Why is glass transparent? - Mark Miodownik

玻璃為什麼是透明的呢? - Mark Miodownik

譯者: Bernice Huang 審譯者: Regina Chu

Take a look out your window,

朝窗外看看，

put on your glasses if you wear them.

如果你有眼鏡，把它戴上

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

你可能也需要一副望遠鏡

or a magnifying lens.

或是放大鏡

Now, what do you see?

那麼，現在你看到了什麼？

Well, whatever it is,

不論是什麼

it's not the multiple layers of glass

你眼前出現的

right in front of you.

總不會是一層層的玻璃

But have you ever wondered

你曾否想過

how something so solid can be so invisible?

這麼堅固的東西 怎麼可能如此剔透？

To understand that,

要了解其中原因

we have to understand what glass actually is,

我們得先了解玻璃究竟是什麼

and where it comes from.

以及它是從哪裡來的

It all begins in the Earth's crust,

這一切都得從地殼開始說起

where the two most common elements are

組成地殼最主要的兩種成分是

silicon and oxygen.

矽和氧

These react together to form silicon dioxide,

這兩種成分經由 化學變化後形成二氧化矽

whose molecules arrange themselves

當中的分子排列

into a regular crystalline form known as quartz.

組成規則的晶體 也就是我們所知的石英

Quartz is commonly found in sand,

石英在砂子裡很常見

where it often makes up most of the grains

它是常見組成砂粒

and is the main ingredient in most type of glass.

以及大部分玻璃種類的主要成分

Of course, you probably noticed that glass

當然，你或許已經注意到

isn't made of multiple tiny bits of quartz,

玻璃並不是由許多 細小的石英顆粒組成的

and for good reason.

這背後有其道理在

For one thing, the edges of the rigidly formed grains

首先，當光線照射到砂粒粗糙的邊緣

and smaller defects within the crystal structure

以及晶體結構中的微小瑕疵時

reflect and disperse light that hits them.

會向四面八方反射分散

But when the quartz is heated high enough

但若石英加熱到一定溫度時

the extra energy makes the molecules vibrate

多餘的能量促使石英分子振動

until they break the bonds holding them together

直到打斷分子之間的鍵結

and become a flowing liquid,

而變成流動的液體

the same way that ice melts into water.

就如同冰溶化成為水一般

Unlike water, though, liquid silicon dioxide

但不同於水的是，液態的二氧化矽

does not reform into a crystal solid when it cools.

冷卻後不會變回固態的晶體

Instead, as the molecules lose energy,

反之，當二氧化矽分子的能量減弱

they are less and less able

他們越來越不可能

to move into an ordered position,

回復到規律整齊的排列

and the result is what is called an amorphous solid.

結果形成所謂的非晶態固體

A solid material with the chaotic structure of a liquid,

具有液體般混亂結構的固體

which allows the molecules to freely fill in any gaps.

其中的分子可自由移動 填充任何的間隙

This makes the surface of glass uniform

這使玻璃表面 即使由微觀的角度看來

on a microscopic level,

也是平整的

allowing light to strike it

因此光線照射上去

without being scattered in different directions.

也不會四處散射

But this still doesn't explain

但這仍然不能解釋

why light is able to pass through glass

為何光線能夠穿透玻璃

rather than being absorbed as with most solids.

而不是像其他固體一樣被吸收

For that, we need to go all the way down

為此，我們得進入

to the subatomic level.

原子內的世界來了解

You may know that an atom consists of a nucleus

你可能知道 一個原子的組成包含一個原子核

with electrons orbiting around it,

以及若干圍繞在周圍的電子

but you may be surprised to know

但你可能會很驚訝地發現

that it's mostly empty space.

原子裡大部分是空蕩蕩的

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

事實上，如果將原子 比喻成一個體育場這麼大

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

原子核就像是一顆在場中央的豌豆

while the electrons would be like grains of sand

而電子便是

in the outer seats.

在場外圍座位的砂粒

That should leave plenty of space

因此

for light to pass through

光線有大量的空間能夠穿透

without hitting any of these particles.

而不會撞擊到這些粒子

So the real question is not

所以真正的問題並不是

why is glass transparent,

為什麼玻璃是透明的

but why aren't all materials transparent?

而是為什麼其他的材料不是透明的？

The answer has to do with the different energy levels

這個問題的答案

that electrons in an atom can have.

與原子內的電子 具有不同程度的能量有關

Think of these as different rows of seats

你可以把它想成是體育場裡

in the stadium stands.

一排排的座位

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

一開始，一顆電子 被指定坐在某一排

but it could jump to a better row,

但若是它有足夠的能量

if it only had the energy.

就可以跳到比較好的座位

As luck would have it,

如果幸運的話

absorbing one of those light photons

吸收穿過原子的光子

passing through the atom can provide

正好可以提供

just the energy the electron needs.

這個電子所需的能量

But there's a catch.

不過還有一個問題

The energy from the photon

這個光子提供的能量

has to be the right amount

必須正好等於

to get an electron to the next row.

把電子送到下一排所需的能量

Otherwise, it will just let the photon pass by,

不然，電子就只得任由光子通過

and it just so happens that in glass,

這就恰如發生在玻璃當中

the rows are so far apart

由於排與排之間相隔非常遙遠

that a photon of visible light

可見光的光子

can't provide enough energy for an electron

無法提供電子足夠的能量

to jump between them.

在排與排之間跳躍

Photons from ultraviolet light, on the other hand,

另一方面，紫外線的光子

give just the right amount of energy,

便提供恰恰好的能量

and are absorbed,

而被吸收

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

這就是為什麼隔著玻璃 皮膚不會被曬黑的原因

This amazing property of being both

玻璃這種兼具堅固而透明

solid and transparent has given glass many uses

令人驚歎的特質 賦予了玻璃多種用途

throughout the centuries.

達數世紀之久

From windows that let in light

從能透入光線

while keeping out the elements,

卻將其他元素阻隔在外的窗戶

to lenses that allow us to see both

到能讓我們看到

the vast worlds beyond our planet,

地球以外的浩瀚世界

and the tiny ones right around us.

以及我們週遭的渺小事物

It is hard to imagine

實在很難想像

modern civilization without glass.

沒有玻璃的現代文明

And yet for such an important material

對於玻璃這麼重要的一個物質

we rarely think about glass and its impact.

我們卻鮮少想到它及其影響

It is precisely because the most important

就是因為玻璃最重要的

and useful quality of glass is

也最有用的特質就是

being featureless and invisible

平凡而且看不見

that we often forget that it's even there.

所以我們常常忘記它的存在