and how they interact on the most fundamental level.

身為粒子物理學家的我,研究最基本的粒子

For most of my research career, I've been using accelerators,

我研究,粒子和粒子之間,如何在最基礎層次上交互作用

such as the electron accelerator at Stanford University, just up the road,

多數研究生涯中,我一向都在使用加速器

to study things on the smallest scale.

就像離此不遠的史丹福大學,也有一台一樣的,那種電子加速器。

But more recently, I've been turning my attention

粒子物理學家,向來是從最細微,最小尺度來研究物質

to the universe on the largest scale.

但是最近，我的注意力轉向了

Because, as I'll explain to you,

宇宙間最大尺度的物質。那是什麼?

the questions on the smallest and the largest scale are actually very connected.

稍後我將立刻向各位解釋-但是,我為什麼轉移注意力呢？

So I'm going to tell you about our twenty-first-century view of the universe,

因為,最小和最大尺度兩者間,其實有微妙的高度關聯

what it's made of and what the big questions in the physical sciences are --

所以,我即將要談,21世紀對宇宙的最新看法

at least some of the big questions.

宇宙的構成成分是什麼，目前物理學最熱門的議題為何?

So, recently, we have realized

即便不能完整含括全部最重要議題,至少也含有其中好幾個。

that the ordinary matter in the universe --

最近，我們意識到

and by ordinary matter, I mean you, me,

宇宙中的普通物質

the planets, the stars, the galaxies --

我說的「普通」物質,也就是你,我自己

the ordinary matter makes up only a few percent

行星，恆星，銀河系

of the content of the universe.

這些都是算為普通物質,且只不過佔宇宙的

Almost a quarter, or approximately a quarter

幾個百分比而已

of the matter in the universe, is stuff that's invisible.

近乎四分之一，或者大約四分之一

By invisible, I mean it doesn't absorb in the electromagnetic spectrum.

宇宙中的物質,全是些看不見的東西

It doesn't emit in the electromagnetic spectrum. It doesn't reflect.

所謂不可見，我指的是它不吸收電磁波

It doesn't interact with the electromagnetic spectrum,

在電磁波頻譜中,它既不放射,也不反射。

which is what we use to detect things.

它和電磁波譜,沒有互動可言

It doesn't interact at all. So how do we know it's there?

而電磁波,正是我們平常用來檢測物質的方法

We know it's there by its gravitational effects.

當它根本對電磁波不作反應,你如何知道它存在呢？

In fact, this dark matter dominates

透過重力效應,是可以知道的。

the gravitational effects in the universe on a large scale,

事實上,在宇宙中,大尺度物質

and I'll be telling you about the evidence for that.

的重力效應,全是由「暗物質」在操縱

What about the rest of the pie?

相關證據,稍後我會再和各位分享

The rest of the pie is a very mysterious substance called dark energy.

現在先講,這大餅圖中,還有一大塊無名,那是什麼？

More about that later, OK.

剩下的一大塊,是一種稱為「暗能量」,極神秘物質

So for now, let's turn to the evidence for dark matter.

細節,稍後再說

In these galaxies, especially in a spiral galaxy like this,

現在，我們來談談「暗物質存在」的證據

most of the mass of the stars is concentrated in the middle of the galaxy.

在這些星系中，尤其是在一個像這樣的螺旋星系中

This huge mass of all these stars keeps stars in circular orbits in the galaxy.

大部分恆星的「質量」(mass)都集中在星系的中央附近

So we have these stars going around in circles like this.

這是很巨大的質量。也因為它,恆星在星系中,沿著圓形軌道在運動

As you can imagine, even if you know physics, this should be intuitive, OK --

所以我們看到這些恒星沿圓圈這樣運動

that stars that are closer to the mass in the middle will be rotating at a higher speed

不難想像-這和懂不懂物理沒差別-直覺上就應該知道

than those that are further out here, OK.

