How quantum mechanics explains global warming - Lieven Scheire

翻译人员: Xiangyu Zheng 校对人员: Shan Liu

You've probably heard that

你可能听说过

carbon dioxide is warming the Earth,

二氧化碳正在让地球变暖

but how does it work?

但这是什么原理呢？

Is it like the glass of a greenhouse

二氧化碳像是温室的玻璃？

or like an insulating blanket?

或者像是隔热的毛毯？

Well, not entirely.

其实不全是这样。

The answer involves a bit

答案关系到一些

of quantum mechanics, but don't worry,

量子力学的知识，但是不用担心

we'll start with a rainbow.

让我们从彩虹说起

If you look closely at sunlight separated

如果你透过三棱镜

through a prism,

仔细观察被分散的阳光

you'll see dark gaps where bands of color went missing.

你会看到光谱中有一些暗掉的缺口 一部分颜色的波段消失了

Where did they go?

它们去哪里了？

Before reaching our eyes,

在到达我们的眼睛之前

different gases absorbed those

很多气体就已经吸收掉

specific parts of the spectrum.

波谱中特定的一些频段

For example, oxygen gas snatched up

例如，氧气夺走了

some of the dark red light,

一些深红色光线

and sodium grabbed two bands of yellow.

钠夺取了黄色的两个波段

But why do these gases absorb

但为什么这些气体会

specific colors of light?

吸收特定颜色的光呢？

This is where we enter the quantum realm.

我们现在就要进入量子学领域了

Every atom and molecule has a set number

每个原子和分子都有

of possible energy levels for its electrons.

一定数量的电子能量等级

To shift its electrons from the ground state

使电子从基态

to a higher level,

跃迁到一个更高的能级

a molecule needs to gain a certain amount of energy.

分子需要获得一个特定量的能量

No more, no less.

不能多，也不能少

It gets that energy from light,

分子从光线中获得这种能量

which comes in more energy levels than you could count.

光线里含有数不胜数的能量层级

Light consists of tiny particles called photons

光由被称为“光子”的微小粒子组成

and the amount of energy in each photon

每个光子里储存的能量

corresponds to its color.

与其颜色对应

Red light has lower energy and longer wavelengths.

红色光线能量较低，波长较长

Purple light has higher energy and shorter wavelengths.

紫色光线能量较高，波长较短

Sunlight offers all the photons of the rainbow,

阳光提供了彩虹里所有颜色的光子

so a gas molecule can choose

所以一个气体分子可以选择

the photons that carry the exact amount of energy

带有它们所需的特定能量值的光子

needed to shift the molecule to

用以把分子提升到

its next energy level.

下一个能级

When this match is made,

匹配上之后

the photon disappers as the molecule

光子将消失，因为分子

gains its energy,

获取了它的能量

and we get a small gap in our rainbow.

从而造成了光谱里的缺口

If a photon carries too much or too little energy,

如果一个光子携带的能量太多或太少

the molecule has no choice but

分子就只好

to let it fly past.

让它飞过

This is why glass is transparent.

这就是玻璃透明的原因

The atoms in glass do not pair well

玻璃里的原子

with any of the energy levels in visible light,

和可见光里的波段不匹配

so the photons pass through.

所以这些光子全部直接通过

So, which photons does carbon dioxide prefer?

那么，二氧化碳选择吸收哪些光子呢？

Where is the black line in our rainbow

彩虹光谱中的哪一条黑线

that explains global warming?

能解释全球变暖呢？

Well, it's not there.

其实，不在那儿

Carbon dioxide doesn't absorb light directly

二氧化碳不直接从阳光中

from the Sun.

吸收光线

It absorbs light from a totally

它吸收的光线来自一个

different celestial body.

完全不同的天体

One that doesn't appear to be emitting light at all:

一个看起来根本不发光的天体：

Earth.

