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我们如何知道爱因斯坦的广义相对论不完全正确

How we know that Einstein's General Relativity can't be quite right

Today I want to explain
今天我想和大家说说
how we know that the way Einstein thought about gravity cannot be correct.
我们是如何知道 爱因斯坦对引力的看法是不正确的
Einstein’s idea was that gravity is not a force,
爱因斯坦的观点是 引力不是力
but it is really an effect caused by the curvature of space and time.
实际上它是时空弯曲造成的效应
Matter curves space-time in its vicinity,
物体使它周围的时空发生弯曲
and this curvature in return affects how matter moves.
这种时空弯曲又反过来影响物体的运动
This means that, according to Einstein,
这意味着 根据爱因斯坦的理论
space and time are responsive.
时间和空间是可变的
They deform in the presence of matter
时空会因物体的存在而扭曲
and not only matter, but all types of energies,
并且不光是物体 任何形式的能量
including pressure and momentum flux and so on.
如压力 动量通量等 都会让时空扭曲
Einstein called his theory “General Relativity”
爱因斯坦称这个理论为“广义相对论”
because it’s a generalization of special relativity.
因为它是狭义相对论的广泛化
Both are based on “observer independence”,
两者都是建立在“独立于观察者”的基础上
that is the idea that the laws of nature should not depend on the motion of an observer.
其理念是自然法则不应受观察者运动状态的影响
The difference between General Relativity and Special Relativity is
广义相对论和狭义相对论的区别是
that in Special Relativity space-time is flat, like a sheet of paper,
在狭义相对论里 时空是扁平的 就像一张纸
while in General Relativity it can be curved, like the often named rubber sheet.
而在广义相对论里 时空是像橡胶板那样可弯曲的
General Relativity is an extremely well-confirmed theory.
广义相对论得到了广泛的证实
It predicts, for example,
例如 它预测
that light rays bend around massive objects, like the sun,
光在经过像太阳之类的大质量物体时会弯曲
which we have observed.
我们已经观察到这一点了
The same effect also gives rise to gravitational lensing, which we have also observed.
这个效应还会导致引力透镜 我们也观察到了
General Relativity further predicts that the universe should expand, which it does.
广义相对论进一步预测宇宙会膨胀 确实如此
It predicts that time runs more slowly in gravitational potentials, which is correct.
它还预测引力会使时间变慢 同样没错
General Relativity predicts black holes,
广义相对论预测了黑洞的存在
and it predicts just how the black hole shadow looks like,
还预测了黑洞阴影是什么样的
which is what we have observed.
我们看到的正是如此
It also predicts gravitational waves, which we have observed.
它还预测了引力波 这也被我们观察到了
And the list goes on.
我还能接着举例
So, there is no doubt that General Relativity works extremely well.
所以毫无疑问 广义相对论非常有道理
But we already know that it cannot ultimately be the correct theory for space and time.
但是 我们知道它不可能是关于时空的终极理论
It is an approximation that works in many circumstances, but fails in others.
它接近正确理论 能解释很多现象 但不是万能的
We know this because
我们知道这一点是因为
General Relativity does not fit together with another extremely well confirmed theory,
它与另一个被广泛证实的理论无法统一
that is quantum mechanics.
那就是量子力学
It’s one of these problems that’s easy to explain but extremely difficult to solve.
这个无法兼容的问题 解释起来容易但解决起来却很难
Here is what goes wrong if you want to combine gravity and quantum mechanics.
如果要结合引力理论和量子力学 问题就来了
We know experimentally that particles have some strange quantum properties.
通过实验 我们知道粒子有某些奇特的量子特性
They obey the uncertainty principle
这些粒子遵循不确定原理
and they can do things like being in two places at the same time.
比如 粒子够能同时处于两个不同的位置
Concretely, think about an electron going through a double slit.
举个实例 想一下电子穿过双缝的实验
Quantum mechanics tells us that the particle goes through both slits at the same time.
量子力学告诉我们 粒子会同时穿越两条缝隙
Now, electrons have a mass
电子具有质量
and masses generate a gravitational pull by bending space-time.
