They're exactly what they sound like.

這是一些星團的照片。

They are these huge collections of galaxies,

它們貌如其名，

bound together by their mutual gravity.

是多個星系的龐大集合。

So most of the points that you see on the screen

它們通過相互的引力而吸引在一起。

are not individual stars,

因此，你在屏幕上看到的大部分的點

but collections of stars, or galaxies.

並非是單獨的恆星，

Now, by showing you some of these images,

而是一系列恆星， 或者是我們所稱之星系。

I hope that you will quickly see that

現在看了​​這些圖片之後

galaxy clusters are these beautiful objects,

我希望你已經發現，

but more than that,

星團是多麼美麗的物體，

I think galaxy clusters are mysterious,

但絕非僅限於此

they are surprising,

我認為星團神秘莫測、

and they're useful.

令人嘆為觀止，

Useful as the universe's most massive laboratories.

並且具有巨大使用價值。

And as laboratories, to describe galaxy clusters

其價值，就如同是 宇宙裡規模最大的實驗室。

is to describe the experiments

要描述星團，就跟評估一個實驗室一樣，

that you can do with them.

要去描述這個實驗室 能讓你做的實驗。

And I think there are four major types,

我認為這包括四種主要類型：

and the first type that I want to describe

我想描述的第一類

is probing the very big.

是探測「極大」。

So, how big?

到底有多大？

Well, here is an image of a particular galaxy cluster.

這是某個星團的照片。

It is so massive that the light passing through it

它的質量非常大， 以至於光在經過的時候，

is being bent, it's being distorted

也會由於其引力的作用，

by the extreme gravity of this cluster.

而發生彎曲。

And, in fact, if you look very carefully

事實上，如果你仔細看，

you'll be able to see rings around this cluster.

你能夠看到這個星團周圍的光環。

Now, to give you a number,

如果要給出一個具體數字，

this particular galaxy cluster

這個星團的質量

has a mass of over one million billion suns.

有超過10的15次方個太陽那麼大。

It's just mind-boggling how massive these systems can get.

這些系統質量之巨大 簡直讓人瞠目結舌。

But more than their mass,

但除了質量巨大這個特點之外，

they have this additional feature.

它們還有其他特殊之處。

They are essentially isolated systems,

這些星系基本上可以是孤立的系統。

so if we like, we can think of them

如果願意的話，我們可以將它們

as a scaled-down version of the entire universe.

想像為整個宇宙的縮小版。

And many of the questions that we might have

我們對於宏觀的宇宙

about the universe at large scales,

還存在很多疑問。

such as, how does gravity work?

比如，引力是怎麼起作用的？

might be answered by studying these systems.

這些問題可能可以通過 研究這些系統來找到答案。

So that was very big.

這，就是「極大」。

The second things is very hot.

第二個，是「極熱」。

Okay, if I take an image of a galaxy cluster,

好的，如果我拿出一幅星團的照片，

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.

剩下的，只是這個巨大的藍色斑塊。

This is in false color.

當然，這些顏色都不是真的。

It's actually X-ray light that we're seeing.

我們實際看到的是X射線。

And the question is, if it's not galaxies,

但問題是，假如發出X射線的，不是這些星系，

what is emitting this light?

又是什麼呢？

The answer is hot gas,

答案是高溫氣體，

million-degree gas --

一百萬度的氣體。

in fact, it's plasma.

事實上，這些氣體是等離子。

And the reason why it's so hot

而它們的溫度如此之高的原因，

goes back to the previous slide.

在於前一張幻燈片。

The extreme gravity of these systems

這些系統的超強引力

is accelerating particles of gas to great speeds,

將氣體粒子加速到非常高的速度，

and great speeds means great temperatures.

而高速則意味著高溫。

So this is the main idea,

這是主要的推測，

but science is a rough draft.

但是科學畢竟是一副草圖。

There are many basic properties about this plasma

其中尚存在等離子氣體的很多基本特徵，

that still confuse us,

讓我們無法解釋，

still puzzle us,

仍然是個謎，

and still push our understanding

仍需不斷增加我們對超高溫物理的理解。

of the physics of the very hot.

第三個是：研究「極小」。

Third thing: probing the very small.

要解釋這個類型，我要向大家說

Now, to explain this, I need to tell you

一件讓人困擾的事實。

a very disturbing fact.

宇宙中的大部分物質

Most of the universe's matter

並非由原子構成。

is not made up of atoms.

你們以前都被騙了。

You were lied to.

宇宙的大部分物質是由一種 非常神秘的物質組成，

Most of it is made up of something very, very mysterious,

我們稱之為暗物質。

which we call dark matter.

暗物質並不喜歡與周圍物質反應，

Dark matter is something that doesn't like to interact very much,

除非是在有引力的情況下。

except through gravity,

當然，我們也希望更多地了解暗物質。

and of course we would like to learn more about it.

假設你是粒子物理學家，

If you're a particle physicist,

你會想知道，物體撞擊時，會出現什麼情況。

you want to know what happens when we smash things together.

暗物質也不例外。

And dark matter is no exception.

那麼，我們該怎麼做呢？

Well, how do we do this?

為了回答這個問題，

To answer that question,

我們不得不提出另一個問題。

I'm going to have to ask another one,

那就是：要是星團發生碰撞，會有什麼結果？

which is, what happens when galaxy clusters collide?

