one bridge . and it turns out , history created a eulerian path of its own . during world war ii , the soviet air force destroyed two of the city 's bridges , making a eulerian path easily possible . though , to be fair , that probably was n't their intention . these bombings pretty much wiped königsberg off the map , and it was later rebuilt as the russian city of kaliningrad . so while königsberg and her seven bridges may not be around anymore , they will be remembered throughout history by the seemingly trivial riddle which led to the emergence of a whole new field of mathematics .

but the more he wrestled with it , the more it seemed there might be something there after all . the answer he came up with had to do with a type of geometry that did not quite exist yet , what he called the geometry of position , now known as graph theory . euler 's first insight was that the route taken between entering an island or a riverbank and leaving it did n't actually matter .

the “ geometry of position ” is now known as which branch of mathematics ?

translator : tom carter reviewer : bedirhan cinar lawn signs sprouting everywhere . round-the-clock ads on radio and television . the phone rings . it 's a robo-call from the president , or his opponent , asking for your money , and your vote . and while you 're at it , watch their youtube videos and like them on facebook . election time . we all know the look and feel of modern campaigns . but what was it like in the early days of the republic , when , say , george washington ran for office ? well , in fact , he did n't run . when washington became the first president in 1789 , there were no political parties , no conventions or primaries , no campaign , no election season . not really any candidates . even the year was odd . literally . 1789 was the only presidential election ever held in an odd year . after the framers invented the constitution and the presidency 225 years ago , the country set about the business of choosing its first executive . agreeing with ben franklin , many people thought `` the first man at the helm will be a good one , '' and by that , franklin meant george washington . greatest hero of the revolution , washington presided over the convention that created the constitution , rarely speaking . he never discussed the job of president , or of wanting it . and when the first presidential election took place , it was a crazy-quilt affair , with many hands stitching the pattern . under the new constitution , each state was given a number of electors . who would cast a vote for two names . the man with the most votes would be president , the second-place finisher was vice president . ah , but who picked the electors ? that was left up to the states . six of them let the people decide , or at least white men over 21 who owned property . in new jersey , some women voted , a right later taken away . but in other states , the legislature picked the electors . at that time , many people thought democracy was one step away from mob rule and a decision this important should be left to wiser men . these electors then voted for president . all the states had to do was get their votes in on time . but there were glitches . only 10 of the 13 states voted . rhode island and north carolina had n't ratified the constitution and could n't vote . new york missed the deadline for naming its electors , and also was not counted . when the votes were tallied , it was unanimous . george washington won easily . john adams trailed far behind , finishing second , and became the vice president . told of his victory , george washington was not surprised . at mount vernon , his bags were already packed . he moved to new york city , the nation 's temporary capital , and he would have to figure out just what a president was supposed to do . since that first election , american democracy and elections have come a long way . the constitution has been changed to open up voting to more people : black men , women , native americans , and eighteen-year-olds included . getting that basic right extended to all those people has been a long , hard struggle . so when you think you ca n't stand any more of those lawn signs , and tv ads , just remember : the right to vote was n't always for everyone , and that 's a piece of history worth knowing .

when the votes were tallied , it was unanimous . george washington won easily . john adams trailed far behind , finishing second , and became the vice president .

in what year was george washington first elected president ?

hmmm , that 's not what we want , is it ? today 's digital cameras do a lot for us , but there 's no replacement for the human eye . it 's important to learn how cameras work with light to create an image , that way we 'll know what 's going on when it 's time to capture a moment . there are three variables that determine if you 're getting the right amount of light for the correct exposure . with a manual camera , we 're able to change any of the variable ourselves . different settings can result in really different pictures . let 's look at the process together . first , see this here ? this is the aperture . it 's the hole that light passes through . if we make the aperture big , we 'll have more light , true , but the sharpness of your photo will decrease very quickly from your focus point , backward and forward . this is what we call shallow depth of field . if we have a very small aperture , we 'll have less light but a deeper depth of field . for portraits , it can be nice to have a sharp figure separate from a somewhat blurry background so i would suggest a large aperture . aperture is measured in f-stops . this can get a little confusing because lower numbers mean bigger apertures and higher numbers mean smaller apertures . next , there 's shutter speed to think about . the shutter acts like a curtain that covers the sensor , and it only opens when you release the shutter button . if we want less light , we open the shutter for a shorter time . if we want more light , we open it for a longer time , but we run the risk of getting a motion-blurred picture . the speed is measured in seconds and fractions of seconds . for shooting sports or anything with a lot of movement , we 'll need faster speeds . for taking awesome night landscapes , longer exposures will be better , but we 'll need a tripod to steady the shot and prevent motion blur . another cool thing we can do with light exposures is light painting , drawing in the dark with a torch or the light of a cell phone . lastly , iso sensitivity controls how sensitive the sensor is to light . if we use low sensitivity , we 'll need more light to register a photo . with a higher sensitivity , we 'll be able to get a picture with less available light . 100 iso is a low sensitivity , while 6400 iso is a high one . if we increase sensitivity , we 'll be able to use faster speeds and smaller apertures , but we 'll get noisier images . good thing we have something to tell us if we 're getting the correct amount of light to get a good exposure , the light meter . sound good to you ? now it 's time to get out there and practice taking pictures under different conditions , so you know what to do any time you want to take the best picture .

with a manual camera , we 're able to change any of the variable ourselves . different settings can result in really different pictures . let 's look at the process together .

we can get the same amount of light combining the three variables with different settings . so , why should we choose one combination or another ? describe an example .

if you line up the entire text of `` moby dick , '' which was published in 1851 , into a giant rectangle , you may notice some peculiar patterns , like these words , which seem to predict the assassination of martin luther king , or these references to the 1997 death of princess di . so , was herman melville a secret prophet ? the answer is no , and we know that thanks to a mathematical principle called ramsey theory . it 's the reason we can find geometric shapes in the night sky , it 's why we can know without checking that at least two people in london have exactly the same number of hairs on their head , and it explains why patterns can be found in just about any text , even vanilla ice lyrics . so what is ramsey theory ? simply put , it states that given enough elements in a set or structure , some particular interesting pattern among them is guaranteed to emerge . as a simple example , let 's look at what 's called the party problem , a classic illustration of ramsey theory . suppose there are at least six people at a party . amazingly enough , we can say for sure that some group of three of them either all know each other , or have never met before , without knowing a single thing about them . we can demonstrate that by graphing out all the possibilities . each point represents a person , and a line indicates that the pair know each other . every pair only has two possibilities : they either know each other or they do n't . there are a lot of possibilities , but every single one has the property that we 're looking for . six is the lowest number of guests where that 's guaranteed to be the case , which we can express like this . ramsey theory gives us a guarantee that such a minimum number exists for certain patterns , but no easy way to find it . in this case , as the total number of guests grows higher , the combinations get out of control . for instance , say you 're trying to find out the minimum size of a party where there 's a group of five people who all know each other or all do n't . despite five being a small number , the answer is virtually impossible to discover through an exhaustive search like this . that 's because of the sheer volume of possibilities . a party with 48 guests has 2^ ( 1128 ) possible configurations , more than the number of atoms in the universe . even with the help of computers , the best we know is that the answer to this question is somewhere between 43 and 49 guests . what this shows us is that specific patterns with seemingly astronomical odds can emerge from a relatively small set . and with a very large set , the possibilities are almost endless . any four stars where no three lie in a straight line will form some quadrilateral shape . expand that to the thousands of stars we can see in the sky , and it 's no surprise that we can find all sorts of familiar shapes , and even creatures if we look for them . so what are the chances of a text concealing a prophecy ? well , when you factor in the number of letters , the variety of possible related words , and all their abbreviations and alternate spellings , they 're pretty high . you can try it yourself . just pick a favorite text , arrange the letters in a grid , and see what you can find . the mathematician t.s . motzkin once remarked that , `` while disorder is more probable in general , complete disorder is impossible . '' the sheer size of the universe guarantees that some of its random elements will fall into specific arrangements , and because we evolved to notice patterns and pick out signals among the noise , we are often tempted to find intentional meaning where there may not be any . so while we may be awed by hidden messages in everything from books , to pieces of toast , to the night sky , their real origin is usually our own minds .

it 's the reason we can find geometric shapes in the night sky , it 's why we can know without checking that at least two people in london have exactly the same number of hairs on their head , and it explains why patterns can be found in just about any text , even vanilla ice lyrics . so what is ramsey theory ? simply put , it states that given enough elements in a set or structure , some particular interesting pattern among them is guaranteed to emerge .

does ramsey theory tell you exactly how many elements that a system must contain to assure that a certain combination exists ( i.e. , letters in a phrase ?

austrian physicist erwin schrödinger is one of the founders of quantum mechanics , but he 's most famous for something he never actually did : a thought experiment involving a cat . he imagined taking a cat and placing it in a sealed box with a device that had a 50 % chance of killing the cat in the next hour . at the end of that hour , he asked , `` what is the state of the cat ? '' common sense suggests that the cat is either alive or dead , but schrödinger pointed out that according to quantum physics , at the instant before the box is opened , the cat is equal parts alive and dead , at the same time . it 's only when the box is opened that we see a single definite state . until then , the cat is a blur of probability , half one thing and half the other . this seems absurd , which was schrödinger 's point . he found quantum physics so philosophically disturbing , that he abandoned the theory he had helped make and turned to writing about biology . as absurd as it may seem , though , schrödinger 's cat is very real . in fact , it 's essential . if it were n't possible for quantum objects to be in two states at once , the computer you 're using to watch this could n't exist . the quantum phenomenon of superposition is a consequence of the dual particle and wave nature of everything . in order for an object to have a wavelength , it must extend over some region of space , which means it occupies many positions at the same time . the wavelength of an object limited to a small region of space ca n't be perfectly defined , though . so it exists in many different wavelengths at the same time . we do n't see these wave properties for everyday objects because the wavelength decreases as the momentum increases . and a cat is relatively big and heavy . if we took a single atom and blew it up to the size of the solar system , the wavelength of a cat running from a physicist would be as small as an atom within that solar system . that 's far too small to detect , so we 'll never see wave behavior from a cat . a tiny particle , like an electron , though , can show dramatic evidence of its dual nature . if we shoot electrons one at a time at a set of two narrow slits cut in a barrier , each electron on the far side is detected at a single place at a specific instant , like a particle . but if you repeat this experiment many times , keeping track of all the individual detections , you 'll see them trace out a pattern that 's characteristic of wave behavior : a set of stripes - regions with many electrons separated by regions where there are none at all . block one of the slits and the stripes go away . this shows that the pattern is a result of each electron going through both slits at the same time . a single electron is n't choosing to go left or right but left and right simultaneously . this superposition of states also leads to modern technology . an electron near the nucleus of an atom exists in a spread out , wave-like orbit . bring two atoms close together , and the electrons do n't need to choose just one atom but are shared between them . this is how some chemical bonds form . an electron in a molecule is n't on just atom a or atom b , but a+ b . as you add more atoms , the electrons spread out more , shared between vast numbers of atoms at the same time . the electrons in a solid are n't bound to a particular atom but shared among all of them , extending over a large range of space . this gigantic superposition of states determines the ways electrons move through the material , whether it 's a conductor or an insulator or a semiconductor . understanding how electrons are shared among atoms allows us to precisely control the properties of semiconductor materials , like silicon . combining different semiconductors in the right way allows us to make transistors on a tiny scale , millions on a single computer chip . those chips and their spread out electrons power the computer you 're using to watch this video . an old joke says that the internet exists to allow the sharing of cat videos . at a very deep level , though , the internet owes its existance to an austrian physicist and his imaginary cat .

but if you repeat this experiment many times , keeping track of all the individual detections , you 'll see them trace out a pattern that 's characteristic of wave behavior : a set of stripes - regions with many electrons separated by regions where there are none at all . block one of the slits and the stripes go away . this shows that the pattern is a result of each electron going through both slits at the same time . a single electron is n't choosing to go left or right but left and right simultaneously .

electrons passing through a pair of slits form an interference pattern of stripes , but electrons passing through a single slit do not . explain how this shows that schrödinger cat states ( superpositions that are not in one state or the other , but both at the same time ) exist for very small particles .

most atoms do n't ride solo , instead they bond with other atoms . and bonds can form between atoms of the same element or atoms of different elements . you 've probably imagined bonding as a tug of war . if one atom is really strong , it can pull one or more electrons off another atom . then you end up with one negatively charged ion and one positively charged ion . and the attraction between these opposite charges is called an ionic bond . this is the kind of sharing where you just give away your toy to someone else and then never get it back . table salt , sodium chloride , is held together by ionic bonds . every atom of sodium gives up one electron to every atom of chlorine , ions are formed , and those ions arrange themselves in a 3d grid called a lattice , in which every sodium ion is bonded to six chloride ions , and every chloride ion is bonded to six sodium ions . the chlorine atoms never give the sodium atoms their electrons back . now , these transactions are n't always so cut-and-dried . if one atom does n't completely overwhelm the other , they can actually share each other 's electrons . this is like a pot luck where you and a friend each bring a dish and then both of you share both dishes . each atom is attracted to the shared electrons in between them , and this attraction is called a covalent bond . the proteins and dna in our bodies , for example , are held together largely by these covalent bonds . some atoms can covalently bond with just one other atom , others with many more . the number of other atoms one atom can bond with depends on how its electrons are arranged . so , how are electrons arranged ? every atom of a pure , unbonded element is electrically neutral because it contains the same number of protons in the nucleus as it does electrons around the nucleus . and not all of those electrons are available for bonding . only the outermost electrons , the ones in orbitals furthest from the nucleus , the ones with the most energy , only those participate in bonding . by the way , this applies to ionic bonding too . remember sodium chloride ? well , the electron that sodium loses is the one furthest from its nucleus , and the orbital that electron occupies when it goes over to chlorine is also the one furthest from its nucleus . but back to covalent bonding . carbon has four electrons that are free to bond , nitrogen has three , oxygen two . so , carbon is likely to form four bonds , nitrogen three , and oxygen two . hydrogen only has one electron , so it can only form one bond . in some special cases , atoms can form more bonds than you 'd expect , but they better have a really good reason to do so , or things tend to fly apart . groups of atoms that share electrons covalently with each other are called molecules . they can be small . for example , every molecule of oxygen gas is made up of just two oxygen atoms bonded to each other . or they could be really , really big . human chromosome 13 is just two molecules , but each one has over 37 billion atoms . and this neighborhood , this city of atoms , is held together by the humble chemical bond .

the number of other atoms one atom can bond with depends on how its electrons are arranged . so , how are electrons arranged ? every atom of a pure , unbonded element is electrically neutral because it contains the same number of protons in the nucleus as it does electrons around the nucleus .

choose a molecule from the video , and write a complete and correct lewis structure for it . what information ( about protons , neutrons , and electrons ) gets transferred from the full view we show in the video to the lewis structure ? why do you think lewis structures are a useful tool for chemists ?

