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连接整个宇宙的量子力学

The Quantum Theory that Connects the Entire Universe

感谢Brilliant赞助《科学秀》
Thanks to Brilliant.org for supporting SciShow.
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我之前已经说过一遍了 现在再说一遍
I’ve said it before and I’ll say it again:
量子力学很奇怪
quantum mechanics is weird.
同时制作这个题材的视频也很难 但我们正在做
It’s also hard to make videos above, but we’re doing it!
它是超微领域的物理学
It’s the physics of the super-tiny,
理论的核心观点是能量不连续的光谱
and it’s built around the idea that energy isn’t
它只能以一份一份的形式运行
a smooth spectrum — it can only come in set amounts.
尽管量子力学的观点非常古怪
But as weird as the implications of that are,
但它经受住了每一次实验的检验
it’s stood up to every experimental test thrown at it.
随着我们对它有了更深入的理解
And as we’ve learned more about it,
我们已经能更好地用它来解决问题
we’ve got better at using it to solve problems and
发明一系列有用的东西 如激光和半导体
invent all kinds of useful things, like lasersand semiconductors.
虽然 我们能用这个理论进行数学运算
Although we understand how to use the math behind the theory,
但要理解它的含义仍然是艰难的挑战
understanding what it means has proven to be a difficult challenge.
关于量子力学有许多不同的解读
There are a number of different interpretations of quantum mechanics out there,
而每一种的看法都不相同
each of which looks at the theory differently.
它们对于量子力学的表现
They all make the same predictions
也就是表面的现象 实验室里发生的事
about what quantum mechanics looks like on the surface —
都有相同的预测
so what will actually happen in experiments in the labs —
但他们用的运算方式及其含义
but the math, and the meaning of the math,
却有很大区别
can look very different.
这里面水很深
There’s a lot going on under the hood.
导航波理论就是比较有争议的解读之一
One of the more controversial interpretationsis called pilot wave theory.
乍看之下很吸引人
At first glance it looks appealing:
它能帮你避开量子力学出了名的
it allows you to get around the uncertainty and randomness
不确定性和随机性
that quantum mechanics is famous for.
但这里有个陷阱
But there’s a catch:
去除随机性 在某种层面上意味着脱离现实
getting rid of the randomness involves breaking reality in other ways.
20世纪20年代 哥本哈根诠释被提出
The conventional interpretation of quantummechanics is called the Copenhagen interpretation,
此后就成为了量子力学的惯用解释
after the institute where it was devised inthe 1920s.
它包含了许多量子力学方面
It includes a lot of the more well-known ideas
知名的观点 例如
around quantum mechanics, like that something
物质能同时以粒子和波的形式存在
can be a particle and a wave at the same time.
以及一些事物
It also says that certain things,
例如电子的自旋方向
like which way an electron is spinning,
要等到你观察它时才会确定下来
aren’t really set until you observe them,
在你观察它前
and until you do,
电子正同时向两个方向自旋
the electron is spinning in both directions at once.
这种粒子同时处在多种状态下的观念
This concept, that particles are in multiple states
我们称它称为叠加态
at the same time, is known as superposition,
薛定谔与既生又死的猫的实验就是为了验证它
and it’s what inspired Erwin Schrödinger’s famous dead-and-alive cat.
薛定谔曾经是量子力学方面的先驱之一
Schrödinger was one of the pioneers of quantum mechanics,
他实际上想要借
and his cat-in-the-box thought experiment
盒子里的猫的实验表明
was actually meant to show that
这个理论的一些推论非常……荒唐可笑
some implications of the theory were just … ridiculous.
但是结果表明
But it turns out that
这只可怜的猫实际上是叠加态的绝佳例证
poor cat was actually a good illustration of superposition —
并且 是的
and that, yes,
当你将量子理论观点运用在我们更熟知的
a lot of quantum mechanics makes no sense
宏观世界中 大部分都会遭遇滑铁卢
when you try to apply it to the larger world we’re more familiar with.
在假想实验中
In the thought experiment,
把一只猫放进有一烧瓶剧毒物质的盒子里
you hide a cat in a box with a flask of deadly poison.
但只有在一个放射性原子衰变时
But the poison will only be released
有毒物质才会释放出来
If a radioactive atom decays,
这里原子衰变与否的概率各占一半
which has, say, a 50 % chance of happening.
