Dark matter: The matter we can't see - James Gillies

Translator: Andrea McDonough Reviewer: Jessica Ruby

翻译人员: Tianshu Wang 校对人员: Gabriella Hu

The ancient Greeks had a great idea:

古希腊人有个很好的想法：

The universe is simple.

宇宙很简单。

In their minds,

在他们看来，

all you needed to make it were four elements:

宇宙的一切 都由四种元素组成：

earth,

土壤、空气、火，

air,

fire,

and water.

还有水。

As theories go, it's a beautiful one.

这个美妙的理论继续发展，

It has simplicity and elegance.

它既简单，又优雅。

It says that by combining

它说，只要用不同的方式

the four basic elements in different ways,

组合这四种元素，

you could produce all the wonderful diversity of the universe.

就能得到宇宙中 多样的一切。

Earth and fire, for example,

比如说，土壤和火

give you things that are dry.

能合成干燥的东西。

Air and water, things that are wet.

空气和水能合成湿的。

But as theories go, it had a problem.

但是随着理论发展， 问题来了。

It didn't predict anything that could be measured,

它的预测里， 没有能被测量的东西，

and measurement is the basis of experimental science.

而测量是实验科学的基础。

Worse still, the theory was wrong.

更糟的是， 这个理论根本不对。

But the Greeks were great scientists of the mind

不过，希腊人是伟大的哲学家

and in the 5th century B.C.,

而且在公元前5世纪，

Leucippus of Miletus came up

留基伯提出了

with one of the most enduring scientific ideas ever.

有史以来最久经考验的理论。

Everything we see is made up

我们能看到的一切

of tiny, indivisible bits of stuff called atoms.

都由一种叫原子的 看不见的微粒组成。

This theory is simple and elegant,

这个理论简单而优美，

and it has the advantage

而且比起四元素说

over the earth, air, fire, and water theory

of being right.

它更有希望被证实。

Centuries of scientific thought and experimentation

几个世纪的科学思考和实验

have established that the real elements,

证实了真实的物质，

things like hydrogen,

比如氢、碳、或者铁，

carbon,

and iron,

can be broken down into atoms.

都能被分解成原子。

In Leucippus's theory, the atom is the smallest,

留基伯的理论中，

原子是物质最小的组成部分，

indivisible bit of stuff that's still recognizable

as hydrogen,

就像氢、碳、或者铁。

carbon,

or iron.

The only thing wrong with Leucippus's idea

留基伯理论中唯一的错误，

is that atoms are, in fact, divisible.

就是原子其实仍然可分。

Furthermore, his atoms idea turns out

而且人们发现，他的理论

to explain just a small part

只能解释宇宙组成的一小部分。

of what the universe is made of.

What appears to be the ordinary stuff of the universe

宇宙中看似常见的物质，

is, in fact, quite rare.

事实上相当稀少。

Leucippus's atoms, and the things they're made of,

留基伯的原子， 以及它们的组成

actually make up only about 5%

其实只占了宇宙的5%。

of what we know to be there.

Physicists know the rest of the universe,

物理学家知道，

95% of it,

宇宙剩下的95%

as the dark universe,

都是暗宇宙，

made of dark matter and dark energy.

即暗物质和暗能量，

How do we know this?

我们是怎么知道的？

Well, we know because we look at things

因为如果我们看着什么，

and we see them.

我们就会看见什么。

That might seem rather simplistic,

看起来很简单， 其实非常深奥。

but it's actually quite profound.

All the stuff that's made of atoms is visible.

所有组成原子的物质 都是可见的。

Light bounces off it, and we can see it.

它们反射光，从而被我们看见。

When we look out into space,

当我们仰望星空，

we see stars and galaxies.

就能看见星星和星系。

Some of them, like the one we live in,

其中有一些， 和银河系一样，

are beautiful, spiral shapes, spinning gracefully through space.

美丽，螺旋状， 在宇宙中优雅地旋转。

When scientists first measured the motion

科学家在1930年代

of groups of galaxies in the 1930's

第一次测量了星系群的运动

and weighed the amount of matter they contained,

和它们包含物质的重量，

they were in for a surprise.

他们非常惊讶。

They found that there's not enough visible stuff

他们发现 没有足够的可见物质

in those groups to hold them together.

来让物质聚在一起。

Later measurements of individual galaxies

接下来对各个星系的单独测量

confirmed this puzzling result.

也证实了 这个令人困惑的结果。

There's simply not enough visible stuff in galaxies

星系中没有 足够的可见物质

to provide enough gravity to hold them together.

来产生足够支持它们的引力。

From what we can see,

在我们看来，它们会飞散开， 可是它们没有。

they ought to fly apart, but they don't.

So there must be stuff there

that we can't see.

所以一定有什么物质 是我们看不见的。

We call that stuff dark matter.