比較靠近星系質量中央的恆星,繞行運轉時,速度較高

So what you would expect is that if you measured the orbital speed of the stars,

和外圈的恆星相比,同意嗎

that they should be slower on the edges than on the inside.

如果你測量這些恒星運動的軌道速度

In other words, if we measured speed as a function of distance --

應該是邊緣的會比裏面的慢

this is the only time I'm going to show a graph, OK --

換句話說，如果我們以速度作為距離的函數

we would expect that it goes down as the distance increases

這篇短講不會有很多圖表,這是唯一一張

from the center of the galaxy.

我們認為,速度會隨它和星系中央的距離增加

When those measurements are made,

而減慢

instead what we find is that the speed is basically constant,

當我們實際進行測量的時候

as a function of distance.

出乎意料，我們卻發現這些速度都是幾乎不變動的「恆量」

If it's constant, that means that the stars out here

當你以距離為函數

are feeling the gravitational effects of matter that we do not see.

若它為恆量時,這意味著,這些恆星

In fact, this galaxy and every other galaxy

正感受得到,一些我們看不見的物質所產生的重力效應

appears to be embedded in a cloud of this invisible dark matter.

這個星系以及其他每一個星系

And this cloud of matter is much more spherical than the galaxy themselves,

似乎都是內嵌在這樣一個不可見的暗物質雲層中

and it extends over a much wider range than the galaxy.

而這片物質雲,比星系本身,更加的接近於球形

So we see the galaxy and fixate on that, but it's actually a cloud of dark matter

而且這片物質雲的範圍,比星系本身更廣得多

that's dominating the structure and the dynamics of this galaxy.

所以,當我們看見的是星系,注視著的,是星系,但實際上那背後有一團暗物質雲

Galaxies themselves are not strewn randomly in space;

主導著這星系的結構和運動

they tend to cluster.

這些星系,在太空中,並非任意的散佈

And this is an example of a very, actually, famous cluster, the Coma cluster.

它們有成群聚合的傾向

And there are thousands of galaxies in this cluster.

舉一個例,非常有名的后髮座（Coma）星系團

They're the white, fuzzy, elliptical things here.

這個星系團中有數以千計的星系

So these galaxy clusters -- we take a snapshot now,

這些白色的，模糊的，橢圓的東西就是星系

we take a snapshot in a decade, it'll look identical.

這些星系團-我們幫它拍一張照片

But these galaxies are actually moving at extremely high speeds.

十年後再拍一張,它還是一點都不會改變

They're moving around in this gravitational potential well of this cluster, OK.

但是,星系團,其實是在極高速的運動狀態中

So all of these galaxies are moving.

它們其實是在這個星系團的一個「重力勢阱」中運動著

We can measure the speeds of these galaxies, their orbital velocities,

所以,所有這些星系都在運動

and figure out how much mass is in this cluster.

我們可以藉由測量這些運動，它們的軌道速率

And again, what we find is that there is much more mass there

計算得出星系團中有多少「質量」

than can be accounted for by the galaxies that we see.

再一次，我們發現實際上那裏的質量

Or if we look in other parts of the electromagnetic spectrum,

要比按照「看得見的」星系,計算得出的結果還多

we see that there's a lot of gas in this cluster, as well.

當我們看其他部分的電磁波譜

But that cannot account for the mass either.

也看得到星系團裏有很多氣體

In fact, there appears to be about ten times as much mass here

但那些氣體並不能解釋這些質量的存在

in the form of this invisible or dark matter

事實上，這裏多出來的質量大約有10倍

as there is in the ordinary matter, OK.

是以暗物質型態,存在著

It would be nice if we could see this dark matter a little bit more directly.

暗物質是普通物質的10倍。

I'm just putting this big, blue blob on there, OK,

我想,如果大家都能更直接地看到暗物質,豈不更妙

to try to remind you that it's there.

所以,我在這裏放一個大藍色泡泡

Can we see it more visually? Yes, we can.

