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绝对的寒冷——绝对零度 – 译学馆
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绝对的寒冷——绝对零度

Absolute Cold | Space Time

PBS数字影像工作室制作
[PBS Digital Studios chime]
本期视频由Curiosity Stream平台制作播出
This episode is brought to you by curiosity stream
冬季或许即将来临 不过令人欣慰的是
winter may be coming but be comforted
真正的绝对零度 并不可能存在
true absolute zero is impossible
量子的涨落现象 会让我们的温度 始终都处于绝对零度之上
we’ll always have quantum fluctuations to warm our chilly bones
[太空时间主题音乐]
[Space Time theme music]
热量的本质 表面上看似神秘
the mystical seeming quality of heat
不过就是物质中粒子的运动
is nothing more than the motion of a substance component particles.
而温度 也只是对物质内部动能的一种衡量单位
Temperature is just a measure of internal kinetic energy .
因此 要是内部动能相对缺乏 就会让人感觉到寒冷
So then the feeling of cold is the relative absence of internal kinetic energy.
而要是将温度降得足够低 以至于让所有粒子都停止运动 那么又会怎么样呢?
But what if we reduce temperature so much that all particle motion ceases ?
这样的绝对低温状态 就是开氏温标上的0度
This state of absolute cold is the zero point in the Kelvin temperature scale.
即零下273.15摄氏度
corresponding to negative 273.15 Celsius
许多实验物理学家 都曾在其科学研究生涯中 试图将物质冷却到绝对零度
many experimental physicists have spent their careers trying to cool things to absolute zero .
我们目前凭借着激光和磁场
Using lasers and magnetic fields,
已经成功将某些物质的温度
we’ve now managed to cause certain substances
降低到了十亿分之一开氏度
to less than a billionth of a Kelvin.
继而 揭示出了物质的一些奇特的量子状态
Doing so has revealed some bizarre quantum states of matter.
不过 我们受到量子力学的限制 永远可能无法将温度降低到绝对零度
but quantum mechanics may also prevent us from ever reaching absolute zero.
对这种低温限制的理解 将让我们对量子真空的本质能所领悟
Understanding the limit to cold will lead us to an understanding of the nature of the quantum vacuum itself.
固 液 气这三种物质状态 我们所有人都非常熟悉
We’re all familiar with the states of matter solid liquid gas.
任何的固体被加热 最终都将融化为液体
Heat up any solid and eventually it’ll melt into a liquid,
而继续加热 所有的液体也都将蒸发为气体
pumping more energy and all liquids will vaporize into gas.
而这并不是结束
Now that’s not the end of it .
要是再继续加热的话
Yet more heat causes
气体之中的电子 便会从原子的缚束中逃逸出来
electrons in any gas to escape the bonds of their atoms.
从而 形成鲜为人知的”等离子体”
resulting in the less known plasma state.
在这些物质状态中
In these states of matter,
粒子个体能量的浮动范围 是非常大的
particles have an enormous range of individual energies :
比如有些粒子会运动或震动得很快 有些则会很慢
some moving or vibrating fast, some slow.
而温度仅仅就是这些无数粒子平均动能的体现
temperature just represents the average kinetic energy of the countless particles .
从理论上说 物质可以拥有比绝对零度高的任何温度
and while a substance can zən serə nekənɪ theoretically have any temperature above absolute zero .
不过 物质内部的粒子却不行
its component particles cannot
作为量子世界的“生物” 这些粒子的震动或移动 只能在特定的能级上进行
those particles are quantum creatures that can only occupy certain energy levels of vibration or motion.
而这些能级 与原子内彼此独立的电子轨道层十分相似
much like the discrete electron orbitals in an atom.
我们观测到粒子在能级之间跳跃产生的光谱 继而揭示出了这种量子特性
this quantum nature is revealed when we look at the spectrum of light produced as those particles hop between energy levels.
这种量子现象 被普朗克定律称为“黑体辐射”
this is the black body radiation described by Planck’s law.
“黑体辐射”的数学公式
it’s mathematical form
对亚原子世界的量子特性 首次进行了间接性的描述
was our first hint at the quantum nature of the subatomic world .
