One of the funny things about owning a brain is that you have no control over the things that it gathers and holds onto, the facts and the stories. And as you get older, it only gets worse. Things stick around for years sometimes before you understand why you're interested in them, before you understand their import to you. Here's three of mine. When Richard Feynman was a young boy in Queens, he went for a walk with his dad and his wagon and a ball. He noticed that when he pulled the wagon, the ball went to the back of the wagon. He asked his dad, "Why does the ball go to the back of the wagon?" And his dad said, "That's inertia." He said, "What's inertia?" And his dad said, "Ah. Inertia is the name that scientists give to the phenomenon of the ball going to the back of the wagon." (Laughter) "But in truth, nobody really knows." Feynman went on to earn degrees at MIT, Princeton, he solved the Challenger disaster, he ended up winning the Nobel Prize in Physics for his Feynman diagrams, describing the movement of subatomic particles. And he credits that conversation with his father as giving him a sense that the simplest questions could carry you out to the edge of human knowledge, and that that's where he wanted to play. And play he did. Eratosthenes was the third librarian at the great Library of Alexandria, and he made many contributions to science. But the one he is most remembered for began in a letter that he received as the librarian, from the town of Swenet, which was south of Alexandria. The letter included this fact that stuck in Eratosthenes' mind, and the fact was that the writer said, at noon on the solstice, when he looked down this deep well, he could see his reflection at the bottom, and he could also see that his head was blocking the sun. I should tell you -- the idea that Christopher Columbus discovered that the world is spherical is total bull. It's not true at all. In fact, everyone who was educated understood that the world was spherical since Aristotle's time. Aristotle had proved it with a simple observation. He noticed that every time you saw the Earth's shadow on the Moon, it was circular, and the only shape that constantly creates a circular shadow is a sphere, Q.E.D. the Earth is round. But nobody knew how big it was until Eratosthenes got this letter with this fact. So he understood that the sun was directly above the city of Swenet, because looking down a well, it was a straight line all the way down the well, right past the guy's head up to the sun. Eratosthenes knew another fact. He knew that a stick stuck in the ground in Alexandria at the same time and the same day, at noon, the sun's zenith, on the solstice, the sun cast a shadow that showed that it was 7.2 degrees off-axis. If you know the circumference of a circle, and you have two points on it, all you need to know is the distance between those two points, and you can extrapolate the circumference. 360 degrees divided by 7.2 equals 50. I know it's a little bit of a round number, and it makes me suspicious of this story too, but it's a good story, so we'll continue with it. He needed to know the distance between Swenet and Alexandria, which is good because Eratosthenes was good at geography. In fact, he invented the word geography. (Laughter) The road between Swenet and Alexandria was a road of commerce, and commerce needed to know how long it took to get there. It needed to know the exact distance, so he knew very precisely that the distance between the two cities was 500 miles. Multiply that times 50, you get 25,000, which is within one percent of the actual diameter of the Earth. He did this 2,200 years ago. Now, we live in an age where multi-billion-dollar pieces of machinery are looking for the Higgs boson. We're discovering particles that may travel faster than the speed of light, and all of these discoveries are made possible by technology that's been developed in the last few decades. But for most of human history, we had to discover these things using our eyes and our ears and our minds. Armand Fizeau was an experimental physicist in Paris. His specialty was actually refining and confirming other people's results, and this might sound like a bit of an also-ran, but in fact, this is the soul of science, because there is no such thing as a fact that cannot be independently corroborated. And he was familiar with Galileo's experiments in trying to determine whether or not light had a speed. Galileo had worked out this really wonderful experiment where he and his assistant had a lamp, each one of them was holding a lamp. Galileo would open his lamp, and his assistant would open his. They got the timing down really good. They just