宇宙真正的本质是什么？
What is the true nature of the universe?
为了回答这个问题 人类提出很多猜想来描述这个世界
To answer this question, humans come up with stories to describe the world.
我们检验我们的猜想并学会什么要保留 什么要丢弃
We test our stories and learn what to keep and what to throw away.
但是我们了解得越多 我们的猜想就变得越复杂和怪异
But the more we learn, the more complicated and weird our stories become.
其中一些猜想过于古怪以至于
Some of them so much so,
很难知道它们到底是什么
that it’s really hard to know what they’re actually about.
就像弦理论
Like string theory.
一个著名的 有争议的并且经常不被理解的
A famous, controversial and often misunderstood story,
有关世界万物本质的猜想
about the nature of everything.
我们为什么会想到它？它是对的吗？
Why did we come up with it and is it correct?
或者它只是一个我们应该丢弃的想法
Or just an idea we should chuck out?
为了理解现实的本质
To understand the true nature of reality,
我们近距离地观测事物 并感到惊叹
we looked at things up close and were amazed.
不论是尘埃中的美妙风景
Wonderous landscapes in the dust,
充满稀奇古怪生物的动物园
zoos of bizarre creatures,
还是复杂的蛋白质组合
complex protein robots.
它们都是由分子组成的结构
All of them made from structures of molecules
甚至由数不尽的更小的东西
made up of countless even smaller things:
——原子 组成
Atoms.
我们曾以为它们是现实世界的最基本物质
We thought they were the final layer of reality,
直到我们用力地将它们一起撞碎
until we smashed them together really hard
发现了不能再被分解的东西
and discovered things that can’t be divided anymore:
基本粒子
Elementary particles.
但是现在 我们有一个问题
But now, we had a problem:
它们太小以至于我们不再能观察到它们
They are so small that we could no longer look at them.
思考一下：什么是“看见”？
Think about it: what is seeing?
为了能看见东西 我们需要光——一种电磁波
To see something, we need light, an electromagnetic wave.
这束光波撞击到物体表面
This wave hits the surface of the thing
然后反射到你的眼睛里
and gets reflected back from it into your eye.
它会携带一些物体的信息
The wave carries information from the object
便于大脑去创造这个物体的图像
that your brain uses to create an image.
因此 如果不与物体相互作用 你就无法看到东西
So you can’t see something without somehow interacting with it.
“观察”是一个主动而不是被动的接触过程
Seeing is touching, an active process, not a passive one.
对于大部分物体而言 这不算什么问题
This is not a problem with most things.
但粒子实在是太微小了
But particles are very, very, very small
小到那些我们用来“观察”的电磁波
So small that the electromagnetic waves we used to see
都显得太过巨大而无法触碰粒子
are too big to touch them.
可见光也仅仅是掠过它们
Visible light just passes over them.
我们可以试着通过制造更多波长更短的电磁波
We can try to solve this by creating electromagnetic waves
来解决这个问题
with more and much smaller wavelengths.
但波长越短 意味着需要更多能量
But more wavelengths, means more energy.
所以当我们用高能电磁波
So when we touch a particle
去触碰一个粒子时
with a wave that has a lot of energy
它会改变这个粒子
it alters it.
当我们看到这个粒子时 它就会被改变
By looking at a particle, we change it.
所以我们无法对基本粒子进行精确测量
So we can’t measure elementary particles precisely.
这个重要的事实被命名为：
This fact is so important that it has a name:
海森堡不确定性原理
The Heisenberg uncertainty principle.
它是所有量子物理学说的基础
The basis of all quantum physics.
那么粒子看起来到底是什么样呢？
So, what does a particle look like then?
它的性质又是什么？
What is its nature?
我们无从得知
We don’t know.
如果努力地观察
If we look really hard,
我们能够看到一个模糊的球状物
we can see a blurry sphere of influence,
但这仍然不是粒子本身
but not the particles themselves.
