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用实验给你展示量子力学的神奇 – 译学馆
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用实验给你展示量子力学的神奇

Is This What Quantum Mechanics Looks Like?

看看这个
Check this out
我现在用把这个扬声器放在培养皿旁 培养皿里装有硅油 这样让它处在振动状态下
I’m using this speaker to vibrate a petri dish containing silicon oil
现在我用牙签往培养皿表面滴一小滴硅油
Now if I take this toothpick and make a little droplet on the surface
这一小滴硅油会停留在培养皿表面 并在上面不停地徘徊
the droplet will stay there, hovering above the surface
其实这一小滴硅油是在培养皿表面上弹跳
The droplet is actually bouncing
而且如此弹跳还会持续很长时间
and it will keep bouncing for a very long time
这种现象是由于这小滴硅油和培养皿表面之间的空气造成的
Now the reason for this is a little layer of air between the droplet and the surface
硅油弹跳频率很快 以至于空气层的厚度一直维持在100纳米以上
And the droplets bouncing so rapidly that that layer never shrinks to about 100 nanometers
厚到油滴无法和液面结合
Which is what it would take for the droplet to recombine with the oil
每当小油滴接触培养皿表面 就会激起波浪
Now, every time the droplet lands on the surface, it creates a wave
但这种波很特别
But this is a special type of wave
是由装有硅油的培养皿振动引起的
Driven by the vibration of the oil bath
被称为驻波
It is a standing wave
也就是说 这种波浪不会向外扩散
Meaning that it is not traveling out
只会上下跳动
It’s just oscillating up and down
因此 这小小的油滴引起了驻波
So the droplet makes the wave
它下一次跳动时会和激起的驻波相互作用
And then it interacts with that wave on its next bounce
如果油滴落在波浪的一侧 它就会向前运动
If the drop lands on one side of the wave, it is pushed forwards
当油滴的跳动和波浪达到同步的时候
And as long as the bounce of the droplet remains synchronized with the wave
油滴就会落在波浪的前端 不断地向前运动
It will keep landing on the front side of the wave getting pushed farther forwards
这样的油滴被称为”Walkers”
Droplets like these are known as “Walkers”
早在上世纪70年代就已经发现了油滴的跳动
The bouncing oil drops has been known about since the 1970s
但是直到近年才发现 可以用小小的油滴
But only recently has it been discovered that you can use these little droplets
来展现量子力学的诸多奇妙现象
to replicate many of the strange phenomena of quantum mechanics
这并不是一个量子体系 这些油滴直径大约有1毫米
Now obviously this is not a quantum system, the droplets are about a millimeter in diameter
但是想想量子级别的粒子 如电子
But you can think of the droplets like, uh, quantum particles, say electrons
有一项实验找到了量子力学的重要特征 这就是双缝实验
One experiment that captures the key features of quantum mechanics is the Double-Slit Experiment
如果向两道窄缝中射入一束电子
If you send a beam of electrons at two narrow slits
那么 电子不会像粒子那样运动 也不会在通过窄缝后凝结成一团
Well, the electrons, rather than behaving like particles and ending up in two clumps behind the slits
而会出现干扰现象
They produce an interference pattern
即使一次向同一窄缝射入单个电子
Even when you send each electron through one at a time
由于运动的油滴 驻波会直接穿过两道窄缝
With Walking droplets, the pilot wave goes through both slits
和自身形成干涉
Interfering with itself, while the droplet only goes through one slit
而油滴本身却不是沿着直线 通过其中一道狭缝
The droplet doesn’t move in a straight line though
与波浪的相互作用导致它方向偏离
It’s deflected by its interaction with the wave
最后油滴的分布状况
The resulting distribution of where the droplets end up
看起来和量子双缝干扰现象类似
Looks very similar to quantum double-slit interference patterns
以隧道为例
Or take tunneling
在量子力学中粒子穿过障碍是可能的
In quantum mechanics, it’s possible for a particle to get through a barrier
因为经典力学中它没有足够能量穿过障碍
that it wouldn’t classically have enough energy to get over
这已经被Walkers证实
This has been demonstrated with Walkers by
是通过硅油表面下方制造位置很浅的障碍证明的
creating a shallow barrier under the surface of the oil
通常障碍物会反射导频波和弹跳的油滴
Usually the barrier reflects the pilot wave and its bouncing droplet
但极少情况下油滴会穿越边界
But in rare cases, the droplet does cross the boundary
油滴穿过障碍物的可能性
