But look deep into the atomic structure of any of them,

但深入地以原子結構的角度來看它們

and you'll see a world in constant flux.

那你將會看到一個不斷擾動的世界

Stretching,

延展

contracting,

收縮

springing,

彈跳

jittering,

抖動

drifting atoms everywhere.

飄移的原子到處都是

And though that movement may seem chaotic, it's not random.

看到這種種的移動你可能以為它們是亂動的，但它們並不是隨機在動的

Atoms that are bonded together,

幾乎所有的物質都是藉由

and that describes almost all substances,

原子的鍊結組合而成

move according to a set of principles.

它們是遵照一套規則在移動的

For example, take molecules, atoms held together by covalent bonds.

例如，拿分子來說，它們是原子們藉由共價鍵鍊結在一起

There are three basic ways molecules can move:

分子有三種基本方式來移動:

rotation,

旋轉

translation,

平移

and vibration.

和振動

Rotation and translation move a molecule in space

旋轉和平移是在同一空間上讓一個分子移動

while its atoms stay the same distance apart.

原子彼此間的距離不會改變

Vibration, on the other hand, changes those distances,

振動，換句話說，就是改變原子之間的距離

actually altering the molecule's shape.

事實上這還改變了分子的形狀

For any molecule, you can count up the number of different ways it can move.

就任何分子來說，我們都可以將其所有不同的移動方式加總起來

That corresponds to its degrees of freedom,

而這跟它們裡頭原子組成結構

which in the context of mechanics

的自由度有關係

basically means the number of variables we need to take into account

基本上意思就是我們要去解析整個系統

to understand the full system.

需要考慮到的變因數目

Three-dimensional space is defined by x, y, and z axes.

三度空間裡定義了x，y和z軸

Translation allows the molecule to move in the direction of any of them.

換位就是分子能夠在任意一軸上移動

That's three degrees of freedom.

這樣就有三個自由度了

It can also rotate around any of these three axes.

它們也可以沿著這三個軸轉動

That's three more,

這樣又有三個了

unless it's a linear molecule, like carbon dioxide.

除非是像二氧化碳這樣形狀像是直線的分子

There, one of the rotations just spins the molecule around its own axis,

你看，其轉動只是在相對應的軸上旋轉

which doesn't count because it doesn't change the position of the atoms.

因為這並沒有改變原子在其軸上的位置，所以不能算是一個自由度

Vibration is where it gets a bit tricky.

振動就有一點難懂了

Let's take a simple molecule, like hydrogen.

我們就拿最簡單的氫分子來說

The length of the bond that holds the two atoms together is constantly changing

兩個氫原子間鍊結的長度是一直在改變的

as if the atoms were connected by a spring.

就好像兩原子間連結了一條彈簧一樣

That change in distance is tiny, less than a billionth of a meter.

但這距離的改變是非常微小的，比一奈米還小

The more atoms and bonds a molecule has, the more vibrational modes.

一個分子裡有越多原子鍊結在一起，那們就有越多的振動方式

For example, a water molecule has three atoms:

例如，一個由三個原子組成的水分子:

one oxygen and two hydrogens, and two bonds.

一個氧原子和兩個氫原子，和兩條鍊結

That gives it three modes of vibration:

這讓水分子有三種振動方式

symmetric stretching,

對稱的伸縮

asymmetric stretching,

不對稱的伸縮

and bending.

和彎曲

More complicated molecules have even fancier vibrational modes,

更複雜的分子甚至有令人意想不到的振動方式

like rocking,

像是搖動

wagging,

擺動

and twisting.

和扭轉

If you know how many atoms a molecule has, you can count its vibrational modes.

如果你知道一個分子由多少原子組成，那麼你就可以數出它有多少振動方式

Start with the total degrees of freedom,

先從總自由度開始算

which is three times the number of atoms in the molecule.

算法是三乘上一個分子內的原子總數

That's because each atom can move in three different directions.

這是因為每個原子都可以在三度空間中沿著三個軸向移動

Three of the total correspond to translation

平移則共有三種方式

when all the atoms are going in the same direction.

因為平移時所有原子都往同一方向移動

And three, or two for linear molecules, correspond to rotations.

然後有三種，直線形狀的分子則有兩種，轉動方式

All the rest, 3N-6 or 3N-5 for linear molecules,

所以其它，3乘上原子數目減去6，直線分子則是減去5，的移動數目

are vibrations.

就是所有振動的方式了

So what's causing all this motion?

所以，到底是甚麼原因造成這些運動呢？

Molecules move because they absorb energy from their surroundings,

分子的運動是因為吸收了環境中的能量

mainly in the form of heat or electromagnetic radiation.

主要是吸收了熱能或是電磁輻射

When this energy gets transferred to the molecules,

當這些能量轉移到分子上

they vibrate,

分子就會振動

rotate,

轉動

or translate faster.

或是快速平移

Faster motion increases the kinetic energy of the molecules and atoms.

快速的運動使得分子和原子的動能增加

We define this as an increase in temperature and thermal energy.

我們知道這會使得溫度和熱能上升

This is the phenomenon your microwave oven uses to heat your food.

我們的微波爐就是利用這種現象來加熱食物

The oven emits microwave radiation, which is absorbed by the molecules,

微波爐發出的微波輻射會被食物分子吸收

especially those of water.

特別是水分子

They move around faster and faster,

它們移動越來越快

bumping into each other and increasing the food's temperature and thermal energy.

並且會撞在一起，這會讓食物的溫度和其熱能升高

The greenhouse effect is another example.

溫室效應則是另一個例子

Some of the solar radiation that hits the Earth's surface

有些太陽輻射照射到地球表面時

is reflected back to the atmosphere.

會被反射回大氣層

Greenhouse gases, like water vapor and carbon dioxide absorb this radiation

溫室氣體，像是水蒸氣和二氧化碳吸收了這些輻射之後

and speed up.

就加速移動了起來

These hotter, faster-moving molecules emit infrared radiation in all directions,

這些較熱，快速移動的分子會向不同方向發射出遠紅外線

including back to Earth, warming it.

包含向著地球發射，這樣就造成暖化了

Does all this molecular motion ever stop?

這些分子的運動有沒有可能停止呢？

You might think that would happen at absolute zero,

你可能會認為在絕對零度下，這已是宇宙中的最低溫了

the coldest possible temperature.

這些運動會停止

No one's ever managed to cool anything down that much,

目前還沒有人有辦法讓溫度達到如此的低溫

but even if we could,

但就算我們有辦法

molecules would still move due to a quantum mechanical principle

分子仍會依量子動力學的規則來運動

called zero-point energy.

稱為零點能量

In other words, everything has been moving since the universe's very first moments,

換句話說，所有物體從宇宙初始就一直在運動

and will keep going long, long after we're gone.

而且還會一直保持運動狀態，直到人類消失的未來