我们只知道它们真实存在
We just know they exist.
既然如此
But if that’s the case,
该如何对它们进行科学研究呢？
how can we do any science with them?
我们遵循前人的足迹 发明了一个全新的理论
We did what humans do and invented a new story:
一个有关数学的奇幻故事：
A mathematical fiction.
质点的假设
The story of the point particle.
科学家认为一个粒子是空间中的一个点
We decided that we would pretend that a particle is a point in space.
任何电子都是一个拥有一定电荷量和质量的点
Any electron is a point with a certain electric charge and a certain mass.
它们之间没有任何区别
All indistinguishable from each other.
这样一来 物理学家就能够定义它们
This way physicists could define them
并计算出它们之间的相互作用
and calculate all of their interactions.
这就是量子场论 它解决了很多问题
This is called Quantum Field Theory, and solved a lot of problems.
所有粒子物理的标准模型
All of the standard model
都建立在它的基础之上
of particle physics is built on it
并且它很好地对很多事情作出预言
and it predicts lots of things very well.
例如 电子的某些量子特性
Some quantum properties of the electron for example
已经被检测到并且精确到了
have been tested and are accurate up to
0.0000000000002％
0.0000000000002%.
所以即便粒子并非真正的质点
So, while particles are not really points,
通过这种假设
by treating them as if they were,
我们也得到了一幅宇宙的美丽图景
we get a pretty good picture of the universe.
这个想法不仅推动了科学进步
Not only did this idea advance science,
也促进了现实世界中一些日常技术的诞生
it also led to a lot of real-world technology we use everyday.
但是还有一个重要问题：重力
But there’s a huge problem: Gravity.
在量子力学中 所有物理基本作用力都是由某些粒子携带的
In quantum mechanics, all physical forces are carried by certain particles.
但是 根据爱因斯坦的广义相对论
But according to Einstein’s general relativity,
重力与宇宙中的其他力不同
gravity is not a force like the others in the universe.
如果宇宙是一幕戏剧 粒子就是其中的演员
If the universe is a play, particles are the actors,
而重力就是舞台
but gravity is the stage.
简而言之 重力是关于几何学的理论
To put it simply, gravity is a theory of geometry,
是关于时空自身距离的
the geometry of space-time itself,
需要绝对精确描述的几何学
of distances, which we need to describe with absolute precision.
但是由于在量子世界里
But since there is no way
我们无法精确地测量物体
to precisely measure things in the quantum world,
所以有关重力的学说无法在量子物理中实现
our story of gravity doesn’t work with our story of quantum physics.
当物理学家尝试通过创造一个新粒子
When physicists tried to add gravity
来将重力引入量子物理时
to the story by inventing a new particle,
就会出现数学运算崩溃的严重问题
their mathematics broke down and this is a big problem.
如果我们能将重力
If we could marry gravity to
与量子物理和标准模型相结合
quantum physics and the standard model,
我们就拥有了一个可以解释世间万物的理论
we would have the theory of everything.
一些非常聪明的人据此创造了一个新理论
So, very smart people came up with a new story.
他们提出这样一个问题：有什么会比一个点更加复杂？
They asked: What is more complex than a point?
那就是线——线或者弦
A line- A line or a string.
弦理论由此诞生
String theory was born.
弦理论之所以如此迷人
What makes string theory so elegant,
是因为它将许多不同的基本粒子
is that it describes many different elementary particles
描述为弦上不同的振动模式
as different modes of vibration of the string.
就像小提琴琴弦的不同震动能够
Just like a violin string vibrating differently can
发出许多不同的音符
give you a lot of different notes,
一条弦也可以提供不同的粒子
a string can give you different particles
更重要的是 它涵盖了重力
Most importantly, this includes gravity.
弦理论宣称要统一所有基本的宇宙间的力
String theory promised to unify all fundamental forces of the universe.
这引发了巨大的轰动
This caused enormous excitement and hype.
