Why is glass transparent? - Mark Miodownik

玻璃为何是透明的? ——马克·米奥多尼克

翻译人员: Nan Hu 校对人员: Dong Mao

Take a look out your window,

向窗外张望一下

put on your glasses if you wear them.

有必要的话 戴上眼镜

You might want to grab a pair of binoculars, too,

也许你还想拿副望远镜

or a magnifying lens.

或是放大镜

Now, what do you see?

现在 你看到了什么

Well, whatever it is,

无论你看到了什么

it's not the multiple layers of glass

答案都可能不是那一层层

right in front of you.

近在咫尺的玻璃

But have you ever wondered

但是你是否想知道

how something so solid can be so invisible?

为什么有如此固态的东西却看不见呢

To understand that,

要明白这点

we have to understand what glass actually is,

我们首先要知道玻璃究竟是什么

and where it comes from.

以及它是怎样形成的

It all begins in the Earth's crust,

所有一切都始于地壳

where the two most common elements are

在它其中最基本的两种元素:

silicon and oxygen.

硅和氧

These react together to form silicon dioxide,

它们相互作用形成二氧化硅

whose molecules arrange themselves

二氧化物的分子自动排列

into a regular crystalline form known as quartz.

形成晶体状物被称为石英

Quartz is commonly found in sand,

石英通常在沙中被发现

where it often makes up most of the grains

沙大多由颗粒组成

and is the main ingredient in most type of glass.

而颗粒是多数玻璃的主要原料

Of course, you probably noticed that glass

当然 你可能注意到玻璃

isn't made of multiple tiny bits of quartz,

并不是由许多石英粒组成的

and for good reason.

这点显而易见

For one thing, the edges of the rigidly formed grains

一方面 晶体结构内部严格形成的颗粒边缘

and smaller defects within the crystal structure

或者很小的瑕疵

reflect and disperse light that hits them.

反射及散射照向它们的光

But when the quartz is heated high enough

但是当石英加热到足够热时

the extra energy makes the molecules vibrate

产生的热量就会让分子产生震动

until they break the bonds holding them together

直到它们打破以前的链结

and become a flowing liquid,

进而形成流动的液体

the same way that ice melts into water.

就和冰融化成水一样

Unlike water, though, liquid silicon dioxide

但是和水不同的是 液态的二氧化硅

does not reform into a crystal solid when it cools.

冷却之后不会形成固态晶体

Instead, as the molecules lose energy,

相反 当分子失去能量后

they are less and less able

它们就更不太可能

to move into an ordered position,

移动形成一个有秩序的状态

and the result is what is called an amorphous solid.

这样的结果就是人们所说的非晶型固体

A solid material with the chaotic structure of a liquid,

一种具有混乱液体结构的固态物质

which allows the molecules to freely fill in any gaps.

使得分子可以自由填补任何缝隙

This makes the surface of glass uniform

这样就让玻璃表面

on a microscopic level,

在微观层面上是一致的

allowing light to strike it

光可以穿透它

without being scattered in different directions.

但不会散射出去

But this still doesn't explain

但是这还是不能解释

why light is able to pass through glass

为什么光可以穿透玻璃

rather than being absorbed as with most solids.

而不是像其他大多固体那样被吸收

For that, we need to go all the way down

关于这个 我们需要进一步谈论到

to the subatomic level.

亚原子层面上

You may know that an atom consists of a nucleus

你或许知道原子是由原子核

with electrons orbiting around it,

以及围绕着它的电子共同形成的

but you may be surprised to know

但是你有可能很意外的发现

that it's mostly empty space.

它的大部分体积都是空的

In fact, if an atom were the size of a sports stadium,

事实上 如果把一个原子比作一座体育场那么大

the nucleus would be like a single pea in the center,

那么原子核可能就是体育场中心的一颗豆子

while the electrons would be like grains of sand

而中子就像是沙粒

in the outer seats.

环绕于四周的座位上

That should leave plenty of space

这样一来，就会留有大量的缝隙

for light to pass through

让光可以穿过它

without hitting any of these particles.

却不会碰到其他颗粒

So the real question is not

所以真正的问题并不是

why is glass transparent,

为什么玻璃是透明的

but why aren't all materials transparent?

而是为什么所有物质都不透明？

The answer has to do with the different energy levels

答案可以归结于与原子内中子所拥有的

that electrons in an atom can have.

不同能级有关

Think of these as different rows of seats

若把它们视为体育场里

in the stadium stands.

一排排的座位

An electron is initially assigned to sit in a certain row,

一个电子首先被安排到一个固定的座位

but it could jump to a better row,

但是它可以跳到另一个更好的座位

if it only had the energy.

只要它有足够的能量

As luck would have it,

如果幸运

absorbing one of those light photons

吸收一个穿过这个原子的光子

passing through the atom can provide

刚好可以提供

just the energy the electron needs.

电子所需要的能量

But there's a catch.

但有个问题

The energy from the photon

来自光子的能量

has to be the right amount

必须正好合适

to get an electron to the next row.

才能使得电子跳到下一排

Otherwise, it will just let the photon pass by,

否则 光子就会穿过这些电子

and it just so happens that in glass,

就像光穿过玻璃一样

the rows are so far apart

排与排分开的太远

that a photon of visible light

以至于可见光的光子

can't provide enough energy for an electron

不能提供足够能量让电子

to jump between them.

在两排之间跳动

Photons from ultraviolet light, on the other hand,

但另一方面 紫外线光子

give just the right amount of energy,

刚好可以提供足够能量

and are absorbed,

进而被吸收

which is why you can't get a suntan through glass.

这就是为什么透过玻璃你不会被晒黑的原因

This amazing property of being both

这种既是固体又是透明状的特性

solid and transparent has given glass many uses

让玻璃在几个世纪以来

throughout the centuries.

得到了大量的应用

From windows that let in light

从可以让光照入

while keeping out the elements,

却又能把其他物质挡在外面的窗户

to lenses that allow us to see both

到能让我们同时看到

the vast worlds beyond our planet,

地球以外的广袤星空

and the tiny ones right around us.

以及眼前的微小世界的镜片

It is hard to imagine

很难想象

modern civilization without glass.

没有玻璃的现代文明会是怎样

And yet for such an important material

但是对于这样如此重要的物质

we rarely think about glass and its impact.

我们却很少思考它以及它的作用

It is precisely because the most important

这恰恰是因为玻璃最重要的

and useful quality of glass is

以及最有用的特质是

being featureless and invisible

使其变得无特征并不可见

that we often forget that it's even there.

以至于我们都忘了它的存在