can you imagine a party where every movement , from the slightest gesture to walking across the room , and every visual detail , from furniture to hemline length , were governed by a complex system of rules and procedures ? for centuries , such rituals were commonplace for european nobility . and while they 've gone out of fashion , we recognize the components under a familiar label : ballet . ballet , from italian `` balletto , '' or little dance , originated in renaissance italy as a combination of social dance and choreographed display at aristocratic gatherings . in many aspects , it was a way of controlling people in court with acceptable forms of behavior , such as the manner in which people stepped , bowed , or took someone 's hand . it also involved rules governing everything from attire to where one could walk or sit in relation to the king . over time , the study of ballet became a central element of court life , and proper grasp of the etiquette could make or break one 's success as a courtier . many of these court gestures can still be seen in modern ballet techniques . ballet was brought to france in the 16th century by catherine de ' medici , the italian wife of king henry ii . as celebrations became more lavish , so did the dance , with dancing masters teaching elaborate steps to young nobles and story elements providing a unifying theme . the focus shifted from participation to performance , and the form acquired more theatrical trappings , such as professionally designed sets and a slightly raised platform or stage with curtains and wings . but it was in the 17th century court of louis xiv that ballet was refined into the art we know today . louis himself had been trained in ballet from childhood . his early role as the sun god apollo at age fifteen cemented the central role ballet would play during his reign . it also earned him the title of sun king , with his splendid golden costume and choreography that promoted the idea of the king as a divinely ordained ruler . louis would go on to perform 80 roles in 40 major ballets , either as a majestic lead , or sometimes playing minor or comedic parts before emerging in the lead role as the end . he trained daily in ballet , as well as fencing and riding , and through his example , dancing became an essential skill for all gentlemen of the era . but louis xiv 's main contribution to ballet was not as a performer . his founding of the royal academy of dance in 1661 shifted control of ballet from local guilds to the royal court . as director , he appointed his personal ballet master and frequent performance partner pierre beauchamp , who codified the five main positions of the body still used today . through is collaborations with jean-baptiste lully , the director of the royal music academy , and famed playwright molière , beauchamp helped establish ballet as a grand spectacle . and in 1669 , a separate ballet academy was founded . the paris opera ballet survives today as the oldest ballet company in the world . ballet moved away from the royal court to the theater and survived the democratic revolutions and reforms that followed over the next century . with the advent of the romantic movement , fantasy and folklore themes became common motifs . and though the influence of ballet in france would decline , other countries , such as russia , would play a major role in its further development . fortunately , today most of us do n't have to learn a complicated set of steps just to socialize at a wedding . instead , we can go to the theater to see professionals who spend their lives training rigorously to perform feats that would have been unimagineable in louis xiv 's day .

he trained daily in ballet , as well as fencing and riding , and through his example , dancing became an essential skill for all gentlemen of the era . but louis xiv 's main contribution to ballet was not as a performer . his founding of the royal academy of dance in 1661 shifted control of ballet from local guilds to the royal court .

at the time of louis xiv , knowing ballet was a key component element of :

in 2010 , $ 30 billion worth of fruits and vegetables were wasted by american retailers and shoppers in part because of cosmetic problems and perceived spoilage . that 's a poor use of about 30 % of the produce on the market , not to mention the water and energy required to grow and transport it , and the landfill space getting used up by rotting fruit . so what are those cosmetic problems ? you 've probably passed over a spotty apple in the grocery store , or accidentally sunk your thumb into a mushy patch on a tomato . these blemishes can doom produce to the trash can . but what are they anyway , and are they actually bad for you ? those spots are evidence of an epic battle between plants and microbes . like humans , plants coexist with billions of fungi and bacteria . some of these microbes are beneficial to the plant , suppressing disease and helping it extract nutrients . others are pathogens , attacking the produce , still alive as it sits in a store display or your refrigerator and siphoning off molecules they can use themselves . the good news is they 're almost never bad for you . these fungi and bacteria have spent millions of years developing strategies to overcome a plant 's immune system . but healthy human immune systems are different enough that those strategies just do n't work on us . so in a plant , what does this process look like ? microbes can reach plants in a number of ways , like getting splashed onto it during watering or fertilization . under the right conditions , the microbes grow into large enough colonies to attack the waxy outer layer of fruit or leaves . their target : the delicious sugars and nutrients inside . this type of pathogen often makes spots like this . a clump of bacteria drains the nutrients and color from the fruit 's cells making that yellow halo . it then moves outward , leaving a black spot of dead cells in its wake . each spot , which could contain hundreds of thousands of microbes is actually caused by a combination of microbial attack and the host defending itself . for example , this is the bacterial pathogen pseudomonas syringae . once on a tomato , it enters the fruit and leaves , multiplies in the space between the cells , and produces toxins and proteins that allow it to disrupt the plant 's immune response . one toxin coronatine makes plants ' stomata open up , allowing bacteria to enter more freely . coronatine also activates pathways leading to chlorophyll degradation , which you can see as yellow spots . as the bacteria continue to feed and multiply , they start to kill off the plant cells . that explains spots , but what about mushy blemishes ? those are usually caused when the fruit is attacked by microbes after it 's detached from the plant . if the plant is wounded during transport , necrotic fungi can infiltrate through the wound , kill the cells , absorb their nutrients , and leave your food looking mushy or brown . those spots in particular can taste pretty bad . you 're eating dead and decomposing tissue , after all . but you can usually salvage the rest of the fruit . the non-mushy spots , like the ones you typically see on apples or tomatoes , are just on the surface and do n't usually affect flavor . of course , microbes that do make us sick , like e. coli and salmonella , can hitch a ride on vegetables , too . but because they 're not plant pathogens , they do n't typically cause spots . they just hang out invisibly on the surface . so it 's washing fruit and veggies , not avoiding the spotty ones , that will help you avoid getting sick . so the next time you 're at the grocery store , do n't be afraid to pick up funky-looking fruit . some stores will even give you a discount . wash them well and store them properly , as some produce like apples and cabbages will keep in the fridge for weeks . the spotty ones may not be eye candy , but they 're safe and just as delicious .

the non-mushy spots , like the ones you typically see on apples or tomatoes , are just on the surface and do n't usually affect flavor . of course , microbes that do make us sick , like e. coli and salmonella , can hitch a ride on vegetables , too . but because they 're not plant pathogens , they do n't typically cause spots .

you can avoid getting sick from salmonella and e. coli by :

most atoms do n't ride solo , instead they bond with other atoms . and bonds can form between atoms of the same element or atoms of different elements . you 've probably imagined bonding as a tug of war . if one atom is really strong , it can pull one or more electrons off another atom . then you end up with one negatively charged ion and one positively charged ion . and the attraction between these opposite charges is called an ionic bond . this is the kind of sharing where you just give away your toy to someone else and then never get it back . table salt , sodium chloride , is held together by ionic bonds . every atom of sodium gives up one electron to every atom of chlorine , ions are formed , and those ions arrange themselves in a 3d grid called a lattice , in which every sodium ion is bonded to six chloride ions , and every chloride ion is bonded to six sodium ions . the chlorine atoms never give the sodium atoms their electrons back . now , these transactions are n't always so cut-and-dried . if one atom does n't completely overwhelm the other , they can actually share each other 's electrons . this is like a pot luck where you and a friend each bring a dish and then both of you share both dishes . each atom is attracted to the shared electrons in between them , and this attraction is called a covalent bond . the proteins and dna in our bodies , for example , are held together largely by these covalent bonds . some atoms can covalently bond with just one other atom , others with many more . the number of other atoms one atom can bond with depends on how its electrons are arranged . so , how are electrons arranged ? every atom of a pure , unbonded element is electrically neutral because it contains the same number of protons in the nucleus as it does electrons around the nucleus . and not all of those electrons are available for bonding . only the outermost electrons , the ones in orbitals furthest from the nucleus , the ones with the most energy , only those participate in bonding . by the way , this applies to ionic bonding too . remember sodium chloride ? well , the electron that sodium loses is the one furthest from its nucleus , and the orbital that electron occupies when it goes over to chlorine is also the one furthest from its nucleus . but back to covalent bonding . carbon has four electrons that are free to bond , nitrogen has three , oxygen two . so , carbon is likely to form four bonds , nitrogen three , and oxygen two . hydrogen only has one electron , so it can only form one bond . in some special cases , atoms can form more bonds than you 'd expect , but they better have a really good reason to do so , or things tend to fly apart . groups of atoms that share electrons covalently with each other are called molecules . they can be small . for example , every molecule of oxygen gas is made up of just two oxygen atoms bonded to each other . or they could be really , really big . human chromosome 13 is just two molecules , but each one has over 37 billion atoms . and this neighborhood , this city of atoms , is held together by the humble chemical bond .

the proteins and dna in our bodies , for example , are held together largely by these covalent bonds . some atoms can covalently bond with just one other atom , others with many more . the number of other atoms one atom can bond with depends on how its electrons are arranged . so , how are electrons arranged ?

the number of other atoms an atom can bond with ( covalently ) depends on ________ .

in 1997 , a french woman named jeanne calment passed away after 122 years and 164 days on this earth , making her the oldest known person in history . her age was so astounding that a millionaire pledged $ 1 million to anyone who could break her record . but in reality , living to this age or beyond is a feat that very few , maybe even no humans , are likely to accomplish . human bodies just are n't built for extreme aging . our capacity is set at about 90 years . but what does aging really mean and how does it counteract the body 's efforts to stay alive ? we know intuitively what it means to age . for some , it means growing up , while for others , it 's growing old . yet finding a strict scientific definition of aging is a challenge . what we can say is that aging occurs when intrinsic processes and interactions with the environment , like sunlight , and toxins in the air , water , and our diets , cause changes in the structure and function of the body 's molecules and cells . those changes in turn drive their decline , and subsequently , the failure of the whole organism . the exact mechanisms of aging are poorly understood . but recently , scientists have identified nine physiological traits , ranging from genetic changes to alterations in a cell 's regenerative ability that play a central role . firstly , as the years pass , our bodies accumulate genetic damage in the form of dna lesions . these occur naturally when the body 's dna replicates , but also in non-dividing cells . organelles called mitochondria are especially prone to this damage . mitochondria produce adenosine triphosphate , or atp , the main energy source for all cellular processes , plus mitochondria regulate many different cell activities and play an important role in programmed cell death . if mitochondrial function declines , then cells and , later on , whole organs , deteriorate , too . other changes are known to occur in the expression patterns of genes , also known as epigenetic alterations , that affect the body 's tissues and cells . genes silenced or expressed only at low levels in newborns become prominent in older people , leading to the development of degenerative diseases , like alzheimer 's , which accelerate aging . even if we could avoid all these harmful genetic alterations , not even our own cells could save us . the fact remains that cellular regeneration , the very stuff of life , declines as we age . the dna in our cells is packaged within chromosomes , each of which has two protective regions at the extremities called telomeres . those shorten every time cells replicate . when telomeres become too short , cells stop replicating and die , slowing the body 's ability to renew itself . with age , cells increasingly grow senescent , too , a process that halts the cell cycle in times of risk , like when cancer cells are proliferating . but the response also kicks in more as we age , halting cell growth and cutting short their ability to replicate . aging also involves stem cells that reside in many tissues and have the property of dividing without limits to replenish other cells . as we get older , stem cells decrease in number and tend to lose their regenerative potential , affecting tissue renewal and maintenance of our organs original functions . other changes revolve around cells ' ability to function properly . as they age , they stop being able to do quality control on proteins , causing the accumulation of damaged and potentially toxic nutrients , leading to excessive metabolic activity that could be fatal for them . intercellular communication also slows , ultimately undermining the body 's functional ability . there 's a lot we do n't yet understand about aging . ultimately , does longer life as we know it come down to diet , exercise , medicine , or something else ? will future technologies , like cell-repairing nanobots , or gene therapy , artificially extend our years ? and do we want to live longer than we already do ? starting with 122 years as inspiration , there 's no telling where our curiosity might take us .

even if we could avoid all these harmful genetic alterations , not even our own cells could save us . the fact remains that cellular regeneration , the very stuff of life , declines as we age . the dna in our cells is packaged within chromosomes , each of which has two protective regions at the extremities called telomeres .

cellular senescence :

in 1879 , amateur archaeologist marcelino sanz de sautuola and his young daughter maria explored a dark cave in northern spain . when maria wondered off by herself , she made an amazing discovery . they were standing inside a site of ancient art , the walls and roofs decorated with prehistoric paintings and engravings , ranging from 19,000 to 35,000 years old . similar marks of our ancestors have been preserved in caves all over the world . the oldest we 've found were made up to 40,000 years ago . what do these images tell us about the ancient human mind and the lives of their creators ? these early artists mixed minerals , clay , charcoal , and ochre with spit or animal fat to create paint . they drew with their hands and tools , like pads of moss , twigs , bones , and hair . in many instances , their images follow the contours of the cave to create depth and shade . the most common depictions are of geometric shapes , followed by large mammals , like bison , horses , mammoths , deer , and boars . human figures appear rarely , as well as occasional hand prints . some have theorized that these artworks are the creation of hunters , or of holy men in trance-like states . and we 've found examples created by men , women , and even children . and why did they create this art ? perhaps they were documenting what they knew about the natural world , like modern scientists , or marking their tribal territory . maybe the images were the culmination of sacred hunting rituals or spiritual journeys . or could they be art for art 's sake , the sheer joy and fulfillment of creation ? as with many unsolved mysteries of the ancient world , we may never know for sure , barring the invention of a time machine , that is . but while the answers remain elusive , these images are our earliest proof of human communication , testifying to the human capacity for creativity thousands of years before writing . they are a distinct visual language that imagines the world outside the self , just like modern art forms , from graffiti and painting to animated virtual-reality caves .

they drew with their hands and tools , like pads of moss , twigs , bones , and hair . in many instances , their images follow the contours of the cave to create depth and shade . the most common depictions are of geometric shapes , followed by large mammals , like bison , horses , mammoths , deer , and boars .

cave paints are thought to the work of :

translator : tom carter reviewer : bedirhan cinar lawn signs sprouting everywhere . round-the-clock ads on radio and television . the phone rings . it 's a robo-call from the president , or his opponent , asking for your money , and your vote . and while you 're at it , watch their youtube videos and like them on facebook . election time . we all know the look and feel of modern campaigns . but what was it like in the early days of the republic , when , say , george washington ran for office ? well , in fact , he did n't run . when washington became the first president in 1789 , there were no political parties , no conventions or primaries , no campaign , no election season . not really any candidates . even the year was odd . literally . 1789 was the only presidential election ever held in an odd year . after the framers invented the constitution and the presidency 225 years ago , the country set about the business of choosing its first executive . agreeing with ben franklin , many people thought `` the first man at the helm will be a good one , '' and by that , franklin meant george washington . greatest hero of the revolution , washington presided over the convention that created the constitution , rarely speaking . he never discussed the job of president , or of wanting it . and when the first presidential election took place , it was a crazy-quilt affair , with many hands stitching the pattern . under the new constitution , each state was given a number of electors . who would cast a vote for two names . the man with the most votes would be president , the second-place finisher was vice president . ah , but who picked the electors ? that was left up to the states . six of them let the people decide , or at least white men over 21 who owned property . in new jersey , some women voted , a right later taken away . but in other states , the legislature picked the electors . at that time , many people thought democracy was one step away from mob rule and a decision this important should be left to wiser men . these electors then voted for president . all the states had to do was get their votes in on time . but there were glitches . only 10 of the 13 states voted . rhode island and north carolina had n't ratified the constitution and could n't vote . new york missed the deadline for naming its electors , and also was not counted . when the votes were tallied , it was unanimous . george washington won easily . john adams trailed far behind , finishing second , and became the vice president . told of his victory , george washington was not surprised . at mount vernon , his bags were already packed . he moved to new york city , the nation 's temporary capital , and he would have to figure out just what a president was supposed to do . since that first election , american democracy and elections have come a long way . the constitution has been changed to open up voting to more people : black men , women , native americans , and eighteen-year-olds included . getting that basic right extended to all those people has been a long , hard struggle . so when you think you ca n't stand any more of those lawn signs , and tv ads , just remember : the right to vote was n't always for everyone , and that 's a piece of history worth knowing .

and while you 're at it , watch their youtube videos and like them on facebook . election time . we all know the look and feel of modern campaigns .

how involved are you in the presidential election ? do you vote ? do you volunteer on campaigns ? do you donate money ? do you feel like you 're knowledgable enough to make an informed decision about who to vote for ? where do you go to get your information ?