放射性衰变是一个量子力学过程
Radioactive decay is a quantum mechanical process.
一个原子是否衰变
Whether or not it happens to an individual atom
完全是随机的
is exactly the kind of random event that
依据量子力学的主流解释 完全无法预测
the mainstream interpretation of quantum mechanicssays is entirely unpredictable.
你不能预测它
You cannot predict it.
打开盒子之前
Before you open the box,
你不会知道原子有没有衰变
you have no idea whether or not the atom decayed, and therefore
因此也不知道有毒物质是否释放了
no idea whether the poison was released ornot.
正常情况下 如果有一半几率猫还活着
Normally, if there was a 50/50 chance a cat was alive,
我们会说猫或生或死
you’d say the cat was either alive or dead —
只是不知道到底会是哪种情况
you just wouldn’t know which.
但哥本哈根诠释和常规概率论的不同在于
But here’s where the Copenhagen interpretationis different from regular probability.
在被观察前
Before it’s observed,
原子处于衰变和未衰变的叠加态
the atom is in a superposition of decayed and not-decayed,
这意味着它同时处在两种状态下
meaning it’s both at the same time.
所以猫是既生又死的
So the cat would be both alive and dead.
一旦我们打开盒子
Once you open the box,
就会把叠加态转换成实际可观测到的一种情况比方说猫活着
you turn the superposition into one state you actually observe — let’s say alive.
没有猫咪在制作这集视频的过程中受到伤害
No kitties were harmed in the making of thisepisode.
但是打开盒子并不能表明
But opening the box does not tell you
猫在整个过程中一直都活着
that the cat was always alive that whole time.
我们打开盒子之前
Before you opened the box,
它真实的状态是生和死的叠加态
its true state was the superposition of alive and dead.
叠加态不会在日常生活中出现
Now, superpositions don’t appear in everyday life,
但根据哥本哈根诠释
but according to the Copenhagen interpretation,
在微观粒子层面上 到处都存在着叠加态
on the tiny scale of particles, they’re everywhere,
这显然很奇怪
which is obviously very weird.
但我们的每个实验都印证了这个观点
But the idea fits every experiment we’ve ever done,
随着时间推移 物理学家们就默认
and over time, physicists have
现实有时……就是让人摸不着头脑
come to accept that reality is sometimes … kind of blurred.
这就是导航波理论试图解决的问题
That’s what pilot wave theory tries to fix.
这个理论由另一位量子力学先驱
The theory was first proposed in 1927
路易·德布罗意在1927年首次提出
by another pioneer of quantum mechanics: Louis de Broglie.
自此一直被搁置 直到20世纪50年代
It was shelved until the 1950s,
大卫·玻姆重新发现并改进它
when David Bohm rediscovered and improved it.
今天它也被称为德布罗意-玻姆理论
Today it’s also known as the de Broglie-Bohmtheory.
它主张区分粒子和波
It works by distinguishing between particles and waves,
而不是如哥本哈根诠释一样
instead of treating them as the
把它们视作相同的东西
same thing like the Copenhagen interpretationdoes.
导航波理论中也有粒子和波
In pilot wave theory, there are still particles and waves,
但它们是分别存在的
but they exist separately:
有个方程可以用来计算单个粒子的速度
there’s an equation that gives you a particle’s velocity,
并且这个方程需要用到波
and that equation depends on the wave.
波与粒子相互作用 引导粒子的运动方向
The wave interacts with the particle by guiding the way it moves — or pilots it,
或者说给它导航
in other words.
这就是“导航波”名字的由来
That’s where the name “pilot wave” comesfrom.
这种波存在于我们研究的所有系统
This wave spans the entire system you’re looking at,
小到几个电子
whether that’s just a few electrons
大到全宇宙
or the whole universe.
由于这个中央波的存在
Because of this central wave,
物质属性在观察之前已经固定了
the properties of matter are set before you observe them,
不存在叠加态
instead of being superimposed.
你可能无法提前
You may not have the information you
获知这些属性究竟是什么
need to figure out what those properties are in advance,
但是信息就在那里
but the information is out there.
有点像抛一枚硬币
It’s a little bit like flipping a coin,
然后用手盖住它
then covering it with your hand.
我们不需要观察
You know it’s either heads or tails,
就知道结果不是正面就是反面
even before you look at it,
肉眼无法捕捉旋转的硬币
It was too fast for you to follow the spinning
但如果有一台高速相机
with your eyes, but if you had a high-speed
