What is the coldest thing in the world? - Lina Marieth Hoyos

譯者: Lilian Chiu 審譯者: Helen Chang

The coldest materials in the world aren’t in Antarctica.

世界上最冷的材料不在南極洲，

They’re not at the top of Mount Everest

也不在聖母峰的頂端

or buried in a glacier.

或埋在冰河當中。

They’re in physics labs:

答案在物理實驗室中：

clouds of gases held just fractions of a degree above absolute zero.

保存在只比絕對零度 再高一點點的氣體雲。

That’s 395 million times colder than your refrigerator,

那種溫度比你的冰箱還要冷 三億九千五百萬倍，

100 million times colder than liquid nitrogen,

比液態氮還要冷一億倍，

and 4 million times colder than outer space.

比外太空還要冷四百萬倍。

Temperatures this low give scientists a window into the inner workings of matter,

這麼低的溫度，可說是一扇窗， 讓科學家能看見物質的內在運作，

and allow engineers to build incredibly sensitive instruments

也讓工程師能建造出 極敏感的儀器，

that tell us more about everything

讓我們能更了解各種事物，

from our exact position on the planet

從我們在地球上的確切位置，

to what’s happening in the farthest reaches of the universe.

到宇宙中最能到達的 最遠之處發生了什麼事。

How do we create such extreme temperatures?

我們要如何創造出 這種極端的溫度？

In short, by slowing down moving particles.

簡言之，就是減慢在移動的微粒。

When we’re talking about temperature, what we’re really talking about is motion.

當我們談到溫度時， 其實我們是在談運動。

The atoms that make up solids,

原子構成固體、

liquids,

液體，

and gases

和氣體，

are moving all the time.

它們時時刻刻都在移動。

When atoms are moving more rapidly, we perceive that matter as hot.

當原子的移動速度更快時， 我們就會覺得該物質很熱。

When they’re moving more slowly, we perceive it as cold.

當原子的速度較慢， 我們就會感到冷。

To make a hot object or gas cold in everyday life,

在日常生活中，若要讓 一個熱的物體或氣體變冷，

we place it in a colder environment, like a refrigerator.

我們會把它放到比較冷的 環境中，比如放入冰箱。

Some of the atomic motion in the hot object is transferred to the surroundings,

在熱物體中的一些原子運動 就會被轉換到周圍環境，

and it cools down.

物體就會冷卻下來。

But there’s a limit to this:

但這有一個限制：

even outer space is too warm to create ultra-low temperatures.

即使是外太空也沒有 冷到可以創造出超低溫。

So instead, scientists figured out a way to slow the atoms down directly –

所以，科學家換了一種方式， 想辦法直接將原子減速，

with a laser beam.

用激光束就可做到。

Under most circumstances,

在大部分的情況下，

the energy in a laser beam heats things up.

激光束中的能量會把東西加溫。

But used in a very precise way,

但若能非常精確地使用它，

the beam’s momentum can stall moving atoms, cooling them down.

激光束的動量可以拖住 移動的原子，讓它們冷卻下來。

That’s what happens in a device called a magneto-optical trap.

有種裝置叫做磁光陷阱， 就是用這個原理。

Atoms are injected into a vacuum chamber,

原子被注入到真空室當中，

and a magnetic field draws them towards the center.

裡面有個磁場會把它們拉向中心。

A laser beam aimed at the middle of the chamber

一道激光束瞄準真空室的中間，

is tuned to just the right frequency

調整到正確的頻率，

that an atom moving towards it will absorb a photon of the laser beam and slow down.

原子會朝激光束移動，吸收 激光束的光子，接著緩慢下來。

The slow down effect comes from the transfer of momentum

這種減速效應， 是來自動量的轉換，

between the atom and the photon.

在原子和光子間的轉換。

A total of six beams, in a perpendicular arrangement,

總共用六道光束， 以垂直方式排列，

ensure that atoms traveling in all directions will be intercepted.

能夠確保向任何方向 移動的原子都會被攔截下來。

At the center, where the beams intersect,

在中心，也就是光束交錯的地方，

the atoms move sluggishly, as if trapped in a thick liquid —

原子緩慢移動，好像被困在 濃稠的液體中似的——

an effect the researchers who invented it described as “optical molasses.”

發明這項效應的研究者 將它稱為「光蜜糖」。

A magneto-optical trap like this

像這樣的磁光陷阱

can cool atoms down to just a few microkelvins —

能將原子冷卻到僅幾 microkelvin （接近絕零度），

about -273 degrees Celsius.

大約是攝氏 -273 度。

This technique was developed in the 1980s,

這項技術是八○年代時 開發出來的，

and the scientists who'd contributed to it

負責開發它的科學家們

won the Nobel Prize in Physics in 1997 for the discovery.

在 1997 年因為這項發現 而贏得了諾貝爾物理獎。

Since then, laser cooling has been improved to reach even lower temperatures.

在那之後，雷射冷卻就一直 被改良，以達到更低的溫度。

But why would you want to cool atoms down that much?

但，為什麼會想要 把原子冷卻到那麼低溫？

First of all, cold atoms can make very good detectors.

首先，冷原子是非常好的偵測器。

With so little energy,

它們的能量非常低，

they’re incredibly sensitive to fluctuations in the environment.

所以會對環境中的波動非常敏感。

So they’re used in devices that find underground oil and mineral deposits,

所以它們會被用在找尋 地底石油以及礦床的裝置中，

and they also make highly accurate atomic clocks,

它們也能被用來製做 極精準的原子鐘，

like the ones used in global positioning satellites.

比如用在全球定位衛星上的鐘。

Secondly, cold atoms hold enormous potential

第二，冷原子有極大的潛能，

for probing the frontiers of physics.

可以探究物理的邊境。

Their extreme sensitivity makes them candidates

它們極度敏感，因此，

to be used to detect gravitational waves in future space-based detectors.

未來的太空探測器會考慮 用它們來偵測重力波。

They’re also useful for the study of atomic and subatomic phenomena,

在研究原子和亞原子現象時， 它們也很有用，

which requires measuring incredibly tiny fluctuations in the energy of atoms.

這類研究需要測量 非常小的原子能量波動。

Those are drowned out at normal temperatures,

常溫下，當原子速度 約為每秒數百公尺時，

when atoms speed around at hundreds of meters per second.

這類波動會被掩蓋而難以測量。

Laser cooling can slow atoms to just a few centimeters per second—

雷射冷卻能讓原子慢下來， 速度變成只有每秒幾公分——

enough for the motion caused by atomic quantum effects to become obvious.

這樣就足以讓原子量子效應 所造成的運動變明顯了。

Ultracold atoms have already allowed scientists to study phenomena

極冷的原子已經讓科學家 可以研究一些現象，

like Bose-Einstein condensation,

比如玻色—愛因斯坦凝聚，

in which atoms are cooled almost to absolute zero

在這種現象中，原子 被冷卻到幾乎是絕對零度，

and become a rare new state of matter.

變成物質的一種罕見新狀態。

So as researchers continue in their quest to understand the laws of physics

研究者還在持續努力 了解物理法則，

and unravel the mysteries of the universe,

試圖解開宇宙的謎，

they’ll do so with the help of the very coldest atoms in it.

這時，最冷的原子 就會是他們的好幫手。