提醒你們:「暗物質就在那兒!」

And so let me lead you through how we can do this.

但,是否可以在視覺上「看」見它呢？可以。

So here's an observer:

現在我帶大家實際瞭解,怎樣看見暗物質：

it could be an eye; it could be a telescope.

這裏是一個觀察者

And suppose there's a galaxy out here in the universe.

無論是一隻眼睛；或者也可以是一個望遠鏡

How do we see that galaxy?

假設在宇宙中有一個星系

A ray of light leaves the galaxy and travels through the universe

我們怎樣看得到那個星系的呢？

for perhaps billions of years

一束光從那星系離開、穿過宇宙

before it enters the telescope or your eye.

經過了也許幾十億年

Now, how do we deduce where the galaxy is?

然後進入望遠鏡,或映入你的眼簾中

Well, we deduce it by the direction that the ray is traveling

現在,你如何猜測星系的位置在哪裡？

as it enters our eye, right?

嗯,我們按光線來的方向,去猜,它的位置

We say, the ray of light came this way;

當光線抵達我們的眼睛時,我們就是這樣猜的

the galaxy must be there, OK.

例如，這束光這樣出來

Now, suppose I put in the middle a cluster of galaxies --

我猜星系一定在那。

and don't forget the dark matter, OK.

現在,假設我在螢幕中央放一個星系團--

Now, if we consider a different ray of light, one going off like this,

別忘了,連暗物質也在那兒

we now need to take into account

現在，如果我們考慮,另外一束這樣走的光線

what Einstein predicted when he developed general relativity.

我們現在需要考慮

And that was that the gravitational field, due to mass,

當愛因斯坦他發展出廣義相對論時,曾經預言過的

will deflect not only the trajectory of particles,

也就是,由於有「質量」的關係而發生的「重力場」

but will deflect light itself.

不僅會使粒子的運動軌跡偏轉

So this light ray will not continue in a straight line,

而且也會使光本身偏轉

but would rather bend and could end up going into our eye.

所以這束光不會沿直線行進

Where will this observer see the galaxy?

而是，會彎曲，並最終仍抵達、進入我們的眼睛

You can respond. Up, right?

這個觀察者,會看到的星系,是在哪裡呢？

We extrapolate backwards and say the galaxy is up here.

你們會回答。上面。對嗎？

Is there any other ray of light

我們向後倒推，然後斷定星系在這裏

that could make into the observer's eye from that galaxy?

這裏還有其他,也從這個星系而來,

Yes, great. I see people going down like this.

並且也進入觀察者眼睛的光線嗎？

So a ray of light could go down, be bent

是的,非常好。我看到你們有人比向下的手勢。

up into the observer's eye,

一束光,它也可以往下走,然後彎曲

and the observer sees a ray of light here.

並進入觀察者的眼睛,

Now, take into account the fact that we live in

這觀察著便會在這裏,看到一束光。

a three-dimensional universe, OK,

現在,考慮到,我們生活在一個

a three-dimensional space.

有三度空間的宇宙中

Are there any other rays of light that could make it into the eye?

太空是三度空間的

Yes! The rays would lie on a -- I'd like to see -- yeah, on a cone.

那麼,還有其他光線,可以進入我們的眼睛嗎？

So there's a whole ray of light -- rays of light on a cone --

是的，光線可以排列呈現-按你們比出來的手勢-它是個,圓錐形

that will all be bent by that cluster

所以,許多束光,匯聚成一個圓錐形

and make it into the observer's eye.

意思是,這些光都經過了星系團的彎曲

If there is a cone of light coming into my eye, what do I see?

然後進入觀察者的眼睛裡

A circle, a ring. It's called an Einstein ring. Einstein predicted that, OK.

因為有呈圓錐形的光,這樣進入我的眼睛,所以,我會看到什麼？

Now, it will only be a perfect ring if the source, the deflector

一個圓圈,或環形。這被稱為「愛因斯坦環」--因為愛因斯坦首先預測到這個現象

and the eyeball, in this case, are all in a perfectly straight line.

