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黑洞是什么? – 译学馆
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黑洞是什么?

What are Black Holes? - Sixty Symbols

有时候人们会问我对黑洞是什么感觉
Sometimes people ask me how do I feel about black holes,
是否觉得它们恐怖或吓人?
whether I find them scary or intimidating
它们是有点恐怖
Well they, they are a bit
但它们也可以是惹人喜爱的
but they can be cuddly too
这里有两个好玩的玩具黑洞
These are two cuddly toy black holes that I got
是我准备用来送给我小姨子的礼物
as a present for my sister-in-law.
我很喜欢它们
I just I just like them
它们是挺可爱的
They’re just little cuddly.
这是小黑洞宝宝
There’s a little baby one, and
还有这个稍微大一些
there’s a slightly bigger, you know,
可以当黑洞妈妈 如果你喜欢
mummy black hole, if you like Oh,
什么是黑洞?What is a black hole?
黑洞是太空中
well a black hole is a region of space
连光都无法逃离的区域
in which light can’t escape from
物质在引力的作用下挤在一起
Material comes together under the force of gravity
它们试图克服引力 但如果物质太多 引力便无法克服
tries to fight that [uh] if you get too much material you can’t overcome that Force and
最终 数学和物理定律
eventually mathematics and the laws of physics
将我们带入了这种奇怪的体系
take us into this strange regime
黑洞是一个恒星消亡时的产物
Well, it’s an object which which forms when a star dies.
它的质量是许多个太阳的总和
It’s something that’s got many masses of the sun,
并且发生了塌缩 在其自身重力的作用下
has collapsed, and its own gravitational pull
物质被压缩在
It’s got a lot of mass packed
在一个极小的范围内
in a very small region
最终塌缩到一个光都无法逃离的点
Eventually it collapses to the point where not even light can escape
形成 “事件穹界”
from it and it forms something called an event Horizon
它像一个壳
But it’s like a shell, if you like
在事件穹界内
and that event Horizon is the
光无法逃逸
within that event horizon light can’t escape so
所以它是黑色的
so that’s why it’s black
在它的中心有一个数学上不存在的点 称为奇点
At the center it has this mathematical impossibility called a singularity
所以说黑洞不可能有头发 但是这些有 还有眼睛
So they say black holes can’t have hair well these ones do, and eyes.
如果地球压缩成一个黑洞
Do you know what I’d like to make the earth into a black hole
它大概是这么大
you’d actually have to make it about that size