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

in the year 400 c.e . the celts in britain were ruled by romans . this had one benefit for the celts : the romans protected them from the barbarian saxon tribes of northern europe .

the reason why the celts benefited from roman rule was that

the city has just opened its one-of-a-kind fabergé egg museum with a single egg displayed on each floor of a 100-story building . and the world 's most notorious jewel thief already has her eyes on the prize . because security is tight and the eggs are so large , she 'll only get the chance to steal one by dropping it out the window into her waiting truck and repelling down before the police can arrive . all eggs are identical in weight and construction , but each floor 's egg is more rare and valuable than the one below it . while the thief would naturally like to take the priceless egg at the top , she suspects it wo n't survive a 100-story drop . being pragmatic , she decides to settle for the most expensive egg she can get . in the museum 's gift shop , she finds two souvenir eggs , perfect replicas that are perfectly worthless . the plan is to test drop them to find the highest floor at which an egg will survive the fall without breaking . of course , the experiment can only be repeated until both replica eggs are smashed . and throwing souvenirs out the window too many times is probably going to draw the guards ' attention . what 's the least number of tries it would take to guarantee that she find the right floor ? pause here if you want to figure it out for yourself ! answer in : 3 answer in : 2 answer in : 1 if you 're having trouble getting started on the solution , it might help to start with a simpler scenario . imagine our thief only had one replica egg . she 'd have a single option : to start by dropping it from the first floor and go up one by one until it breaks . then she 'd know that the floor below that is the one she needs to target for the real heist . but this could require as many as 100 tries . having an additional replica egg gives the thief a better option . she can drop the first egg from different floors at larger intervals in order to narrow down the range where the critical floor can be found . and once the first breaks , she can use the second egg to explore that interval floor by floor . large floor intervals do n't work great . in the worst case scenario , they require many tests with the second egg . smaller intervals work much better . for example , if she starts by dropping the first egg from every 10th floor , once it breaks , she 'll only have to test the nine floors below . that means it 'll take at most 19 tries to find the right floor . but can she do even better ? after all , there 's no reason every interval has to be the same size . let 's say there were only ten floors . the thief could test this whole building with just four total throws by dropping the first egg at floors four , seven , and nine . if it broke at floor four , it would take up to three throws of the second egg to find the exact floor . if it broke at seven , it would take up to two throws with the second egg . and if it broke at floor nine , it would take just one more throw of the second egg . intuitively , what we 're trying to do here is divide the building into sections where no matter which floor is correct , it takes up to the same number of throws to find it . we want each interval to be one floor smaller than the last . this equation can help us solve for the first floor we need to start with in the 100 floor building . there are several ways to solve this equation , including trial and error . if we plug in two for n , that equation would look like this . if we plug in three , we get this . so we can find the first n to pass 100 by adding more terms until we get to our answer , which is 14 . and so our thief starts on the 14th floor , moving up to the 27th , the 39th , and so on , for a maximum of 14 drops . like the old saying goes , you ca n't pull a heist without breaking a few eggs .

the plan is to test drop them to find the highest floor at which an egg will survive the fall without breaking . of course , the experiment can only be repeated until both replica eggs are smashed . and throwing souvenirs out the window too many times is probably going to draw the guards ' attention .

what kind of search does this problem reduce to if the number of eggs is infinite ?

what 's so great about the great lakes ? they 're known as america 's inland seas . the north american great lakes huron , ontario , michigan , erie , and superior are so massive that they border eight states and contain 23 quadrillion liters of water . that 's enough to cover the land area of the contiguous united states three meters deep . these vast bodies of water span forest , grassland , and wetland habitats , supporting a region that 's home to over 3,500 species . but how did such a vast and unique geological feature come to be ? the story begins near the end of the last ice age over 10,000 years ago , a time when the climate was warming and the glaciers that cloaked the earth 's surface began their slow retreat . these immense ice sheets carved out a series of basins . those basins filled with water as the ice began to melt , creating the world 's largest area of freshwater lakes . over time , channels developed between these basins , and water began to flow in an ongoing exchange that persists to this day . in fact , today , the interconnected great lakes contain almost 20 % of the world 's supply of fresh surface water . the water 's journey begins in the far north of lake superior , which is the deepest , coldest , and clearest of the lakes , containing half the system 's water . lake superior sinks to depths of 406 meters , creating a unique and diverse ecosystem that includes more that 80 fish species . a given drop of water spends on average 200 years in this lake before flowing into lake michigan or lake huron . linked by the straits of mackinac , these two lakes are technically one . to the west lies lake michigan , the third largest of the lakes by surface area . water slowly moves through its cul-de-sac shape and encounters the world 's largest freshwater dunes , many wildlife species , and unique fossilized coral . to the east is lake huron , which has the longest shoreline . it 's sparsely populated , but heavily forested , including 7,000-year-old petrified trees . below them , water continues to flow southeastwards from lake huron into lake erie . this lake 's status as the warmest and shallowest of the five has ensured an abundance of animal life , including millions of migrating birds . finally , the water reaches its last stop by dramatically plunging more than 50 meters down the thundering niagara falls into lake ontario , the smallest lake by surface area . from there , some of this well-traveled water enters the st. lawrence river , eventually reaching the atlantic ocean . in addition to being a natural wonder , the perpetually flowing great lakes bring us multiple benefits . they provide natural water filtration , flood control , and nutrients cycling . by moving water across more than 3,200 kilometers , the great lakes also provide drinking water for upward of 40 million people and 212 billion liters a day for the industries and farms that line their banks . but our dependence on the system is having a range of negative impacts , too . the great lakes coastal habitats are being degraded and increasingly populated , exposing the once pristine waters to industrial , urban , and agricultural pollutants . because less than 1 % of the water leaves the lake 's system annually , decades-old pollutants still lurk in its waters . humans have also inadvertently introduced more than 100 non-native and invasive species into the lakes , such as zebra and quagga mussels , and sea lampreys that have decimated some indigenous fish populations . on a larger scale , climate change is causing the waters to warm , thus reducing water levels and changing the distribution of aquatic life . luckily , in recent years , governments have started to recognize the immense value of this natural resource . partnerships between the united states and canada are underway to reduce pollution , protect coastal habitats , and halt the spread of invasive species . protecting something as massive as the great lakes system will require the collaboration of many organizations , but the effort is critical if we can preserve the wonder of this flowing inland sea .

what 's so great about the great lakes ? they 're known as america 's inland seas .

which of the great lakes is the largest , containing half of all the water in the system ?

one , two , three , four , five , six , seven , eight , nine , and zero . with just these ten symbols , we can write any rational number imaginable . but why these particular symbols ? why ten of them ? and why do we arrange them the way we do ? numbers have been a fact of life throughout recorded history . early humans likely counted animals in a flock or members in a tribe using body parts or tally marks . but as the complexity of life increased , along with the number of things to count , these methods were no longer sufficient . so as they developed , different civilizations came up with ways of recording higher numbers . many of these systems , like greek , hebrew , and egyptian numerals , were just extensions of tally marks with new symbols added to represent larger magnitudes of value . each symbol was repeated as many times as necessary and all were added together . roman numerals added another twist . if a numeral appeared before one with a higher value , it would be subtracted rather than added . but even with this innovation , it was still a cumbersome method for writing large numbers . the way to a more useful and elegant system lay in something called positional notation . previous number systems needed to draw many symbols repeatedly and invent a new symbol for each larger magnitude . but a positional system could reuse the same symbols , assigning them different values based on their position in the sequence . several civilizations developed positional notation independently , including the babylonians , the ancient chinese , and the aztecs . by the 8th century , indian mathematicians had perfected such a system and over the next several centuries , arab merchants , scholars , and conquerors began to spread it into europe . this was a decimal , or base ten , system , which could represent any number using only ten unique glyphs . the positions of these symbols indicate different powers of ten , starting on the right and increasing as we move left . for example , the number 316 reads as 6x10^0 plus 1x10^1 plus 3x10^2 . a key breakthrough of this system , which was also independently developed by the mayans , was the number zero . older positional notation systems that lacked this symbol would leave a blank in its place , making it hard to distinguish between 63 and 603 , or 12 and 120 . the understanding of zero as both a value and a placeholder made for reliable and consistent notation . of course , it 's possible to use any ten symbols to represent the numerals zero through nine . for a long time , the glyphs varied regionally . most scholars agree that our current digits evolved from those used in the north african maghreb region of the arab empire . and by the 15th century , what we now know as the hindu-arabic numeral system had replaced roman numerals in everyday life to become the most commonly used number system in the world . so why did the hindu-arabic system , along with so many others , use base ten ? the most likely answer is the simplest . that also explains why the aztecs used a base 20 , or vigesimal system . but other bases are possible , too . babylonian numerals were sexigesimal , or base 60 . any many people think that a base 12 , or duodecimal system , would be a good idea . like 60 , 12 is a highly composite number that can be divided by two , three , four , and six , making it much better for representing common fractions . in fact , both systems appear in our everyday lives , from how we measure degrees and time , to common measurements , like a dozen or a gross . and , of course , the base two , or binary system , is used in all of our digital devices , though programmers also use base eight and base 16 for more compact notation . so the next time you use a large number , think of the massive quantity captured in just these few symbols , and see if you can come up with a different way to represent it .

the positions of these symbols indicate different powers of ten , starting on the right and increasing as we move left . for example , the number 316 reads as 6x10^0 plus 1x10^1 plus 3x10^2 . a key breakthrough of this system , which was also independently developed by the mayans , was the number zero . older positional notation systems that lacked this symbol would leave a blank in its place , making it hard to distinguish between 63 and 603 , or 12 and 120 .

the number zero is such a fascinating number that many books have been written about it . briefly explain why it was such an important breakthrough for the number system we use today .

the discovery of the structure of dna was one of the most important scientific achievements in the last century , in human history , in fact . the now-famous double helix is almost synonymous with watson and crick , two of the scientists who won the nobel prize for figuring it out . but there 's another name you may know , too , rosalind franklin . you may have heard that her data supported watson and crick 's brilliant idea , or that she was a plain-dressing , belligerent scientist , which is how watson actually described her in `` the double helix . '' but thanks to franklin 's biographers , who investigated her life and interviewed many people close to her , we now know that that account is far from true , and her scientific contributions have been vastly underplayed . let 's hear the real story . rosalind elsie franklin was born in london in 1920 . she wanted to be a scientist ever since she was a teenager , which was n't a common or easy career path for girls at that time . but she excelled at science anyway . she won a scholarship to cambridge to study chemistry , where she earned her ph.d. , and she later conducted research on the structure of coal that led to better gas masks for the british during world war ii . in 1951 , she joined king 's college to use x-ray techniques to study the structure of dna , then one of the hottest topics in science . franklin upgraded the x-ray lab and got to work shining high-energy x-rays on tiny , wet crystals of dna . but the acadmemic culture at the time was n't very friendly to women , and franklin was isolated from her colleagues . she clashed with maurice wilkins , a labmate who assumed franklin had been hired as his assistant . but franklin kept working , and in 1952 , she obtained photo 51 , the most famous x-ray image of dna . just getting the image took 100 hours , the calculations necessary to analyze it would take a year . meanwhile , the american biologist james watson and the british physicist francis crick were also working on finding dna 's structure . without franklin 's knowledge , wilkins took photo 51 and showed it to watson and crick . instead of calculating the exact position of every atom , they did a quick analysis of franklin 's data and used that to build a few potential structures . eventually , they arrived at the right one . dna is made of two helicoidal strands , one opposite the other with bases in the center like rungs of a ladder . watson and crick published their model in april 1953 . meanwhile , franklin had finished her calculations , come to the same conclusion , and submitted her own manuscript . the journal published the manuscripts together , but put franklin 's last , making it look like her experiments just confirmed watson and crick 's breakthrough instead of inspiring it . but franklin had already stopped working on dna and died of cancer in 1958 , never knowing that watson and crick had seen her photographs . watson , crick , and wilkins won the nobel prize in 1962 for their work on dna . it 's often said that franklin would have been recognized by a nobel prize if only they could be awarded posthumously . and , in fact , it 's possible she could have won twice . her work on the structure of viruses led to a nobel for a colleague in 1982 . it 's time to tell the story of a brave woman who fought sexism in science , and whose work revolutionized medicine , biology , and agriculture . it 's time to honor rosalind elsie franklin , the unsung mother of the double helix .

but the acadmemic culture at the time was n't very friendly to women , and franklin was isolated from her colleagues . she clashed with maurice wilkins , a labmate who assumed franklin had been hired as his assistant . but franklin kept working , and in 1952 , she obtained photo 51 , the most famous x-ray image of dna . just getting the image took 100 hours , the calculations necessary to analyze it would take a year .

which of the following factors did not contribute to franklin being left out of the famous 1953 paper ?