而大质量物体 通过弯曲时空产生引力
This brings up the question,
这就带来一个问题
to which place does the gravitational pull go
如果一个电子同时穿越两个缝隙
if the electron travels through both slits at the same time.
那么引力会去哪里呢?
You would expect the gravitational pull to also go to two places at the same time.
你可能会想 引力也同时出现在了两个地方
But this cannot be the case in general relativity,
但根据广义相对论 这是不可能的
because general relativity is not a quantum theory.
因为广义相对论不是量子理论
To solve this problem, we have to understand the quantum properties of gravity.
要解决这个问题 我们必须搞清楚引力的量子特性
We need what physicists call a theory of quantum gravity.
需要物理学家称之为“量子引力学”的理论
And since Einstein taught us that gravity is really about the curvature of space and time,
既然根据爱因斯坦的学说 引力其实和时空弯曲有关
what we need is a theory for the quantum properties of space and time.
那么我们所需的 是关于时空的量子特性的理论
There are two other reasons how we know that General Relativity can’t be quite right.
基于另两个理由 也可知广义相对论不完全正确
Besides the double-slit problem, there is the issue with singularities in General Relativity.
除了双缝实验 广义相对论还遇到了奇点的问题
Singularities are places
奇点指的是
where both the curvature and the energy-density of matter become infinitely large;
时空曲率无限大 且能量密度无限大的点
at least that’s what General Relativity predicts.
至少广义相对论是这么预测的
This happens for example inside of black holes and at the beginning of the universe.
奇点出现在诸如黑洞内部 还有宇宙初期等
In any other theory that we have, singularities are a sign that the theory breaks down
在现有任何其他的理论中 奇点都代表着该理论的终点
and has to be replaced by a more fundamental theory.
因此 势必要被一种更基本的理论所替代
And we think the same has to be the case in General Relativity,
我们认为广义相对论也不例外
where the more fundamental theory to replace it is quantum gravity.
取代它的是一种更为基本的量子引力理论
The third reason we think gravity must be quantized is
引力必须量子化的第三个理由是
the trouble with information loss in black holes.
为解决黑洞信息丢失的难题
If we combine quantum theory with general relativity
如果在引力不量子化的情况下
but without quantizing gravity,
结合量子理论和广义相对论
then we find that black holes slowly shrink by emitting radiation.
那就会发现 黑洞因散发辐射而慢慢变小
This was first derived by Stephen Hawking in the 1970s
这个理论最早于20世纪70年代由斯蒂芬·霍金提出
and so this radiation is also called Hawking radiation.
因此黑洞辐射又名“霍金辐射”
Now, it seems that black holes can entirely vanish by emitting this radiation.
黑洞似乎能通过散发辐射而完全消失
Problem is, the radiation itself is entirely random
问题是 辐射本身是完全不可思议
and does not carry any information besides the temperature.
不携带除温度外的任何信息
So when a black hole is entirely gone and all you have left is the radiation,
那么当黑洞彻底消失时 剩下的只有辐射
you do not know what formed the black hole.
就没法知道黑洞是由什么构成的
Such a process is fundamentally irreversible and therefore incompatible with quantum theory.
这个过程完全不可逆 因此无法和量子理论相容
It just does not fit together.
不仅仅是无法调和
A lot of physicists think that to solve this problem we need a theory of quantum gravity.
许多物理学家认为 要解决这个问题得靠量子引力学
So this is how we know that General Relativity has to be replaced by a theory of quantum gravity.
由此可知 广义相对论必将被量子引力学所取代
This problem has been known since the 1930s.
这个问题在20世纪30年代就提出了
Since then, a lot of attempts has been made to solve it.
此后 物理学家们做了很多努力来尝试解决它
I will tell you about this some other time, so don’t forget to subscribe.
我会在今后的节目中讲 别忘了订阅哦

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视频概述

基于三个理由,我们可知广义相对论不完全正确,必将被更为基本的理论所取代

听录译者

收集自网络

翻译译者

zbz

审核员

审核员SRY

视频来源

https://www.youtube.com/watch?v=Ov98y_DCvRY

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