英语听力：自然百科 穿越银河系的旅行 Through Milky Way—23
时间：2014-05-27 07:52:19
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（单词翻译）
But dark matter does more than simply holds galaxy1 like ours together. Astronomers2 think it binds3 the Milky4 Way into an extraordinary structure along with billions of other galaxies5.
To explore it, we'll take a journey to the very edge of the universe.
We're leaving the galaxy altogether, on a journey that will take us across billions of light years of space and billions of years of time.
What are the great things about telescopes is they are time machines. Because light travels at a finite speed, when we look at distant objects, we see them as they were when the light left them.
As astronomers look back over billions of years, they see a universe
teeming6 with galaxies. But the extraordinary thing is that galaxies are not
scattered7 randomly8 through space. They cluster along delicate
filaments9, forming a vast cosmic web. So what gives the universe this intricate structure, and what does it have to do with the birth of galaxies themselves, the answer is
shrouded10 in darkness. Look back far enough, and gradually all the galaxies disappear.
We've reached a mysterious period of time 12 and a half billion years ago.
There is this time period that we can't see because nothing is formed yet. It’s this
epoch11 that’s called the dark ages.
During the dark ages, the universe was a very different place from the one we live in today. Back then, it was filled with
dense12 clouds of hydrogen gas, like the gas that obscures the stars in the Milky Way today, these clouds block what might lie within.
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