translator : andrea mcdonough reviewer : jessica ruby hello , humans . my name is matt and for the next several moments , you are going to listen to me . mwah , ha , ha , ha , ha . sorry . i 'm just joking . this is my normal voice . have you ever taken direction from a mysterious voice on the computer before ? no ? perfect ! i want to try an experiment with you , but i ca n't tell you what that experiment entails because if i do , it wo n't work . you 'll just have to trust me . this will all make sense soon , hopefully . if you 're sitting down , stand up from your chair and take a step back . in a moment , i 'm going to have you twirl around , so give yourself a bit of space . need to move some furniture around ? take your time . i 'll wait . on the count of three , you 're going to start hopping on one foot . are you ready ? one , two , three ! hop , hop , hop , hop , hop . nice work ! ok , while you 're still hopping , i now want you to begin barking like a dog . ruff , ruff ; ruff , ruff ; ruff , ruff . wow , that 's quite a bark ! and a few more . ruff , ruff , ruff . and three , two , one , stop ! feel free to relax and sit back down . now , i want you think about how much time passed between the moment i said , `` go ! '' and you began hopping on one foot to the moment i said , `` stop ! '' take a guess . i 'm looking for an exact number of seconds or minutes . now , with a pen and paper , write that number down . all done ? the exact time was actually 26 seconds . did you overestimate ? chances are that you did . so , what was the culprit ? the culprit was time perception . although we can make shockingly precise time estimates , when we experience something new , unusual , or dynamic , like hopping on one foot while taking instructions from a voice on the computer , or , say , jumping out of an airplane , we often miscalculate how much time has passed . meaning , if you bungee jump for the first time , your fall to the bottom may seem like it lasted for 10 seconds while the recorded time may actually show that the jump only lasted for 5 . the reason for this difference is unlike your body 's physical drop to the bottom , your brain 's perception of time does not follow a straight line between two points . some scientists even believe your brain follows more of a curved path that is dependent on the amount of information you take in as you fall downwards . for example , david eagleman , a neuroscientist at baylor college of medicine , believes time perception is heavily influenced by the number of memories and data you record onto your brain . when you have a new experience , like jumping off a high dive for the first time , your senses are heightened . you 're taking in more details about sights , sounds , and smells than you normally would . and you store more data onto your brain in the form of memories . so , the more data you store in your brain , like the smell of chlorine as you leapt from the high dive or the color of the water , the longer your perception of that experience . meaning , the number of memories and data you record on your brain has a direct impact on how long you believe that experience to have lasted . have you ever heard a person recount what it 's like to be in a car accident ? although automotive accidents typically last seconds , those involved often say they felt the accident lasted far longer . time perception can also account for why your childhood may have seem to have lasted forever . by adulthood , a year can slip by in a heartbeat , but children record more data onto their brains . this occurs because many of the experiences we have as children are new and unfamiliar to us . the stack of encoded memories on your brain is so dense that reading them back makes you believe your experiences must have taken forever . additionally , when you 're 5 years old , one year is 1/5 of your life . but , when you 're 25 , one year makes up 1/25 , further altering your perception of time . and , if you 're an adult , think about a trip that you may have taken to a far-away land for the first time . did n't those two weeks you spent exploring your surroundings seem to have lasted far longer than 14 days ? though time perception is rooted in both hard science and theory , it provides a great lesson for us on how to live our lives . i 'm sure you have all heard that a person should n't sit on a couch and let life pass them by . well , time perception tells us why that is . if you get up and engage with the world and have new experiences , and maybe even hop around on one foot and bark like a dog , you will literally perceive your own life to have lasted for a longer period of time .

so , what was the culprit ? the culprit was time perception . although we can make shockingly precise time estimates , when we experience something new , unusual , or dynamic , like hopping on one foot while taking instructions from a voice on the computer , or , say , jumping out of an airplane , we often miscalculate how much time has passed .

our perception of time is dependent upon our __________ path between two points in time .

translator : jenny zurawell i am awele . daughter of alice , granddaughter of ruth , great-granddaughter of big momma alice and madir corine , great-great-granddaughter of anna and zitii benyen . it is my hope to find my best possible self in the service of others . now , my daddy , he used to tell me stories . my daddy , he would say , `` i want you to know who you are and where you come from . that will guide you as you discover who you must be . now , you listen to this story , you hear me , baby girl ? it 's not going to be in a book . your teacher is not going to tell it , but you need to understand who you are . '' that became a guiding principle in the stories that i wanted to tell . stories about legacy of who we are . i used to hear all the time that children are the future , but what does that cliché really mean and how are we preparing them ? so i looked for narratives about young people and the legacy that they bring as agents of change . the power that you have right now . today , march 2 , 1955 -- the story that i want to share with you comes from 1955 , march 2 . it 's about a courageous 16-year-old girl , claudette colvin . and it comes full circle today because a week ago today , in san francisco , my middle school students , they performed a program that i had written , `` agents of change , '' starting with the reenactment of plessy v. ferguson from 1892 to 1896 , moving to brown v. board and a student-led strike by barbara rose johns , jumping to claudette colvin and the montgomery bus boycott and ending in 1960 with the sit-in movement , the non-violent movement led by students . so i 'm going to share the story , and i would like to also share the work i do with it , as a case study . i paid my dime at the front of the bus , and then i ran to the back door with the rest of the colored kids so the driver would n't take off before we got on . also , well , whites do n't want us walking down the aisle next to them . when i got back on the bus , colored section was full , so , i sat in the middle section . i took the last row seat on the left , it was right by the window , was n't thinking about anything in particular . `` hey . '' i did n't know the girl next to me either , this older girl . so i just looked out the window . driver went more stops , more people were getting on , colored and white . pretty soon , no more seats were available . `` give me those seats , '' the driver called out . colored folks just started getting up . white folks started taking their seats , but i stayed seated . girl next to me and the other two across -- they stayed seated . i knew it was n't the restricted area . `` make light on your feet ! '' girl next to me got up immediately . she stood in the aisle , then the other two girls . but i told myself , this is n't the restricted area . the driver , he looked up , looked in the window , that mirror . he pulled over . a pregnant lady , mrs. hamilton , got on the bus . she ran to the back and got on , not knowing he was trying to have me relinquish my seat . and she sat right next to me . `` the two of you need to get up so i can drive on . '' `` sir , i paid my dime , i paid my fare . it 's my right , you know , my constitutional -- '' `` constitutional ? ha-ha , let me get the police . '' well he got off and he flagged down two motormen , and they came . and those motormen , they came onto the bus . looked at mrs. hamilton . `` now the two of you need to get up so the driver can drive on . '' `` sir , i paid my dime . i 'm pregnant . if i were to move right now , i 'd be very sick , sir . '' `` sir , i paid my dime too , you know , and it 's my right , my constitutional right . i 'm a citizen of the united states . you just read the 13th and 14th amendment , it 'll tell you so . i know the law . my teacher , she taught it at school . '' you see , my teacher , she taught the constitution , the bill of rights , the declaration of independence , patrick henry 's speech -- i even memorized it . my teacher , she would prick our minds , trying to see what we thinking about . she would say , `` who are you ? hmm ? who are you , sitting right here right now ? the person that people think they see from your outside ? who are you on the inside ? how you think ? how you feel ? what you believe ? would you be willing to stand up for what you believe in even if someone wants to hold you back because you 're different ? do you love your beautiful brown skin , children ? hmm ? are you american ? what does it mean to be an american ? huh ? homework tonight , write me an essay : `` what does it mean to be an american ? '' you need to know who you are , children ! '' my teacher , she would teach us history and current events . she said that 's how we can understand everything that 's going on and we can do something about it . `` sir , all i know is i hate jim crow . i also know if i ai n't got nothing worth living for , i ai n't got nothing worth dying for . so give me liberty or give me death ! ouch ! i do n't care ! take me to jail . '' they dragged her off the bus . next thing , claudette colvin was in a car seat , backseat of the police car , handcuffed through the windows . the following year , may 11 , 1956 , claudette colvin was the star witness in the federal court case browder v. gayle . her , an 18-year-old teenager and two others , women , mrs. browder . their case , browder v. gayle , went up to the supreme court . on the heels of brown v. board of education , the 14th amendment and her powerful testimony that day , the rest is history . now , why is it we do n't know this story ? the montgomery bus boycott -- we hear rosa parks , martin luther king , they will forever be lifted up . but the role women played in that movement , the role of claudette , as an up-stander , it teaches us important lessons that challenge us today . what does it mean to be a participant ? a responsible citizen in a democracy ? and lessons of courage and of faith ? so i find freedom movement history that includes young people so that they can explore these big ideas of identity , your chosen identity , and the imposed identity . what does membership in society mean ? who has it ? how do we make amends ? race and violence in america , as well as participatory citizenship . so these stories allow me to have conversations , to speak the unspeakable , that many are afraid to have . once in eugene , oregon , a young , blond-haired , blue-eyed boy , middle schooler , at the end of a performance in the dialogue said , `` but ms. awele , racism 's over , right ? '' and not wanting to answer for him , i said , `` turn to the person sitting next to you . see if you can come up with evidence . '' and i gave them four minutes to talk . soon , they began to tell stories , evidence of racism in their community . a girl wrote to me , a high school student in san francisco : `` i was going to skip school but then i heard we had an assembly , so i came . and after listening to the students talk and seeing your performance , i thought i should organize my friends and we should go down to a board meeting and tell them that want to have advanced classes for a through g requirements . '' so , i tell you this story today in honor of the legacy of young people that have come before , so that they will have guideposts and signs to be the change that they want to see in this world , as claudette colvin was . because she struck down the constitutionality of segregated seats in montgomery , alabama . thank you . ( applause ) thank you . ( applause )

and after listening to the students talk and seeing your performance , i thought i should organize my friends and we should go down to a board meeting and tell them that want to have advanced classes for a through g requirements . '' so , i tell you this story today in honor of the legacy of young people that have come before , so that they will have guideposts and signs to be the change that they want to see in this world , as claudette colvin was . because she struck down the constitutionality of segregated seats in montgomery , alabama .

makeba quotes legendary leader mahatma gandhi : “ you must be the change you want to see in the world. ” what change do you want to see in the world ? what does it suggest to you about your future path ?

in the 16th century , the mathematician robert recorde wrote a book called `` the whetstone of witte '' to teach english students algebra . but he was getting tired of writing the words `` is equal to '' over and over . his solution ? he replaced those words with two parallel horizontal line segments because the way he saw it , no two things can be more equal . could he have used four line segments instead of two ? of course . could he have used vertical line segments ? in fact , some people did . there 's no reason why the equals sign had to look the way it does today . at some point , it just caught on , sort of like a meme . more and more mathematicians began to use it , and eventually , it became a standard symbol for equality . math is full of symbols . lines , dots , arrows , english letters , greek letters , superscripts , subscripts . it can look like an illegible jumble . it 's normal to find this wealth of symbols a little intimidating and to wonder where they all came from . sometimes , as recorde himself noted about his equals sign , there 's an apt conformity between the symbol and what it represents . another example of that is the plus sign for addition , which originated from a condensing of the latin word et meaning and . sometimes , however , the choice of symbol is more arbitrary , such as when a mathematician named christian kramp introduced the exclamation mark for factorials just because he needed a shorthand for expressions like this . in fact , all of these symbols were invented or adopted by mathematicians who wanted to avoid repeating themselves or having to use a lot of words to write out mathematical ideas . many of the symbols used in mathematics are letters , usually from the latin alphabet or greek . characters are often found representing quantities that are unknown , and the relationships between variables . they also stand in for specific numbers that show up frequently but would be cumbersome or impossible to fully write out in decimal form . sets of numbers and whole equations can be represented with letters , too . other symbols are used to represent operations . some of these are especially valuable as shorthand because they condense repeated operations into a single expression . the repeated addition of the same number is abbreviated with a multiplication sign so it does n't take up more space than it has to . a number multiplied by itself is indicated with an exponent that tells you how many times to repeat the operation . and a long string of sequential terms added together is collapsed into a capital sigma . these symbols shorten lengthy calculations to smaller terms that are much easier to manipulate . symbols can also provide succinct instructions about how to perform calculations . consider the following set of operations on a number . take some number that you 're thinking of , multiply it by two , subtract one from the result , multiply the result of that by itself , divide the result of that by three , and then add one to get the final output . without our symbols and conventions , we 'd be faced with this block of text . with them , we have a compact , elegant expression . sometimes , as with equals , these symbols communicate meaning through form . many , however , are arbitrary . understanding them is a matter of memorizing what they mean and applying them in different contexts until they stick , as with any language . if we were to encounter an alien civilization , they 'd probably have a totally different set of symbols . but if they think anything like us , they 'd probably have symbols . and their symbols may even correspond directly to ours . they 'd have their own multiplication sign , symbol for pi , and , of course , equals .

a number multiplied by itself is indicated with an exponent that tells you how many times to repeat the operation . and a long string of sequential terms added together is collapsed into a capital sigma . these symbols shorten lengthy calculations to smaller terms that are much easier to manipulate .

a capital sigma represents :

would you rather be bitten by a venomous snake or touch a poisonous frog ? wait , what 's the difference between poison and venom , anyway ? let 's say you have the misfortune to be bitten by a venomous rattlesnake . when it bites you , the snake will eject venom from little sacks behind its eyes , through its hollow fangs and into your flesh . that venom will then travel through your bloodstream and all over your body . in most cases , snake venom contains neurotoxins , proteins that can do all sorts of nasty stuff like make your muscles fire uncontrollably , burst your blood cells , and make you go completely numb . but you might get lucky ! snakes do n't always decide you 're worth wasting venom on . in fact , between 20 and 80 % of snake bites are so-called `` dry bites , '' where the snake is just trying to send a message without actually killing you . you see , venom takes energy and resources for the snake to make , and they do n't want to waste it on a warning shot . when it comes to poison , on the other hand , there 's no warning shot . if you pick up a poisonous dart frog to admire its beautiful colors , you 've already gotten deadly poison all over your hands . as it seeps into your skin and travels through your blood , the poison starts to interfere with your nerves , preventing your muscles from contracting . if the frog 's poison reaches your heart , it can cause it to stop . the distinction between venom and poison is purely in the method of delivery . poison has to be inhaled , ingested , or absorbed . venom has to be injected into a wound . chemically , venoms and poisons are both considered toxins , so a snake bite is venomous . a poison dart frog is poisonous . brown recluse spiders are venomous . lionfish and pufferfish are poisonous . and some compounds can be poisons in one animal and venoms in another . tetrodotoxin , a chemical 10,000 times more toxic than cyanide , is found in pufferfish , where it makes them poisonous . it 's also found in the deadly blue-ringed octopus , where it 's a venom delivered by bite . some animals can even be both poisonous and venomous . take the asian tiger snake , for example . not only does it have venom in its fangs but it also absorbs the toxins from the poisonous toads it eats , and then secretes those toxins from special glands on its neck , rendering it poisonous , too . scientists are constantly finding new animals that employ toxins in weird , interesting ways . recently , researchers discovered the very first venomous crustacean . out of 70,000 species of crustaceans , only this one little remipede is venomous . speleonectes tulumensis has figured out how to create a cocktail of toxins that it delivers through its tiny fangs . scientists are n't totally sure how this venom works yet , but they think that it causes the unwitting victims ' neurons to fire over and over and over again until it becomes paralyzed . then , the little remipede closes in , dissolving away the exoskeleton of its prey and sucking out the juices . but poisons and venoms are n't always all bad . for thousands of years , humans have looked for ways to harness the power of these toxic compounds for good . today , we have all sorts of medicines that come from toxins . the poison from cone snails is used as a painkiller . many poisonous plants have been used to treat everything from malaria to irregular heartbeats . and scorpion venom might one day be used to treat heart disease . so , what should you do if something bites or poisons you ? do n't try any of the things you 've seen on the internet or in movies ! do n't try to capture and kill the animal that bit you , and do n't use a tourniquet or knife on your wound . most importantly , do n't panic ! stay calm , and seek medical attention . treatment will mostly depend on what species you encountered . but if you forget the distinction between poison and venom , and tell the parademics that you were poisoned by a viper , they 'll probably forgive you and treat you anyway .

