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引力波

Gravitational Waves Are Awesome

爱因斯坦的广义相对论曾预言
Gravitational waves are ripples in the fabric of spacetime,
引力波是时空布上的波纹
predicted by Einstein’s laws of general relativity,
但是 引力波很难探测到
but they are incredibly difficult to detect.
要探测它们 你需要能精确测量
To see them,you need a detector that can accurately measure distances
比质子长度还小10000倍的探测器
10,000 times smaller than a proton.
太神奇了
That’s crazy!
这就像要以头发丝的精确度
That’s like trying to measure the distance from our Sun
测量太阳到离它最近的恒星的距离
to the nearest star to accuracy of the width human hair.
不过我们现在有一项设备可以做到 ALIGO
But we have a technology on Earth that can do that: ALIGO.
高级激光干涉引力波观测站
The Advanced Laser Interferometer Gravitational-wave Observatory,
早在2015年11月的某个星期一早上
and back in November 2015, on a Monday morning,
人类首次用LIGO检测出引力波
LIGO detected the first gravitational wave that humans have ever directly observed.
它们来自哪里 对空间科学又意味着什么
Where they came from and what this means for space science
这简直难以想象
is nothing short of mind blowing!
我来给你讲个故事
This is the story.
很久很久以前 在很远的地方有一个星系
A long long time ago, in a galaxy far far away.
我不是开玩笑 13亿年前 离我们13亿光年的地方
I’m not kidding, 1.3 billion years ago and 1.3 billion light years away,
有两个黑洞陷入彼此的轨道相互旋转 越靠越近
two black holes were stuck in a perilous orbit around one another,getting closer and closer.
黑洞非常神奇 它们的引力 它们弯曲时空的能力
Black holes are incredible objects, the pull of their gravity – the amount they bend spacetime
强大到连光都逃脱不了
– is so strong that no light can escape them.
没有人知道黑洞里到底有什么
No one knows what exists in the centre of a black hole
因为一般的物理学不适用于黑洞
as normal physics completely breaks down.
我们只知道黑洞的密度超级无敌大
What we do know is that they are infinitely dense.
两个旋转的黑洞中 一个质量是太阳的29倍
One of these orbiting black holes was 29 times the mass of the Sun
另一个是太阳的36倍
and the other was 36 times the mass of the Sun,
但是它们的直径只有200千米
but they were only about 200km wide.
跟太阳的一百万千米比起来 简直小的可怜
Which is tiny in comparison to the Sun which is over a million kilometres wide!
这两个黑洞以极快的速度绕着对方旋转
And these black holes were orbiting each other really really fast,
频率跟搅拌机的叶片差不多
about the same frequency as the blade on a blender.
想象一下 两个大块头飞速旋转
Imagine that, such massive objects rotating so quickly.
会让时空泛起涟漪 这就是引力波
These orbiting masses created ripples in the fabric of spacetime called gravitational waves,
它们靠得越近 引力波就越强
and the closer they orbited the bigger these waves got,
最后 它们会以半光速的速度相撞
until the black holes collided at half of the speed of light.
它们融合以后会生成一个钟形的新黑洞
And when they merged they formed a new black hole that rang kind of like a bell,
同时以引力波的形式释放出巨大的能量
throwing out colossal amounts of energy as gravitational waves
直到它变成一个完美的球体
until it settled into a perfect sphere.
而完成这一切只需要0.2秒
And all of this happened in 0.2 seconds.
在碰撞时 大量质量被转化成引力波能量
And in the collision, they turned a huge amount of mass into gravitational wave energy.
碰撞丢失的质量是太阳质量的3倍
They lost a mass equal to three times the mass of the Sun
都转化成了引力波能量
which got turned into gravitational wave energy
这是用爱因斯坦的质能方程E=mc^2计算出来的
by Einsteins equation E=mc^2.
由此产生的巨大引力波以光速向四周辐射
This created a huge wake of gravitational waves that ripped out in all directions at the speed of light.
这就是触动我的东西 最后五分之一秒
And, and this is the thing that gets me, over that last fifth of a second
这个碰撞释放出的能量 超出整个宇宙中
this collision released more than ten times more energy than
其他所有恒星释放出的总量的十倍之多
total output of all of the stars in the entire rest of the Universe!
真是很让人费解啊
It just completely boggles the mind!
与此同时 我们的地球
Meanwhile on Earth At this exact time
跟现在所看到的大不相同
our planet was looking very different to what we see now.
那时的地球就是一块荒地
It was a barren wasteland
没有草没有树 其实 动植物都没有
there was no grass or trees, in fact no plants or animals at all.
这个阶段的生命体就是
Life at this stage had only come as far as
一些生活在海洋的微小多细胞生物
microscopic multicellular creatures that lived in the sea.
当引力波穿越空间来到地球