Yeah yeah, that’s right
如果它真是黑洞的话
Yeah so if that really was a black hole it
在这么小的范围内 质量可能比地球要大
would be probably more massive than the Earth contained within a
在地球上 你往空中抛一个东西
Little tiny region Here on Earth if you throw something up in the air
它会掉下来
It comes back down again, okay,
如果你用力抛
and if you throw it a bit harder
它会飞得高一点
It goes a bit higher,
但还是会掉下来
but it will tend to come back down again.
如果你有足够的力量把它抛起来
If you throw something hard enough
事实上它可能完全脱离地球
It’ll actually escape from the Earth entirely
[火箭引擎发射的声音]
[Sounds of a rocket engine firing]
也不一定非要是火箭
A rocket [uh] doesn’t have to be
你可以发射一个推进器
I mean, you know you could fire a projectile up
只要它达到这种逃逸速度
anything as long as it’s traveling at this escape velocity,
它就可以离开地球的重力
escape speed, it will escape from the
越来越小直至消失
Earth’s Gravity keep going and going and going off to infinity
而不是像其它物体那样围着地球转并掉下来
Rather than eventually turning around and coming back.
如果把地球压缩一点
If you were to make the earth a bit more
地球引力会变强
Compressed then the gravitational pull would get a bit more intense
物体逃离地球
And so actually you’d have to throw
需要用更大的力
something a bit harder to get it to
来克服地球引力
escape from the Earth’s pull of gravity
如果继续压缩地球
And if you kept squishing the Earth and squishing the Earth
最终当引力大到一定程度
eventually you’d reach a point where the gravitational
逃逸速度
pull was so strong that that escape velocity became
相当于光速
equal to the speed of light and
而又因为我们不可能
Because we can’t get anything to go
让除了光以外的任何物体达到光速
at the speed of light apart from light, and in particular
特别是我们无法超过光速
we definitely can’t get anything to go faster
那就意味着如果把地球压缩到一个点
than light, that means if you then squish
没有任何物体能逃离
it a tiny bit more then nothing can escape
甚至光也无法逃逸
not even light can escape
没有任何物体能逃离因为
nothing can escape from it because suddenly in order
你需要
to escape from it you have to make something
比光速还快
travel faster than light in order to do so
在广义相对论中
But a black hole
黑洞实际上比这更具有灾难性
in general relativity is actually more sinister than that
不仅仅是光不能逃离
It’s not just that light can’t escape,
在广义相对论里
a black hole in G.R., there is
没有任何办法能从黑洞中逃逸
literally no way to get out of it
如果只是逃逸速度很高 你总是可以
[um] If it was just a matter of the escape velocity being high you could always build a ladder
达到那个逃逸速度然后离开
Climb out of it and
用一个足够强大的火箭
with a sufficiently powerful rocket get away
但是没那么简单 时间和空间
[uh] But there’s actually more to that space and time
当你进入事件视界的时候坍塌在一起
Collapses in on itself as you enter the event Horizon of a black hole in G.R.
并且完全没有方法从中逃逸
And there’s literally no way to escape from it Brady:
我们都知道黑洞里有个叫奇点的东西 但根据你所说
Now, we all know black holes involve these things called singularities, but from what you’re saying
不需要
it sounds like you don’t
达到奇点的程度
have to get as far as a singularity
就可以使光无法逃逸
to get to a point where light can’t escape.
它可以比奇点的体积大很多
It could be quite a lot bigger than a singularity. Professor:
的确如此 而且事实上 很长时间以来
Indeed and in fact, so these the kind of the thought experiment
我通过广义相对论做出了一些思维实验
I’ve just gone through predates general relativity by a long time
我记得好像是拉普拉斯还是谁
I think probably laplace or someone was the first
第一个想到这个的
people who — person — who actually thought this
他意识到在某一点
through and realized there was a point
你会创造出一个东西叫做
where you would create a thing called a
黑洞
black hole and in, you know,
如果只考虑牛顿力学的引力
if you, just dealing with Newtonian Gravity
仍然存在黑洞 你可以创造一个黑洞
you still have a black, you can create black holes
但是只有你说 好吧
It’s only when you then say okay
然后呢?你尝试并解决了
So what, when you try and solve the set
广义相对论的方程式
of equations as to what’s going on within general relativity
当你全部做完之后才明白
When you’ve gone through this process that’s when you realize
实际上你创造出了一个奇点
that you actually create a singularity by doing that.
在广义相对论里 时间和空间被压缩
In G.R. space and time becomes compressed such
你在时空里做的任何一个运动
that any movement you make in time or space
都把你带向
Takes you towards
物质中心 这就是
that center of the thing and actually that’s what led
霍金和彭罗斯在60年代表示
[uh] Hawking and Penrose in the late 60s to suggest that
在黑洞中心必须有一个奇点的原因
you have to have a singularity at the center of a black hole essentially.
最终方程不可避免地无解了 你又重来
And then eventually your equations inevitably break down and so you have to repeat,
黑洞的存在
the very existence of black holes and the
以及你以为的奇点
singularity that you’ve seemed
那个看起来存在于黑洞的中心
It looks like you have at the center of them,
都表明爱因斯坦的理论不是完整的
tells you that Einstein’s theory is not a complete theory
最多只是一个有效的理论
It’s at best an effective theory that needs to
当你开始讨论时它就需要被别的所替代
be replaced by something else when you start talking about,
高能量
you know, high energies, strong
强引力场 等等 即便是谈到光子
gravitational fields, and so on and so forth Even when you get to photons, things with no
完全没有质量的物质 它们依然被引力所牵引
mass at all, they still get pulled by gravity,
我们可以从这个叫做引力透镜的现象里直接看到
and we can see that directly through this phenomenon called gravitational lensing
当光从一个质量巨大的物体旁边穿过时
That way you’ve got like light from something passing a massive body,
比如一个星系之类的
like a galaxy or something like that,
你可以实际上看到光的路径
you can actually see that the path
被弯曲了
of light has been bent
被引力弯曲了 所以的确引力有影响作用
by gravity and so actually gravity is affecting
甚至连光的路径都被改变了
even light its path is being diverted by
所以光也被引力场牵引
it so it’s being pulled by the
所以 甚至光都不对引力免疫
Gravitational field so even lights not immune to gravity.
