宇宙时空之旅（2014）

Cosmos: A SpaceTime Odyssey S01E13

Part 2 April 25, 2021, 12:41 p.m.

他发现这里的辐射强度
he found that the radiation
是地面上的两倍多
was more than twice as strong as on the ground.
辐射一定来自于地球外
The radiation must be coming from above.
这就是为什么地面上强度更低
That's why its intensity was weaker on the ground--
因为辐射的绝大部分被地球大气层吸收了
the Earth's atmosphere was absorbing most of it.
有人认为辐射来自于太阳
Some thought that the radiation might come from the Sun.
为验证这一假设赫斯安排
To test that idea, Hess timed one of his ascents
在一次日食时升空观测
to coincide with a solar eclipse.
然而日食对于辐射强度并没有影响
But the eclipse had no effect on the radiation.
赫斯还发现
Hess also found that
不论白天和黑夜辐射强度是一样的
the radiation was just as strong at night as in daylight.
辐射来自天外但又不是来自太阳
It was coming from above, but not from the Sun.
赫斯当时不知道的是
What Hess did not know
太阳风的速度并没有这么快
was that the solar wind doesn't move that quickly.
因此虽然是错误的原因
And so, for the wrong reason,
他却得到了正确的结论
he came to the right conclusion.
赫斯发现了宇宙线
Hess had discovered cosmic rays--
亚原子粒子流以近乎光速
showers of subatomic particles that crisscross the universe
在宇宙中纵横穿梭
at literally the speed of light.
如果没有地球大气层的屏蔽作用
Without the shielding effect of the Earth's atmosphere,
宇宙线将是致命的
they would be lethal.
有些宇宙线携带的能量相当高
Some cosmic rays can carry as much energy
就像是步♥枪♥射出的子弹
as a bullet fired from a rifle.
几十年后人们才发现这些宇宙线可能来自
It would take decades to trace those cosmic rays back
一场剧烈得难以想象的死亡爆♥炸♥
to a death of unimaginable violence.
维克托·赫斯在奥地利上空
The cosmic rays that Victor Hess detected
检测到的宇宙线成为科学家们的迷题
in the skies above Austria posed a mystery to scientists.
地球上矿物的放射性
Radioactivity in minerals on Earth--
比如铀矿
like uranium ore--
来自于原子的衰变
comes from the disintegration of atoms.
然而宇宙线的起源却不同
But cosmic rays were of a different nature.
它们比赫斯当时世界上已知的
They were far more powerful
任何东西都强大得多
than anything known in Hess's world.
科学家们为宇宙线可能的来源
Scientists wondered for two decades
思索了二十年
what could possibly produce cosmic rays.
弗里茨·兹威基出现了
Enter Fritz Zwicky,
你肯定没听说过他但他是最聪明的人之一
the most brilliant man you've never heard of.
1933年他和一名同事发现了
In 1933, he and a colleague discovered
有些恒星会在几周内变得
that some stars flare up to become as bright
像它所在的整个星系一样亮
as their entire galaxy for a few weeks,
然后再黯淡下来
before fading out again.
弗里茨·兹威基是第一个理解
Fritz Zwicky was the first person
这一现象的人
to understand what just happened.
他正确地推测出
He correctly surmised that
这是大质量恒星的死亡方式
this is the way a massive star dies--
它把内部物质轰向太空
it blows its guts out into space.
他把这种恒星死亡的过程叫做"超新星爆发"
He called this kind of stellar death a "supernova"...
并预言死亡中的恒星其直径
and predicted that the dying star would shrink
将从150万千米收缩到仅15千米
from about a million miles across to only ten.
恒星尸体的密度如此之大
This corpse would be so dense
上面沙粒般大小的物质就将
that a single grain of it would weigh as much
和埃及巨大的金字塔一样重
as the great pyramid in Egypt.
它将几乎完全由
It would consist almost entirely
被称作中子的亚原子粒子构成
of subatomic particles called neutrons,
所以他把这些奇异的天体称为"中子星"
so he named these bizarre objects "neutron stars."
在兹威基预言中子星存在的三十五年之后
And 35 years after Zwicky predicted their existence,
天文学家们开始寻找这些天体
astronomers began to find them.
如果它们快速旋转并有规律地发出脉冲和能量
We call them "pulsars" when they spin rapidly and
我们就把它们称为"脉冲星"
emit regular pulses and radio energy.
超新星爆发和中子星
Supernovas and neutron stars could account
是很大一部分宇宙线的来源
for a wide range of cosmic rays,
但不包括能量最高的那些宇宙线
but not the most energetic ones.
已知科学尚无法解释那一部分的来源
Nothing yet known to science can explain them,
但我们并不气馁
and we're fine with that.
这正是我对科学着迷的地方
It's one of the things I love about science,