或者类似的工具 就很容易知道结果
camera or something you’d be able to figureit out.
哥本哈根诠释主张
The Copenhagen interpretation says that type
对于放射性衰变之类的现象来说
of information doesn’t exist for something
这样的信息不存在
like radioactive decay, so
所以在观察以前 一个原子可以同时处于
until you observe it, an atom can be both decayed and not decayed
衰变和未衰变的状态
at the same time — and
薛定谔的猫可以既生又死
Schrodinger’s cat can be both alive and dead.
但导航波理论认为这种信息是存在的
Pilot wave theory says the information doesexist.
就像硬币的例子
Like with the coin,
你可能没有工具获取不到相关的信息
you may not have access to the knowledge that
来告诉你原子是否衰变了
would tell you whether the atom decayed
而且在实际层面上
— so on a practical level,
我们无法运用数学来解决这个问题
we can’t really use the math to figure it out.
但是信息就在那里
But the information is out there,
原子状态非此即彼 不可叠加
and the atom is one or the other, not both.
这和我们在日常生活中对现实的认知
That’s a little closer to how we perceive reality
接近了一些 很好
in everyday life, so that is nice.
但问题在于 这里有个折衷的过程
The problem is, there’s a tradeoff:
导航波理论从本质上
in a very intrinsic way, pilot wave theory breaks
打破了物理学中的另一个大规则 定域性
a different, really big rule in physics: locality.
定域性原理是指
Locality is the idea
宇宙中一切物体只能影响与它相邻的事物
that everything in the universe can only ever affect its immediate surroundings.
而不能在没有发射任何信号的情况下
You can’t interact with something far away
与相距很远的事物相互作用
without sending some kind of signal to it,
而那个信号需要通过
and that signal needs to be transmitted through the space
两者间的空间被传播
between you and that thing.
最重要的是 这意味着所有信号的传播需要时间
Most importantly, this means that all signalstake time to travel.
所以我们看见闪电之后才听到雷声
That’s why you see lightning before youhear thunder.
我们还知道信号传播的速度
We also know that there should be an
是存在上限的
upper limit to how fast these signals can move:
爱因斯坦发现宇宙中
Einstein worked out that the universe’s
速度的上限是光速
speed limit is the speed of light. Now,
哥本哈根诠释实际上在某些情况下违背了定域性
the Copenhagen interpretation actuallydoes violate locality in certain situations.
例如 可以生成两个
For example, you can generate two electrons
自旋一直相反的电子
in a way that means they must have opposite spins.
不过 在你观察它们之前
Until you actually observe their spins, though,
每个电子都处于叠加态中
each electron is in superposition,
同时向两个方向旋转
spinning in both directions at the same time.
但如果我们让两个电子彼此远离
But if you send the two electrons away from each other,
直到它们被远远分开
wait until they’re really far apart,
再依次观察它们
and observe one right after the other,
也总会发现它们的自旋方向相反
you’ll always find that they spin in opposite directions.
事实就是这样的
That’s true even if there’s no time
甚至没有信号能以超光速
for a signal to pass from the first to the second
瞬间从一个电子传递到另一个电子
without moving faster than the speed of light.
爱因斯坦非常不喜欢这个理论
Einstein really did not like this,
但是我们检验过了 事实就是如此
but we’ve tested it, and we know it happens.
支持哥本哈根诠释
If you’re going by the Copenhagen interpretation,
就意味着支持电子以某种方式用超越光速
that means somehow the electrons are affecting
在影响彼此
each other faster than the speed of light. Still,
但至少
at least
在哥本哈根诠释中 违反定域性是例外而非惯例
in the Copenhagen interpretation violating locality is the exception rather than the rule.
另一方面 导航波理论
Pilot wave theory, on the other hand,
却全盘推翻了定域性理论
is entirely based on the idea that locality does not need
认为它不存在
to be a thing,
即使相距数光年 粒子也能即刻彼此影响
and particles can affect each other instantaneously even if they’re light-years apart.
这是导航波理论的主要观点
That’s the whole point of the pilot wave.
体系中的所有粒子都通过一种波
All particles in a system are tied to each other
紧密联系在一起 延伸一下就是
through that one wave, so by extension,
宇宙中所有粒子即时相互影响
all particles in the universe affect each other —
没有我们预期的 信号以光速传播
