了解宇宙是如何运行的（2010）

We live in the universe that lasts long enough
我们可以继续存在下去 膨胀速度不快也不慢
that we can be here, but expands gently enough
我们有时间形成我们的世界
that we have time to form.
宇宙已经延续了一百三十八亿年
The universe has lasted for 13.8 billion years,
多亏两股对立的力量：引力和膨胀
thanks to the opposing forces of gravity and expansion.
但这一幕平衡好戏会持续多久呢？
But just how stable is this balancing act?
我们的宇宙是否有足够数目的物质
Does our universe have just the right amount of stuff in it
防止膨胀失去控制
to keep it from runaway expansion
或者灾难性的大坍塌？
or catastrophic collapse?
在二十世纪二十年代 科学家们做数学计算
In the 1920s, scientists did the math,
结果令人担忧
and the results were anything but reassuring.
物质越多 引力就越大
The more matter you have, the more gravity you have.
在高密度的宇宙里 如果有过多的物质
If you have lots of matter in a very dense universe,
也许宇宙会重新开始坍塌
perhaps the universe begins to re-collapse.
相反 如果物质数目不足
Or, if you have very little matter,
宇宙会在大冻结中死去
the universe would freeze to death.
所以临界密度（二者之间的界线） 是多少？
So what is the critical density, the border between the two?
大约是每立方米五个氢原子
It's approximately five hydrogen atoms per cubic meter.
把五个氢原子放进一立方码的空间里
So think of a cubic yard, and put just five hydrogen atoms
这就是临界点
inside, and that is the tipping point.
如果放进的氢原子多于五个
If you put more than five atoms,
那么宇宙就开始坍塌
then the universe will begin to collapse.
如果放进的氢原子少于五个
If you have less than five atoms,
那么宇宙就继续膨胀
then the universe just keeps on going.
如果我们认为宇宙处于平衡态
If we thought the universe was balanced
临界密度问题向我们显示
on a tightrope before, the critical density question
这种平衡是多么的脆弱
showed us that the rope was more like a razor blade.
天文学家们做额外的测量
Yet, when astronomers took additional measurements,
他们对观察到的感到欣喜
they liked what they saw.
宇宙似乎有适当数目的物质
The universe appeared to contain just the right amount
维持在临界密度
of matter to stay at the critical density.
越来越多的间接证据
More and more, the indirect evidence
和理论的论据表明
and the theoretical arguments suggested
宇宙必须在坍塌的宇宙和
that the universe must be exactly at the boundary
一直膨胀的宇宙之间
between a universe that would collapse
取得精确的平衡
and one that would expand forever,
我们正摇摆于宇宙膨胀的危险边缘
that we were teetering on the hairy edge of expansion.
宇宙看似处于完美的平衡
The universe seemed so perfectly balanced
它会平静地步入晚年
that it would head quietly into old age.
在二十世纪七十年代 天文学家们做的一个观察
Then, in the 1970s, astronomers made an observation
令他们感到震惊
that shocked them.
宇宙充满了看不见的物质
The cosmos was filled with invisible stuff,
它的引力会导致灾难性的坍塌
and its gravity could cause a catastrophic collapse.
宇宙的平衡及及可危
The universe is balanced on a tightrope.
向哪一方倾斜 都会导致早死
On each side of the drop lies an early death,
一种结果是 失控的宇宙膨胀造成的大冻结
a Big Freeze, fueled by the runaway stretching of space,
别一种结果是 引力过度扩张造成的大坍塌
or a big crunch, the result of gravity overcoming expansion.
四十年前 科学家们相信
40 years ago, scientists believed we'd stay balanced
我们永远会在两种命运之间 处于平衡状态
between these fates for eternity.
现在 事情发生极大的变化
Now things have changed tremendously,
因为我们发现了 四十年前我们从未了解的东西
because we've discovered something we never knew about 40 years ago.
在二十世纪七十年代 天文学家们大吃一惊
In the 1970s, astronomers are stunned.
某种望远镜看不到的 未知的物质形态
Some unknown form of matter, invisible to telescopes,
使我们认为那里该有的东西 相形见绌
dwarfs what we thought was out there,
不是一部分 而是五倍的质量
not a fraction more, but five times more.
我们过去时常认为引力来自恒星
We used to think that gravity came from stars
以及我们看得见的物体 仅此而已
and objects you can see, end of story.
现在 我们认识到这些都是错误的
Now, we realize that that naive picture is actually wrong.
天文学家们
Astronomers make the discovery,
通过研究宇宙的规律性 有所发现
studying the clockwork nature of our universe.
太阳的巨大引力牵引着地球
The huge gravity of the sun holds the earth
和其它的行星 共舞一曲精致的圆形的舞蹈
and all the other planets in a delicate circular dance.