這是一張照片。

Here is an image.

既然我們可以把星團

Since galaxy clusters are representative

看作縮小版的宇宙。

slices of the universe, scaled-down versions.

星團大部分也是由暗物質構成，

They are mostly made up of dark matter,

就是你所看到的藍紫色的那些。

and that's what you see in this bluish purple.

紅色代表高溫氣體，

The red represents the hot gas,

當然，你可以看到很多星系。

and, of course, you can see many galaxies.

這些就相當於

What's happened is a particle accelerator

一部巨型粒子加速器。

at a huge, huge scale.

這很重要，

And this is very important,

因為這意味著

because what it means is that very, very small

那些難以在實驗室裡 檢測到的細微現象

effects that might be difficult to detect in the lab,

可能由於基數不斷地疊加，

might be compounded and compounded

而使我們於自然界觀測得到。

into something that we could possibly observe in nature.

相當有趣。

So, it's very funny.

為什麼星團可以 教我們暗物質的知識？

The reason why galaxy clusters

為什麼星團可以指導我們 「極小」物質之物理？

can teach us about dark matter,

這正正是因為星團相當巨型。

the reason why galaxy clusters

第四個：「奇異」之物的物理。

can teach us about the physics of the very small,

我剛才說的聽上去已經很瘋狂了，

is precisely because they are so very big.

但是，如果有比那些更瘋狂的，

Fourth thing: the physics of the very strange.

我認為就是暗能量了。

Certainly what I've said so far is crazy.

我把一個球扔向空中，

Okay, if there's anything stranger

我會預計它將上升，

I think it has to be dark energy.

但是我不會想到

If I throw a ball into the air,

球會以持續加速度上升。

I expect it to go up.

同樣道理，宇宙學家們理解

What I don't expect is that it go up

為什麼宇宙在膨脹。

at an ever-increasing rate.

但他們不理解的是

Similarly, cosmologists understand why

為什麼宇宙膨脹的速度持續加快。

the universe is expanding.

他們給引起加速膨脹的原因

They don't understand why it's expanding

取了個名字，

at an ever-increasing rate.

叫做暗能量。

They give the cause of this

同樣，我們希望更多地了解暗能量。

accelerated expansion a name,

其中一個問題是

and they call it dark energy.

暗能量是如何在 最大程度上影響宇宙？

And, again, we want to learn more about it.

這取決於能量的強弱，

So, one particular question that we have is,

或者結構的形成的快慢。

how does dark energy affect the universe

但是這個擁有如此大型結構的 宇宙所存在的問題是

at the largest scales?

宇宙大得恐怖。

Depending on how strong it is,

這是一張電腦模擬圖。

maybe structure forms faster or slower.

我們需要想方法簡化它。

Well, the problem with the large-scale structure

我喜歡用類比的方式來看待它。

of the universe is that it's horribly complicated.

如果我想理解鐵達尼號沉沒的過程，

Here is a computer simulation.

最重要的，

And we need a way to simplify it.

不是去模擬船身所有碎片的位置。

Well, I like to think about this using an analogy.

最重要的是，

If I want to understand the sinking of the Titanic,

追踪船體最大的兩個斷裂快的位置。

the most important thing to do

同樣，我可以通過追踪

is not to model the little positions

宇宙中最大的部件，

of every single little piece of the boat that broke off.

對宇宙有最大程度的了解，

The most important thing to do is

而最大的部件就是這些星團。

to track the two biggest parts.

現在我即將結尾。

Similarly, I can learn a lot about the universe

大家可能覺得有點上當了。

at the largest scales

我的意思是，

by tracking its biggest pieces

一開始我談到星團具有哪些價值。

and those biggest pieces are clusters of galaxies.

我也給了一些理由。

So, as I come to a close,

但是他們真正的用處在哪裡呢？

you might feel slightly cheated.

為了回答這個

I mean, I began by talking about

我要引用亨利·福特的一句話。

how galaxy clusters are useful,

當有人問他關於汽車的事情時，

and I've given some reasons,

他這樣說：

but what is their use really?

「如果我之前問人們他們想要什麼，

Well, to answer this,

他們只會回答說，更快的馬。」

I want to give you a quote by Henry Ford

如今，我們社會面臨很多、很多棘手的問題。

when he was asked about cars.

這些問題的解決之道並非顯而易見。

He had this to say:

辦法不是「更快的馬」。

"If I had asked people what they wanted,

而是需要更多的科學智慧。

they would have said faster horses."

所以沒錯，我們需要有針對性，

Today, we as a society are faced

我們需要專心，

with many, many difficult problems.

但我們也要謹記，

And the solutions to these problems are not obvious.

創新、創造力和靈感，

They are not faster horses.

當我們開闊眼界時，

They will require an enormous amount of

當我們退後一步時，

scientific ingenuity.

當我們聚焦問題時，

So, yes, we need to focus,

這三樣——創新、創造力和靈感——自會來到。

yes, we need to concentrate,

要做到以上，恐怕除了 研究學習我們周圍的宇宙，

but we also need to remember that

就別無其他更好的辦法了。謝謝。

innovation, ingenuity, inspiration --

（掌聲）

these things come

when we broaden our field of vision

when we step back

when we zoom out.

And I can't think of a better way to do this than

by studying the universe around us. Thanks.

(Applause)