在奇特的低温物质状态下 量子世界的影响会变得愈发明显
the influence of the quantum world becomes far more apparent in the strange states of matter that exist at the cold end of the heat spectrum.
“玻色-爱因斯坦冷凝物” 就是例证
an example is the bose-einstein condensate
随着我们将某些物质的内部能量减弱
as we sap the energy of certain substances
这些物质的粒子 便会掉到最低一级的能态上去
its particals drop into the lowest possible energy state
而物质绝大部分的粒子 一旦处于这样相同的量子态下
once nearly all particles occupy that one quantum state
这些粒子就会呈现出 相同的单一连续的波函数
they share a single coherent wave function.
这些粒子 从而行为变得出奇的一致
this causes them to behave in a strange collective way
而且 不会受到单个粒子能量激发的影响
they become immune to individual excitation —
即 单一的粒子 无法从最低能态之中 再次碰撞挣脱出来
— individual particles can no longer be bumped or jostled out of that lowest state
这就意味着 这些粒子流动起来 不会受到丝毫的阻力
this means that they flow with no resistance whatsoever
在某一些固体中 电子会两两成对
in certain solids, bonded pairs of electrons
被称为“库珀对”
Cooper Pairs
随着冷凝到低温状态
condensed into this state
物质中流动的“库珀对” 不会受到任何阻力
they flow unrestricted through the material
从而让物质形成了超导体
making it a superconductor.
要是此时物质还能在达到玻色-爱因斯坦凝聚的临界温度
However if the entire substance can somehow remain fluid
情况下保持液态
when it reaches the critical temperature for Bose–Einstein condensation
它就变成了我们所称的超流体
it becomes what we call a superfluid.
它粘度为零 可以通过最小的空缺
It has zero viscosity; it can pass through the smallest openings,
永远保持旋转状态
sustain whirlpools that last forever,
甚至“爬过”它的容器壁
and even climb over the walls of its container.
在实验室中 只有一种物质
Only one substance is known to produce a superfluid
能产生超流体
for conditions possible in a lab.
那就是氦
And that’s Helium.
尤其是氦-4
In particular, Helium-4.
氦-4的自旋为0 这使它变成了一个玻色子
Helium-4 has a total spin of zero, which makes it a boson. So:
——一个整体自旋的粒子
a particle with integer spin.
玻色子的量子状态
Bosons are able to occupy the
与其他半整体
same quantum state as each other
旋转的费米子不一样
unlike the half-integer spin fermions which cannot.
氦的另一个特性是
The other unique property of Helium is
它不可能冻住
that it can’t be frozen —
即使到最低温度 它仍然是液体
it remains a liquid down to the smallest possible temperature.
其他物质在变成超流体之前就会冻成固体
Every other substance freezes into a solid before it can become a superfluid.
氦的不冻性揭示了一个更深层次的量子奥秘
The unfreezability of Helium reveals an even deeper quantum mystery. See,
物质变冷的程度有绝对限制
there’s an absolute limit to how cold a substance can become.
理论上 绝对零度意味着没有热能
In theory, absolute zero temperature means no thermal energy
所以没有任何内部的粒子运动
so no internal motion of particles whatsoever.
但一个粒子完全静止意味着什么
But what does it mean for a particle to be completely still? Well,
它对于它相邻粒子的位置是固定的
its position relative to its neighbors would be fixed
它的动量将为零
and its momentum would be zero.
然而量子力学最基本的定律不允许这一点
However, the most fundamental law of quantum mechanics forbids this.
海森堡不确定性原理
The Heisenberg Uncertainty Principle
告诉我们
tells us that there’s an absolute limit
特定性质组合的可知性是绝对有限的
in the knowability of particular combinations of properties.
例如 粒子的位置越精确
For example, the more precisely a quantum particle’s position is defined,
其动量越小
the less defined is its momentum.
这与测量无关
And this isn’t about measurement;
一个位置明确的粒子具有完全不明确的动量
a particle with a perfectly-defined position has a perfectly-undefined momentum.