And while the gravitational waves tore through space towards us
地球上所以的复杂生命体都在进化生长
all of the complex life on earth evolved and grew:
出现了动物和植物 两栖动物开始爬上岸
plants and animals developed, amphibians crawled on land,
很多生物都灭绝了 爬行动物 恐龙和哺乳动物
there was extinctions, reptiles and dinosaurs and mammals, more extinctions.
灵长类动物进化到人类文明
Primates evolved into all of human civilization
直到2015年11月12号星期六
right up until Saturday 12th November 2015
那天科学家们打开了LIGO 开始了第一次测试
when the scientists at LIGO turned it on to begin their initial tests.
仅仅2天 嘣 引力波飞速而来
A mere two days later and … boop … the gravitational waves flew past us
我们第一次直接检测到了引力波
and the first direct detection on Earth was made.
而且 引力波发出的声音就是 嘣
And that sound … boop … is actually what these waves sounded like.
虽然引力波是时空中的涟漪而非空气中的
Even though gravitational-waves are ripples in spacetime and not ripples in the air
它们以相同的频率震动
they vibrate at similar frequencies,
所以我们能把它们转化成声波来听到
so we can actually turn them into sound waves and listen to them
嘣 虽然它的声音一点都不特别
boop … It might not sound very impressive,
但引力波的探测却是科学的一大进步
but detection of gravitational waves means a huge amount for science.
这个探测结果意义重大
The results of this detection have already been profound.
这是我们第一次直接探测出黑洞
This is the very first time that black holes have been directly detected,
其实 只有引力的波才能直接检测它们
in fact gravitational waves are the only way you can directly detect them!
设想一下 这个年代我们所有跟宇宙有关的知识
Consider this: all of our knowledge about the Universe to this date
都来自测量光的望远镜
has come to us through telescopes that measure light
从电磁波谱的光 像无线电波 可见光
from the electromagnetic spectrum like radio waves, visible light,
X射线 或是通过检测器检测原子内的粒子
x-rays, or through detectors that measure subatomic particles.
但目前所存在的望远镜完全看不到引力波
But all of these existing telescopes are completely blind to gravitational waves.
这说明引力波在天文学上是个全新的东西
This means that gravitational wave astronomy is an entirely NEW THING,
一个全新的观察宇宙的方法
a whole new way to observe the Universe.
它已经解决了一些重要的科学问题
And it has already solved some important science questions:
引力波真的存在
gravitational waves exist,
黑洞真的存在 引力波以光速传播
blackholes exist, and gravitational waves travel at the speed of light.
这里介绍LIOG检测器如何工作
Here’s how LIGO detectors work.
它有两座L型的建筑组成
There are two L shaped buildings,
一座在华盛顿的汉福德
one in Hanford Washington,
另一座在路易斯安那州的利文斯顿
and another in Livingstone Louisiana make up LIGO
还有另外一个叫做VIRGO检测器
and also there’s another detector called VIRGO
在意大利的比萨附近
which is in Italy near Pisa.
地球上有几个检测器
Having several detectors on Earth
意味着科学家们能够核实来自太空的信号
means that scientists can verify a signal from space
通过看它是否出现在所有不同的检测器上
by seeing if it appears at all of the different detectors,
它们也相隔得很远因为这意味着他们能大概
and they are far apart because it means they can see roughly
通过对信号进行三个角度测量来了解引力波方向
in what direction the wave is coming from by triangulating the signal
即使这些波以光速传播
Even with these waves travelling at light speed
检测器之间也有几毫秒的误差
there is a delay of a few milliseconds between each of the detectors.
每一所L型的建筑都建有一个激光干涉仪
Each of these L shaped buildings houses a thing called a laser interferometer
激光从那里发射
where a laser is produced,
然后分成两束 从长达4千米的长臂飞出
then split into two beams which each fly down a 4km long arm,
然后被垂在顶端的重达40千克的
and then they are reflected off a 40kg pure silicon
纯硅质量测试仪进行反射
test mass which is hung from the ceiling.
它像钟摆一样悬挂于顶端
It is hung from the ceiling on a series of pendulums
以隔绝任何外界的干扰
to insulate it from any outside disturbances
例如卡车经过或是人们打喷嚏之类的
like trucks moving past, or people sneezing.
当你试着去检测灵敏度比原子核还要小的距离时
When you are trying to detect distances with a sensitivity less than the nucleus of an atom,
排除外部噪声非常重要
getting rid of external noise is very important.
每条长臂来回反射激光400次
Each arm bounces the laser back and forth 400 times
使得它的有效长度达到1600米
to make the arm effectively 1600km long,
并且每次激光都被放大让它变得更强
and each time around the laser is boosted to make it stronger.
在旅程最后 这束激光以这种方式被收集重合
