One of the funny things about owning a brain is that
关于大脑有一个非常有趣的现象
you have no control over the things that it gathers and holds onto, the facts and the stories.
那就是我们无法控制大脑收集和掌握的信息，无论是事实还是故事。
And as you get older, it only gets worse.
而且年纪越大，情况就越糟糕。
Things stick around for years sometimes before you understand why you're interested in them,
有时候这些事物已经跟随你许多年了，你却还没弄清为何会对这些事物感兴趣，
before you understand their import to you. Here's three of mine.
还没了解他们对你的重要性。我这有三个例子。
When Richard Feynman was a young boy in Queens,
理查德·费曼小的时候住在纽约皇后区，
he went for a walk with his dad and his wagon and a ball.
有一次他和他爸爸推着车出去散步，车上有一个球。
He noticed that when he pulled the wagon, the ball went to the back of the wagon.
他注意到当他拉动车子的时候，球就会滚到车的后面。
He asked his dad, 'Why does the ball go to the back of the wagon?'
他问爸爸：“为什么球会滚到车的后面？”
And his dad said, 'That's inertia.' He said, 'What's inertia?'
爸爸回答说：“这叫惯性。”他接着问：“什么叫惯性？”
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.'
爸爸说：“啊。惯性嘛，就是科学家们给球滚到车后面这种现象取的名字。
'But in truth, nobody really knows.'
但事实上，没人明白这是怎么回事。”
Feynman went on to earn degrees at MIT, Princeton, he solved the Challenger disaster,
费曼后来在麻省理工学院和普林斯顿获得了学位，他解决了挑战者号航天飞机失事事件的谜团，
he ended up winning the Nobel Prize in Physics for his Feynman diagrams, describing the movement of subatomic particles.
他最后获得了诺贝尔物理学奖，因为他提出了描述粒子运动的费曼图。
And he credits that conversation with his father as giving him a sense
他把这归功于和父亲的那次对话，让他认识到
that the simplest questions could carry you out to the edge of human knowledge,
最简单的问题可以将你带入人类知识的前沿，
and that that's where he wanted to play. And play he did.
而且那就是他想有所作为的地方。他确实成功了。
Eratosthenes was the third librarian at the great Library of Alexandria, and he made many contributions to science.
埃拉托斯特尼是亚历山大图书馆的第三任馆长，他为科学做出了很多贡献。
But the one he is most remembered for began in a letter that he received as the librarian,
但他最为人们所铭记的成就是由他在当图书馆馆长时收到的一封信开始的，
from the town of Swenet, which was south of Alexandria.
这封信来自亚历山大南边的一个叫塞尼的小镇。
The letter included this fact that stuck in Eratosthenes' mind, and the fact was that the writer said,
信中的一个事实在埃拉托斯特尼的脑中挥之不去，写信的人说
at noon on the solstice, when he looked down this deep well,
在夏至的正午时分，当他向一口深井望下去的时候，
he could see his reflection at the bottom, and he could also see that his head was blocking the sun.
他可以看到井底的倒影，并发现他的头正遮挡着太阳。
I should tell you -- the idea that Christopher Columbus discovered that the world is spherical is total bull.
现在我告诉大家，哥伦布发现地球是圆的这个说法纯属是胡说八道，
It's not true at all.
根本不是真的。
In fact, everyone who was educated understood that the world was spherical since Aristotle's time.
事实上，所有受过教育的人都知道地球是圆的，这是自从亚里士多德时代开始的，
Aristotle had proved it with a simple observation.
而且亚里士多德本人还通过一个非常简单的观测证明过这个说法。
He noticed that every time you saw the Earth's shadow on the Moon, it was circular,
他注意到地球在月亮上的影子是圆的，
and the only shape that constantly creates a circular shadow is a sphere, Q.E.D. the Earth is round.
而且唯一能够持续的产生圆形影子的形状就是球体，证明完毕。地球是圆的。
But nobody knew how big it was until Eratosthenes got this letter with this fact.