當然,弧形原本應該是相當完美的弧,前提是,如果光源,偏導體和眼球

If they're slightly skewed, we'll see a different image.

正好全都在一條筆直的線上

Now, you can do an experiment tonight over the reception, OK,

如果它們被略微偏轉，我們將會看到一個不同的圖像

to figure out what that image will look like.

你們今晚就可以在接待櫃檯,做一個試驗

Because it turns out that there is a kind of lens that we can devise,

你就看到這個圖像會是什麼樣子

that has the right shape to produce this kind of effect.

因為我們可以設計一種透鏡

We call this gravitational lensing.

它的形狀,很合適用來產生這種現象

And so, this is your instrument, OK.

我們稱它為重力透鏡

(Laughter).

所以,這就是你們的儀器

But ignore the top part.

（笑聲）

It's the base that I want you to concentrate, OK.

但是請忽略上半部

So, actually, at home, whenever we break a wineglass,

只看它底座的部分就好了

I save the bottom, take it over to the machine shop.

所以,我家無論誰打破一隻高腳酒杯

We shave it off, and I have a little gravitational lens, OK.

我都把底部留著用,先拿到玻璃店去

So it's got the right shape to produce the lensing.

把頭切掉,然後重力透鏡就出現了,妙吧

And so the next thing you need to do in your experiment

它的形狀很合適產生透鏡效果

is grab a napkin. I grabbed a piece of graph paper -- I'm a physicist. (Laughter)

這個實驗的下一步驟就是

So, a napkin. Draw a little model galaxy in the middle.

找一張餐巾紙-本人是物理學者,所以我會拿一張有學問一點的方格紙.(笑聲)

And now put the lens over the galaxy,

ok,拿一張餐巾紙。在正中央畫一個小小的星系模型。

and what you'll find is that you'll see a ring, an Einstein ring.

然後把透鏡挪到星系正上方

Now, move the base off to the side,

然後你將看到一個,愛因斯坦環

and the ring will split up into arcs, OK.

把杯底透鏡往旁邊挪一點

And you can put it on top of any image.

環會分裂成好幾個弧

On the graph paper, you can see

把它移到任何圖像上都可以

how all the lines on the graph paper have been distorted.

在方格紙上你可以看到

And again, this is a kind of an accurate model

方格的線條產生怎樣的扭曲

of what happens with the gravitational lensing.

所以，你可以說,這是一種非常精確的模型

OK, so the question is: do we see this in the sky?

用來解釋「重力透鏡」產生的現象為何

Do we see arcs in the sky when we look at, say, a cluster of galaxies?

下一個問題：在天空中,我們看的到這現象嗎?

And the answer is yes.

當我們觀察一個星系團的時候,看的到弧形嗎?

And so, here's an image from the Hubble Space Telescope.

答案是:可以。

Many of the images you are seeing

這是來自哈柏望遠鏡的圖像。

are earlier from the Hubble Space Telescope.

現在看到的許多圖像

Well, first of all, for the golden shape galaxies --

來自稍早的哈柏望遠鏡拍攝所得

those are the galaxies in the cluster.

首先,先說這些金色的星系

They're the ones that are embedded in that sea of dark matter

它們是星系團中的星系

that are causing the bending of the light

也被內嵌在一團暗物質中

to cause these optical illusions, or mirages, practically,

那團暗物質,就是使光發生彎曲的物質

of the background galaxies.

就是它們,引起了我們對「後景星系」

So the streaks that you see, all these streaks,

的視錯覺,或者說,幻影

are actually distorted images of galaxies that are much further away.

你所看到的這些條紋,所有這些條紋

So what we can do, then, is based on how much distortion

其實都是來自更遠處的星系,扭曲的圖像

we see in those images, we can calculate how much mass

我們能做的,就是根據所見的這些圖像

there must be in this cluster.

