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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)
擁有大腦的有趣之處在於 你無法控制大腦如何收集與保留 事實和故事。而當你越來越老, 事情只會變得更糟 有些事情會留在你的腦袋裡很多年 你根本不知道為什麼會一直記著這些事 也不清楚到底是怎麼把它記起來的。 以下我有三個例子 當理查 · 費曼還是一個小男孩, 住在皇后區 有一次他和他的父親去散步, 拉著他的玩具拖車 上面放了一個球。他注意到,當他拉車的時候 球會往拖車後面跑 他問他的爸爸, "為什麼球會跑到拖車的後面呢?" 他的父親說, "這是慣性。" 他問說, "慣性是什麼?" 他的父親說, "啊。 慣性是科學家們給的名稱 用來描述球跑去拖車後面的這種現象。 但事實是, 沒有人真正知道這現象到底是怎麼一回事。" 費曼後來取得了學位 在麻省理工學院、 普林斯頓大學, 他還解決了挑戰者號太空梭爆炸的謎團, 他還得到了諾貝爾物理學獎, 因為他在描述亞原子粒子的運動方面的成就 他把一切歸功於那次與他父親的對話 給了他一個啟發: 從最簡單的問題開始, 可以帶領你探索到人類知識的前鋒, 這就是他想做的 而他也如此做到了 第二個例子, 艾拉托斯特尼是亞歷山大 一個偉大圖書館的第三任館長 他在科學方面有很多貢獻。 其中最讓人津津樂道的 是在他當圖書館館長時, 收到了一封信 寄自亞歷山大城南邊的斯威尼特鎮。 這封信提到的一件事, 一直在艾拉托斯特尼的心中揮之不去 寫信的人說, 當他在夏至的中午 望進一口深井的時候 他可以看到井底的水面, 有陽光反射, 而且他的頭 正好可以擋住太陽。 而我應該告訴你, 關於克里斯多夫 · 哥倫布 發現地球是球形的這回事 根本就是胡扯。完全不正確。 事實上, 受過教育的人都知道地球是圓的 因為在亞里斯多德的年代, 他就已證明了這事 只靠簡單的觀察。 他注意到, 每次在月亮上看到地球的影子(月食) 影子是圓的 而唯一能每次都造成圓影的形狀 就是一個球體, 所以證明地球是圓的。 但沒有人知道地球有多大 直到艾拉托斯特尼有了這封信跟井的這回事。 他想到太陽是斯威尼特鎮的正上方 因為向井下頭看, 這是一條直線 從太陽經過寫信者的頭, 一路到井底。 艾拉托斯特尼知道另一個事實。 他知道在亞歷山大城當地立了一根棍子 在同一時間、 同一天中午, 太陽正在天頂的時候 陽光照出的棍子的陰影與鉛直線偏了 7.2 度。 現在, 如果你知道一個圓的圓心角 還有圓上的兩個點 你只要知道這兩點之間的距離 就可以推算出圓周長。 360 度除以 7.2 度等於 50。 我知道正好整除有些太巧了, 讓人有點懷疑這個故事的可信度 但這是一個好故事, 所以我們會繼續談下去。 他需要知道斯威尼特鎮 和亞歷山大城之間的距離 這是容易的, 因為艾拉托斯特尼很擅長地理學。 事實上, 地理學這個名詞就是他發明的。 斯威尼特鎮 和亞歷山大之間的道路 是一條經商者常走的路, 經商者需要知道路程要多久。 所以實際的距離很重要, 所以他也非常精確地知道 這兩個城市之間的距離是 500 英哩。 乘上 50 倍, 就是 25,000 英哩, 這跟地球實際的大小只有 1% 的誤差。 在二千二百年前, 他就能做到這樣的事。 現在, 我們生活在一個時代, 價值數十億元的設備正在尋找希格斯玻色子。 我們發現可能比光速更快的粒子 而所有的這些發現都是靠著 在過去幾十年中所發展出來的科技。 但在人類歷史的大多數時間, 我們只能靠我們的眼睛和耳朵, 還有思考能力, 來發現新事物。 阿曼德斐索是在巴黎的實驗物理學家。 他的專長是精煉和確認其他人的研究結果, 這聽起來可能有點的遜, 但事實上, 這就是科學的靈魂 因為若不能獨立的被重複驗證, 就不能被稱為科學事實。 他很熟悉伽利略的一個實驗 是關於光是不是有速度的。 伽利略曾做了這個特別的實驗 他和他的助手各拿了一盞燈, 當伽利略打開他的燈, 他的助手看到光後, 也同樣地打開燈。 他們把時間抓得很準。 他們只管自己的開燈時機。 然後他們站在兩個山頭 相距兩英里, 兩人做一樣的事情, 伽利略的假設是, 如果光有一個特定的速度, 他應該會注意到在從他的助手燈回來的光的延遲。 但光的速度對伽利略來說太快了。 他對光的速度的臆測差了好幾個數量級 (10的n次方) 他猜測光大概只比聲音的速度快 10 倍。 斐索聽說了這個實驗。他住在巴黎, 他設立了兩個實驗站 相距大約五英里半, 在巴黎。他解決了伽利略的實驗中的問題, 他只用了一塊相對來說很小的設備。 他用的就像這個。 我先把遙控器收起來, 因為我想讓你的大腦也來思考一下。 這就是齒輪的樣子。它有一大堆的凹槽 還有一堆的凸齒。 這是斐索用來發送離散脈衝光的作法。 他讓一束光穿過這些凹口之一。 射到另一個實驗站的鏡子反射 來回各五英里, 這束光回來後 會通過這個凹口被看到。 但當他把齒輪轉得更快時, 有趣的事情發生了。 他觀察到如同反射的光被關上的門擋住了 眼睛看不到反射回來的光了。 這是為什麼? 這是因為反射的光並沒有 通過發射時相同的凹口。 實際上是擊中一顆凸齒。 他把齒輪轉得夠快 對光的現象充分的觀察 再依據兩個地點之間的距離 還有他的齒輪的轉速與齒數 他計算出與實際光速誤差不到 2% 的數值。 他在 1849 年作出了這樣的實驗。 這也是為什麼讓我對科學一直有興趣的緣故。 每當我在理解一個概念時遇到了問題, 我會回去研究發現了這個概念的研究者。 我觀察他們如何逐漸搞懂整件事情。 當你看到了研究者如何思考, 看到他們如何發現事物, 你就會知道 其時他們跟我們沒有什麼不同。 我們都是血肉之軀。我們都能使用相同的工具。 我很喜歡把科學的不同分支稱做研究領域的說法。 大多數人認為科學是封閉的黑箱, 當事實上它是一個開放的領域。 而且我們大家都是探險家。 貢獻出這些發現的人只是想得比我們努力些 對於他們所研究的事情, 有著更多的好奇心 他們的好奇心改變了人們對這個世界的觀點, 也因此而改變了世界。 他們能改變這個世界, 當然你也可以。 謝謝。 (掌聲)