the distinction between venom and poison is purely in the method of delivery . poison has to be inhaled , ingested , or absorbed . venom has to be injected into a wound .

which has to be inhaled , ingested , or absorbed ?

to human eyes , the world at night is a formless canvas of grey . many nocturnal animals , on the other hand , experience a rich and varied world bursting with details , shapes , and colors . what is it , then , that separates moths from men ? moths and many other nocturnal animals see at night because their eyes are adapted to compensate for the lack of light . all eyes , whether nocturnal or not , depend on photoreceptors in the retina to detect light particles , known as photons . photoreceptors then report information about these photons to other cells in the retina and brain . the brain sifts through that information and uses it to build up an image of the environment the eye perceives . the brighter the light is , the more photons hit the eye . on a sunny day , upwards of 100 million times more photons are available to the eye than on a cloudy , moonless night . photons are n't just less numerous in darkness , but they also hit the eye in a less reliable way . this means the information that photoreceptors collect will vary over time , as will the quality of the image . in darkness , trying to detect the sparse scattering of randomly arriving photons is too difficult for the eyes of most daytime animals . but for night creatures , it 's just a matter of adaptation . one of these adaptations is size . take the tarsier , whose eyeballs are each as big as its brain , giving it the biggest eyes compared to head size of all mammals . if humans had the same brain to eye ratio , our eyes would be the size of grapefruits . the tarsier 's enlarged orbs have n't evolved to make it cuter , however , but to gather as much light as possible . bigger eyes can have larger openings , called pupils , and larger lenses , allowing for more light to be focused on the receptors . while tarsiers scan the nocturnal scene with their enormous peepers , cats use gleaming eyes to do the same . cats ' eyes get their shine from a structure called the tapetum lucidum that sits behind the photoreceptors . this structure is made from layers of mirror-like cells containing crystals that send incoming light bouncing back towards the photoreceptors and out of the eye . this results in an eerie glow , and it also gives the photoreceptors a second chance to detect photons . in fact , this system has inspired the artificial cats ' eyes we use on our roads . toads , on the other hand , have adapted to take it slow . they can form an image even when just a single photon hits each photoreceptor per second . they accomplish this with photoreceptors that are more than 25 times slower than human ones . this means toads can collect photons for up to four seconds , allowing them to gather many more than our eyes do at each visual time interval . the downside is that this causes toads to react very slowly because they 're only receiving an updated image every four seconds . fortunately , they 're accustomed to targeting sluggish prey . meanwhile , the night is also buzzing with insects , such as hawk moths , which can see their favorite flowers in color , even on a starlit night . they achieve this by a surprising move - getting rid of details in their visual perception . information from neighboring photoreceptors is grouped in their brains , so the photon catch of each group is higher compared to individual receptors . however , grouping photoreceptors loses details in the image , as fine details require a fine grid of photoreceptors , each detecting photons from one small point in space . the trick is to balance the need for photons with the loss of detail to still find their flowers . whether eyes are slow , enormous , shiny , or coarse , it 's the combination of these biological adaptations that gives nocturnal animals their unique visual powers . imagine what it might be like to witness through their eyes the world that wakes up when the sun goes down .

bigger eyes can have larger openings , called pupils , and larger lenses , allowing for more light to be focused on the receptors . while tarsiers scan the nocturnal scene with their enormous peepers , cats use gleaming eyes to do the same . cats ' eyes get their shine from a structure called the tapetum lucidum that sits behind the photoreceptors .

tarsiers have huge eyes because :

françois-marie arouet was born in paris in 1694 his father , a well-established lawyer , sent him to the best school in the capital , and by all accounts , he was a brilliant student . the young arouet , decided at an early age to make his name as a writer , or rather to remake his name , as the first thing he did was to change his name to voltaire . the 18th century is often referred to as the age of reason , or the age of enlightenment , but sometimes more fairly simply as the age of voltaire . so , changing his name was a good call . the age of arouet , which is not of work quite as well . voltaire was precociously talented as a poet . at the age of only 24 , he had his first verse tragedy performed at the comédie-française . by then , he 'd already begun work on an epic poem about the french religious civil wars of the 16th century , about the french religious civil wars of the 16th century , by pragmatically converting from protestantism to catholicism . this was to be a subject dear to voltaire 's heart , for under the guise of writing a national epic , he was dwelling at length on the bloody consequences of religious intolerance . right from the start , voltaire 's views on religion were expressed robustly . he was not an atheist . in part , because he thought that some minimal belief in a deity was useful for social cohesion . voltaire 's god had created the world , instilled in us a sense of good and evil and then basically taken a back seat . this was known as rational religion , or in the 18th century called natural religion , or deism . and it had no truck with metaphysics of any kind . voltaire was basically a man of reason , who loathed fanaticism , idolatry and superstition . that men can kill each other to defend some bit of religious doctrine , which they scarcely understand , is something he found repellent . and he reserved his greatest hatred for the clerics , who exploited the credulity of believers to maintain their own power base . voltaire wanted religion but not the church . for obvious reasons , the catholic authorities were not keen for voltaire 's poem about henry iv , la henriade , to be published in france . so voltaire decided to go and publish it in london instead , and in 1726 , went and traveled to england . what began as a business trip soon turned , however , into something quite different . and voltaire ended up staying in england for some two and a half years . he learned to speak english fluently , got to know writers and politicians , and became a great admirer of english protestant culture . he decided to write a book about his experience of england . and the letters concerning the english nation appeared first in english in 1733 . the french authorities were horrified . the book was censored and voltaire only narrowly avoided prison . that 's because the book presented an informal portrait of english culture , in a witty and ironical style looking in turn at religion , politics , science and literature , in ways that were critical implicitly of french culture and politics . here , for example , is how voltaire presents the royal exchange , a handsome building in the heart of the city of london , where merchants from across the world would meet to transact business . `` take a view of the royal exchange , '' voltaire wrote , where the representatives of all nations meet for the benefit of mankind . there the jew , the muhammadan and a christian transact together as though they all profess the same religion , and give the name of infidel to none but the bankrupts . there the presbyterian confides in the anabaptist , and the churchman depends on the quaker ’ s word . at the breaking up of this pacific and free assembly , some will withdraw to the synagogue , and others to take a glass . this man goes and is baptised in a great tub , in the name of the father , son and holy ghost : that man has his son ’ s foreskin cut off , whilst a set of hebrew words ( quite unintelligible to him ) are mumbled over his child . if one religion only were allowed in england , the government would very possibly become arbitrary ; if there were but two , the people would cut one another ’ s throats ; but as there as such a multitude , they all live happy and in peace . '' voltaire 's message is clear . religious differences are trivial and separate men , while trade is important and brings them together . his conclusion , that the plurality of religions in england leads to a more peaceful society , is , of course , a covert criticism of france , where the catholic church was so dominant . the letters concerning the english nation , also discuss locke and newton , thinkers then poorly known in france the subject-matter might seem challenging , but voltaire is a past master popularising difficult material . ask any schoolchild today what they know about newton , and they 'll tell you about the apple falling on his head , and the survival of this anecdote is due entirely to voltaire . he heard it from newton 's niece and immediately understood that this simple homely image was the perfect way of conveying the simplicity of newton 's explanation of the force of gravity . after voltaire used the story in his letters concerning the english nation , everyone remembered it and voltaire left his mark on english popular culture . voltaire struggled with the question of good and evil the problem at the heart of his best-known work , candide which was published in 1759 and was a best seller from the moment it appeared . translated into every possible language , it remains the most widely read work of the european enlightenment . it 's even left its mark on our language expressions like 'pour encourager les autres ' to encourage the others or 'il faut cultiver le jardin ' , we must cultivate our garden have entered common usage . 'in the best of all possible worlds ' , yes , that 's another one speakers of french or english quote candide , without even realising it . and that 's the sure mark of a classic . candide is a timeless work , as satire of the human condition , but it 's also work of the enlightenment and its philosophical theme is announced in the title : `` candide '' or `` optimism '' . the hero of candide , as his name tells us , is an innocent anti-hero . he is in thrall to his tutor , pangloss , who preaches the philosophy of optimism . this is not 'optimism ' in the modern sense of looking on the bright side . optimism , spelled with a capital o and as expounded by the german philosopher , leibniz , was an attempt to answer the age-old problem of evil . why , if god is good , does he permit the existence of evil in the world ? to which the 18th century leibnizian optimist replies , evil is all part of some greater pattern of good : 'all partial evil , universal good ' as the english poet `` pope '' put it . in other words , evil does n't really exist at all . it 's just something which man imagines because of his limited view of the world . you might think this sounds like a bit of a confidence trick , voltaire certainly did , but this idea did find widespread acceptance in the 18th century . candide 's great mission was to put this philosophy to the test . ejected from his comfortable home in an obscure german castle , after trying to seduce the baron 's beautiful daughter , cunégonde , voltaire 's hero , candide , undergoes many trials and tribulations : conscripted into the army , he fights in a war , then deserts , only to find himself a witness to an earthquake in lisbon . candide is repeatedly brought face to face with evil in its most extreme forms : moral evil , in the case of the earthquake , where man is not apparently to blame ; and most of all human evil , such as the war , where man is very definitely to blame . pangloss 's breezy optimism is clearly an inadequate response to enormities of evil on this scale . eventually , even candide comes to realize this : to quote from the book , 'and sometimes pangloss would say to candide : after 1760 , voltaire took up residence in the château at ferney , just outside geneva . by now , he was the most famous living writer in europe , and he became widely known as the ‘ patriarch of ferney ’ . he took up a number of public causes . in 1761 , a protestant merchant jean calas , was accused of murdering his son and sentenced by the judges of toulouse to be tortured and then broken on the wheel . the legal processes were , to say the least , irregular , and the suspicions grew that the judges in his catholic city had acted with excessive zeal out of religious bigotry . voltaire became involved in the case and mounted an energetic campaign to rehabilitate calas ’ memory and help the members of his family , who had been left destitute . he wrote letters to those in authority and published a stream of pamphlets , culminating in 1763 in his traité sur la tolérance , which begins with the historical facts of the calas case and broadens out into a history of religious intolerance in european culture . voltaire 's writings had enormous impact on public opinion , and eventually the judges in paris quashed the judgment of the toulouse court . too late to save calas , but a huge victory for voltaire , who had learnt an important lesson about how change could be brought about through the pressure of public opinion . voltaire said of himself that he ‘ wrote to act ’ , and he wanted his writings to change the way people thought and behaved . in leading his crusades against fanaticism , he even invented a campaign slogan , ecrasez l ’ infâme ! , which translates roughly as ‘ crush the despicable ! ’ . l ’ infâme stands here for everything that voltaire hates , everything that he had spent his life fighting : superstition , intolerance , irrational behaviour of every kind . we should never forget that voltaire was also a brilliant writer , one of the greatest stylist the french language has ever known . the power of his ideas had a lot to do with the power of his expression . many writers made fun of miracles . no one did so hilariously as voltaire . always , voltaire had an ear for the telling phrase : it 's a good line , even in english , and better still in the original french where it is more memorable because it is a classical alexandrine line in 12 syllables : si dieu n ’ existait pas , il faudrait l ’ inventer . voltaire 's legacy in our present debates about religious toleration remain extremely potent . hardly a week passes without an article in the press quoting : ‘ i disapprove of what you say , but i will defend to the death your right to say it. ’ this rallying cry of tolerant multiculturalism is so potent that if voltaire had n't said it , we would have had to invent it , which is what happened . the expression was invented by an english woman in 1906 . no matter , it expresses a truth which is fundamentally important to our culture , so we have adopted the phrase and decided that voltaire said it . voltaire , his name has become synonymous with a set of liberal values : freedom of speech , rejection of bigotry and superstition , belief in reason and tolerance . it 's a unique , and nowadays , extremely precious legacy .

voltaire 's god had created the world , instilled in us a sense of good and evil and then basically taken a back seat . this was known as rational religion , or in the 18th century called natural religion , or deism . and it had no truck with metaphysics of any kind .

define the concept of natural religion .

what do an ancient greek philosopher and a 19th century quaker have in common with nobel prize-winning scientists ? although they are separated over 2,400 years of history , each of them contributed to answering the eternal question : what is stuff made of ? it was around 440 bce that democritus first proposed that everything in the world was made up of tiny particles surrounded by empty space . and he even speculated that they vary in size and shape depending on the substance they compose . he called these particles `` atomos , '' greek for indivisible . his ideas were opposed by the more popular philosophers of his day . aristotle , for instance , disagreed completely , stating instead that matter was made of four elements : earth , wind , water and fire , and most later scientists followed suit . atoms would remain all but forgotten until 1808 , when a quaker teacher named john dalton sought to challenge aristotelian theory . whereas democritus 's atomism had been purely theoretical , dalton showed that common substances always broke down into the same elements in the same proportions . he concluded that the various compounds were combinations of atoms of different elements , each of a particular size and mass that could neither be created nor destroyed . though he received many honors for his work , as a quaker , dalton lived modestly until the end of his days . atomic theory was now accepted by the scientific community , but the next major advancement would not come until nearly a century later with the physicist j.j. thompson 's 1897 discovery of the electron . in what we might call the chocolate chip cookie model of the atom , he showed atoms as uniformly packed spheres of positive matter filled with negatively charged electrons . thompson won a nobel prize in 1906 for his electron discovery , but his model of the atom did n't stick around long . this was because he happened to have some pretty smart students , including a certain ernest rutherford , who would become known as the father of the nuclear age . while studying the effects of x-rays on gases , rutherford decided to investigate atoms more closely by shooting small , positively charged alpha particles at a sheet of gold foil . under thompson 's model , the atom 's thinly dispersed positive charge would not be enough to deflect the particles in any one place . the effect would have been like a bunch of tennis balls punching through a thin paper screen . but while most of the particles did pass through , some bounced right back , suggesting that the foil was more like a thick net with a very large mesh . rutherford concluded that atoms consisted largely of empty space with just a few electrons , while most of the mass was concentrated in the center , which he termed the nucleus . the alpha particles passed through the gaps but bounced back from the dense , positively charged nucleus . but the atomic theory was n't complete just yet . in 1913 , another of thompson 's students by the name of niels bohr expanded on rutherford 's nuclear model . drawing on earlier work by max planck and albert einstein he stipulated that electrons orbit the nucleus at fixed energies and distances , able to jump from one level to another , but not to exist in the space between . bohr 's planetary model took center stage , but soon , it too encountered some complications . experiments had shown that rather than simply being discrete particles , electrons simultaneously behaved like waves , not being confined to a particular point in space . and in formulating his famous uncertainty principle , werner heisenberg showed it was impossible to determine both the exact position and speed of electrons as they moved around an atom . the idea that electrons can not be pinpointed but exist within a range of possible locations gave rise to the current quantum model of the atom , a fascinating theory with a whole new set of complexities whose implications have yet to be fully grasped . even though our understanding of atoms keeps changing , the basic fact of atoms remains , so let 's celebrate the triumph of atomic theory with some fireworks . as electrons circling an atom shift between energy levels , they absorb or release energy in the form of specific wavelengths of light , resulting in all the marvelous colors we see . and we can imagine democritus watching from somewhere , satisfied that over two millennia later , he turned out to have been right all along .