knew their timing. And then they stood at two hilltops, two miles distant, and they did the same thing, on the assumption from Galileo that if light had a discernible speed, he'd notice a delay in the light coming back from his assistant's lamp. But light was too fast for Galileo. He was off by several orders of magnitude when he assumed that light was roughly ten times as fast as the speed of sound. Fizeau was aware of this experiment. He lived in Paris, and he set up two experimental stations, roughly 5.5 miles distant, in Paris. And he solved this problem of Galileo's, and he did it with a really relatively trivial piece of equipment. He did it with one of these. I'm going to put away the clicker for a second because I want to engage your brains in this. So this is a toothed wheel. It's got a bunch of notches and it's got a bunch of teeth. This was Fizeau's solution to sending discrete pulses of light. He put a beam behind one of these notches. If I point a beam through this notch at a mirror, five miles away, that beam is bouncing off the mirror and coming back to me through this notch. But something interesting happens as he spins the wheel faster. He notices that it seems like a door is starting to close on the light beam that's coming back to his eye. Why is that? It's because the pulse of light is not coming back through the same notch. It's actually hitting a tooth. And he spins the wheel fast enough and he fully occludes the light. And then, based on the distance between the two stations and the speed of his wheel and the number of notches in the wheel, he calculates the speed of light to within two percent of its actual value. And he does this in 1849. This is what really gets me going about science. Whenever I'm having trouble understanding a concept, I go back and I research the people that discovered that concept. I look at the story of how they came to understand it. What happens when you look at what the discoverers were thinking about when they made their discoveries, is you understand that they are not so different from us. We are all bags of meat and water. We all start with the same tools. I love the idea that different branches of science are called fields of study. Most people think of science as a closed, black box, when in fact it is an open field. And we are all explorers. The people that made these discoveries just thought a little bit harder about what they were looking at, and they were a little bit more curious. And their curiosity changed the way people thought about the world, and thus it changed the world. They changed the world, and so can you. Thank you. (Applause)
Jedna od zanimljivih stvari u vezi sa posedovanjem mozga je da nemamo kontrolu nad onim što on prikuplja i čega se drži, nad podacima i pričama. Kako starite, to se samo pogoršava. Stvari ponekad ostaju tu negde godinama pre nego što shvatite zašto vas interesuju, pre nego što shvatite njihovu važnost po vas. Ovo su tri koje su meni važne. Kada je Ričard Fajnman bio mlad momak u Kvinsu otišao je u šetnju sa svojim ocem, kolicima i lopticom. Primetio je da se, kada povuče kolica, loptica vraća nazad prema kolicima. Kada je upitao oca: „Zašto se lopta vraća prema kraju kolica?”, otac mu je odgovorio: „To je inercija.” Upitao je: „Šta je inercija?”, a otac mu je odgovorio: „Inercija je ime koje naučnici daju pojavi da se lopta vraća unazad u kolicima, (Smeh) ali istina je da to niko zaista ne zna.” Fajnman je dobio nekoliko diploma na MIT, Prinstonu, rešio je katastrofu Čelendžer i na kraju dobio Nobelovu nagradu za fiziku za Fajnmanov dijagram koji objašnjava kretanje subatomskih čestica. Zaslugu za to pripisuje upravo tom razgovoru sa ocem jer mu je dao osećaj da najjednostavnija pitanja mogu da vas odvedu do ivica ljudskog znanja i da je upravo to mesto gde on želi da se igra. I igrao se. Eratosten je bio treći bibliotekar u velikoj Aleksandrijskoj biblioteci i dao je brojne doprinose nauci, ali ono po čemu je ostao zapamćen počelo je pismom koje je primio kao bibliotekar iz grada Svenet koji se nalazio južno od Aleksandrije. Pismo je sadržalo činjenicu koja se zadržala u njegovom umu, a ta činjenica bila je da je pisac rekao da je u podne na ravnodnevnicu, kada je pogledao u duboki bunar video sopstveni odraz, kao i da njegova glava blokira Sunce. Sad, trebalo bi da naglasim - ideja da je Kristofer Kolumbo otkrio da je zemlja okrugla je totalna glupost. To uopšte nije istina. Svako ko je bio obrazovan razumeo je da je Zemlja okrugla još od Aristotelovog doba, a Aristotel je to dokazao jednostavnim pomatranjem. Primetio je da svaki put kada vidimo Zemljinu senku na Mesecu, ona je kružna, a jednini oblik koji stalno pravi