地球

If you're wondering why our planet

如果你在想为什么我们的星球

doesn't seem to be glowing,

看起来不发光

it's because the Earth doesn't emit visible light.

那是因为地球不发射可见光

It emits infared light.

它发射的是红外光

The light that our eyes can see,

我们眼睛能看得见的光

including all of the colors of the rainbow,

包括彩虹里的所有颜色

is just a small part of the larger spectrum

都只是电磁辐射大光谱里的

of electromagnetic radiation,

一小部分

which includes radio waves, microwaves,

大光谱里有无线电波，微波

infrared, ultraviolet, x-rays,

红外线，紫外线，X射线

and gamma rays.

和伽马射线

It may seem strange to think of these things as light,

把这些都当成是光线可能有点奇怪

but there is no fundamental difference

但是可见光和电磁射线之间

between visible light and other electromagnetic radiation.

没有根本的区别

It's the same energy,

它们都是能量

but at a higher or lower level.

只不过在能级上有高低之分

In fact, it's a bit presumptuous to define

其实，我们用自身的局限来定义“可见光”

the term visible light by our own limitations.

是有点自大的

After all, infrared light is visible to snakes,

毕竟，蛇类看得见红外线

and ultraviolet light is visible to birds.

鸟类看得见紫外线

If our eyes were adapted to see light of

如果我们的眼睛能看见1900兆赫的光线

1900 megahertz, then a mobile phone

那么一个移动电话

would be a flashlight,

将会变成手电

and a cell phone tower

而一个手机信号塔

would look like a huge lantern.

将看起来像个大灯笼

Earth emits infrared radiation

地球发出红外射线

because every object with a temperature

因为每个温度在绝对零度之上的物体

above absolute zero will emit light.

都会发出光线

This is called thermal radiation.

这被称作“热辐射”

The hotter an object gets,

一个物体越热

the higher frequency the light it emits.

它发出的光线频率越高

When you heat a piece of iron,

当你加热铁的时候

it will emit more and more frequencies of infrared light,

它将会发出越来越高频率的红外光

and then, at a temperature of around 450 degrees Celsius,

然后，当温度达到450摄氏度时

its light will reach the visible spectrum.

它发出的光将达到可见光范围

At first, it will look red hot.

刚开始，它看起来是赤热的红色

And with even more heat,

得到更多热量时

it will glow white

它发的光将变白

with all of the frequencies of visible light.

发出可见光波段里所有的光

This is how traditional light bulbs

这是传统灯泡的

were designed to work

设计原理

and why they're so wasteful.

也是为什么它们如此浪费能源

95% of the light they emit is invisible to our eyes.

它们发出的光中95%都是我们眼睛看不见的光

It's wasted as heat.

它以热量的形式浪费掉了

Earth's infrared radiation would escape to space

如果我们的大气层中

if there weren't greenhouse gas molecules

没有温室气体分子的话

in our atmophere.

地球的红外射线会逃到太空中

Just as oxygen gas prefers the dark red photons,

就像氧气偏爱深红色光子一样

carbon dioxide and other greenhouse gases

二氧化碳和其它温室气体

match with infrared photons.

和红外线光子匹配

They provide the right amount of energy

它们提供了正好合适的能量

to shift the gas molecules into their higher energy level.

用来使气体分子升到它们更高一层的能级

Shortly after a carbon dioxide molecule

当一个二氧化碳分子

absorbs an infrared photon,

吸收了红外光子之后

it will fall back to its previous energy level,

不久它便会回到之前的能级

and spit a photon back out in a random direction.

并分离出一个光子，以随机的方向射出

Some of that energy then returns

这些能量的一部分

to Earth's surface,

就返回了地球表面

causing warming.

导致变暖

The more carbon dioxide in the atmosphere,

大气层里的二氧化碳越多

the more likely that infrared photons

红外光子反回到地球表面的

will land back on Earth

可能性就越大

and change our climate.

使我们的气候随之改变