How and when did our universe begin?
宇宙是何时、又是如何诞生的？
How did it get to look like this? How will it end?
它如何变成我们所见的这样？它将如何结束？
Humans have been discussing these questions for as long as they've been around without ever reaching much agreement.
人类自始以来一直都在讨论这些问题，但是向来没有明确的结论。
Today, cosmologists are working hard to find the answers.
如今，宇宙学家正努力寻找答案。
But how can anyone hope to find concrete answers to such profound questions?
但是，对于如此深刻的问题，如何能期望得到确定的答案呢？
And how is it possible to explore and study something as huge as the universe, most of which we'll never be able to reach?
还有，要如何才可能探索和研究宇宙这般大的事物呢？要知道我们永远无法到达宇宙中的大部分地区。
The answer is light. And although light from distant parts of the universe can take billions of years to reach us,
答案是光。虽然来自宇宙中遥远区域的光需要数十亿年才能到达我们这里，
it carries six unique messages that, when put together,
但是这些光携带了六种独特的信号，如果将这些信息整合起来，
can disclose an amazing amount of information to astronomers who know how to look for it.
天文学家就可以从中揭示出大量的信息，而天文学家知道如何去寻找这些信号。
Just as sunlight can be split up into the familiar rainbow,
就像太阳光可以被分离为我们所熟知的彩虹，
splitting the light from distant objects exposes different patterns of colors depending on its source.
分离来自遥远天体的光也能发现不同的颜色模式，这种模式取决于光的源头。
This distinctive light barcode can reveal not only an object's composition,
这一独特的光条形码不仅可以揭示天体的化学组成，
but also the temperature and pressure of its constituent parts.
还可以告诉我们其各部分的温度和压力。
There's even more we can discover from light.
我们还可以从光里发现更多。
If you've ever stood on a train platform,
如果你曾站在一个火车站台上，
you might have noticed that the train sounds different depending on its direction
你可能会发现不同方向的火车听起来不同，
with the pitch ascending when it approaches you and descending when it speeds away.
当火车朝向你时听起来音调较高，而远离时听起来音调较低。
But this isn't because the train conductor is practicing for a second career.
但是这不是因为火车司机在玩。
Rather, it's because of something called the Doppler effect
而是由于多普勒效应，
where sound waves generated by an approaching object are compressed, while those from a receding object are stretched.
接近中的物体所发出的声波会被压缩，而远离中的物体所发出的声波会被拉长。
But what has this to do with astronomy?
可是，这和天文学有什么关系？
Sound does not travel through a vacuum.
声音无法在真空中传播。
In space, no one can you hear you scream!
在太空中，没人能听到你的呼喊！
But the same Doppler effect applies to light whose source is moving at exceptional speed.
但是，当光源以特定的速度运动时，其发出的光也有多普勒效应。
If it's moving towards us, the shorter wavelength will make the light appear to be bluer.
如果光源朝我们移动，光的波长会变短，使其变得更蓝。
While light from a source that's moving away will have a longer wavelength, shifting towards red.
当光源远离我们时，光的波长会变长，使其趋于红色。

So by analyzing the color pattern in the Doppler shift of the light from any object observed with a telescope,
因此，对于任何通过望远镜所观测的天体，我们可以分析其带有多普勒效应的颜色模式，
we can learn what it's made of, how hot it is and how much pressure it's under,
由此可知天体的成分、温度和压力，
as well as whether it's moving, in what direction and how fast.
同时可知它是否运动、运动的方向和运动速度。
And these six measurements, like six points of light, reveal the history of the universe.
这六种量度，就像光的六个点，揭示了宇宙的历史。
The first person to study the light from distant galaxies was Edwin Hubble, and the light he observed was redshifted.
第一个研究来自遥远星系的光的人是埃德温·哈勃，他所观测到的光是被红移的。
The distant galaxies were all moving away from us, and the further away the were, the faster they were receding.
遥远的星系都在远离我们，越远的星系其远离速度越快。
Hubble had discovered our universe is expanding, providing the first evidence for the Big Bang theory.
哈勃由此发现了宇宙正在膨胀，这也是大爆炸理论的第一个证据。
Along with the idea that the visible universe has been constantly expanding from a densely packed single point,
除了说可见宇宙从一个密度极高的点开始持续膨胀以外，
one of this theory's most important predictions is that the early universe consisted of just two gases:
这一理论的重要预言之一是早期宇宙只有两种气体：
hydrogen and helium, in a ratio of three to one.
氢气和氦气，其比例约为三比一。
And this prediction can also be tested with light.
这一预言也可以通过光来验证。
If we observe the light from a remote, quiet region of the universe and split it,
如果我们观测来自宇宙中一个遥远而安静的区域的光，并把它分离开来，
we do indeed find the signatures of the two gases in just those proportions.
我们的确发现了这两种气体所留下的信号，且呈现正确的比例。
Another triumph for the Big Bang. However, many puzzles remain.
大爆炸理论的又一胜利。然而，还有很多疑问。
Although we know the visible universe is expanding, gravity should be applying the brakes.
虽然我们知道可见的宇宙正在膨胀，但引力会踩下刹车。
But recent measurements of light from distant dying stars show us that they're farther away than predicted.
但是针对来自遥远的濒死恒星的光的测量告诉我们它们比预想的还要远。
So the expansion of the universe is actually accelerating.
因此，宇宙膨胀实际上正在加速。
Something appears to be pushing it, and many scientists believe that something is dark energy,
看来有什么东西正在推动它，很多科学家相信这是暗能量，
making up over 2/3 of the universe and slowly tearing it apart.
暗能量构成了2/3的宇宙，并在缓慢地撕开宇宙。
Our knowledge of the behavior of matter and the precision of our instruments
我们对于物质行为的知识以及我们的仪器所具有的精度，
means that simply observing distant stars can tell us more about the universe than we ever thought possible.
意味着仅仅通过观测遥远的恒星就能告诉我们宇宙的很多故事，远超我们过去的想象。
But there are other mysteries, like the nature of dark energy upon which we have yet to shed light.
但是还有其它未解之谜，比如暗能量的本质，至今我们还是一无所知。