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But this still doesn't explain why light is able to pass through glass rather than being absorbed as with most solids.
但是這還是不能解釋為什么光可以穿透玻璃而不是像其他大多固體那樣被吸收。
For that, we need to go all the way down to the subatomic level.
關于這個，我們需要進一步談論到亞原子層面上。
You may know that an atom consists of a nucleus with electrons orbiting around it, but you may be surprised to know that it's mostly empty space.
你或許知道原子是由原子核以及圍繞著它的電子共同形成的，但是你有可能很意外的發現它的大部分體積都是空的。
In fact, if an atom were the size of a sports stadium, the nucleus would be like a single pea in the center, while the electrons would be like grains of sand in the outer seats.
事實上，如果把一個原子比作一座體育場那么大，那么原子核可能就是體育場中心的一顆豆子，而中子就像是沙粒環繞于四周的座位上。
That should leave plenty of space for light to pass through without hitting any of these particles.
這樣一來，就會留有大量的縫隙讓光可以穿過它卻不會碰到其他顆粒。
So the real question is not why is glass transparent, but why aren't all materials transparent?
所以真正的問題并不是為什么玻璃是透明的，而是為什么所有物質都不透明？
The answer has to do with the different energy levels that electrons in an atom can have.
答案可以歸結于與原子內電子所擁有的不同能級有關。
Think of these as different rows of seats in the stadium stands.
若把它們視為體育場里一排排的座位。
An electron is initially assigned to sit in a certain row, but it could jump to a better row, if it only had the energy.
一個電子首先被安排到一個固定的座位，但是它可以跳到另一個更好的座位，只要它有足夠的能量。
As luck would have it, absorbing one of those light photons passing through the atom can provide just the energy the electron needs.
如果幸運吸收一個穿過這個原子的光子剛好可以提供電子所需要的能量。
But there's a catch.
但有個問題。
The energy from the photon has to be the right amount to get an electron to the next row.
來自光子的能量必須正好合適才能使得電子跳到下一排。
Otherwise, it will just let the photon pass by, and it just so happens that in glass, the rows are so far apart that a photon of visible light can't provide enough energy for an electron to jump between them.
否則，光子就會穿過這些電子就像光穿過玻璃一樣排與排分開的太遠，以至于可見光的光子不能提供足夠能量讓電子在兩排之間跳動。
Photons from ultraviolet light, on the other hand, give just the right amount of energy, and are absorbed, which is why you can't get a suntan through glass.
但另一方面，紫外線光子剛好可以提供足夠能量進而被吸收，這就是為什么透過玻璃你不會被曬黑的原因。
This amazing property of being both solid and transparent has given glass many uses throughout the centuries.
這種既是固體又是透明狀的特性讓玻璃在幾個世紀以來得到了大量的應用。
From windows that let in light while keeping out the elements, to lenses that allow us to see both the vast worlds beyond our planet, and the tiny ones right around us.
從可以讓光照入卻又能把其他物質擋在外面的窗戶，到能讓我們同時看到地球以外的廣袤星空，以及眼前的微小世界的鏡片。
It is hard to imagine modern civilization without glass.
很難想象沒有玻璃的現代文明會是怎樣。
And yet for such an important material we rarely think about glass and its impact.
但是對于這樣如此重要的物質，我們卻很少思考它以及它的作用。
It is precisely because the most important and useful quality of glass is being featureless and invisible that we often forget that it's even there.
這恰恰是因為玻璃最重要的以及最有用的特質，是使其變得無特征并不可見，以至于我們都忘了它的存在。