但是没有人知道地球有多大，直到埃拉托斯特尼看到这封信里描述的事实。
So he understood that the sun was directly above the city of Swenet, because looking down a well,
他知道当时太阳在直射塞尼，因为向井底看的时候，
it was a straight line all the way down the well, right past the guy's head up to the sun.
一条垂直光线经过那个人正挡着太阳的头部，直射到井底。
Eratosthenes knew another fact.
埃拉托斯特尼还知道另一个事实。
He knew that a stick stuck in the ground in Alexandria at the same time and the same day, at noon,
他知道在同一天的同一时间，也就是夏至的正午，在亚历山大插一根棍子，
the sun's zenith, on the solstice, the sun cast a shadow that showed that it was 7.2 degrees off-axis.
从太阳投射的影子得知，光线偏离轴线7.2度。
If you know the circumference of a circle, and you have two points on it,
如果你知道一个圆周边，在圆上取两个点，
all you need to know is the distance between those two points, and you can extrapolate the circumference.
只需要知道这两点之间的距离，然后就可以推算周长了。
360 degrees divided by 7.2 equals 50.
360度除以7.2等于50。
I know it's a little bit of a round number, and it makes me suspicious of this story too,
我知道这是个整数，这也让我对这个故事产生了怀疑，
but it's a good story, so we'll continue with it.
但它仍是个不错的故事，所以我们继续讲下去。

He needed to know the distance between Swenet and Alexandria, which is good because Eratosthenes was good at geography.
他需要知道塞尼和亚历山大之间的距离，这个问题很好解决，因为埃拉托斯特尼很擅长地理。
In fact, he invented the word geography.
事实上，是他创造了地理这个词。
The road between Swenet and Alexandria was a road of commerce,
塞尼和亚历山大之间的路是一条商业之路，
and commerce needed to know how long it took to get there. It needed to know the exact distance,
商人们需要知道多久能到达目的地，就有必要知道两地的确切距离，
so he knew very precisely that the distance between the two cities was 500 miles.
所以埃拉托斯特尼非常精确的知道两地之间距离500英里。
Multiply that times 50, you get 25,000, which is within one percent of the actual diameter of the Earth.
再乘以50，得到25000，这与地球实际周长的误差不到百分之一，
He did this 2,200 years ago.
但他在2200年前就做到了。
Now, we live in an age where multi-billion-dollar pieces of machinery are looking for the Higgs boson.
现在我们生活的时代有价值几十亿美金的机器用来寻找希格斯玻色子。
We're discovering particles that may travel faster than the speed of light,
我们正在探究比光速传播更快的粒子，
and all of these discoveries are made possible by technology that's been developed in the last few decades.
这一切科学探索成为可能是依靠过去几十年来的科技进步。
But for most of human history, we had to discover these things using our eyes and our ears and our minds.
但是在大部分人类历史上，我们不得不用自己的眼睛、耳朵和大脑来探索问题。
Armand Fizeau was an experimental physicist in Paris.
阿曼德·斐索是巴黎一名实验物理学家，
His specialty was actually refining and confirming other people's results,
他的专业领域是确认和完善他人的成果，
and this might sound like a bit of an also-ran, but in fact, this is the soul of science,
这听上去似乎有点无足轻重。但事实上，这正是科学的精髓，
because there is no such thing as a fact that cannot be independently corroborated.
因为没有一件事实不可以被独立证明。
And he was familiar with Galileo's experiments in trying to determine whether or not light had a speed.
他很熟悉伽利略试图判断光是否拥有速度的实验。
Galileo had worked out this really wonderful experiment where he and his assistant had a lamp,
伽利略完成了这一精彩绝伦的实验，他和助手各有一盏灯，
each one of them was holding a lamp.
他们每人提一盏灯，
Galileo would open his lamp, and his assistant would open his.
伽利略打开他的灯，助手也打开自己的灯。
They got the timing down really good. They just knew their timing.
他们的时机把握得很好。他们很清楚自己的时机。
And then they stood at two hilltops, two miles distant, and they did the same thing,
他们分别站在两个山顶上，距离两英里，然后做同样的事情，
on the assumption from Galileo that if light had a discernible speed,
按照伽利略的假设，如果光线拥有可识别速度，
he'd notice a delay in the light coming back from his assistant's lamp.
