Is light a particle or a wave? - Colm Kelleher

光是粒子还是波？——科尔姆•凯勒尔

Translator: Andrea McDonough Reviewer: Bedirhan Cinar

翻译人员: Yinglei Li 校对人员: Binglei Shea

You look down and see a yellow pencil lying on your desk.

你看到下方书桌上有一支黄色的铅笔

Your eyes, and then your brain, are collecting

然后你的眼睛和大脑

all sorts of information about the pencil:

开始搜集关于这支铅笔的各种信息

its size,

color,

它的尺寸

颜色

shape,

distance,

形状

距离

and more.

等等

But, how exactly does this happen?

那么我们是怎么做到的？

The ancient Greeks were the first

最早是古希腊人

to think more or less scientifically

从科学角度

about what light is and how vision works.

研究光和视觉的运作机制

Some Greek philosophers,

包括柏拉图和毕达哥拉斯在内的

including Plato and Pythagoras,

古希腊哲学家们

thought that light originated in our eyes

认为光从我们的眼睛发射出来

and that vision happened when little, invisible probes

其中微小无形的探测器

were sent to gather information about far-away objects.

收集到远处物体的信息从而形成视觉

It took over a thousand years

从那以后过了一千多年

before the Arab scientist, Alhazen,

阿拉伯科学家阿尔哈曾

figured out that the old, Greek theory of light couldn't be right.

才发现古希腊人关于光的理论是错误的

In Alhazen's picture, your eyes don't send out

阿尔哈曾认为我们的眼睛并不放出

invisible, intelligence-gathering probes,

无形的信息收集探测器

they simply collect the light that falls into them.

眼睛只用来收集照射过来的光

Alhazen's theory accounts for a fact

阿尔哈曾的理论能够解释一个

that the Greek's couldn't easily explain:

古希腊人无法解释的现象

why it gets dark sometimes.

那就是：为什么有时候眼前会一片黑暗

The idea is that very few objects actually emit their own light.

理论的核心在于只有少数物体能主动发光

The special, light-emitting objects,

人们把典型的发光物体

like the sun

如太阳

or a lightbulb,

are known as sources of light.

灯泡

称作光源

Most of the things we see,

大部分我们看到的东西

like that pencil on your desk,

比如那支桌上的铅笔

are simply reflecting light from a source

仅仅反射了来自光源的光

rather than producing their own.

自身并没有发光

So, when you look at your pencil,

因此你看着铅笔时

the light that hits your eye actually originated at the sun

眼睛接收到的光实际上来自太阳

and has traveled millions of miles across empty space

光线跨越了无际的太空

before bouncing off the pencil and into your eye,

才照射到铅笔，随后反射到你的眼睛里

which is pretty cool when you think about it.

这么一想一定觉得很酷吧

But, what exactly is the stuff that is emitted from the sun

那么太阳发射的光究竟是什么？

and how do we see it?

我们又是如何看到它的？

Is it a particle, like atoms,

它是如同原子一样的粒子

or is it a wave, like ripples on the surface of a pond?

还是如同水面涟漪一样的波？

Scientists in the modern era would spend a couple of hundred years

现代科学家花了数百年时间

figuring out the answer to this question.

才找到答案

Isaac Newton was one of the earliest.

艾萨克·牛顿是最早发现答案的一位

Newton believed that light is made up

牛顿认为

of tiny, atom-like particles, which he called corpuscles.

光由一种类似原子的微小粒子组成，并称之为“微粒”

Using this assumption, he was able to explain some properties of light.

基于这一假设，光的一些属性得到了解释

For example, refraction,

例如，折射

which is how a beam of light appears to bend

当一束光从空气射入水中时

as it passes from air into water.

它看上去弯曲了

But, in science, even geniuses sometimes get things wrong.

不过，即便是天才科学家也免不了会犯错

In the 19th century, long after Newton died,

牛顿死后过了很久，在19世纪时

scientists did a series of experiments

科学家做了一系列实验

that clearly showed that light can't be made up

确切地表明

of tiny, atom-like particles.

光不可能是由类似原子的微小粒子组成的

For one thing, two beams of light that cross paths

证据在于，当两束光交叉照射时

don't interact with each other at all.

不会相互影响

If light were made of tiny, solid balls,

如果光的成份是微小的固态粒子

then you would expect that some of the particles from Beam A

那情况就应该是来自A光束的粒子

would crash into some of the particles from Beam B.

撞上来自B光束的粒子

If that happened, the two particles involved in the collision

如果真是这样，那相互碰撞的粒子

would bounce off in random directions.

将会弹向四面八方

But, that doesn't happen.

然而事实并非如此

The beams of light pass right through each other

实际上，光束会穿过彼此

as you can check for yourself

你自己也可以做个实验

with two laser pointers and some chalk dust.

有两支激光笔和粉笔灰就行了

For another thing, light makes interference patterns.

另一个证据就是光有干涉现象

Interference patterns are the complicated undulations that happen

干涉现象是一种复杂的波动现象

when two wave patterns occupy the same space.

当两列波的频率相同时，就会发生干涉

They can be seen when two objects

如果两样物体同时触碰平静的水面

disturb the surface of a still pond,

就能看到干涉现象

and also when two point-like sources of light

两个点光源距离很近时

are placed near each other.

也会发生干涉

Only waves make interference patterns,

只有波才有干涉现象

particles don't.

粒子没有

And, as a bonus, understanding that light acts like a wave

发现光有波的属性之后

leads naturally to an explanation of what color is

自然而然地就能解释颜色是如何产生的

and why that pencil looks yellow.

那支铅笔怎么会是黄色的

So, it's settled then, light is a wave, right?

所以，没错，光就是波

Not so fast!

可不能这么快下结论

In the 20th century, scientists did experiments

到了20世纪，科学家从实验中发现

that appear to show light acting like a particle.

光有粒子的属性

For instance, when you shine light on a metal,

比如，当你向一块金属照射光线时

the light transfers its energy to the atoms in the metal

光间断性地以一种称为“量子”的形式

in discrete packets called quanta.

将能量转移到金属原子中

But, we can't just forget about properties like interference, either.

但光依然有干涉这样的属性

So these quanta of light aren't at all like

因此光量子并不全然是

the tiny, hard spheres Newton imagined.

牛顿想象地那样微小的固态球体

This result, that light sometimes behaves like a particle

光有时呈现粒子性

and sometimes behaves like a wave,

有时又呈现波的属性

led to a revolutionary new physics theory called

开创了一项革命性的物理理论

quantum mechanics.

成为“量子力学”

So, after all that, let's go back to the question,

经过以上分析，让我们回到问题本身

"What is light?"

“光是什么？”

Well, light isn't really like anything

光并非我们习以为常的

we're used to dealing with in our everyday lives.

普通物质

Sometimes it behaves like a particle

有时它像粒子

and other times it behaves like a wave,

有时又像波

but it isn't exactly like either.

用两者任意一方来定义光都不全面