太阳的质量控制这些轨道的速度
The sun's mass controls the speed of these orbits.
太阳质量越大 行星的轨道运行速度
If it were more massive, the planets would orbit
就会越快
much more quickly.
太阳质量越小 行星公转一圈
And if it were smaller, it would take much longer
就要花更多的时间
for a planet to complete an orbit.
星系也是有规律地运行
Galaxies run like clockwork, too.
星系中心的巨大质量 牵引外部的恒星
The vast mass at the center pulls the outer stars
在圆形的、像行星一样的轨道上运行
into circular, planet-like orbits.
天文学家们在二十世纪七十年代
Astronomers make precise measurements
精确地测量这些星系的轨道
of these galactic orbits in the 1970s.
结果使一切发生改变
The results change everything.
星系正在快速地旋转
The galaxies were spinning too fast.
太快了
Way too fast.
甚至导致星系中心的超大质量黑洞
Even accounting for the supermassive black holes
有十分之九的质量 我们说不清去向
at their center, nine-tenths of their mass was missing.
公平地说 星系应该飞散
By rights, the galaxy should fly apart.
公平地说 地球早在几十亿年前
By rights, the earth should have been flung
就应该被扔到空旷的外♥围♥空间去了
into intergalactic space billions of years ago.
银河系不应该存在 可是
We should have no Milky Way galaxy, and yet,
我们的宇宙充满了星系
our universe is full of galaxies.
一定有另外一种巨大的引力源
An immense additional source of gravity
正在控制着星系
must be holding galaxies together.
但是不论天文学家的望远镜指向哪儿
but no matter where astronomers point their telescopes,
都看不见它
they see nothing.
既看不到微光 也看不到阴影
Not a glimmer, not a shadow.
无论这位新成员是什么 它不发出光线
Whatever this new stuff is, it doesn't emit light,
不反射光线 甚至不阻挡光线
reflect light, or even block light.
它们被称为暗物质
They call it dark matter.
我们已知宇宙的大部分物质
What we've learned is that most of the matter in the universe
都是不寻常的 都没有原子
is not ordinary stuff. It's not atoms.
它不是我们在地球上的实验室里
It's not particles we've yet detected in any experiment
发现的任何粒子
done here on earth.
它是某种我们称为暗物质的新粒子
It's some new kind of particle that we call the dark matter.
暗物质充满了宇宙
Dark matter fills the universe,
是普通物质的五倍
outstripping normal matter by 5-to-1.
大量的丝状暗物质 分布在宇宙各个角落
Vast filaments spread out throughout the cosmos,
明亮的星系团是暗物质最稠密的地方
and bright galaxies cluster where dark matter is thickest.
暗物质提供最基础的元素
Dark matter provides the scaffolding that underlies
不管宇宙中的物质如何构造自身
how the matter in the universe structures itself,
不管它去往何方 不管它做什么
where it goes, and what it does.
所以 暗物质主宰着
So, dark matter dictated
宇宙如何演化
how the universe unfolded.
大爆♥炸♥之初
It seems as if out of the hot Big Bang,
暗物质首先浓缩 早于普通原子
dark matter condensed first, before atoms,
暗物质开始形成块状
and dark matter began to become clumpy.
暗物质在形成块状后
The clumpiness then began to attract atoms
就开始吸引原子 进而形成星系
as they were formed later, and that formed galaxies.
在某种意义上 暗物质
And in some sense, the dark matter therefore
提供了诞生星系的摇篮
provides kind of a womb that allows the birth of our galaxy.
暗物质主宰了宇宙
Dark matter holds the universe together,
但它也会威胁并毁灭宇宙
but it also threatens to destroy it.
过去几十年 最令人惊异的发现之一就是暗物质
One of the most amazing discoveries of the past few decades is dark matter,
宇宙中存在的物质比我们知道的
the fact that there's much more matter in the universe
要多得多
than we were aware of.
所有的物质都有引力
And all of that matter has a lot of gravity.
所以 新物质一定有新的引力
So all this new matter, all this new gravity
使膨胀的宇宙慢下来
must be slowing down the expansion of the universe.
暗物质甚至会使宇宙的天平
Dark matter may even tip the cosmic scales
偏向引力
in favor of gravity,
战胜膨胀的力量 将整个宇宙
defeating expansion and pulling the entire universe
拉向炽热的死神
towards a death by fire.
这被称为大坍塌
It's called the big crunch,
宇宙大戏就此谢幕
and this is how it would play out.
一瞬间 宇宙失去控制
For a fraction of a second, the universe stalls,
膨胀与收缩之间的平衡被打破
poised between expansion and contraction.
然后 引力触发了一场大灾难
Then, gravity kicks off a cataclysm.
当你望向星空 你看到的第一件事
When you looked out, the very first things
已经调转方向
as it began to turn around that you began to see
曾经远离我们而去的星系