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The coldest materials in the world aren't in Antarctica.
史上最寒冷的物体并非在南极。
They're not at the top of Mount Everest or buried in a glacier.
它们既不在珠穆朗玛峰上，也不藏在冰川之下。
They're in physics labs: clouds of gases held just fractions of a degree above absolute zero.
它们存在于实验室中：这些一团团的气体的温度只比绝对零度高零点几度。
That's 395 million times colder than your refrigerator,
这个温度比你家里的冰箱还要冷39.5亿倍，
100 million times colder than liquid nitrogen, and 4 million times colder than outer space.
比液态氮冷10亿倍，以及比外太空冷4百万倍。
Temperatures this low give scientists a window into the inner workings of matter, and allow engineers to build incredibly sensitive instruments
如此低的温度让科学家有机会一窥物质的内部运作，也让工程师能够制造敏感度极高的仪器，
that tell us more about everything from our exact position on the planet to what's happening in the farthest reaches of the universe.
这些仪器可丰富我们的知识，比如更精确地确定我们在地球的位置或了解宇宙远方所发生的事。
How do we create such extreme temperatures?
我们如何才能创造出这种极端的温度呢？
In short, by slowing down moving particles.
简单来说，只要降低运动粒子的速度。
When we're talking about temperature, what we're really talking about is motion.
当我们谈及温度的时候，我们实际上是在讨论运动。
The atoms that make up solids, liquids, and gases are moving all the time.
组成固体、液体以及气体的粒子，一直处于运动之中。
When atoms are moving more rapidly, we perceive that matter as hot.
当原子运动快时，我们感受到物质是热的。
When they're moving more slowly, we perceive it as cold.
当原子运动慢时，我们则觉得是冷的。
To make a hot object or gas cold in everyday life, we place it in a colder environment, like a refrigerator.
日常生活中为了让热的固体或气体降温，我们将其放在更冷的环境中，比如冰箱里。
Some of the atomic motion in the hot object is transferred to the surroundings, and it cools down.
热物体中的原子运动被部分的传递到周围环境里，然后它就冷下来了。
But there's a limit to this: even outer space is too warm to create ultra-low temperatures.
但是这有一个限制：即使是外太空也太温暖了，无法创造出极端低的温度。
So instead, scientists figured out a way to slow the atoms down directly -- with a laser beam.
所以相反，科学家们找到了一个直接降低原子速度的方法--用激光束。
Under most circumstances, the energy in a laser beam heats things up.
在大多数情况下，激光束中的能量会加热物体。
But used in a very precise way, the beam's momentum can stall moving atoms, cooling them down.
但是如果被用以特定的方式，激光束的动量可以阻止运动的原子，从而降低温度。
That's what happens in a device called a magneto-optical trap.
这就是在一种名叫磁场-光学陷阱的仪器中发生的事情。
Atoms are injected into a vacuum chamber, and a magnetic field draws them towards the center.
原子被注入真空的盒子中，然后磁场会将它们向中间吸引。
A laser beam aimed at the middle of the chamber
一束激光束正对盒子的中央，
is tuned to just the right frequency that an atom moving towards it will absorb a photon of the laser beam and slow down.
它的频率被调的正好可以让向其运动的原子吸收一个激光束光子，进而减速。
The slow down effect comes from the transfer of momentum between the atom and the photon.
减速效果来自原子和光子之间的动量转换。
A total of six beams, in a perpendicular arrangement, ensure that atoms traveling in all directions will be intercepted.
六束激光，以垂直的布局保证向各个方向运动的原子都会被拦截。
At the center, where the beams intersect, the atoms move sluggishly, as if trapped in a thick liquid
在光束交汇的中央，原子运动的格外缓慢，就像陷入了粘稠的液体，
an effect the researchers who invented it described as "optical molasses."
该效果被发现它的研究人员称作“光学糖浆”。
A magneto-optical trap like this can cool atoms down to just a few microkelvins -- about -273 degrees Celsius.
像这样的磁场-光学陷阱可以将原子冷却到零点几开尔文--大概-273摄氏度。
This technique was developed in the 1980s,
这项技术于上世纪八十年代被发展出来，
and the scientists who'd contributed to it won the Nobel Prize in Physics in 1997 for the discovery.
对此有贡献的科学家们在1997年因为他们的发现赢得了诺贝尔物理学奖。
Since then, laser cooling has been improved to reach even lower temperatures.
自此，激光冷却进一步完善，可以达到更低的温度。
But why would you want to cool atoms down that much?
但是为什么要把原子冷却到如此之低的温度呢？
First of all, cold atoms can make very good detectors.
首先，极寒原子可以成为很好的检测物质。
With so little energy, they're incredibly sensitive to fluctuations in the environment.
它们拥有很少的能量，对周围的波动异常敏感。
So they're used in devices that find underground oil and mineral deposits,
所以它们是被用在寻找地下石油和矿藏的装置之中，
and they also make highly accurate atomic clocks, like the ones used in global positioning satellites.
它们也能制造高精度原子钟，例如全球定位卫星中的原子钟。
Secondly, cold atoms hold enormous potential for probing the frontiers of physics.
其次，极寒原子蕴藏着探索物理学前沿的巨大潜力。
Their extreme sensitivity makes them candidates to be used to detect gravitational waves in future space-based detectors.
它们极端的敏感性使他们可以在未来的空间探测仪中被用来探测引力波。
They're also useful for the study of atomic and subatomic phenomena,
它们对原子和次原子现象的研究也有帮助，
which requires measuring incredibly tiny fluctuations in the energy of atoms.
这种研究需要测度原子能量的极其微小的波动。
Those are drowned out at normal temperatures, when atoms speed around at hundreds of meters per second.
原子在常温中被射出，此时原子速度大概在每秒几百米。
Laser cooling can slow atoms to just a few centimeters per second -- enough for the motion caused by atomic quantum effects to become obvious.
激光冷却可以使原子降速到每秒几厘米--对观测由原子量子效果造成的运动够用了。
Ultracold atoms have already allowed scientists to study phenomena like Bose-Einstein condensation,
极寒原子已经帮助科学家研究了诸如玻色–爱因斯坦凝聚等现象，
in which atoms are cooled almost to absolute zero and become a rare new state of matter.
在该凝聚中原子被降温到接近绝对零度，然后成为一种少见的物质新状态。
So as researchers continue in their quest to understand the laws of physics and unravel the mysteries of the universe,
所以随着研究人员继续试图理解物理学定律并解开宇宙谜题的同时，
they'll do so with the help of the very coldest atoms in it.
他们会需要极寒原子的帮助。
