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《理解量子力学》#1 简介

Introduction to Quantum Mechanics | QM 1

想象你正在通过观看别人玩来试图学习国际象棋
Imagine trying to learn the rules of chess by just watching someone play.
你不得不去猜想一些规则
You ’ d have to guess some rules
来适用于你看到的每一步下法
that fit every move you ’ ve seen
但到目前为止
so far, but you can ’ t
你不能确信它们是否是正确的
be sure those are the right ones.
有时你会看到一些不遵循这些规则的新下法
Sometimes you ’ ll see something new that doesn ’ t follow those rules,
那么你就需要
so you need
去改变原有的规则
to change them.
理查德·费曼认为这是一个对物理学家实际做的事情的很好的比喻
Richard Feynman said that is a good analogy for what physicists actually do.
我们看到的下法就是我们的实验 然后我们制定规则
The moves we watch are our experiments and we make rules, i.e.
比如物理学定律
laws of physics, that
适用于目前为止我们看到的任何事情
fit everything we’ve seen so far.
在二十世纪早期我们看到一些
In the early 1900s we saw some very
非常奇怪的下法 并认识到要解释它们
strange moves being played and realised that to explain them,
我们不得不摒弃掉一些
we have to reject some
最基本的假设并提出一些其它的
of our most basic assumptions and come up with something else.
量子力学就是可替代的法则之一
Quantum Mechanics is that alternative setof rules.
我将会解释
I ’ m going to explain one
这些革命性的实验中的一个
of those revolutionary experiments and we ’ ll see exactly why its
我们将会看到为什么它意义非凡
implications are so drastic. First,
首先 想象一个情景
imagine this scenario.
某人正在朝一面很远的墙射击某种粒子
Someone is shooting some sort of particle at a far away wall,
我们有兴趣的地方是
and we ’ re interested
那些粒子会在哪里碰壁
in where they land.
但在粒子和墙之间还有一堵开着两扇门的墙
But there ’ s a wall in between them with two doors in it.
他们每次仅射击一个粒子
They shoot the particles one at a time,
当一个粒子被射击出去的时候
and if a particle makes it, it goes through one
会穿过其中一扇门并撞击到门后面的墙上
door or the other and lands somewhere behind that door,
因此不久我们就可以得到
so after a while we just get two
两束粒子带
bunches of particles.
显然对于任何类型的粒子都是一样的
That ’ s obviously true for any type of particle,
甚至是非常小的粒子 小到只有原子大小
even really small ones, like as small as atoms
甚至电子大小
or even electrons
但是 这里有一个
But well, there is one
技术上的困难来对非常小的粒子做这个实验
technical difficulty doing this experiment with small particles-
我们无法实际看到它们
we can’t actually see them. But,
不过我们可以像这样来做
we can still do the experiment like this:
我们把后墙涂上特殊的材料
we coat the back wall with special material
因此当粒子撞击后墙时
so that when the particle hits it,
会产生一个反应点亮这个撞击的地方
there ’ s a reaction and it lights up at that spot so
我们就可以看到粒子在哪里撞击了
we can still see where they land. Except,
然而 当这个实验用极小粒子做的时候
when this experiment is done with small particles,
结果却根本不像我们期待的那样
the results don ’ t look
而是像这样的
like we’d expect at all, they look likethis.
这是不是很诡异
This isn ’ t just weird,
这应该是不可能的-按照以下最简单的逻辑
it should be impossible – according to the following foolproof logic.
如果我们使用相同的粒子
If we do the experiment
在仅开一扇门的时候做这个实验
with the same particles when there is only one door is open, they
粒子如我们所愿的在后墙形成一条撞击带
predictably land in a bunch behind the door.
而在两扇门都打开的时候
-When the two doors are open,
每一个粒子必须只能够通过这个门或那个门
each particle must go through one door or the other, even
即便是我们不能实际看到它们穿过
though we can’t see which one it went through.
然后我们假设其中的一个粒子穿过了这扇门
-Then say one of our particles goes throughthis door.
另外一扇门虽然也开放
The fact that the other door also happens
但不会影响粒子穿过的效果
to be open isn ’ t going to effect where it goes.
因此对于这个粒子来说它的走向是和开单扇门是一样的
So then it should go where it would have in the single door experiment.
每一个粒子显然都应该是这样的
Each of these is obviously true,
放在一起就意味着这些粒子
yet together they imply that the particles must land in
一定会形成两条撞击带
two bunches.
然而结果并不是这样
But they don’t.
因此如果你要一个理论能解释这个实验
So if you want a theory that explains
你必须放弃
this experiment you must give up at least one of
至少一条以上所说的真理
these obviously true statements.
这就是量子力学所做的 这就是为什么它看上去好奇怪
This is what quantum mechanics does and that ’ s why it ’ s is so strange,
它必须是奇怪的
it has to be.
量子力学所抛弃的假设是
The assumption that quantum mechanics rejects is
每个粒子只穿过一扇门
that each particle goes through just one
而量子力学中
door. Instead,
有两个替代的规则
it has these two rules: First,
首先是叠加原理
the superposition principle.
是指假设
Say there ’ s a situation were there
一个物体有几个不同的状态可能性
’ s a few different options for an object, but there
但我们无法知道它实际处于哪个状态
is no way to tell what the object actuallydid. Then,
叠加原理的解释是 在某种意义上来说
this rule says that in some sense,
就是这个物体在同一个时间可以是处于所有可能的状态下
