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The ancient Greeks had a great idea: The universe is simple.
古希腊人有个伟大的想法：宇宙很简单。
In their minds, all you needed to make it were four elements: earth, air, fire, and water.
在他们看来，宇宙的一切都由四种元素组成：土壤、空气、火还有水。
As theories go, it's a beautiful one. It has simplicity and elegance.
这个美妙的理论继续发展，它既简单，又优雅。
It says that by combining the four basic elements in different ways,
该理论称，只要用不同的方式组合这四种元素，
you could produce all the wonderful diversity of the universe.
你就能得到宇宙中多样的一切。
Earth and fire, for example, give you things that are dry.
比如说土加火，就会有一些干的东西。
Air and water, things that are wet. But as theories go, it had a problem.
而空气加水，就会得到湿的东西。但依照这理论，会有一个问题。
It didn't predict anything that could be measured, and measurement is the basis of experimental science.
它没办法预测出任何可以测量的事物，而测量又是实验科学的基础。
Worse still, the theory was wrong.
更糟的是，这理论是错的。
But the Greeks were great scientists of the mind and in the 5th century B.C.,
但希腊人仍是思想上伟大的科学家，在公元前5世纪，
Leucippus of Miletus came up with one of the most enduring scientific ideas ever.
米利都的留基伯提出有史以来最经得起考验的科学思想之一。
Everything we see is made up of tiny, indivisible bits of stuff called atoms.
我们看到的每样东西，都由微小、看不见的东西组成，这东西称作原子。
This theory is simple and elegant, and it has the advantage over the earth, air, fire, and water theory of being right.
这个理论既简单又优雅，而它超越了土、空气、水、火的理论，更接近事实。
Centuries of scientific thought and experimentation have established that the real elements,
几世纪以来的科学思想及实验，证实了实体的物质，
things like hydrogen, carbon, and iron, can be broken down into atoms.
像是氢气、碳、还有铁，都可以分解成原子。
In Leucippus's theory, the atom is the smallest, indivisible bit of stuff that's still recognizable as hydrogen, carbon, or iron.
在留基伯的理论中，原子是最小的、不可分的物质，可以区分为氢原子、碳原子、铁原子。
The only thing wrong with Leucippus's idea is that atoms are, in fact, divisible.
留基伯的想法里，唯一有问题的是，事实上原子也还可以再细分。
Furthermore, his atoms idea turns out to explain just a small part of what the universe is made of.
而且，他的原子说最终只解释了宇宙组成的一小部分。
What appears to be the ordinary stuff of the universe is, in fact, quite rare.
平常所见到的物质，实际上在宇宙中非常稀少。
Leucippus's atoms, and the things they're made of, actually make up only about 5% of what we know to be there.
留基伯讨论的原子、还有它们组成的物质，事实上只占了我们知道的物质的大约5%。
Physicists know the rest of the universe, 95% of it, as the dark universe, made of dark matter and dark energy.
物理学家认为其余的宇宙，就是那95%，是暗宇宙，由暗物质和暗能量组成。
How do we know this? Well, we know because we look at things and we see them.
我们是怎么知道的呢？嗯，我们会知道是因为我们有观察到。
That might seem rather simplistic, but it's actually quite profound.
听起来很简单，但实际上有点复杂。
All the stuff that's made of atoms is visible. Light bounces off it, and we can see it.
所有原子组成的物质是看得见的。它会反射光线，然后我们就看得到。
When we look out into space, we see stars and galaxies.
当我们观察宇宙时，我们会看到星星和银河。
Some of them, like the one we live in, are beautiful, spiral shapes, spinning gracefully through space.
有些就像我们居住的地方一样，很美丽、有螺旋的结构、优雅地在太空中旋转。
When scientists first measured the motion of groups of galaxies in the 1930's
当科学家在20世纪30年代第一次观测星系团，
and weighed the amount of matter they contained, they were in for a surprise.
并同时估算其质量时，他们大为震惊。
They found that there's not enough visible stuff in those groups to hold them together.
他们发现并没有足够的可见物质让这些星系团聚在一起。
Later measurements of individual galaxies confirmed this puzzling result.
之后对单独星系的观察证实了这个谜样的结果。
There's simply not enough visible stuff in galaxies to provide enough gravity to hold them together.
星系里就是没有足够的可见物质来提供足够的重力，让它们聚在一起。
From what we can see, they ought to fly apart, but they don't.
在我们看来，它们会飞散开，可是它们没有。
So there must be stuff there that we can't see. We call that stuff dark matter.
所以一定有什么东西是我们看不到的。我们把这东西称作暗物质。
The best evidence for dark matter today comes from measurements of something called the cosmic microwave background,
现今关于暗物质最有力的证据，来自于对于一种叫作宇宙微波背景辐射的观测，
the afterglow of the Big Bang, but that's another story.