他就会注意到从助手那里返回光线的延时。
But light was too fast for Galileo.
但对于伽利略来讲，光线实在是太快了，
He was off by several orders of magnitude when he assumed that light was roughly ten times as fast as the speed of sound.
当他假设光速大约是声速的10倍时，他少说了好几个数量级。
Fizeau was aware of this experiment.
斐索很清楚这个实验。
He lived in Paris, and he set up two experimental stations, roughly 5.5 miles distant, in Paris.
他住在巴黎，于是他在那里建立了两个实验站点，大约相距5.5英里。
And he solved this problem of Galileo's, and he did it with a really relatively trivial piece of equipment.
他解决了伽利略的问题，而且他的实验器材相对来讲十分普通，
He did it with one of these.
他就是用的这个。
I'm going to put away the clicker for a second because I want to engage your brains in this.
我要把这个遥控器先放在一边，因为我要让你们的大脑也活跃起来。
So this is a toothed wheel. It's got a bunch of notches and it's got a bunch of teeth.
这是一个齿轮，有一串凹槽，还有一串轮齿。
This was Fizeau's solution to sending discrete pulses of light.
这就是斐索发送离散脉冲光的方法。
He put a beam behind one of these notches.
他将一束光线放在其中一个凹槽后面。
If I point a beam through this notch at a mirror, five miles away,
如果我让这束光线通过这个凹槽射向一面五公里之外的镜子
that beam is bouncing off the mirror and coming back to me through this notch.
这束光线就会由镜面反射回来，通过这个凹槽回到我这里。
But something interesting happens as he spins the wheel faster.
但当他快速转动齿轮时，有趣的现象发生了。
He notices that it seems like a door is starting to close on the light beam that's coming back to his eye.
他注意到，就好像是有一扇门在阻挡着返回他视野的光线。
Why is that? It's because the pulse of light is not coming back through the same notch.
为什么会这样？这是因为光线返回的时候通过的不是同一个凹槽。
It's actually hitting a tooth. And he spins the wheel fast enough and he fully occludes the light.
实际上，光线撞到了一个轮齿上。当他把齿轮转得足够快的时候，光线就被完全阻挡了。
And then, based on the distance between the two stations and the speed of his wheel and the number of notches in the wheel,
然后，根据两个实验站点的距离和齿轮的转速以及齿轮上凹槽的数量，
he calculates the speed of light to within two percent of its actual value. And he does this in 1849.
他计算出了光的速度，和真实的光速只有百分之二的误差。而他在1849年就做到了。
This is what really gets me going about science.
这就是我从事科学研究的原因。
Whenever I'm having trouble understanding a concept, I go back and I research the people that discovered that concept.
每当我理解不了某个概念时，我就回过头研究那些发现这个概念的人们。
I look at the story of how they came to understand it.
我要看看他们是如何理解这个概念的。
What happens when you look at what the discoverers were thinking about when they made their discoveries,
当你看到这些科学发现者是如何思考他们的探索研究的时候，
is you understand that they are not so different from us.
你就会明白其实他们和我们没有什么不同。
We are all bags of meat and water. We all start with the same tools.
我们都是塞着肉、装着水的皮囊，使用的都是同样的工具。
I love the idea that different branches of science are called fields of study.
我喜欢这种把不同的科学分支称为学科领域的说法，
Most people think of science as a closed, black box, when in fact it is an open field. And we are all explorers.
大多数人认为科学就是一个封闭的黑匣子，实际上它却是一片广阔天地。我们都是探险家。
The people that made these discoveries just thought a little bit harder about what they were looking at,
那些在科学探索中取得成就的人，仅仅是对他们看到的东西思考得更认真一点，
and they were a little bit more curious.
并且他们的好奇心更多一点罢了。
And their curiosity changed the way people thought about the world, and thus it changed the world.
他们的好奇心改变了人们看世界的方法，进而改变了这个世界。
They changed the world, and so can you. Thank you.
他们改变了世界，你们大家也可以。谢谢。