atomic theory was now accepted by the scientific community , but the next major advancement would not come until nearly a century later with the physicist j.j. thompson 's 1897 discovery of the electron . in what we might call the chocolate chip cookie model of the atom , he showed atoms as uniformly packed spheres of positive matter filled with negatively charged electrons . thompson won a nobel prize in 1906 for his electron discovery , but his model of the atom did n't stick around long .

who developed the `` chocolate chip cookie '' model of the atom ?

translator : andrea mcdonough reviewer : bedirhan cinar you 've probably heard of the boston tea party , something about a bunch of angry colonists dressed as native americans throwing chests of tea into the water . but the story is far more complicated , filled with imperial intrigue , corporate crisis , smuggling , and the grassroots origins of the american revolution . the first thing you need to know about tea in the 1700 's is that it was really , really popular . in england , each man , woman , and child consumed almost 300 cups of this stuff every year . and , since the english colonized america , americans were crazy about tea too . by the 1760 's , they were drinking over a million pounds of tea every year . so , when britain wanted to increase taxes on tea in america , people were not happy , mostly because they had no say in tax decisions made in london . remember that famous phrase , `` no taxation without representation '' ? the american colonists had long believed that they were not subject to taxes imposed by legislature in which they lacked representation . in fact , rather than paying the taxes , they simply dodged the tax collectors . since the east coast of america is hundreds of miles long and british enforcement was lax , about 3/4 of the tea americans were drinking was smuggled in , usually from holland . but the british insisted that parliament did have the authority to tax the colonists , especially after britain went deeply into debt fighting the french in the seven years ' war . to close the budget gap , london looked to americans , and in 1767 imposed new taxes on a variety of imports , including the american 's beloved tea . america 's response : no thanks ! they boycotted the importation of tea from britain , and instead , brewed their own . after a new bunch of british customs commissioners cried to london for troops to help with tax enforcement , things got so heated that the red coats fired on a mob in boston , killing several people , in what was soon called the boston massacre . out of the terms of the 1773 tea act , parliament cooked up a new strategy . now the east india company would sell the surplus tea directly through hand-picked consignees in america . this would lower the price to consumers , making british tea competitive with the smuggled variety while retaining some of the taxes . but the colonists saw through the british ploy and cried , `` monopoly ! '' now it 's a cold and rainy december 16 , 1773 . about 5,000 bostonians are crowded into the old south meeting house , waiting to hear whether new shipments of tea that have arrived down the harbor will be unloaded for sale . when the captain of one of those ships reported that he could not leave with his cargo on board , sam adams rose to shout , `` this meeting can do no more to save the country ! '' cries of `` boston harbor a teapot tonight ! '' rang out from the crowd , and about 50 men , some apparently dressed as native americans , marched down to griffin 's wharf , stormed aboard three ships , and threw 340 tea chests overboard . an infuriated british government responsded with the so-called coercive acts of 1774 , which , among other things , closed the port of boston until the locals compensated the east india company for the tea . that never happened . representatives of the colonies gathered at philadelphia to consider how best to respond to continued british oppression . this first continental congress supported destruction of the tea , pledged to support a continued boycott , and went home in late october 1774 even more united in their determination to protect their rights and liberties . the boston tea party began a chain reaction that led with little pause to the declaration of independence and a bloody rebellion , after which the new nation was free to drink its tea , more or less , in peace .

after a new bunch of british customs commissioners cried to london for troops to help with tax enforcement , things got so heated that the red coats fired on a mob in boston , killing several people , in what was soon called the boston massacre . out of the terms of the 1773 tea act , parliament cooked up a new strategy . now the east india company would sell the surplus tea directly through hand-picked consignees in america .

the 1773 tea act was designed to

you 're swimming in the ocean when something brushes your leg . when the tingling sets in , you realize you 've been stung by a jellyfish . how do these beautiful , gelatinous creatures pack such a painful punch ? jellyfish are soft because they are 95 % water and are mostly made of a translucent gel-like substance called mesoglea . with such delicate bodies , they rely on thousands of venom-containing stinging cells called cnidocytes for protection and prey capture . even baby jellyfish , the size of a pencil eraser , have the ability to sting . larval jellyfish , ephyrae , look like tiny flowers pulsating in the sea . as they grow , they become umbrella-shaped with a bell at the top and descending tentacles around the margin . the largest species of jellyfish , the lion 's mane , has tentacles that can extend more than 100 feet , longer than a blue whale . these tentacles contain most of the stinging cells , although some species have them on their bells , too . venom is ejected via a nematocyst , a whip-like hollow tubule , which lies coiled under high osmotic pressure . when mechanical or chemical stimuli activate an external trigger , the lid of the cell pops open and sea water rushes in . this forces a microscopic barbed harpoon to shoot out , penetrate and inject venom into its victim . nematocyst discharge can occur in less than a millionth of a second , making it one of nature 's fastest biomechanical processes . nematocysts can continue to fire even after a jellyfish has died , so it 's important to remove lingering tentacles stuck to the skin . rinsing with vinegar will usually render undischarged nematocysts inactive . seawater can also help remove residual nematocysts . but do n't use fresh water because any change in salt balance alters the osmotic pressure outside of the cnidocyte and will trigger the nematocyst to fire . that 's why urinating on the affected area , a common folk remedy , may do more harm that good , depending on the composition of the urine . most jellyfish stings are a painful nuisance , but some can be deadly . an indo-pacific box jelly , also called a sea wasp , releases venom which can cause contraction of the heart muscles and rapid death in large doses . there 's an anti-venom , but the venom is fast-acting , so you 'd need immediate medical intervention . despite the impressive power in their tentacles , jellies are n't invincible . their stinging cells are no match for the armor of thick-skin predators , like the leatherback turtle and ocean sunfish . these predators both have adaptations that prevents slippery jellyfish from escaping after they are engulfed : backwards pointing spines in the turtle 's mouth and esophagus and recurved teeth behind the sunfish 's cheeks . even tiny lobster slipper larvae can cling to the bell of a jellyfish and hitch a ride , snacking on the jelly while they preserve their own energy for growth . small agile fish use the jellies as moving reefs for protection , darting between tentacles without ever touching them . nudibranchs , which are sea slugs covered in protective slime , can actually steal the jelly 's defenses by eating the cnidocytes and transferring them to specialized sacks for later use , as weapons against their own predators . even humans might benefit from the sting of a jellyfish one day . scientists are working on manipulating cnidocytes to deliver medicine , with nematocysts rarely 3 % of the size of a typical syringe needle . so , the next time you 're out in the ocean , be careful . but also , take a second to marvel at its wonders .

this forces a microscopic barbed harpoon to shoot out , penetrate and inject venom into its victim . nematocyst discharge can occur in less than a millionth of a second , making it one of nature 's fastest biomechanical processes . nematocysts can continue to fire even after a jellyfish has died , so it 's important to remove lingering tentacles stuck to the skin .

the nematocyst can eject in less than a _____ of a second :

denis diderot left a dungeon outside paris on november 3 , 1749 . he 'd had his writing burned in public before , but this time , he 'd gotten locked up under royal order for an essay about a philosopher 's death bed rejection of god . to free himself , denis promised never to write things like that again . so he got back to work on something a little like that , only way worse , and much bigger . in 1745 , publisher andré le breton had hired diderot to adapt the english cyclopedia , or a universal dictionary of arts and sciences for french subscribers . a broke writer , diderot survived by translating , tutoring , and authoring sermons for priests , and a pornographic novel once . le breton paired him with co-editor jean le rond d'alembert , a math genius found on a church doorstep as a baby . technical dictionaries , like the cyclopedia , were n't new , but no one had attempted one publication covering all knowledge , so they did . the two men organized the french enlightenment 's brightest stars to produce the first encyclopedia , or rational dictionary of the arts , sciences , and crafts . assembling every essential fact and principle in , as it turned out , over 70,000 entries , 20,000,000 words in 35 volumes of text and illustrations created over three decades of researching , writing , arguging , smuggling , backstabbing , law-breaking , and alphabetizing . to organize the work , diderot adapted francis bacon 's `` classification of knowledge '' into a three-part system based on the mind 's approaches to reality : memory , reason , and imagination . he also emphasized the importance of commerce , technology , and crafts , poking around shops to study the tools and techniques of parisian laborers . to spotlight a few of the nearly 150 philosoph contributers , jean jacques rousseau , diderot 's close friend , wrote much of the music section in three months , and was never reimbursed for copy fees . his entry on political economy holds ideas he 'd later develop further in `` the social contract . '' d'alembert wrote the famous preliminary discourse , a key statement of the french enlightenment , championing independent investigative reasoning as the path to progress . louis de jaucourt wrote a quarter of the encyclopedia , 18,000 articles , 5,000,000 words , unpaid . louis once spent 20 years writing a book on anatomy , shipped it to amsterdam to be published uncensored , and the ship sank . voltaire contributed entries , among them history , elegance , and fire . diderot 's entries sometimes exhibit slight bias . in `` political authority , '' he dismantled the divine right of kings . under `` citizen , '' he argued a state was strongest without great disparity in wealth . not surprising from the guy who wrote poetry about mankind strangling its kings with the entrails of a priest . so diderot 's masterpiece was n't a hit with the king or highest priest . upon release of the first two volumes , louie xv banned the whole thing but enjoyed his own copy . pope clement xiii ordered it burned . it was `` dangerous , '' `` reprehensible , '' as well as `` written in french , '' and in `` the most seductive style . '' he declared readers excommunicated and wanted diderot arrested on sight . but diderot kept a step ahead of being shut down , smuggling proofs outside france for publication , and getting help from allies in the french regime , including the king 's mistress , madame de pompadour , and the royal librarian and censor , malesherbes , who tipped diderot off to impending raids , and even hid diderot 's papers at his dad 's house . still , he faced years of difficulty . d'alembert dropped out . rousseau broke off his friendship over a line in a play . worse yet , his publisher secretly edited some proofs to read less radically . the uncensored pages reappeared in russia in 1933 , long after diderot had considered the work finished and died at lunch . the encyclopedia he left behind is many things : a cornerstone of the enlightenment , a testament to france 's crisis of authority , evidence of popular opinions migration from pulpit and pew to cafe , salon , and press . it even has recipes . it 's also irrepressibly human , as you can tell from diderot 's entry about a plant named aguaxima . read it yourself , preferably out loud in a french accent .

his entry on political economy holds ideas he 'd later develop further in `` the social contract . '' d'alembert wrote the famous preliminary discourse , a key statement of the french enlightenment , championing independent investigative reasoning as the path to progress . louis de jaucourt wrote a quarter of the encyclopedia , 18,000 articles , 5,000,000 words , unpaid .

what would a supporter of the french enlightenment most likely deem the path to progress ?

this is tungsten , i think . tungsten is a very hard and heavy element . it has a number of very important uses . it is used in the filament of light bulbs , the ordinary sort of light bulbs because it has more or less the highest boiling point of any element and therefore you can use it as the filament and it can get very hot without very much evaporation on to the walls . if you add iodine in the gas around the bulb you can run it at even higher temperatures , the so called quartz halogen lamps and sometimes you see these in up-market cars . yes , it ’ s tungsten . so this is tungsten . tungsten is used as an element material to form the very , very fine wire that we may have used in old-style electric light bulbs . it is a really quite wonderful metal and it is actually used in nature . but here we have a really quite beautiful sample . this is a single crystal of tungsten which is mounted . tungsten carbide , the compound of tungsten and carbon is used in the very tip , the balls in the tip of a biro pen or ball point pen . really quite amazing . i have got some other tungsten here somewhere and in fact here is a very fine wire of tungsten and this is precisely the material which was used in the formation of very early electric light bulbs . a really quite amazing metal . there is also quite a nice book by oliver sacks , who is an englishman who now lives in america , called uncle tungsten . there are not many books that have chemical names in the title and this is a story of his childhood and how chemistry really had a big effect on him . that ’ s lovely .

if you add iodine in the gas around the bulb you can run it at even higher temperatures , the so called quartz halogen lamps and sometimes you see these in up-market cars . yes , it ’ s tungsten . so this is tungsten .

where can you find a piece of tungsten carbide ?