the object will do all of them at the same time.
在量子力学里这叫做“态叠加原理”
In quantum mechanics this is called a superposition.
回到我们例子里的实验
Going back to our example we don ’
我们不知道粒子会通过哪扇门
t know which door the particle goes through, so quantum
因此量子力学认为粒子处于叠加状态-两个门都穿过了
mechanics says it is in a superposition, goingthrough both doors.
这种说法的点在哪里呢?
What’s the point of proposing this?
好 现在粒子可以和自己产生干扰
Well now the particle can interfere with itself,
并且这种干扰可以解释
and this interference explains that strange
我们看到的奇怪的图案
pattern we saw.
但为什么我们现实中从来没看到过物体处于叠加状态呢?
But how come we never see objects in a superposition?
我们看到的是物体在一个时间点上仅处于一个位置
We only ever see things in one place at a time,
在一个时间点上仅有一个速度
and only going at one speed at a time,
并且只有生存或死亡状态 绝不可能又生又死
and certainly only dead or alive, never both?
这里我们就要用到第二个规则
That ’ s where the second rule of quantum mechanics comes in,
叫做测量原理
called the measurement rule.
比如说你有一个处于几个状态叠加的粒子
Say you have a particle that’s in a superpositionof several states:.
当你去测量它的时候 它会坍缩到只有一种状态
When you measure it, it must collapse to just one of those states.
并且 没有任何方法
But also, there ’ s no way to accurately
可以精确的预测到它将会坍缩到哪个状态
predict which one it ’ s going to collapse to. Instead,
也就是说 量子力学只告诉我们不同状态的可能性
quantum mechanics just tells us about the probability of the different options.
总而言之 量子力学说的是
In summary, Quantum mechanics says,
当这些物体没有被人或东西观察时
while someone or something isn ’ t observing objects,
它们的活动是很诡异的
they act weird,
它们处于马上可能做的所有事情的
doing a superposition of all the possible things they could be doing at
叠加状态
once.
但你不能捕捉到它们正在做什么
You can ’ t catch them in the act though,
因为如果你尝试去捕捉 它们会坍缩到
because if you try, they collapse to just
只做一件事情
doing one thing.
你无法看到在你背后发生的每件事情因为它们互相产生了干扰
You can see if it was happening behind your back though because of interference.
这里有很多问题
There are so many questions here.
比如 叠加状态实际到底是什么?
For example, what actually is a superposition?
粒子在物理上是被劈开了么?
Does the particle physically split up?
这是否意味着有多重世界
Or does it mean there are multiple universes and
且在每一个世界里
in each universe, the particle is doing
粒子都正在做不同的事情?
something different?
或者实际上粒子根本就只是在做一件事情
Or is the particle actually just doing one thing after all,
但我们不知道是哪件
but we don ’ t know which?
有关测量规则 也是模棱两可的
How about the measurement rule, that alsoseems ambiguous.
对粒子来说谁需要一直被观察?
Who needs to be doing the measurement forit to count?
粒子是否是有意识的?
Does it have to be a conscious being?
为什么宇宙会在意被人观察?
Why does the universe even care that it’sbeing watched?
这些显然都是很重要的问题
These are all important obvious questions
去解释量子力学
about the interpretation of quantum mechanics,
然而大部分问题都还没有答案
and yet most of them aren ’ t answered yet,
这使得量子力学
which is what makes quantum mechanics such
成为一个非常有趣的领域
an interesting field.
这可能也让它变得很难学
That might make it seem difficult to learn,
但真的不是这样
but it ’ s really not!
我相信你们所有人都是有能力的
I think that all of you are capable,
因此我会做一系列视频
so I want to make a series of videos teaching you
用最诚实的方法教你们
quantum mechanics in an honest way.
我们将学到更多的量子力学规则和预测
We ’ ll learn more about the rules and predictions
同时也包括
of Quantum mechanics, as well as the different
这个理论的不同解释
interpretations of the theory.
希望你们喜欢
I hope you’ll come along for it.
但在我结束之前
But before I let you go,
我想给你一些问题去思考
I ’ d like to give you some questions to try answer about what
我们刚刚学的
we just learnt.
首先
First.
如果我们测量粒子会通过哪扇门
What do you think would have happened
你认为将会发生什么?
if we measured which door the particles went through?
第二
Second.
对于那些曾经看过我视频的观众
For people who have watched my videos before,
你们可能记得玻姆力学
you might remember that Bohmian mechanics
这是量子力学的另一种理论
is an alternative theory to Quantum mechanics.
玻姆力学使用了这些基本假设中的
Which of those basic assumptions does
哪一个来切入解释
Bohmian Mechanics break in order to explain the two-door
双门实验?
experiment?
把你的回答放在留言里 未来我也会公布答案
Leave answers in the comments and I’ll putsolutions up. Also,
事实上我很好奇
I ’ m actually curious- what
到目前为止 你对量子力学有哪些值得一提的问题?
are the obvious question for you about quantum mechanics
不管怎样
so far? Anyway,
我希望你和我一样从中得到乐趣
I hope you had fun, I did!
下次再见!
See you next time!

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视频概述

理解量子力学的两个基本规则

听录译者

收集自网络

翻译译者

柳叶飞飞刀

审核员

审核员D

视频来源

https://www.youtube.com/watch?v=b_ddt6J1Bio

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