区别是
Now the thing that’s different
光不会减速
is that light doesn’t slow down because light always travels
因为光的速度永远保持不变
at the speed of light,
你可以这么想
so if you think about, you know,
假如你在一个压缩的物体上
you’re on one of these incredibly compact objects
然后把一束光向上射出 会发生什么?
and you’re shining a light upwards and so, what happens?
这不像在空气里扔一块石头
It’s not like throwing a rock in the air
石头重新掉下来
that it comes back down again, with light
光会一直以光速远离你
it will keep traveling away from you at the speed of light,
但是光在消耗能量
but it’s using up energy.
还有另一种可能 也许是
Might be another way to think about these things is the energy
是将动能转换成另一种能量
that you’re turning the kinetic energy of something
如果一块岩石远离地球表面时 动能转化成势能
If it’s a rock into its potential energy as it goes away
光也是一样的
from the surface is the same with light,
但光失去能量
but the way that light loses its energy
不是通过减速来实现的
isn’t by slowing down,
光失去能量的方法是变化颜色
the way that light loses energy is by changing color.
光通过颜色变化失去能量
It would lose its energy by changing color by,
从光谱的蓝色一端开始
you know, starting at the the blue end
到达光谱的红色一端
of the spectrum and ending up at the red end of the spectrum
在红色之后 变成红外线 无线电
and then beyond red it would turn into infrared, radio waves,
最终 在逃逸之前
and actually, before it escaped, it
光用完了所有的能量 然后红移到什么也没有
would have used up all its energy and kind of red shifted to nothingness,
没有剩下的能量来逃逸
there’ll be no energy left to escape
所以这些我们称之为
So little lone black holes,
恒星质量黑洞的孤独小黑洞 可以成为
which we call stellar-Mass black holes, can be one of
恒星演变的其中一个终结方式
the several end points to the evolution of a star
他们绝不是最常见的终结方式
They’re by no means the most common
所以大部分恒星 比如我们的太阳
end point so most stars like our own sun
最终会变成白矮星
Will turn into a white dwarf at the end
然后衰落成几乎什么都没有
of their life, and then fade into basically nothingness.
如果一颗恒星
If you have a star
有足够大的质量
that’s massive enough, and the mass of
而且质量几乎掌管了恒星的整个生命周期
the star governs pretty much its entire life,
它要么会变成一颗中子星
it will either turn into a neutron star
通过一次超新星爆发 或者如果它质量更大
through a Supernova, or if it’s even more massive,
它会变成密度更大的一个物体
it’ll turn into an even denser object.
那就是黑洞
which is the black hole, and so,
所以存在很多恒星
you know, there are a lot of stars out there
很多黑洞
so there are a lot of black holes out there
但是黑洞不是在银河系里普遍存在 到处都是的
[um] but they’re by no means sort of ubiquitous and and littering the Galaxy
我们知道引力一直存在
we know there’s always gravity,
因此一直有东西把物体拉扯到一起
so there’s always something pulling things together
所以
so the
一个更突出的问题是
sort of sometimes the more salient question is
是什么阻止了所有恒星坍塌成黑洞
what stops everything collapsing into black holes and so,
比如说 在太阳中
for example, in something like the sun,
在中心发生着核聚变
you’ve got the nuclear fusion in the middle
在产生能量 加热所有东西
which is producing the energy, which is heating things up,
使得太阳膨胀着
which is kind of keeping it puffed up,
如果你关闭核聚变反应
but if you were to turn off that nuclear fusion,
那么太阳就会开始坍塌
then the sun would start to collapse down and
引力会不断拉扯
gravity would pull it and pull it and
最后
pull it and then you say, okay,
什么东西阻止了这一切?
so what else could stop it?
核聚变的来源被切断了
I’m no longer got my source of fusion,
结果证明有一些东西可以帮助阻止塌陷
and it turns out there are few things that might help out.
比如一种电子简并压力
[um] So this thing called Electron degeneracy pressure
大概意思就是 电子不喜欢互相被挤在一起
[um] Which is, you know, which is a very electrons basically don’t like being squashed close together
所以电子简并压力可以阻止
And so Electron Degeneracy pressure will stop something
太阳一直坍塌成一个黑洞
like the sun from collapsing all the way to a black hole
太阳会变成一个叫白矮星的物体
It’ll turn it into a thing called a white dwarf,
被电子简并压力所支持
which is held up by Electron degeneracy pressure.
如果质量再大一点 即使是电子简并压力也不能阻止引力
if it was a bit more massive than even electron degeneracy pressure wouldn’t do it,
引力再一次占据优势了
gravity would win again,
然后就会
so it would say’to hell
把电子都挤在一起
with this’ squash all the electrons together
然后进一步塌陷
And then it will collapse down further, to
到达原子核密度
kind of nuclear density, at that point you
那是一个中子星就被创造出来了
create a thing called a neutron star
然后有一种中子简并压力
And there’s a thing called neutron degeneracy pressure,
就是中子不喜欢被压在一起
which is that neutrons don’t like being squashed very close together either
然后就停止了塌陷过程 恒星终结成了中子星 如果比这质量还大一点
[um] And so that will halt the collapsing and end up with a neutron star, but then it’s a little bit more massive than that,
可能是太阳两倍的质量
so maybe about twice the mass
比那更多一点
of the sun, bit more than that,
即使是电子简并压力 中子简并压力都不能阻止引力
then even electron, even the neutron degeneracy pressure won’t stop it
恒星会持续塌陷
and then it will keep collapsing, and then,
据我们所知 就没有什么可以停止塌陷
as far as we know, there’s nothing that will stop that collapse.
我们可能遗漏了一些物理原理 可能有些过程
Now maybe we’re missing some physics. Maybe there is some process
我们不知道的过程可以停止坍塌
we don’t know about which would actually halt that collapse,
我们不知道那是什么
but we don’t know what it is
但它们都很无聊
but they’re the boring ones, let me tell
有趣的东西是
you about the interesting ones, the interesting ones are
在银河系中心的
the ones that live in the middle of
质量巨大的物体
Galaxies which are enormous they’re very very massive

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视频概述

黑洞、引力以及恒星的几种结局

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视频来源

https://www.youtube.com/watch?v=gcsaK3QYsdo

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