And the probability of the droplet crossing the barrier
会随着障碍物宽度的增加而急剧减少 就像量子的隧道效应一样
Decreases exponentially with increasing width of the barrier, just as in quantum tunneling
也许这些Walkers最令人惊奇的地方在于他们显示出量子化 就像电子必定绕着原子核转动
Perhaps the most surprising thing about these Walkers is they exhibit quantization, just like electrons bound to atoms
这里Walkers被束缚在一个圆形的围栏里
Here the Walker is confined to a circular corral
和导频波相互作用时油滴看起来随机地四处移动
The droplet seems to move around randomly as it interacts with its pilot wave
油滴和导频波之间的复杂相互作用使得油滴运动轨迹混乱不堪
The complex interaction between the droplet and the wave leads to chaotic motion of the droplet
但是随着时间推移 一种新的现象出现
But over time, a pattern builds up
这是任意一点发现油滴的概率密度
This is the probability density of finding the droplet at any point within
范围在围栏之内 它看起来很像
the corral and it looks very similar to
电子的概率密度
the probability density of electrons
而且是被束缚在量子围栏里
confined in a quantum corral
这些相似性绝非偶然
all of these similarities are no coincidence
这些运动的小油滴实际上创造了
the walking droplets actually create a
一个理论的明显物理事实
remarkable physical realization of a
这理论由de Brogile提出
theory proposed by de Broglie nearly a
时间是大约一百年前
hundred years ago in the early days of
是量子力学产生的早期
quantum mechanics he postulated that all
他规定每个粒子都有一种波
particles have a wave that accompanies
伴随它们并引导它们的移动
them and guides their motion and that
这种波是由粒子
wave is actually created by tiny
微小的跳动引起的
oscillations of the particle
现在这个导频波理论被边缘化
Now this pilot wave theory was marginalized when
因为标准哥本哈根诠释
the standard Copenhagen interpretation
被广泛接受
became widely adopted
哥本哈根诠释排斥的是
the Copenhagen interpretation excludes anything that
不能被直接观测的物质
cannot be directly observed and it says
还写道一个粒子所能知道的一切
everything that can be known about a
被包含在所谓的
particle is contained in its so-called
“波函数”中 但是接受这个观点
“Wave Function” but adopting this view
会迫使你摒弃一些常识
forces you to give up on some common
比如有些说法
sense notions like the idea that
粒子有固定的位置
particles have a definite position and
和动量 即使它们不能被测量
momentum even when they’re not being measured
这也意味着
and it also meant that the
我们的宇宙
universe was
不再是确定的状态
no longer deterministic
量子力学本质就是随机的
randomness is built into standard quantum mechanics
比如以双缝实验为例
for example take the double-slit experiment
根据量子力学原理
according to quantum mechanics the wave
电子的波函数是
function of the electron is a
是运动的电子出现重叠
superposition of the electron going
电子通过一个窄缝 其他电子也同时通过窄缝
through one slit and the other slip simultaneously
用波函数可以计算
using this wave function you can calculate the probability of
电子可能在某个位置的概率
where the electron is likely to be and
当你在屏幕上发现了这个电子
then when you detected at the screen the
电子就会在那一点随即出现
electron pops up at one point at random
这种分布情况
that was in that distribution we say
我们称之为波函数坍缩
that its wave function collapses
在你测量的时候
instantaneously at the moment of
不能说
measurement you can’t say that the
电子在测量之前就出现在那儿了
electron was there before you measured
甚至不能说
it and you can’t even say that the
电子肯定通过了一个窄缝
electron must have gone through one slit
或者另一个窄缝
or the other
把这和展示的图片比较一下
compare that with the picture provided
通过这里跳动的小油滴
by the bouncing droplets in this case
导频波可以穿过两条窄缝
the pilot wave goes through both slits
但是油滴却只能通过其中一个窄缝
but the droplet only goes through one
油滴与波
the droplet is pushed around by its
相互作用被推向一边
interaction with the wave so that the
所以分布结果相同
resulting statistical distribution is
油滴不可能同时出现在两个地方
the same the droplet never exists in two
也没有随机的因素
places at once and there’s no randomness
如果有任何的不确定性
if there is any uncertainty it’s just
只是因为我们没注意到发生了什么
due to our ignorance of what’s going on
不是因为它不存在