因此当尽量完全固定
So try to fix a particle’s position
一个粒子的位置
perfectly — try to hold it still —
并尽量保持它时 它的动量就会进入量子朦胧状态
and its momentum enters a state of quantum haziness.
这种动量可能会有很大的波动
That momentum can then fluctuate, potentially to very high values.
在最低温度下 粒子也有量子振动这种运动
At the lowest temperatures particle motion acquires a sort of quantum buzz.
这转化成最小数值的平均能量
This translates to a very real minimum in average energy
和最低温度
and to a minimum temperature.
这个温度只比绝对零度高一点点
That temperature is just a teensy bit higher than absolute zero.
我们把量子系统的最低能量称为零点能量
We call the lowest-possible energy of a quantum system its zero-point energy.
对于构成任何形式的物质的一组粒子
For a group of particles that make up any form of matter
零点能量实际上不是零
that zero-point energy isn’t actually zero.
它们总有一点动能剩余
There’s always a little bit of kinetic energy remaining
所以温度不可能达到绝对零度
and so it’s impossible to reach absolute zero in temperature.
其他的量子系统也有非零的零点
Other quantum systems also have non-zero zero-points
这导致了更奇怪的现象
and that leads to even stranger phenomena.
例如 充满我们宇宙的量子场
For example,The quantum fields that fill our
也由于不确定的原理而波动
universe also fluctuate due to the uncertainty principle
产生了我们所知的真空能
resulting in what we know as vacuum energy.
甚至在把海森堡带进它之前
And some quantum fields have an intrinsic non-zero zero-point
一些量子场有一个非零的零点
before even bringing Heisenberg into it.
这引出了著名的希格斯机制
This leads to the famous Higgs mechanism
并可能导致膨胀和暗能量现象
and possibly also the phenomena of inflation and dark energy.
要了解宇宙 我们需要了解它如何表现出
To understand the universe we need to understand how it behaves
缺乏热量 缺乏光线和缺乏物质的状态
absent heat, absent light, and absent matter.
但我们已经超越了自己
But we’re getting ahead of ourselves.
当我们深入到最冷 最黑暗
We’ll need another episode to explore the quantum nature of nothing
最空的时空时 我们将需要另一集
as we peer deeper into the coldest, darkest,
来探索虚无的量子特性
and emptiest patches of spacetime.
本视频由Curiosity Stream提供
This episode is brought to you by Curiosity Stream:
它提供来自世界上最好的电影制作人的
a subscription streaming service that offers documentaries and non-fiction titles
纪录片和非小说类图书
from some of the world’s best filmmakers
包括独家原创作品
including exclusive originals.
这也是研究我们在Space time中
It’s also a great place to study up
所涉及到的一些概念的一个好地方
on some of the concepts we cover in Space Time.
例如布赖恩•格林的《探索量子史》
For example, Brian Greene’s “Exploring Quantum History”
更深入地研究海森堡不确定性原理
delves much more deeply into the Heisenberg Uncertainty Principle.
假如你好奇可以来看
Check it out if you’re curious.
如果你在
Get unlimited access today and
curiositystream.com/spacetime中注册
for our audience the first two months are free
并使用优惠码“SPACETIME”
if you sign up at curiositystream.com/spacetime
你就可以在今天得到无限制访问权限 前两个月免费
and use the promo code”spacetime” during the sign-up process.
本周我们迎来了一百万订阅用户的疯狂里程碑 哇
This week we hit the crazy milestone of one million subscribers. Wow!
当我们在2015年初开始制作
We never would’ve guessed we’d reach
Space Time时 我们从未想到我们会达到这一点
this point when we started making Space Time early in 2015.
我们不知道这里有这么多
We had no idea there’d be such an amazing community
聪明 好奇的人们
of smart, curious folk out there.
我们非常感激找到你
We are so incredibly grateful to have found you,
你也找到了我们
and that you found us.
当然 我们必须给第一百万订阅者一件
Of course we have to give a Space Time T-shirt to our one-millionth subscriber,
space time的T恤衫 SevenFive 就是你
SeventyFive, that means you.