扭曲程度的大小,計算出在這團星系中

And it's an enormous amount of mass.

可能有多少的「質量」

And also, you can tell by eye, by looking at this,

這個質量的總量是非常龐大的

that these arcs are not centered on individual galaxies.

你也可以藉由觀察它（圖像）而得知一個現象

They are centered on some more spread out structure,

這些弧線的中心並不是些單一的星系

and that is the dark matter

這些弧線的中心,是一些更廣,更大的結構

in which the cluster is embedded, OK.

那個結構,就是暗物質

So this is the closest you can get to kind of seeing

星系團,是被嵌入在暗物質中的

at least the effects of the dark matter with your naked eye.

這是最接近於看到

OK, so, a quick review then, to see that you're following.

以肉眼看得到的暗物質效果

So the evidence that we have

非常快的回顧一下剛才所說的，希望你們都還跟的上。

that a quarter of the universe is dark matter --

我們有證據顯示

this gravitationally attracting stuff --

證明宇宙有1/4是,暗物質

is that galaxies, the speed with which stars orbiting galaxies

這是些,受重力作用,被吸引住的東西

is much too large; it must be embedded in dark matter.

這些恆星,圍繞星系運動的速率太大

The speed with which galaxies within clusters are orbiting is much too large;

必須被嵌在暗物質中

it must be embedded in dark matter.

是星系在星系團中,運動速度太大

And we see these gravitational lensing effects, these distortions

以至於星系也必須,被嵌在暗物質裡

that say that, again, clusters are embedded in dark matter.

從我們所看到的這些重力透鏡的效應,這些扭曲

OK. So now, let's turn to dark energy.

我們說,這證明,星系團是嵌在,暗物質中

So to understand the evidence for dark energy, we need to discuss something

好。現在我們轉向「暗能量」

that Stephen Hawking referred to in the previous session.

所以為了瞭解暗能量的證據，我們需要討論一些

And that is the fact that space itself is expanding.

史蒂芬霍金在上一段節目中談到的那個現象,

So if we imagine a section of our infinite universe --

也就是宇宙正在擴張的事實。

and so I've put down four spiral galaxies, OK --

所以如果我們想像無限宇宙中一小部分，

and imagine that you put down a set of tape measures,

我放4個漩渦星系，

so every line on here corresponds to a tape measure,

假設你放一支卷尺

horizontal or vertical, for measuring where things are.

也就是,這裏的每一條線都對應一個卷尺

If you could do this, what you would find

水平或垂直,好測量東西的位置。

that with each passing day, each passing year,

這樣一來，你將發現

each passing billions of years, OK,

時間每過去一天，或一年，

the distance between galaxies is getting greater.

或經過的是幾十億年

And it's not because galaxies are moving

星系間的距離正在變得更大。

away from each other through space.

然而這並不是因為星系正在彼此因移動而

They're not necessarily moving through space.

在空間中,漸行漸遠

They're moving away from each other

以空間來講,它們不一定是「在動」。

because space itself is getting bigger, OK.

有此漸行漸遠的現象,是因

That's what the expansion of the universe or space means.

空間本身正在擴張。

So they're moving further apart.

這是宇宙或者空間擴張的意思。

Now, what Stephen Hawking mentioned, as well,

它們相隔越來越遠。

is that after the Big Bang, space expanded at a very rapid rate.

正如史蒂芬霍金也提到的，

But because gravitationally attracting matter

在大爆炸之後，宇宙空間以非常快的速率擴張。

is embedded in this space,

但是因為重力而發出吸引效應的物質

it tends to slow down the expansion of the space, OK.

嵌在這個空間中,

So the expansion slows down with time.

而它是傾向於減慢空間擴張速率的。

So, in the last century, OK, people debated

所以擴張的速率就隨著時間經過,而減慢。

about whether this expansion of space would continue forever;

上個世紀，大家都在辯論著

whether it would slow down, you know,