One of the most amazing facts in physics is this:
在物理学中最神奇的一个事实是：
everything in the universe, from light to electrons to atoms,
宇宙中的任何事物，从光到电子再到原子，
behaves like both a particle and a wave at the same time.
都同时表现得既像粒子又像波。
All of the other weird stuff you might have heard about quantum physics,
你可能听说过这些关于物理学的怪事，
Schrodinger's Cat, God playing dice, spooky action at a distance,
薛定谔的猫，掷骰子的上帝，超距作用，
all of it follows directly from the fact that everything has both particle and wave nature. This might sound crazy.
所有这些事情都遵从一个事实：任何事物都同时具有粒子性和波动性。这听起来可能很疯狂。
If you look around, you'll see waves in water and particles of rock, and they're nothing alike.
看看你的四周，你可以看见水中的水波和石头当中的颗粒，但他们没有一点相像之处。
So why would you think to combine them?
那我们为什么会将这两者联系在一起呢？
Physicists didn't just decide to mash these things together out of no where.
物理学家们并不是无缘无故地把它们混搭在一起。
Rather, they were led to the dual nature of the universe through a process of small steps,
实际上，他们通过一点一点的过程，
fitting together lots of bits of evidence, like pieces in a puzzle.
把许多证据像拼图一样组合起来，发现了波粒二象性。
The first person to seriously suggest the dual nature of light was Albert Einstein in 1905,
阿尔伯特·爱因斯坦在1905第一次正式提出了光的波粒二象性，
but he was picking up an earlier idea from Max Planck.
但他的理论是建立在早先马克斯·普朗克的观点基础之上的。
Planck explained the colors of light emitted by hot objects, like the filament in a light bulb,
普朗克的理论很好的解释了为什么像灯丝这样的热物质会放出不同颜色的光，
but to do it, he needed a desperate trick:
但是它建立在一个近乎不可能的前提下：
he said the object was made up of oscillators that could only emit light in discrete chunks,
他认为这样的物体由振荡器构成，只能向外发射特定的、不连续的能量块（量子），
units of energy that depend on the frequency of the light.
能量单位的大小取决于光的频率。
Planck was never really happy with this, but Einstein picked it up and ran with it.
普朗克对自己的理论一直不满意，而爱因斯坦在此基础上进行了深入研究。
He applied Planck's idea to light itself,
他将普朗克的观点应用到光线本身，
saying that light, which everybody knew was a wave, is really a stream of photons, each with a discrete amount of energy.
他认为，众所周知光线是一种波，但实际上光线是粒子流，每颗粒子都由不连续的能量组成。
Einstein himself called this the only truly revolutionary thing he did,
爱因斯坦称这是他唯一做过的革命性的事，
but it explains the way light shining on a metal surface knocks loose electrons.
这恰好能够解释光线照在金属表面发生的电子逃逸的现象。
Even people who hated the idea had to agree that it works brilliantly.
即使是反对这一观点的人都不得不同意它是极其合理的。
The next puzzle piece came from Ernest Rutherford in England.
接下来补全这块拼图的是英国人欧内斯特·卢瑟福。

In 1909, Ernest Marsden and Hans Geiger, working for Rutherford,
1909年，卢瑟福的助手汉斯·盖革和欧内斯特·马斯登
shot alpha particles at gold atoms and were stunned to find that some bounced straight backwards.
用α粒子轰击金箔，令人震惊的是，一部分α粒子被直接反弹了回去。
This showed that most of the mass of the atom is concentrated in a tiny nucleus.
这表明原子的大部分质量都集中在非常小的核上。
The cartoon atom you learn in grade school, with electrons orbiting like a miniature solar system, that's Rutherford's.
你上小学时见到的电子环绕原子核运动的模型，很像小型的太阳系，这就是由卢瑟福提出的。
There's one little problem with Rutherford's atom: it can't work.
但是卢瑟福的原子模型有一个问题：它解释不通。
Classical physics tells us that an electron whipping around in a circle emits light,
经典物理学告诉我们，一个电子做圆周运动会产生光，
and we use this all the time to generate radio waves and X-rays.
我们一直运用这个原理来产生无线电波和X射线。
Rutherford's atoms should spray X-rays in all directions for a brief instant before the electron spirals in to crash into the nucleus.
在电子旋转至撞到原子核以前，卢瑟福原子应在瞬间向各个方向上发出X光。
But Niels Bohr, a Danish theoretical physicist working with Rutherford,
但是和卢瑟福一起工作的丹麦物理学家波尔明确指出原子是存在的，
pointed out that atoms obviously exist, so maybe the rules of physics needed to change.
所以可能很多物理法则都需要改变。
Bohr proposed that an electron in certain special orbits doesn't emit any light at all.
波尔提出，在特定轨道中的电子不会产生光。
Atoms absorb and emit light only when electrons change orbits,
原子只在电子改变轨道时吸收并发射光线，
and the frequency of the light depends on the energy difference in just the way Planck and Einstein introduced.
而且光的频率取决于能量的差异，就像爱因斯坦和普朗克介绍的那样。
Bohr's atom fixes Rutherford's problem and explains why atoms emit only very specific colors of light.
波尔的原子解决了卢瑟福的问题，还解释了为什么原子只产生特定颜色的光。
Each element has its own special orbits, and thus its own unique set of frequencies.
每一种元素都有自己特殊的轨道，因此有独一无二的频率。
The Bohr model has one tiny problem: there's no reason for those orbits to be special.
波尔模型有一个小问题：无法解释轨道的特殊性。
But Louis de Broglie, a French PhD student, brought everything full circle.
但法国一个名叫路易·维克多·德布罗意的博士生补齐了这个缺口。
He pointed out that if light, which everyone knew is a wave, behaves like a particle,
他指出如果光像一个粒子一样运动，而不是人们所熟知的波
maybe the electron, which everyone knew is a particle, behaves like a wave.
也许电子会像波一样运动，而不是人们所熟知的粒子。
And if electrons are waves, it's easy to explain Bohr's rule for picking out the special orbits.
而且如果电子是波，就可以很容易解释波尔的特殊轨道定律了。
Once you have the idea that electrons behave like waves, you can go look for it.
当你知道电子像波一样运动后，你就知道如何观察它了。
And within a few years, scientists in the US and UK had observed wave behavior from electrons.
在短短几年内，美国和英国的科学家就观察到了电子的波动性。
These days we have a wonderfully clear demonstration of this:
现在我们可以轻而易举地证明：
shooting single electrons at a barrier with slits cut in it.
向有缝隙的障碍物上射出单电子。
Each electron is detected at a specific place at a specific time, like a particle.
每一个电子都会在特定的时间和位置被检测到，像粒子一样。
But when you repeat the experiment many times,
但当你重复这个实验很多次之后，
all the individual electrons trace out a pattern of stripes, characteristic of wave behavior.
所有的独立电子会脱离条纹模式表现出波的特性。
The idea that particles behave like waves, and vice versa, is one of the strangest and most powerful in physics.
粒子具有波动性的概念和它的逆定理是物理学中最奇怪的也是最重要的理论。
Richard Feynman famously said that this illustrates the central mystery of quantum mechanics.
理查德·费曼曾说过一句著名的话，这个（波粒二象性）解开了量子力学的中心谜团。
Everything else follows from this, like pieces of a puzzle falling into place.
其它一切理论都从这里开始，像拼图一样完善着我们的认知。