我们叫它们：暗物质。

The best evidence for dark matter today

如今，暗物质存在的最佳证明

comes from measurements of something

是测量一种

called the cosmic microwave background,

叫“宇宙微波背景辐射”的余辉，

the afterglow of the Big Bang,

产生在宇宙大爆炸中，

but that's another story.

那又是另一个故事了。

All of the evidence we have

我们所有的证据

says that dark matter is there

都表明了暗物质存在，

and it accounts for much of the stuff

并且是布满天穹的美丽星系的 主要成分。

in those beautiful spiral galaxies

that fill the heavens.

So where does that leave us?

所以我们要怎样呢？

We've long known that the heavens

我们早就知道

do not revolve around us

地心说是错的，

and that we're residents of a fairly ordinary planet,

我们生活的星球， 其实相当普通，

orbiting a fairly ordinary star,

它的恒星也很普通，

in the spiral arm of a fairly ordinary galaxy.

位于一个普通星系的旋臂。

The discovery of dark matter took us

发现暗物质

one step further away from the center of things.

使我们又揭开了 物质的一层面纱。

It told us that the stuff we're made of

我们发现，组成我们的物质

is only a small fraction of what makes up the universe.

只是宇宙极小的一部分。

But there was more to come.

剩下的还有很多。

Early this century,

本世纪初， 科学家研究了宇宙的外围

scientists studying the outer reaches of the universe

confirmed that not only is everything moving apart

并证实，所有东西 都在互相原理，

from everything else,

as you would expect in a universe

想想开天辟地的大爆炸 这并不令人意外，

that began in hot, dense big bang,

but that the universe's expansion

而且，宇宙膨胀的速度

also seems to be accelerating.

似乎也在加快。

What's that about?

这是怎么回事？

Either there is some kind of energy

要么有一种能量

pushing this acceleration,

推动了这种加速，

just like you provide energy to accelerate a car,

就像你让汽车加速一样，

or gravity does not behave exactly as we think.

要么就是引力的作用 和我们想的不完全一样。

Most scientists think it's the former,

大多数科学家相信前者，

that there's some kind of energy driving the acceleration,

即有一种能量，推动了加速，

and they called it <i>dark energy</i>.

他们叫它：暗能量。

Today's best measurements allow us to work out

当下最好的测量 使我们能够算出

just how much of the universe is dark.

宇宙中暗部分有多大。

It looks as if dark energy makes up

看起来，暗能量

about 68% of the universe

组成了宇宙的68%，

and dark matter about 27%,

暗物质则占27%，

leaving just 5% for us

我们，和我们能看见的

and everything else we can actually see.

只有5%。

So what's the dark stuff made of?

那暗物质和暗能量的组成是什么？

We don't know,

but there's one theory, called <i>supersymmetry</i>,

我们不知道，

但有一个叫“超对称”的理论

that could explain some of it.

可以解释其中的一部分。

Supersymmetry, or SUSY for short,

超对称简称SUSY，

predicts a whole range of new particles,

预测了很多新粒子，

some of which could make up the dark matter.

其中的一些也许可以组成暗物质。

If we found evidence for SUSY,

如果能证明SUSY，

we could go from understanding 5% of our universe,

我们就能从理解宇宙的5%，

the things we can actually see,

也就是我们能看见的东西，

to around a third.

到理解大约三分之一。

Not bad for a day's work.

对一天的工作来说，并不赖。

Dark energy would probably be harder to understand,

理解暗能量也许会更难，

but there are some speculative theories out there

但也有一些投机理论

that might point the way.

也许能指出道路。

Among them are theories that go back

其中一些理论 能追溯到

to that first great idea of the ancient Greeks,

古希腊人的最早的伟大想法，

the idea that we began with several minutes ago,

就是我们几分钟前讲过的

the idea that the universe must be simple.

宇宙一定很简单的想法。

These theories predict that there is just a single element

这些理论预言，宇宙的多样

from which all the universe's wonderful diversity stems,

全都来自一个元素，

a vibrating string.

也就是“弦 ”。

The idea is that all the particles we know today

我们知道的一切微粒

are just different harmonics on the string.

都是弦的不同谐波。

Unfortunately, string theories today

不幸的是，

are, as yet, untestable.

弦论至今都无法被证明。

But, with so much of the universe waiting to be explored,

不过，可以探索的宇宙如此广袤，

the stakes are high.

风险很高。

Does all of this make you feel small?

这一切是否让你觉得自己很渺小？

It shouldn't.

不用这样

Instead, you should marvel

相反，你应该惊叹 我们已经发现的一切，

in the fact that, as far as we know,

you are a member of the only species in the universe

你是宇宙中能思考 自己这个奇迹的

able even to begin to grasp its wonders,

唯一物种的一员，

and you're living at the right time

而且你生逢其时，

to see our understanding explode.

能看到我们的探索。