it’s not that it doesn’t exist so pilot
所以导频波能出现许多
wave dynamics can produce many of the
和量子力学原理相同的现象
same results as quantum mechanics does
这意味着精确模拟了量子的活动
this mean that this is really what
才是量子世界的真实情况吗?
quantum particles are doing
也不是
NO
但我想它至少
no but I think it’ll at least suggest
暗示了一点可能性
that this is possible these are possible
这些是能得到和量子力学理论
dynamics that could lead to the
同样统计结果的
statistics which are captured in the
几种可能的动力学理论
quantum mechanical theory and what’s
这个模型吸引人的地方在于
appealing about this is it gives you a
它让你清楚地知道发生了什么
clear idea of what’s going on you don’t
而你不需要摈弃之前的
have to abandon the idea that the
宇宙确定不变的观点
universe is deterministic and you get
你能获取到位置固定 动量确定的粒子
particles with definite position and momenta.
我觉得很棒
I think it’s great that we have
我们在同样的实验中得出了两种截然不同的结论
two competing theories for the same
它们使得你去
experiments and they both asked you to
接受各种各样古怪的事情
accept odd things just different odd
只不过怪在不同的地方
things and it comes down to what you’re
一切取决于你是
comfortable with really whether you
更喜欢标志的哥本哈根诠释
prefer the Copenhagen interpretation is standard quantum mechanics
还是波导理论
or a pilot wave theory
我想知道你心里是怎么想的 在留言区写下你的想法
let me know what you think in the
你对导频波有兴趣吗
comments do you like the pilot waves I
这个模型的确很吸引人
mean it’s definitely a very appealing
至于到底能不能反应真实
picture whether or not correspond to
我们拭目以待
reality that remains to be seen
本季集由Patreon的观众
Hey this episode of Veritasium was supported in part by viewers like you on Patreon
和谷歌决策科学行动支持
and by Google’s Making & Science Initiative which seeks to
谷歌决策和科学行动致力于人们
inspire people to learn more about
学习更多的科学知识 追求科学领域的目标
science and pursue their science goals
我知道有其他人
now I know someone else who is pursuing
在这个周末也追求着科学目标
their science goals this weekend that is
那就是每天变得更聪明
Destin over it Smarter Every Day he
我看的基本上是相同的现象
and I were looking at basically the same
但他看到的是
phenomenon but he was looking at water
小水滴 却不知道为何不这样聚集
droplets and why they don’t coalesce so
如果想知道是怎么回事
if you want to see how that works and
在太空又是怎样的
how it works in space go check it out on
请收看他的Smater Every Day
his channel over at Smarter Every Day
谢谢您的收看
and as always thanks for watching
每次油滴弹跳时只看一个画面
looking at only one frame per bounce you
你可以看到油滴运动是怎样被
can see how the droplets motion is
脚下的波导影响的
guided by the wave it’s effectively
油滴明显地运动 波导却持续不变
surfing on and the wave remains even if
即使油滴都消失不见了 也依然存在
the droplet disappears has happened
有时当油滴遇上了一点灰尘的时候仍会发生
sometimes if it encounters a little bit
这种情况
of dirt
真正令人感到振奋的
what’s really cool about this is the
是导频波存储着一些信息
wave actually stores information about
能知道小油滴去过的位置
where the droplet has been.
这是因为每次小油滴弹跳时
This is because every time the droplet bounces
就会产生圆形波 其中心
it creates a new circular wave centered
位于当前位置 其产生的圆形波
on its present location and that wave
会附着在表面的波场之上
adds to the existing wavefield on the
因此液面随着液滴移动
surface so as the droplet moves the
波不断积累
waves it makes keep adding up, storing
不断存储小油滴所经过的位置信息
the information of where it’s been
事实上你还可以让小油滴
in fact you can actually get the droplet
附着在波的另一边
to land on the backside of the wave so
因此会被推回去
now it’s pushed backwards and it
并从经过的地方折返回去 并不断抹去
retraces it steps erasing each way that
经过的路径
made previously one-at-a-time

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视频概述

量子力学理论有着极其神秘的一面, 在你测量或观察粒子以前,它们的状态是未定的,例如在双狭缝实验中的电子,它似乎能在不同位置上存在,直到你观察它的那一瞬间,这种不确定性才会消失。

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翻译译者

Ljimnn

审核员

与光同尘

视频来源

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

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