you 're facing a giant bowl of energy packed carbon crunchies . one spoonful . two . three . soon , you 're powered up by the energy surge that comes from your meal . but how did that energy get into your bowl ? energy exists in the form of sugars made by the plant your cereal came from , like wheat or corn . as you can see , carbon is the chemical backbone , and plants get their fix of it in the form of carbon dioxide , co2 , from the air that we all breath . but how does a plant 's energy factory , housed in the stroma of the chloroplast , turn a one carbon gas , like co2 , into a six carbon solid , like glucose ? if you 're thinking photosynthesis , you 're right . but photosynthesis is divided into two steps . the first , which stores energy from the sun in the form of adenosine triphosphate , or atp . and the second , the calvin cycle , that captures carbon and turns it into sugar . this second phase represents one of nature 's most sustainable production lines . and so with that , welcome to world 's most miniscule factory . the starting materials ? a mix of co2 molecules from the air , and preassembled molecules called ribulose biphosphate , or rubp , each containing five carbons . the initiator ? an industrious enzyme named rubisco that welds one carbon atom from a co2 molecule with the rubp chain to build an initial six carbon sequence . that rapidly splits into two shorter chains containing three carbons each and called phosphoglycerates , or pgas , for short . enter atp , and another chemical called nicotinamide adenine dinucleotide phosphate , or just nadph . atp , working like a lubricant , delivers energy , while nadph affixes one hydrogen to each of the pga chains , changing them into molecules called glyceraldehyde 3 phosphates , or g3ps . glucose needs six carbons to form , made from two molecules of g3p , which incidentally have six carbons between them . so , sugar has just been manufactured , right ? not quite . the calvin cycle works like a sustainable production line , meaning that those original rubps that kicked things off at the start , need to be recreated by reusing materials within the cycle now . but each rubp needs five carbons and manufacturing glucose takes a whole six . something does n't add up . the answer lies in one phenomenal fact . while we 've been focusing on this single production line , five others have been happening at the same time . with six conveyor belts moving in unison , there is n't just one carbon that gets soldered to one rubp chain , but six carbons soldered to six rubps . that creates 12 g3p chains instead of just two , meaning that all together , 36 carbons exist : the precise number needed to manufacture sugar , and rebuild those rubps . of the 12 g3ps pooled together , two are siphoned off to form that energy rich six carbon glucose chain . the one fueling you via your breakfast . success ! but back on the manufacturing line , the byproducts of this sugar production are swiftly assembled to recreate those six rubps . that requires 30 carbons , the exact number contained by the remaining 10 g3ps . now a molecular mix and match occurs . two of the g3ps are welded together forming a six carbon sequence . by adding a third g3p , a nine carbon chain is built . the first rubp , made up of five carbons , is cast from this , leaving four carbons behind . but there 's no wastage here . those are soldered to a fourth g3p molecule , making a seven carbon chain . added to a fifth g3p molecule , a ten carbon chain is created , enough now to craft two more rubps . with three full rubps recreated from five of the ten g3ps , simply duplicating this process will renew the six rubp chains needed to restart the cycle again . so the calvin cycle generates the precise number of elements and processes required to keep this biochemical production line turning endlessly . and it 's just one of the 100s of cycles present in nature . why so many ? because if biological production processes were linear , they would n't be nearly as efficient or successful at using energy to manufacture the materials that nature relies upon , like sugar . cycles create vital feedback loops that repeatedly reuse and rebuild ingredients crafting as much as possible out of the planet 's available resources . such as that sugar , built using raw sunlight and carbon converted in plant factories to become the energy that powers you and keeps the cycles revolving in your own life .

you 're facing a giant bowl of energy packed carbon crunchies . one spoonful . two .

rubisco makes up about 15 % of the total protein in a chloroplast . why might chloroplasts have evolved to have so much of this one enzyme ?

so the last time we tried to film chlorine experiments we found that the chlorine cylinder itself had a slight problem , it was seized here . but the stig has acquired another cylinder of chlorine . so you know what this means , it means that we feel duty-bound to increase the intensity of our chlorine video and show you some chemistry with chlorine . chlorine is an element that many people have heard of . it ’ s a greenish-yellow gas which consists of , the gas consists of two chlorine atoms bonded together so it ’ s cl2 and it ’ s much heavier than air . incredibly reactive , incredibly poisonous , not a very nice compound at all . ok so neil is about to open the cylinder of chlorine to allow some of the chlorine gas to leak through the pipe into the , to the flask in the fume hood . chlorine sits in the right-hand side of the periodic table in the halogens in group , well , some people say seven , some people say seventeen . really what that says is that chlorine wants another electron to get that noble gas configuration and it will move heaven and earth to get that electron ! so during the first world war it was used as a chemical weapon . the gas could spread across the battlefields and when it came to the trenches , which were holes in the ground , it would fall into the trenches and fill them up . you can see the yellow colour against the white background on the paper , so now we ’ re starting to fill that flask with chlorine ; it ’ s quite dense , so it will stick to the bottom of the flask it ’ s not like a light gas like hydrogen or helium , it won ’ t come upwards . so now you can see the colour in that chlorine is really quite intense . it wasn ’ t a terribly good weapon because it could quite easily , if the wind changed direction , it could blow the gas back to the people who were letting it out . so we ’ ll just put a stopper in to contain the gas while we prepare the rest of the experiment . chlorine is quite corrosive , it reacts with water to make an acid , hcl , hydrochloric acid which can attack people ’ s lungs . the lungs generate fluid , they fill up with fluid and quickly the person drowns in their own fluid . it also corrodes things very easily so all the metal fittings on people ’ s battle dress , the brass buttons , brass buckles , all went green as well . but it ’ s not a terribly effective weapon but when people weren ’ t expecting any sort of chemical weapon it must have been terrifying . ok so we have a small amount of aluminium here which we put on the end of a wire . we ’ re gon na heat the aluminium in that flame and then we ’ re gon na put the hot aluminium into the flask of chlorine , then hopefully we ’ ll see , the chlorine will react with the aluminium and we ’ ll get very rapid formation of aluminium trichloride , alcl3 . the british army created whole regiments of gas soldiers who were all trained chemists , who were sent out to handle these cylinders of gas . and on the german side in the first world war , fritz haber , the inventor of the haber process to make ammonia became very keen on chemical weapons and he was the chief proponent . his wife was really furious about this and in fact shot herself with his revolver , killed herself , the day before he was due to go back to the front . and he , it was said that this was because she objected to his work on chemical weapons . though at the same time there were rumours that he was having an affair with another woman , so there may have been other factors at play as well . so , let ’ s heat up our aluminium . ok , so it ’ s nice and warm , all over . and then we ’ ll drop it or add it into the chlorine glass . now instantly we are seeing aluminium trichloride coming out of the top and reacting with moisture in the air . so now you can see the reaction is getting very intense and we are seeing a flame in the bottom . so the aluminium is being consumed as it ’ s reacting , oxidising strongly in that chlorine-rich air . chlorine is found all over the world , the sea contains sodium chloride , and there are huge deposits of sodium chloride in salt lakes where lakes have dried out , such as in some parts of the states , where you , united states , where you have salt lakes where people can race cars and things across the flat surface and in other parts of the world . all of the aluminium has been consumed now by the chlorine : a very , very rapid reaction . there are many areas , such as in the north of england , in the county of cheshire and also in salzburg in austria , where there are prehistoric deposits of salt from prehistoric salt lakes , which can now be mined really quite easily , and there , so salt and chlorine is a very common element . it ’ s made from sodium chloride solution by electrolysis , by passing an electric current , and it ’ s a very energy intensive process . one percent of the uk ’ s electricity was used , at one time , for making chlorine from sodium chloride , and the chlorine is used particularly for making the plastic pvc . while we got chlorine here , we thought we ’ d do a couple of reactions . so we ’ ve got some chlorine in this flask and you can see the nice yellow colour and i thought what we ’ d try and do now is do a competition reaction again or a reaction with iron . so now the iron , we ’ re gon na heat the iron , this is iron wool which you might use for treating wood , and we ’ re gon na heat that until it ’ s warm and put it in the chlorine , the chlorine will oxidise it to iron chloride . chlorine will react with all sorts of metals . you can make salt by burning the metal sodium in chlorine , and if you put in other metals like aluminium or iron they will also react . aluminium reacts to form aluminium trichloride which is the salt of aluminium and iron will similarly react to form iron chloride , and most metals but not all of them will react with chlorine : lead will not for example . but it is really quite a reactive gas . so really rapid reaction there as the hot iron starts to react with the chlorine to form iron chloride . very , very exothermic again and i think , yes this is very hot , we might have to move it off the paper . so what happens in all of these reactions is that the chlorine removes an electron from the metal to make the chloride ion cl- , and the chloride ion is perfectly innocuous , you can drink , you can eat chloride , whereas chlorine itself is very poisonous . oh it ’ s warm , it ’ s not too hot to touch its like picking up a mug of warm tea or warm coffee . but you can see again the products of the chemical reaction have precipitated out across the flask , and now if i remove the…wire again i can see that all of the iron has been consumed again instantly . the moment that it got into that chlorine-rich flask ; very , very rapid reaction , very , very reactive with chlorine .

chlorine sits in the right-hand side of the periodic table in the halogens in group , well , some people say seven , some people say seventeen . really what that says is that chlorine wants another electron to get that noble gas configuration and it will move heaven and earth to get that electron ! so during the first world war it was used as a chemical weapon .

why is chlorine so reactive ? hint : think about its electron configuration

hi , everybody ! i am a comparative anatomist . a comparative anatomist is someone who studies the structure of the body of lots of different animals . and my favorite animals are whales . i like to study whales because they 're so interesting . they 've adapted to a unique environment of living in the water . and what i 'm going to tell you about is how whales make sounds by basically farting with their face . you know that they do this farting thing with their blowhole ; they blow out air like that , but they also use air in lots of other ways . they use it for sound production , which is what i 'll focus on , but i also study other things they do with air , like keep it out of their bloodstream so they do n't get bubbles , which is what happens to human scuba divers when they get decompression sickness . but i 'd like to start with the story of how these animals make these farting noises , and that story begins with understanding how hard it is to look at whales , because they live underwater and they 're really big , so they 're hard animals to study . and in this picture -- you see that animal in the middle ? that 's a baby whale and it 's already the size of a bus ! when you look at whales , start with the top of their head because their nose is on the top of their head , kind of like a built-in snorkel . they breathe through that because they 're mammals and mammals breathe air . their nose can be opened and closed , as if you were to pinch it like this . you can see it 's open in the bottom frame , where the red arrows are . but not all whales have two nostrils . whales include the groups of dolphins and porpoises , and dolphins and porpoises , the small whales , have only one nostril on the top of their head , and they open and close that nostril by taking what is essentially an upper lip , like this , and turning it back over their nose , like this . that 's how they open and close their nose . so when they make sounds , what they 're basically doing is a raspberry , ( makes raspberry sound ) which is kind of like a fart , right ? or up in new york , we call it a bronx cheer . and the way they do that is by taking that big , fatty structure of a big fat lip , which , as you can see here in this picture , which is a cut through the middle of a dolphin 's head , that big fat lip is that big yellow portion there , and they roll it back and forth over the top of their nose so that they vibrate it , kind of like when you let the air out of a balloon and it makes that weird vibration sound . so this is what it sounds like when they make their noise : ( vibration noise ) hear it ? he 'll do it again when he faces the camera . ( vibration noise ) sounds like it 's farting underwater . what that dolphin is actually doing , though , is echolocation , which is making these series of pulses , and it uses it like a bat uses sonar . well , a bat uses radar , but when it 's underwater it 's sonar , so this animal is using sonar to see its world in sound . trying to understand how this works , you have to look at it as if you were looking at the amplifier speakers of a sound system . the small-toothed whales are basically the `` tweeters , '' and the sound is coming from that little nose that 's moving back and forth and coming out of their forehead . but the big whales are kind of like the `` woofers , '' the big speakers that you have in an amplifier system . and what 's happening is their sound is coming out of the throat . so if you tried to make sound like a whale -- make a sound right now , and go , `` ahhhhhh . '' ok , now put your hand on your throat , on your adam 's apple . you feel that vibration right there ? that is lost energy for you , because that 's not how you communicate to everybody . you do it out of the mouth . but if you open your mouth underwater , no one will hear you . you have to be able to take this energy and amplify it through the water . that 's what whales do . and when you hear their sound -- ( squeaking sound ) it 's kind of like when you squeak the air out of a balloon . so they get a lot of squeaky noises , but they also have this sound : ( vibrating sound ) it sounds like it 's farting , does n't it ? it 's like it 's got this giant whoopee cushion in its throat . so , how do you know that 's what a whale is doing ? well , we study whales that come to us from strandings . these are animals that die on the beach . small whales like dolphins and porpoises are easy ; we can take them to the lab . but the big whales -- we 've got to bring the lab to the whale . and this is what that looks like . i 'm the one in the middle with the red hat . i 'm not a very tall person , so you can see how big this whale was compared to me . the whale is 65 feet long . and my scalpel is this little tool on the side here . it basically looks like a hockey stick with a blade on the end of it . and doing a dissection of a whale is a very difficult process . you literally have to get into your work . it 's kind of like a giant bloody construction zone . you 're wearing a hard hat , you 're working with heavy machinery . in this case , by the way , that 's just the voice box of a blue whale . just the voice box . i 'm only five feet tall -- you can see it 's like 12 feet long . how do we know what 's going on ? well , we look at the voice box , or larynx , and we see -- this is from a baby whale so it 's much smaller . you see this little u-shaped thing i 've outlined in blue . that 's the part that 's vibrating . it 's kind of like our vocal folds . when i put my hand in there , where that blue sleeve is , you can see there 's a sack underneath it . that 's the whoopee cushion . that 's the air bubble or the balloon . so what these animals are doing -- and you can see , there 's this big black balloon in the throat , where the digestive tract , which is in blue , meets the breathing tract , which is in light blue , and right in the middle is that black sack . these animals are using that sack to make these sounds . and so they vibrate that and send it out . small-toothed whales also have air sacks ; they 're all over their heads , so it 's like they 're airheads . they use this to capture as much air as they can to take down with them when they 're diving , because when you dive , pressures increase , and that decreases the volume of air you have available . but more importantly , having that sack allows them to recycle the air that they 're using , because air is a precious commodity . you do n't want to have to go back up to the surface to get more . so when you make a sound underwater , if you 're a whale -- let 's hear you start making a sound , go `` ahhhh . '' but whales keep their mouths closed , so go `` ahhhmm . '' ( audience makes noise ) you 're all humming , right ? but whales keep their nose closed and go , `` mmmm . '' ( makes noise ) what happened ? you ca n't make the sound anymore once you close your nose because you 've pressurized the system . whales , by having air sacks , keep themselves from pressurizing the system , which means the air continues to flow , and so if you had a bag on the end of your nose , you 'd be able to make air continue to flow . so i hope you 've enjoyed that . that 's what a comparative anatomist does for a living . we study the structure of these animals . we try to mimic it ; we apply it back to the human situation , maybe making new technologies for protective devices or maybe even making new treatments for medicines for people 's diseases who mimic these weird environments . so i hope you enjoyed that . thank you . ( applause )

that 's what whales do . and when you hear their sound -- ( squeaking sound ) it 's kind of like when you squeak the air out of a balloon . so they get a lot of squeaky noises , but they also have this sound : ( vibrating sound ) it sounds like it 's farting , does n't it ?