kružnu senku je sfera - znači, Zemlja je okrugla. Međutim, niko nije znao koliko je velika sve dok Eratosten nije dobio pismo sa ovom činjenicom. Razumeo je da je Sunce direktno iznad Sveneta zato sto je gledajući niz bunar video pravu liniju sve do dna bunara, pored njegove glave do Sunca. Eratosten je znao jos jednu činjenicu - znao je da će štap zaboden u zemlju u Aleksandriji u isto vreme i istog dana u podne, na Sunčev zenit, na ravnodnevnicu. Sunce će baciti senku koja će pokazati da je bio 7,2 stepena po osi. Sad, ako znate obim kruga i imate dve tačke na njemu, sve što treba da znate je razmak izmedju te dve tačke i možete da izvedete obim. Trista šezdeset stepeni podeljeno sa 7,2 je 50. Znam da je to okrugao broj, a i mene čini malo sumnjičavim po pitanju ove priče, ali to je dobra priča, pa ćemo nastaviti sa njom. Trebalo mu je da zna udaljenost između Sveneta i Aleksandrije, što je dobro jer je Eratosten bio dobar u geografiji. Zapravo, baš on je izmislio reč geografija. Put između Sveneta i Aleksandrije bio je trgovačka ruta, a trgovcima je trebalo da znaju koliko dugo im treba do tamo; bila im je potrebna tačna udaljenost, pa je on znao veoma precizno da je udaljenost između dva grada 800 kilometara. Pomnožite to sa 50 i dobijate 40 000, što je unutar jednog procenta Zemljinog prečnika. On je to uradio pre 2 200 godina, a mi živimo u vremenu u kom multimilionska mašinerija traži Higsov bozon. Otkrivamo čestice koje mogu da putuju brže od svetlosti, a sve ove pronalaske omogućila je tehnologija koja je otkrivena u prethodnih par decenija. Ipak, tokom većeg dela ljudske istorije morali smo da otkrivamo ovakve stvari koristeći oči, uši i umove. Armand Fizo bio je eksperimentalni fizičar u Parizu. Njegova specijalnost je zapravo bila da preradi i potvrdi rezultate drugih ljudi. Ovo možda zvuči kao gubitak vremena, ali zapravo je to srž nauke zato što ne postoji činjenica koja ne može biti nezavisno potkrepljena činjenicama, a njemu su bili poznati Galileovi eksperimenti dok je pokušavao da odredi da li svetlo ima brzinu. Tako je Galileo završio ovaj sjajan eksperiment u kom su on i njegov asistent imali lampu; svaki je držao po lampu, a Galileo bi otvorio svoju lampu, a njegov asistent bi uradio isto i dobro su podesili vreme. Jednostavno su znali vreme. Zatim bi stajali na dva vrha, udaljeni tri kilometra i uradili bi istu stvar, pod Galileovom pretpostavkom da će, ako svetlost ima uočljivu brzinu, primetiti zastoj kod vraćanja svetlosti iz lampe njegovog asistenta. Svetlost je, međutim, bila prebrza za Galilea. Falilo mu je nekoliko redova veličina kada je pretpostavio da je svetlost okvirno 10 puta brža od zvuka. Fizo je bio upoznat sa ovim eksperimentom. Živeo je u Parizu i napravio je dve eksperimentalne stanice, na udaljenosti od otprilike devet kilometara u Parizu. Rešio je ovaj Galileov problem, a to je uradio sa relativno trivijalnim komadom opreme. Učinio je to sa jednim od ovih. Otkloniću kliker na sekundu zato što želim da angažujete svoje umove. Ovo je nazubljeni točak. Ima gomilu udubljenja i zubaca. Ovo je Fizoovo rešenje za slanje direktnih pulseva svetlosti. Postavio je zrak iza jednog od ovih udubljenja. Ako usmerite zrak kroz udubljenje prema ogledalu udaljenom 8 kilometara, zrak se odbija od ogledala i vraća se ka meni kroz ovo udubljenje. Međutim, nešto interesantno se dešava kada okrenemo brže točak. Primećuje da deluje kao da se vrata zatvaraju na zraku koji se vraća u njegovo oko. Zbog čega se to dešava? Zbog toga se što puls svetlosti ne vraća kroz isto udubljenje. Zapravo udara u zubac, a on okreće točak dovoljno brzo i potpuno zaklanja svetlost. Zatim je, na osnovu udaljenosti između dve stanice, brzine točka i broja udubljenja na točku, izračunao brzinu svetlosti unutar dva procenta njene stvarne vrednosti, a učinio je ovo 1849. godine. To je ono što me tera da nastavim sa ovom naukom. Kad god imam problema sa razumevanjem koncepta, vratim se i istražim ljude koji su otkrili taj koncept. Pogledam priču kako su ga oni razumeli. Kada pogledate u ono o čemu su oni koji su ga otkrili razmišljali dok su ga otkrivali, razumete da nisu mnogo drugačiji od nas samih. Mi smo vreće mesa i vode. Svi krećemo sa istim sredstvima. Sviđa mi se ideja da se različite grane nauke nazivaju grane istraživanja. Većina ljudi vidi nauku kao zatvorenu, crnu kutiju, dok je ona zapravo otvoreno polje, a svi smo mi istraživači. Ljudi koji su došli do ovih otkrića samo su malo više razmišljali o stvarima koje posmatraju i bili su za mrvicu radoznaliji, a njihova radoznalost promenila je način na koji ljudi razmišljaju o svetu i tako su promenili svet. Oni su promenili svet, pa možete i vi. Hvala vam. (Aplauz)