Then after its journey the light is collected and recombined in such a way that
如果每条长臂都一样长
if the arms are the same length
从每条长臂发出的光就会相互抵消 不产生信号
the light from each arm cancels out producing no signal
但如果引力波涟漪般通过
But if a gravitational wave ripples past,
它会拉伸或压缩每条长臂
it will stretch or contract each of the arms
让两条长臂发出的光抵达检测器的时间发生轻微偏移
making the light from each arm arrive at the detector at slightly different times.
这说明当它们重合时 它们不再完全抵消
That means that when they are recombined, they will no longer fully cancel out,
这时就出现了一个信号
and a signal will appear.
这就是发生在十一月十四日的情况
And this is exactly what happened on the 14th November.
我很难想象 如果他们晚两天打开检测器
It’s crazy to me to imagine that if they had turned on this detector just two days later,
他们完全可能错过这个
they would have completely missed the signal
旅行了十三亿年才到达我们的信号
that had been travelling towards us for 1.3 billion years.
这让我不禁怀疑
This makes me wonder
我们已错过了多少从宇宙深处发出的信号
what other signals from deep space have we already missed,
那儿还有什么向我们呼啸而来 等着被我们检测
and what is still out there screaming towards us waiting to be discovered
我们仍然不知道
that we just don’t know about yet.
事实上 在我制作这个视频的时候
In fact at the time that I made this video
LIGO已检测到另一起更强烈的黑洞碰撞
LIGO has detected another even stronger black hole collision,
在以后的岁月里 我们期望能检测到更多
and we can expect a lot more in the coming months and years.
这已经完成了很多科学目标
It has already achieved many of its science goals,
还有更多的科学目标等着被它解决
there are many more it is aiming for.
例如 它可能让我们能更详细的
For example it might be able to give us a more accurate measure
测量宇宙膨胀的速度有多快
of how fast the universe is expanding,
以及宇宙中有多少暗能量
and so how much dark energy there is.
它让我们有可能看到是什么让恒星变成超新星
It will hopefully be able to look at what makes stars go supernova,
也让我们可能探索时空的本质
and might be able to probe the very nature of spacetime
了解它是否由宇宙弦组成
and see if it is made of things called cosmic strings.
但是最让人激动的是我们不知道它能发现什么
But the most exciting thing is that we don’t know what it will find.
这是科学最迷人的部分之一 当你有一个新工具
This is one of the best parts of science, when you’ve got a new tool
来窥视你之前从未接触过的真实的领域
to peer into a realm of reality that you’ve never been able to access before.
谁知道你会发现什么
Who knows what you’ll find?
可能你会发现某些解释宇宙的神秘物质
Maybe you’ll discover things that help explain some of the great mysteries of the Universe,
可能我们会发现我们完全不能解释的东西
maybe we’ll find things that we can’t explain at all,
然后我们不得不提出新的物理现象
and then we have to come up with new physics.
在任何情况下 我都发现它超级有趣
In any case I find it super exciting
我迫不及待的想看看更多的结果
and I can’t wait to see more results.
明白了吧 这些都是引力波天文学的基本要素
So there you go, those are the basics of gravitational wave astronomy.
嘿 我想对上一期视频的所有评论说声谢谢
Hey I just want to say thanks for all the comments on my last video,
我不能全部回复
I wasn’t able to reply to them all,
但全部都读过 有些正面的反馈很有意思
but I did read them all and the amount of positive feedback was amazing.
它让我想继续做更多这类视频来表达感谢
So it makes me want to carry on and make more and more of these videos so thanks for that.
在这个视频里 我还没有畅所欲言
As for this video, I didn’t get to cover everything I wanted to.
有关引力波天文学的资料非常有意思
This filed of gravitational wave astronomy is amazing.
在八分钟没我只能讲这么多了 如果你有问题
In eight minutes you can only cover so much, so if you are left with any questions
请在评论区留言 我会尽力回复的
please put them in the comments and I’ll try to reply to them
或者我会把最受欢迎的问题收集起来
or I’ll collect together the most popular ones
然后做个问题解答之类的东西
and do something later, a Q&A or something like that.
我也建立了赞助人账户
Also I have set up a Patreon account
如果你想支持我做更多这种视频
and so if you want to help support me make these videos
就去看看吧 另外 感谢收看 我们下期再见
go take a look at that, otherwise, thanks for watching and I’ll see you on the next video.

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视频概述

引力波是什么?人们为什么要检测引力波?它又是怎么被检测到的?相信你一定有这些疑问。那么,跟我一起来看看视频吧在里面寻找答案。

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视频来源

https://www.youtube.com/watch?v=AFhOzhe9mg4

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