也就是大爆炸后留下的余光，但这是另一段故事了。
All of the evidence we have says that dark matter is there
所有我们掌握的证据都说明了暗物质的存在，
and it accounts for much of the stuff in those beautiful spiral galaxies that fill the heavens.
而在天空中那些美丽的螺旋星系中，它占据了大部分的质量。
So where does that leave us?
这告诉了我们什么？
We've long known that the heavens do not revolve around us and that we're residents of a fairly ordinary planet,
长久以来，我们知道天空并不是绕着我们旋转，而我们只是一颗平凡行星上的居民，
orbiting a fairly ordinary star, in the spiral arm of a fairly ordinary galaxy.
绕着一颗平凡的恒星、座落在一个平凡星系的螺旋臂上。
The discovery of dark matter took us one step further away from the center of things.
暗物质的发现，带领我们更进一步了解物质的本质。
It told us that the stuff we're made of is only a small fraction of what makes up the universe. But there was more to come.
我们发现，组成我们的物质只是组成宇宙的物质其中的一小部分。但是不只这样。
Early this century, scientists studying the outer reaches of the universe
在本世纪初，研究宇宙外部的科学家
confirmed that not only is everything moving apart from everything else,
证实了不只是物质与物质之间不断远离，
as you would expect in a universe that began in hot, dense big bang,
就如同你想象宇宙诞生于高温、高密度的大爆炸一样，
but that the universe's expansion also seems to be accelerating. What's that about?
宇宙向外的扩张似乎正在加速。这是怎么回事？
Either there is some kind of energy pushing this acceleration, just like you provide energy to accelerate a car,
要不就是有某种能量促成这样的加速，就像是你提供能量让一辆车加速一样；
or gravity does not behave exactly as we think.
要不就是重力和我们想的不完全一样。
Most scientists think it's the former, that there's some kind of energy driving the acceleration, and they called it 'dark energy'.
大多数科学家相信前者是对的，也就是有某种能量促成这种加速，他们把它叫作暗物质。
Today's best measurements allow us to work out just how much of the universe is dark.
当下最好的测量使我们能够算出宇宙中暗部分有多大。
It looks as if dark energy makes up about 68% of the universe and dark matter about 27%,
看似暗能量占了大约68%的宇宙，而暗物质则占27%，
leaving just 5% for us and everything else we can actually see. So what's the dark stuff made of?
剩的5%才是所有其它我们看得到的东西。所以这些黑暗的东西是由什么组成的？
We don't know, but there's one theory, called 'supersymmetry', that could explain some of it.
我们并不知道，但有一个叫“超对称”的理论可以解释一些。
Supersymmetry, or SUSY for short, predicts a whole range of new particles, some of which could make up the dark matter.
超对称，或简称SUSY，预测了一系列新的粒子，其中的一些可以组成暗物质。
If we found evidence for SUSY, we could go from understanding 5% of our universe,
如果我们找到超对称的证据，我们就可以从对宇宙那5%的认识，
the things we can actually see, to around a third. Not bad for a day's work.
也就是我们看得到的那些，进展到大约1/3。还算不错。
Dark energy would probably be harder to understand, but there are some speculative theories out there that might point the way.
暗能量可能更难去了解，但有些猜测的理论也许指出了方向。
Among them are theories that go back to that first great idea of the ancient Greeks,
其中有些可以追溯到古希腊人那第一个伟大的想法，
the idea that we began with several minutes ago, the idea that the universe must be simple.
也就是几分钟前我们开头时的那个认为宇宙一定很简单的想法。
These theories predict that there is just a single element from which all the universe's wonderful diversity stems, a vibrating string.
这些理论预测所有的宇宙万物只由单一一种东西组成，一条振动的弦。
The idea is that all the particles we know today are just different harmonics on the string.
这一想法认为，我们今天知道的所有粒子只是这条弦上不同的波。
Unfortunately, string theories today are, as yet, untestable.
不幸的是，弦论现今还没办法证实。
But, with so much of the universe waiting to be explored, the stakes are high.
不过，宇宙中还有这么多事物等着去探索，这赌注太大了。
Does all of this make you feel small? It shouldn't.
这一切是否让你觉得自己很渺小？不用这样。
Instead, you should marvel in the fact that, as far as we know,
相反地，你应该惊叹--至少到目前为止，
you are a member of the only species in the universe able even to begin to grasp its wonders,
你是这宇宙中唯一一个开始了解宇宙奥秘的物种中的一员，
and you're living at the right time to see our understanding explode.
而且你生逢其时，来见证我们的理解爆发。