弦理论很快升级成为一种有可能解释万物的合理理论
String theory quickly graduated to a possible theory of everything.
不幸的是 随之而来的
Unfortunately, string theory comes
却是一系列问题
with a lot of strings attached.
大多数涵盖一致弦理论的数学
Much of the maths involving a consistent string theory
无法在我们现在这个只拥有三维空间和一条时间线的宇宙中实现
does not work in our universe with its three spatial and one temporal dimensions.
弦理论需要十种维度才能运作
String theory requires ten dimensions to work out.
因此它只能在宇宙模型中运算
So, string theorists did calculations in model universes.
然后尝试脱离其他六种多余的维度
And then try to get rid of
来解释我们目前的宇宙
the six additional dimensions and describe our own universe
但目前为止还没有人成功
But so far, nobody has succeeded
而且弦理论的相关假说
and no prediction
也没有被实验证实
of string theory has been proven in an experiment.
所以目前弦理论仍然没有揭露宇宙的本质
So, string theory did not reveal the nature of our universe.
有人或许会质疑
One could argue that
在这种情况下 弦理论似乎毫无用处
in this case string theory really isn’t useful at all.
科学都是由实验和预言组成的
Science is all about experiments and predictions.
如果做不到这些 科学家又何必要提出弦理论呢？
If we can’t do those, why should we bother with strings?
所以弦理论的用处在于我们应该如何利用它
It really is all about how we use it.
物理学以数学为基础
Physics is based on maths.
2加2等于4
Two plus two makes four.
无论你怎么想 它就是正确的
This is true no matter how you feel about it.
而弦理论中的数学运算也确实取得了一定成效
And the maths in string theory does work out.
这就是弦理论仍然大有用处的原因
That’s why string theory is still useful.
想象一下 如果你要建造一艘航船
Imagine that you want to build a cruise ship,
而你只拥有一只小游艇的蓝图
but you only have blueprints for a small rowing boat.
它们之间有许多差异：
There are plenty of differences:
引擎 材料
the engine, the materials,
以及规模
the scale.
但总有些东西是相通的：
But both things are fundamentally the same:
那就是漂浮的能力
Things that float.
所以通过研究游艇的蓝图
So, by studying the rowing boat blueprints,
最终依然能学到很多建造航船的知识
you might still learn something about how to build a cruise ship eventually.
通过结合弦理论
With string theory,
我们或许能试着去回答一些让物理学家困惑数十年的
we can try to answer some questions about quantum gravity
量子引力的问题
that have been puzzling physicists for decades.
例如黑洞的运作过程 以及信息悖论
Such as how black holes work or the information paradox.
弦理论或许可以为我们指引正确的方向
String theory may point us in the right direction.
在这一理念的鼓舞下
When used in this spirit,
弦理论成为了理论物理学家的有力工具
string theory becomes a precious tool for theoretical physicists
帮助他们在量子世界中获得新发现
and help them discover new aspects of the quantum world
并完成一些叹为观止的数学运算
and some beautiful mathematics.
所以 也许弦理论
So, maybe the story of string theory
并不能解释世间万物
is not the theory of everything.
但就像点粒子的假设一样
But just like the story of the point particle,
它或许会成为一个富有帮助的假设
it may be an extremely useful story.
直至现在 我们仍然不知道现实的真正本质为何
We don’t yet know what the true nature of reality is
但我们会不断提出新理论去探索
but we’ll keep coming up with stories to try and find out.
希望在未来的某一天
Until one day,
我们真的会找到答案
hopefully, we do know.
本视频由瑞士国家科学基金会提供支持
This video was supported by the Swiss National Science Foundation
并在亚历山大•斯芬哲尼的科学指导下完成
and realized with the scientific advice of Alessandro Sfondrini.
同时感谢亚历珊德拉•涅基 皮耶拉贝尔托•马尔凯蒂 大卫•唐以及苏黎世MNG Rämibühl的学生
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