我们不用不懂装懂
we don't have to pretend we have all the answers.
兹威基还提出了一个想法
Zwicky also came up with the idea
星系的引力会使它周围的空间结构扭曲
that the gravity of a galaxy warps the fabric of space around it,
就像透镜一样
to act like a lens.
这将使来自其正后方那些星系的光线
This distorts and magnifies light
发生偏转和放大
from any other galaxy lying directly behind it.
地球上的天文学家将观测到
So, astronomers on Earth would see multiple images
同一遥远星系的多个扭曲的镜像
of that same distant galaxy,
就像在哈哈镜中看到的一样
deformed, as in a funhouse mirror.
这一预言提出四十年后
40 years after this prediction,
我们真的开始发现这些现象
we started finding them too.
兹威基在上世纪三十年代还作出了另一发现
And Zwicky made yet another discovery back in the 1930s.
在研究后发星系团时
While studying the Coma Cluster of galaxies,
他注意到它们运动方式的一些有趣的现象
he noticed something funny about the way they moved.
这些星系运动得太快了
The galaxies were going way too fast,
快到它们本应该相互脱离的
so fast that they should've been flying apart from each other.
因为这些星系中所有的恒星
Because all the stars in all those galaxies
产生的引力都不足以维系这个星系团
had far too little gravity to hold the cluster together.
兹威基认为
Zwicky thought
有别的什么东西把它们约束在了一起
that something else must be binding them to each other.
这一尚未发现的神秘物质
That mysterious missing component
其质量将会是这些恒星
would have to weigh something like 50 times as much
本身质量的五十倍之多
as the stars themselves.
然而没有人关注过这一大胆的假设
But no one paid much attention to this wild notion.
这只是兹威基的另一个疯狂想法
Just another one of Zwicky's crazy ideas.
在我们的太阳系中
In our Solar System,
最内行星水星运行得比
the innermost planet, Mercury, moves much faster
最外行星海王星快得多
than the outermost one, Neptune.
这是理所当然的不是吗
And that makes sense, right?
你越用力推或拉某个物体
The harder you push or pull on something,
它就跑得越快
the faster it goes.
太阳的引力随着距离增加而减弱
The Sun's gravity weakens with increasing distance,
因此越是远离太阳的行星运动得越慢
so, the planets that are farther from the Sun move slowly.
人们都以为一个星系的最外侧的恒星
Everyone expected that the outermost stars in a galaxy
也会有相同表现
would act the same way.
绝大多数恒星向星系中心聚集
Most of the stars are concentrated towards the center,
它们引力的合力会作用到其他恒星上
so, their collective gravity pulls on the other stars
就像太阳引力作用到行星上一样
the same way the Sun pulls on the planets.
然而在上世纪七十年代天文学家
But in the 1970s, when astronomer
薇拉·鲁宾在研究仙女星系时
Vera Rubin studied the Andromeda Galaxy,
她发现其外层恒星并不遵循这一规律
she discovered that the outer stars obeyed no such rule.
不像太阳系中的外层行星
Unlike the outer planets of the Solar System,
星系中的外层恒星
the outer stars in the galaxy
和更靠内层的恒星运动速度是一样的
were all going at the same speed as the stars that were closer in
比人们预计的速度快得多
and they were moving way faster than expected.
"很有意思" 薇拉想
"That's funny," Vera thought.
"仙女星系一定有些什么古怪的地方"
"There must be something weird about the Andromeda Galaxy."
因此她研究了另一个星系
So she looked at another galaxy.
一样的现象
Same story.
第三个星系也是一样
And another.
薇拉研究了六十个星系
Vera studied 60 galaxies
发现它们似乎都
and found that all of them
违反了物理学的核心定律之一
seemed to be violating the Law of Gravity,
万有引力定律
a core principle of physics.
在起初一些有建设性的质疑之后
After some initial healthy skepticism,
她的同事们也开始了研究
her colleagues looked for themselves,
并发现薇拉是正确的
and found that Vera was right.
并不是艾萨克·牛顿的万有引力定律错了
It's not that Isaac Newton had gotten the Law of Gravity wrong,
薇拉·鲁宾发现的是某些
Vera Rubin had discovered that the gravity
质量巨大却又不可见的物质
of something massive and invisible
其引力驱使恒星运动得更快
was forcing the stars to go fast.
这时有人想起了疯狂的老弗里茨·兹威基
And then, someone remembered crazy old Fritz Zwicky,
而星系团中未知的
and the unknown source of gravity
引力来源或许是
in the galaxy clusters
他早在1933年就提出的"暗物质"
that he called "dark matter," back in 1933.