without the time delay you’d get
会有的时间延迟
if there were signals traveling at the speedof light.
换句话说
In other words,
认为猫有没有死的信息
if you say the information that would tell you whether the cat is alive
内嵌在宇宙其余的粒子中
or dead is embedded in the rest of the particles
实际上就是认为
in the universe, you’re also saying those
这些粒子以超越光速某种方式相互影响
particles somehow affect each other fasterthan the speed of light.
与哥本哈根诠释不同
And unlike the Copenhagen interpretation,
这个问题不只出现在特定情况下
it’s not just certain situations that have
它无时无刻不存在于世间万物中
this problem — it’s everything, everywhere,always. So,
一些物理学家不认同导航波理论
uh, some physicists take issue with that. Still,
但它很好地提醒我们
pilot wave theory is a good reminder
我们的物理学理论
that our theories of physics aren’t just
不仅受真实发生的事引导
guided by what’s really happening,
还受到审美和实用性的引导
but also by aesthetic and pragmatic choices.
如果我们认同哥本哈根诠释
If we go with the Copenhagen interpretation,
就要学着接受一些非常奇怪的事情
then we need to accept some really weird things,
例如有时候猫可以既生又死
like cats that are simultaneously dead andalive sometimes.
还要认识到有些事就是不可知的
We also need to accept that some things arejust unknowable.
但如果我们认同导航波理论
But if we subscribe to pilot wave theory,
就要认识到有些效应就是非定域性的
then we need to accept that some effects may be truly non-local.
两种选择都各有利弊
Both choices have their pros and cons,
大部分物理学家认为
and for the most part, physicists have decided
哥本哈根诠释更令人信服
that Copenhagen makes more sense.
多亏由于计算机模拟 导航波理论
Pilot wave theory has seen a bit of a renaissance in recent years, though,
最近几年有复苏迹象
thanks to computer simulations.
我们在现实世界不能接触到超光速信号
In the real world we don’t have access to faster-than-light signals,
但是在计算机上
but on a computer,
却能假设我们可以
we can pretend that we do.
所以物理学家正在运用
So physicists are using the math
导航波理论的运算方法做量子力学模拟
behind pilot waves to do quantum mechanics simulations,
这可以说是对传统研究方法的一个改进
which could be an improvement on conventional methods for some things.
不光有哥本哈根诠释和导航波理论
And it’s not just Copenhagen or pilot waves —
量子力学还有许多其他的诠释呢
there are other interpretations of quantum mechanics out there, too.
物理学的历史上充满一代代人
The history of physics is full of people coming up
想出天马行空 看似不可能的观点
with weird, impossible-sounding ideas that
但最终却是正确的
happen to be right.
也有好些观点是错的
It’s also full of ideas that happen to be wrong,
不过它们还是以有其他用途的
but are still useful in lots of different ways.
所以即使我们仍在探索
So even if we never discover
这个理论是否是宇宙运转的真正机制
whether this theory is actually how the universe works,
我们也还是可以通过探索它的作用
there’s a lot we can learn just
学到许多知识
by exploring it to see what it can do.
如果你喜欢探索这样的理论
And if you enjoy exploring theories like this,
我觉得你会喜欢Brilliant.org上的量子计算课程
I think you’ll like the Quantum Computing course on Brilliant.org,
在这里你可以通过建立你自己的量子线路 操纵传统计算机
where you’ll learn about the laws of quantum mechanics by building
破译密码 了解量子力学的规则
your own quantum circuit and racing a classical computer in solving codebreaking puzzles.
就在Brilliant.org/SciShow
You can check it out at Brilliant.org/SciShow, and right now,
现在通过链接注册的前200人
the first 200 people to sign
可以得到20%的
up at that link will get 20 %
Brilliant年度订阅折扣
off of an annual premium subscription to Brilliant.
到Brilliant.org/SciShow了解更多
So head to Brilliant.org/SciShow to learn more,
这样做的时候
and know that when you do, you’re
你也在支持《科学秀》栏目 非常感谢
also helping to support SciShow, so thanks!
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视频概述

一个量子力学入门科普,关于薛定谔的猫,关于哥本哈根诠释和导航波理论的解释。

听录译者

收集自网络

翻译译者

saw

审核员

审核员_BZ

视频来源

https://www.youtube.com/watch?v=JLv2MX1DnrY

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