在pbsspacetime@gmail.com上给我们发一封电子邮件 我们会将它变成现实
Shoot us an email at pbsspacetime@gmail.com and we’ll make that happen.
对于其他人
And for everyone else,
我们一起尽可能长时间地让Space Time延续下去如何?
how about we keep making Space Time for as long as humanly possible?
上周在Space Time Journal
Last week in Space Time Journal
我们谈到了一个潜在的
Club we talked about the new observation
双重超大质量黑洞吸引力的新观察
of a potential pair of binary supermassive black holes
它们相隔仅一光年
orbiting only one light-year apart.
你们提出了很棒的问题
You guys had the best questions.
RCOATES89问我们
RCOATES89 asks whether we’re going
从失去角动量到形成引力波
to have to wait billions of years
是否需要
for this black hole binary to spiral together
等上数十亿年
from losing angular momentum to gravitational waves.
答案是否定的
Well the­— the answer is no,
我们可能只需等几千到几百万年
we’ll probably only have to wait many thousands to millions of years.
我们确切地知道超大质量黑洞会合并
We know for sure that supermassive black holes do merge —
否则它们不可能这么大
otherwise they could never have got so big. Also,
如果它们不合并 我们会看到更多的双星
we’d see more binaries if they didn’t merge.
所以它们可能会通过拖拽
So they probably lose angular momentum by dragging
星系中心的气体而失去角动量
against gas in the centers of galaxies,
但我们不知道需要多长时间
but we don’t know how long that takes.
希望这个和其他类似的系统能帮助我们解决这个问题
Hopefully this and other systems like it will help us figure that out.
Dillan Burris问道 除了超大质量的黑洞 还有什么存在于星系中心
Dillan Burris asks,”What, besides a supermassive black hole, lives in the centers of galaxies?”
答案是:恒星
Well the answer is stars.
而且是大量的恒星
Lots and lots of stars.
银河系核心的恒星密度
The density of stars in the Milky Way core is
约为银河系星盘的百倍
around a hundred times that of the Milky Way disk.
我们还预计会有大量的恒星残留物
We also expect there to be a good number
比如中子星和黑洞
of stellar remnants like neutron stars and black holes
会从周围的星系向中心坠落
that have fallen towards the center from the surrounding galaxy. And,
当星系通过相互作用
when galaxies get stirred up
或与另一个星系碰撞而运动时
by an interaction or collision with another galaxy
我们认为气体也会进入到核心中
we expect that gas will be driven into the core also.
在那里它可能会引发一些类星体活动
There it might trigger some quasar activity
直到它们全部被黑洞吞噬
until it all gets gobbled up by the black hole.
Joseph Gamble指出
Joseph Gamble points out
如果这一对双星相隔一整个光年
that if this binary pair is a whole light-year apart
那么我们就会看到它们相互围绕
then for us to see them orbiting each other
它们需要更快的速度移动
they’d need to be traveling insanely fast. Well,
观察得好 这完全正确
good observation. That’s absolutely right,
但实际上我们还没有看到它们相互环绕
but actually we haven’t seen them orbiting each other.
我们只知道它们
We just know they must be
一定在轨道上 因为它们可能质量足够大
in orbit because their probable masses are large enough
所以它们应当被引力束缚
that they must be gravitationally bound.
它们要花上数千年
They would actually take a few
才能绕轨道一圈 所以这仍需
thousand years to complete one orbit,
漫长的等待
so that’s still a long wait.
Rubbergnome 对不起
Rubbergnome,I’m sorry I didn’t have more faith
我对你的QFT fu没有更多的信心
in your QFT fu.
你从前一周的剧集中对我拉格朗日算符的批评
Your criticism of my Lagrangian from the previous week’s episode
原来是指我的LaTeX(文档编辑)很糟糕
was just about my bad LaTeX fu —
而不是说这个方程错了
not about the equation being wrong.
我认错
I stand corrected.

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视频概述

地球表面最低温度是-89.2℃,但这也无法与绝对的寒冷:绝对零度(临界温度)(-273.15℃)相比。但为何绝对零度“可望而不可即”?在逐渐接近绝对零度的过程中又会有哪些发现?

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视频来源

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