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And many of the questions that we might have about the universe at large scales,
我们关于宇宙在宏观上有很多问题，
such as, how does gravity work?
比如，引力是怎么起作用的？
might be answered by studying these systems.
这些问题可能可以通过研究这些系统来解决。
So that was very big.
所以这就是“非常大”。
The second things is very hot.
第二个特点是“非常热”。
Okay, if I take an image of a galaxy cluster,
如果我拿出一幅星团的照片，
and I subtract away all of the starlight,
去掉其中所有的星光，
what I'm left with is this big, blue blob.
留下的是这个巨大的蓝色的一团。
This is in false color.
这个颜色不是真的。
It's actually X-ray light that we're seeing.
事实上这是X光。
And the question is, if it's not galaxies,
问题是，如果不是这些星系，
what is emitting this light?
那么是什么在发出这X光呢？
The answer is hot gas,
答案是高温气体，
million-degree gas in fact, it's plasma.
一百万度的气体，事实上是等离子。
And the reason why it's so hot goes back to the previous slide.
温度如此之高的原因要回到前一张幻灯片。
The extreme gravity of these systems is accelerating particles of gas to great speeds,
这些系统的超强引力将气体粒子加速到非常高的速度，
and great speeds means great temperatures.
而高速则意味着高温。
So this is the main idea,
这是主要的想法，
but science is a rough draft.
但是里面的科学还不太明晰。
There are many basic properties about this plasma that still confuse us,
关于等离子气体，还有很多基本性质的问题仍让我们困扰，
still puzzle us,
仍然是谜团，
and still push our understanding of the physics of the very hot.
但它正在推进我们对超高温物理的理解。
Third thing: probing the very small.
第三个问题是：研究“极小”。
Now, to explain this, I need to tell you a very disturbing fact.
为了解释这个，我要说一件很让人困扰的事实。
Most of the universe's matter is not made up of atoms.
宇宙的大部分物质不是由原子构成。
You were lied to.
你们以前被骗了。
Most of it is made up of something very, very mysterious,which we call dark matter.
宇宙大部分是一种非常神秘的物质，我们称为暗物质。
Dark matter is something that doesn't like to interact very much,
暗物质不太与周围发生作用，
except through gravity,
除了通过引力，
and of course we would like to learn more about it.
理所当然的我们希望对其了解更多。
If you're a particle physicist,
如果你是粒子物理学家，
you want to know what happens when we smash things together.
你会想知道当我们撞击物体的时候发生什么。
And dark matter is no exception.
暗物质也不例外。
Well, how do we do this?
那么，我们怎么做呢？
To answer that question,
为了回答这个问题，
I'm going to have to ask another one,
我要问另一个问题，
which is, what happens when galaxy clusters collide?
那就是，当星团碰撞的时候会发生什么？