inflation of the balloon-like air sacs during sound production keeps the respiratory tract from :

it 's a hot day , and you 've just downed several glasses of water , one after the other . behind the sudden urge that follows are two bean-shaped organs that work as fine-tuned internal sensors . they balance the amount of fluid in your body , detect waste in your blood , and know when to release the vitamins , minerals , and hormones you need to stay alive . say hello to your kidneys . the main role of these organs is to dispose of waste products and to turn them into urine . the body 's eight liters of blood pass through the kidneys between 20 and 25 times each day , meaning that , together , these organs filter about 180 liters every 24 hours . the ingredients in your blood are constantly changing as you ingest food and drink , which explains why the kidneys need to be on permanent duty . blood enters each kidney through arteries that branch and branch , until they form tiny vessels that entwine with special internal modules , called nephrons . in each kidney , 1 million of these nephrons form a powerful array of filters and sensors that carefully sift through the blood . this is where we see just how refined and accurate this internal sensing system is . to filter the blood , each nephron uses two powerful pieces of equipment : a blob-like structure called a glomerulus , and a long , stringy , straw-like tubule . the glomerulus works like a sieve , allowing only certain ingredients , such as vitamins and minerals , to pass into the tubule . then , this vessel 's job is to detect whether any of those ingredients are needed in the body . if so , they 're reabsorbed in amounts that the body needs , so they can circulate in the blood again . but the blood does n't only carry useful ingredients . it contains waste products , too . and the nephrons have to figure out what to do with them . the tubules sense compounds the body does n't need , like urea , left over from the breakdown of proteins , and redirects them as urine out of the kidneys and through two long sewers called ureters . the tubes empty their contents into the bladder to be discharged , ridding your body of that waste once and for all . there 's water in that urine , too . if the kidney detects too much of it in your blood , for instance , when you 've chugged several glasses at once , it sends the extra liquid to the bladder to be removed . on the other hand , low water levels in the blood prompt the kidney to release some back into the blood stream , meaning that less water makes it into the urine . this is why urine appears yellower when you 're less hydrated . by controlling water , your kidneys stabilize the body 's fluid levels . but this fine balancing act is n't the kidney 's only skill . these organs have the power to activate vitamin d to secrete a hormone called renin that raises blood pressure , and another hormone called erythropoietin , which increases red blood cell production . without the kidneys , our bodily fluids would spiral out of control . every time we ate , our blood would receive another load of unsifted ingredients . soon , the buildup of waste would overload our systems and we 'd expire . so each kidney not only keeps things running smoothly . it also keeps us alive . lucky then that we have two of these magical beans .

this is why urine appears yellower when you 're less hydrated . by controlling water , your kidneys stabilize the body 's fluid levels . but this fine balancing act is n't the kidney 's only skill .

sift through the video and filter out 5 key services the kidneys provide to the human body . list them .

translator : andrea mcdonough reviewer : bedirhan cinar i 'm going to take you on a journey into some hidden worlds inside your own body using the scanning electron microscope . these microscopes use a beam of electrons to illuminate things that are too small to be seen by the photons of visible light . and to put this in context , if you mentally divide one tiny millimeter into a thousand parts , each one of those parts is a micrometer , or micron for short . if you then divide one micron into another thousand parts , each one of those is a nanometer . and it 's nanometers and microns that are the domain of the scanning electron microscope . so , let 's start with something on the body that we can measure at about 100 microns wide , and that would be a human hair , which now you can see is covered with scales , just like all of our hairs , and in fact , just like all mammal hairs . we 're going to plunge into the body now , and we 've landed in the thyroid gland . here we 're looking at proteins that are being secreted into a storage chamber where they are going to develop into the mature thyroid hormones before being released into the body . and at this point you might be wondering if these colors are real . the answer is no . electron images only happen in black and white . i often colorize my images for various reasons , but i do n't change the structures , so the strucutres that you 're seeing are all exactly as they were when i photographed them in the microscope . we 're going to take a detour and zoom in on the heart muscle now . and the heart muscle has this curious structure that 's kind of like corrugated cardboard . that 's what allows the heart to expand and contract as it 's beating . let 's go look at a lung with pneumonia . here we 've got a white blood cell poking around in an air sac , looking for something to clean out like a little vacuum cleaner . this is your immune systems at work . so what are the kinds of things that we do n't want to be breathing , besides bacteria and viruses ? well , we all know to stay away from asbestos and now we can see why . this is a close-up view of the mineral that asbestos is made from , and now you can see that it 's composed of many tiny , fine little needles . each one of those needles is a single crystal . and in this picture , they 're begininng to pry apart and tangle up into a spiky mess , not for breathing . what else might we want to avoid breathing ? well , how about diesel fuel ? we 're looking here at the particles of diesel soot , and these are extraordinarily tiny . in fact , each one of these little particles is only about 50 nanometers wide . we 'll go and look at some blood now . we 've got a collection of nice , fat , happy , healthy red blood cells , but they 're all tangled up in a network of fibers . this is how the body makes a blood clot . and so , it surrounds a group of red blood cells and other cells , and traps them so the blood ca n't flow . we 've got two more blood cells here , but they 're not normal like the ones in the blood clot image . these are distorted . you can see that they 're curling up and beginning to grow what 's going to become spikes . these are sickle cells and these are what cause the condition of sickle cell amenia . we 've gone into the mouth now and we 've landed on dental plague , which you can see is covered with bacteria , and in fact dental plague is host to about 1,000 different species of bacteria . lovely to think about . and now we are on to other teeth . we 're on the surfaces of the , or the internal surfaces of the teeth themselves . the smaller one is a baby tooth that had just fallen out of the mouth of a young friend of mine , and i want to call your attention to the little holes . those little holes are the tops of a whole network of tiny little tubes that circulate nourishing fluids inside your teeth . and we can see those tubes a little better in the larger picture because some of them are in cross-section . but in fact , this larger picture is showing you a portion of a tusk , which you may know is simply a great big , elongated tooth , so you would expect to see the same features between your teeth and a tusk . but that larger tusk picture is also rough by comparison to the young baby tooth . that 's because it 's many , many thousands of years old . it 's also partly fossilized . and , between these two pictures , now you can see how your teeth relate to the tusk of an ice age mammoth . we 're shooting up north now into the brain , and we can see these pink cells down at the bottom . those are the neurons of memory . and i 'm going to leave you with this picture because i know you 're going to take a lot of happy memories away from your exciting day at ted and now you can visualize where those memories are being stored in your own brain . thank you .

and the heart muscle has this curious structure that 's kind of like corrugated cardboard . that 's what allows the heart to expand and contract as it 's beating . let 's go look at a lung with pneumonia .

what allows the heart to expand and contract ?

translator : andrea mcdonough reviewer : bedirhan cinar the oval office , inauguration day , rose garden signings , and secret service agents with dark sunglasses and cool wrist radios . for a moment , forget all of it . toss out everything you know about the president . now , start over . what would you do if you had to invent the president ? that was the question facing the 55 men who got together in secret to draw up the plans for a new american government in the summer of 1787 in philadelphia , in the same place where the declaration of independence had been written eleven years earlier . declaring independence had been risky business , demanding ferocious courage that put lives and fortunes in jeopardy . but , inventing a new government was no field day either , especially when it 's summer and you 're in scratchy suits , and the windows are closed because you do n't want anybody to hear what you are saying , and the air conditioning does n't work because it wo n't be invented for nearly 200 years . and , when you do n't agree on things , it gets even hotter . for the framers , the question they argued over most while writing the constitution and creating three branches of government had to do with the executive department . one man or three to do the job ? how long should he serve ? what would he really do ? who would pick him ? how to get rid of him if he 's doing a bad job or he 's a crook ? and , of course , they all meant him , and he would be a white man . the idea of a woman or an african american , for instance , holding this high office was not a glimmer in their eyes . but the framers knew they needed someone who could take charge , especially in a crisis , like an invasion or a rebellion , or negotiating treaties . congress was not very good at making such important decisions without debates and delays . but the framers thought america needed a man who was decisive and could act quickly . they called it energy and dispatch . one thing they were dead-set against : there would be no king . they had fought a war against a country with a monarch and were afraid that one man with unchecked powers , in charge of an army , could take over the country . instead , they settled on a president and laid out his powers in article 2 of the constitution . but who would choose him ? not the people , they were too liable to be misled as one framer worried . not the legislature , that would lead to cabal and factions . got it : electors , wise , informed men who have time to make a good decision . and if they did n't produce a winner , then the decision would go to one of the other branches of government , the congress . the house of representatives would step in and make the choice , which they did in 1801 and 1825 . in the long , hot summer of 1787 , compromises were made to invent the presidency , like counting slaves as 3/5 of a person , giving the president command of the army but congress the power to declare war , and unlimited four-year terms . since then , some of those compromises have been amended and the men in office have sometimes been too strong or too weak . but , if you could start from scratch , how would you redesign the oval office ?

they had fought a war against a country with a monarch and were afraid that one man with unchecked powers , in charge of an army , could take over the country . instead , they settled on a president and laid out his powers in article 2 of the constitution . but who would choose him ?

where and when was the constitution written ?

communicating underwater is challenging . light and odors do n't travel well , so it 's hard for animals to see or smell . but sound moves about four times faster in water than in air , so in this dark environment , marine mammals often rely on vocalization to communicate . that 's why a chorus of sounds fills the ocean . clicks , pulses , whistles , groans , boings , cries , and trills , to name a few . but the most famous parts of this underwater symphony are the evocative melodies , or songs , composed by the world 's largest mammals , whales . whale songs are one of the most sophisticated communication systems in the animal kingdom . only a few species are known to sing . blue , fin , bowhead minke whales , and of course humpback whales . these are all baleen whales which use hairy baleen plates instead of teeth to trap their prey . meanwhile , toothed whales do use echolocation , and they and other species of baleen whales make social sounds , such as cries and whistles , to communicate . but those vocalizations lack the complexity of songs . so how do they do it ? land mammals like us generate sound by moving air over our vocal cords when we exhale , causing them to vibrate . baleen whales have a u-shaped fold of tissue between their lungs and their large inflatable organs called laryngeal sacs . we do n't know this for sure because it 's essentially impossible to observe the internal organs of a living , singing whale , but we think that when a whale sings , muscular contractions in the throat and chest move air from the lungs across the u-fold and into the laryngeal sacs , causing the u-fold to vibrate . the resulting sound resonates in the sacs like a choir singing in a cathedral making songs loud enough to propagate up to thousands of kilometers away . whales do n't have to exhale to sing . instead , the air is recycled back into the lungs , creating sound once more . one reason whale songs are so fascinating is their pattern . units , like moans , cries , and chirps are arranged in phrases . repeated phrases are assembled into themes . multiple themes repeated in a predictable pattern create a song . this hierarchical structure is a kind of grammar . whale songs are extremely variable in duration , and whales can repeat them over and over . in one recorded session , a humpback whale sang for 22 hours . and why do they do it ? we do n't yet know the exact purpose , but we can speculate . given that the singers are males and they mostly sing during the mating season , songs might be used to attract females . or perhaps they 're territorial , used to deter other males . whales return to the same feeding and breeding grounds annually , and each discrete population has a different song . songs evolve over time as units or phrases are added , changed , or dropped . and when males from different populations are feeding within earshot , phrases are often exchanged , maybe because new songs make them more attractive to breeding females . this is one of the fastest examples of cultural transmission , where learned behaviors are passed between unrelated individuals of the same species . we can eavesdrop on these songs using underwater microphones called hydrophones . these help us track species when sightings or genetic samples are rare . for example , scientists have been able to differentiate the elusive blue whale 's populations worldwide based on their songs . but the oceans are getting noisier as a result of human activity . boating , military sonar , underwater construction , and seismic surveys for oil are occurring more often which may interfere with whale 's communication . some whales will avoid key feeding or breeding grounds if human noise is too loud . and humpback whales have been observed to reduce their singing in response to noise 200 kilometers away . limiting human activity along migratory routes and in other critical habitats , and reducing noise pollution throughout the ocean would help ensure whales continued survival . if the whales can keep singing and we can keep listening , maybe one day we 'll truly understand what they 're saying .

this hierarchical structure is a kind of grammar . whale songs are extremely variable in duration , and whales can repeat them over and over . in one recorded session , a humpback whale sang for 22 hours .

scientists can track whales by detecting and following their songs . how is this a helpful tool for whale conservation , especially across international boarders and in the high seas ?

what do silk , dna , wood , balloons , and silly putty all have in common ? they 're polymers . polymers are such a big part of our lives that it 's virtually impossible to imagine a world without them , but what the heck are they ? polymers are large molecules made of small units called monomers linked together like the railroad cars from a train . poly means many , and mono means one , and mers or mero means parts . many polymers are made by repeating the same small monomer over and over again while others are made from two monomers linked in a pattern . all living things are made of polymers . some of the organic molecules in organisms are small and simple , having only one of a few functional groups . others , especially those that play structural roles or store genetic information , are macromolecules . in many cases , these macromolecules are polymers . for example , complex carbohydrates are polymers of simple sugars , proteins are polymers of amino acids , and nucleic acids , dna and rna , which contain our genetic information , are polymers of nucleotides . trees and plants are made of the polymer cellulose . it 's the tough stuff you find in bark and stems . feathers , fur , hair , and fingernails are made up of the protein keratin , also a polymer . it does n't stop there . did you know that the exoskeletons of the largest phylum in the animal kingdom , the arthropods , are made of the polymer chitin ? polymers also form the basis for synthetic fibers , rubbers , and plastics . all synthetic polymers are derived from petroleum oil and manufactured through chemical reactions . the two most common types of reactions used to make polymers are addition reactions and condensation reactions . in addition reactions , monomers simply add together to form the polymer . the process starts with a free radical , a species with an unpaired electron . the free radical attacks and breaks the bonds to form new bonds . this process repeats over and over to create a long-chained polymer . in condensation reactions , a small molecule , such as water , is produced with each chain-extending reaction . the first synthetic polymers were created by accident as by-products of various chemical reactions . thinking they were useless , chemists mostly discarded them . finally , one named leo baekeland decided maybe his useless by-product was n't so useless after all . his work resulted in a plastic that could be permanently squished into a shape using pressure and high temperatures . since the name of this plastic , polyoxybenzylmethylenglycolanhydride , was n't very catchy , advertisers called it bakelite . bakelite was made into telephones , children 's toys , and insulators for electrical devices . with its development in 1907 , the plastics industry exploded . one other familiar polymer , silly putty , was also invented by accident . during world war ii , the united states was in desperate need of synthetic rubber to support the military . a team of chemists at general electric attempted to create one but ended up with a gooey , soft putty . it was n't a good rubber substitute , but it did have one strange quality : it appeared to be extremely bouncy . silly putty was born ! synthetic polymers have changed the world . think about it . could you imagine getting through a single day without using plastic ? but polymers are n't all good . styrofoam , for example , is made mainly of styrene , which has been identified as a possible carcinogen by the environmental protection agency . as styrofoam products are being made , or as they slowly deteriorate in landfills or the ocean , they can release toxic styrene into the environment . in addition , plastics that are created by addition polymerization reactions , like styrofoam , plastic bags , and pvc , are built to be durable and food-safe , but that means that they do n't break down in the environment . millions of tons of plastics are dumped into landfills every year . this plastic does n't biodegrade , it just breaks down into smaller and smaller pieces , affecting marine life and eventually making their way back to humans . polymers can be soft or hard , squishy or solid , fragile or strong . the huge variation between means they can form an incredibly diverse array of substances , from dna to nylon stockings . polymers are so useful that we 've grown to depend on them every day . but some are littering our oceans , cities , and waterways with effects on our health that we 're only beginning to understand .

polymers are such a big part of our lives that it 's virtually impossible to imagine a world without them , but what the heck are they ? polymers are large molecules made of small units called monomers linked together like the railroad cars from a train . poly means many , and mono means one , and mers or mero means parts .

polymers are formed by chemical reactions in which a large number of molecules called _______________ are joined to form a chain .