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How simple ideas lead to scientific discoveries

Transcript

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

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