How quantum mechanics explains global warming - Lieven Scheire

譯者: Aaron Shoo 審譯者: Adrienne Lin

You've probably heard that

你可能有聽說，

carbon dioxide is warming the Earth,

二氧化碳正在暖化地球。

but how does it work?

但是怎麼做到的呢？

Is it like the glass of a greenhouse

它們是像溫室的玻璃，

or like an insulating blanket?

還是像隔熱毯？

Well, not entirely.

嗯，也不全然是。

The answer involves a bit

實際情況涉及一點點「量子力學」。

of quantum mechanics, but don't worry,

不過別緊張，

we'll start with a rainbow.

讓我們先從彩虹開始。

If you look closely at sunlight separated

如果仔細看太陽光 被三稜鏡折射出的光譜，

through a prism,

你會看見色塊之間， 有黑色的間隔。

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

Where did they go?

那些顏色跑去哪了？

Before reaching our eyes,

在色光進入我們的眼睛前，

different gases absorbed those

空氣中的氣體分子

就把特定的色光吸收了。

specific parts of the spectrum.

For example, oxygen gas snatched up

比如說，

氧氣會把暗紅光吃掉；

some of the dark red light,

and sodium grabbed two bands of yellow.

鈉會吸掉一部分黃光。

But why do these gases absorb

可是為什麼氣體要吸收色光呢？

specific colors of light?

This is where we enter the quantum realm.

這就要靠量子力學解釋了。

Every atom and molecule has a set number

每個原子或分子，

都有固定的「能階」，

of possible energy levels for its electrons.

容納一定的電子。

To shift its electrons from the ground state

「基態」時的電子要從低能階

to a higher level,

「躍遷」到高能階時，

a molecule needs to gain a certain amount of energy.

分子必須要吸收特定的能量。

No more, no less.

不能太多也不能太少。

It gets that energy from light,

它從光獲取能量，

which comes in more energy levels than you could count.

這些能量可以帶來 你意想不到的能階改變。

Light consists of tiny particles called photons

光中攜帶稱為「光子」的粒子，

and the amount of energy in each photon

不同色光的光子帶有不同能量。

corresponds to its color.

紅光的能量低、波長長，

Red light has lower energy and longer wavelengths.

Purple light has higher energy and shorter wavelengths.

紫光能量高、波長短。

Sunlight offers all the photons of the rainbow,

陽光包含了所有色光的光子，

so a gas molecule can choose

所以氣體可以自由選擇，

the photons that carry the exact amount of energy

分子要躍遷到更高能階時

needed to shift the molecule to

所需的光子和能量。

its next energy level.

When this match is made,

當光子的能量被分子吸收，

the photon disappers as the molecule

光子就會消失，

gains its energy,

and we get a small gap in our rainbow.

我們就只看得到色塊間的黑線。

If a photon carries too much or too little energy,

如果光子攜帶太多或太少的能量，

the molecule has no choice but

分子就會放過它、隨它去。

to let it fly past.

所以玻璃是透明的，

This is why glass is transparent.

The atoms in glass do not pair well

因為玻璃裡的原子在可見光中，

with any of the energy levels in visible light,

老找不到適合的光子，

so the photons pass through.

只好讓它們都通過。

So, which photons does carbon dioxide prefer?

那二氧化碳喜歡哪種光子呢？

Where is the black line in our rainbow

彩虹光譜中的哪條黑線，

that explains global warming?

代表全球暖化的進行呢？

Well, it's not there.

嗯，一條也不是。

Carbon dioxide doesn't absorb light directly

因為二氧化碳不從日光 直接吸收光子，

from the Sun.

而是吸收另一個天體的光，

It absorbs light from a totally

different celestial body.

一個不太算是發光天體的星球：

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

Earth.

地球。

If you're wondering why our planet

可曾想過為什麼

doesn't seem to be glowing,

地球不像恆星閃閃發光？

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

那是因為地球不發出可見光，

只射出紅外線。

It emits infared light.

The light that our eyes can see,

我們肉眼可見的光，

including all of the colors of the rainbow,

包括彩虹中的所有色光，

is just a small part of the larger spectrum

只是廣大「電磁輻射」

of electromagnetic radiation,

光譜中的一小部分。

which includes radio waves, microwaves,

另外還有無線電波、微波、

infrared, ultraviolet, x-rays,

紅外線、紫外線、X光和伽瑪射線。

and gamma rays.

你可能覺得這些不是光，

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

but there is no fundamental difference

但它們本質上並沒有不同；

between visible light and other electromagnetic radiation.

可見光和其他電磁輻射，

同為能量的一種，

It's the same energy,

差別只在能量高低。

but at a higher or lower level.

In fact, it's a bit presumptuous to define

再說，

用人類的眼光去定義 可見光也有失公允。

the term visible light by our own limitations.

After all, infrared light is visible to snakes,

因為蛇其實看得見紅外線，

and ultraviolet light is visible to birds.

鳥類也看得到紫外線。

If our eyes were adapted to see light of

如果我們的眼睛 能看見1900兆赫的光，

1900 megahertz, then a mobile phone

那手機就會像一支支手電筒，

would be a flashlight,

and a cell phone tower

基地台就會像大燈籠。

would look like a huge lantern.

Earth emits infrared radiation

地球發出紅外線，

because every object with a temperature

因為任何有溫度的物體 都會「發光」，

above absolute zero will emit light.

This is called thermal radiation.

就是所謂的「熱輻射」。

The hotter an object gets,

當物體的溫度越高，

the higher frequency the light it emits.

發出的光頻率就越高。

When you heat a piece of iron,

當你燒熱一塊鐵，

it will emit more and more frequencies of infrared light,

它會發出越來越高頻的紅外線。

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

當溫度達攝氏450度左右，

its light will reach the visible spectrum.

就會轉變為可見光。

一開始我們會看到燒得通紅，

At first, it will look red hot.

And with even more heat,

當溫度持續上升，

it will glow white

開始發出白光，

with all of the frequencies of visible light.

也就是所有的可見光。

這就是傳統燈泡的原理，

This is how traditional light bulbs

were designed to work

and why they're so wasteful.

而且很耗能的原因。

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

發出95%以上的光

是我們肉眼不可見的，

It's wasted as heat.

只會一直散發熱能。

Earth's infrared radiation would escape to space

如果大氣中沒有溫室氣體，

if there weren't greenhouse gas molecules

地球的紅外線就會跑到宇宙。

in our atmophere.

就像氧氣喜歡暗紅光，

Just as oxygen gas prefers the dark red photons,

carbon dioxide and other greenhouse gases

二氧化碳和其他溫室氣體

match with infrared photons.

會和紅外線的光子結合。

它們提供剛剛好的能量

They provide the right amount of energy

to shift the gas molecules into their higher energy level.

讓氣體分子轉換到更高能階。

Shortly after a carbon dioxide molecule

當二氧化碳分子吸收紅外線光子，

absorbs an infrared photon,

it will fall back to its previous energy level,

它會降回原來的能階，

and spit a photon back out in a random direction.

再往隨機方向丟出一顆光子。

Some of that energy then returns

部分的能量又會回到地球，

to Earth's surface,

造成暖化。

causing warming.

The more carbon dioxide in the atmosphere,

大氣中的二氧化碳越多，

the more likely that infrared photons

紅外線光子就越會被留在地球，

will land back on Earth

and change our climate.

並改變我們的氣候。