we are amazed by how it seems to go on forever.

我們驚訝於它的恒久

But what will the sky look like

但是在十幾億年前

billions of years from now?

宇宙蒼穹究竟原為何貌？

A particular type of scientist,

有一群特殊的科學家

called a cosmologist,

被稱為“宇宙學家”

spends her time thinking about that very question.

致力於思考這一問題

The end of the universe is intimately linked

宇宙的終結

to what the universe contains.

和宇宙的組成物質緊密相連

Over 100 years ago,

大約一百年前

Einstein developed the Theory of General Relativity,

愛因斯坦提出廣義相對論

formed of equations that help us

其中的方程式幫助

understand the relationship

我們理解

between what a universe is made of

宇宙的內容和形態

and its shape.

之間的關係

It turns out that the universe

事實上，宇宙

could be curved like a ball or sphere.

本可以是彎曲成一個球狀或球體

We call this positively curved or closed.

我們稱之為正向彎曲或封閉

Or it could be shaped like a saddle.

宇宙也可以是馬鞍型的

We call this negatively curved or open.

我們稱之為逆向彎曲或封閉

Or it could be flat.

又或者，它可以使平面的

And that shape determines

而這一形態決定了

how the universe will live and die.

宇宙會如何存在以及終結

We now know that the universe is very close to flat.

我們現在知道 宇宙的形態接近平面

However, the components of the universe

然而，宇宙的組成部份

can still affect its eventual fate.

仍能影響它之後的命運

We can predict how the universe

如果我們測量當下宇宙中

will change with time

不同物質的數量或能量密度

if we measure the amounts or energy densities

我們就能夠預測

of the various components in the universe today.

宇宙會如何隨著時間而改變

So, what is the universe made of?

那麼，宇宙是由什麼組成的呢？

The universe contains all the things that we can see,

宇宙中包含了許多我們能看見的物質

like stars, gas, and planets.

比如恒星、氣體、行星

We call these things ordinary or baryonic matter.

我們將這些物質稱為普通或重子物質

Even though we see them all around us,

儘管我們能看到這些物質環繞著我們

the total energy density of these components

這些物質總體能量密度

is actually very small,

世界非常之小

around 5% of the total energy of the universe.

只佔宇宙總能量的約百分之五

So, now let's talk about what the other 95% is.

所以，讓我們來探討一下 另外的那 95％ 是什麼

Just under 27% of the rest

宇宙能量密度

of the energy density of the universe

剩下的大約 27％

is made up of what we call dark matter.

是由我們所說的“暗物質”促成的

Dark matter is only very weakly interacting with light,

暗物質僅僅非常微弱地與光互相作用

which means it doesn't shine or reflect light

這就意味著它不會像恒星或行星那樣

in the way that stars and planets do,

會發光或反射光線

but, in every other way,

但是，在其他方面

it behaves like ordinary matter --

暗物質表現得與普通物質很類似

it attracts things gravitationally.

它以重力吸引周圍的物質

In fact, the only way we can detect this dark matter

世界上，我們能探測到 這種暗物質的唯一方法

is through this gravitational interaction,

就是通過重力的互相作用

how things orbit around it

周圍物體如何環繞著它

and how it bends light

它又是如何通過 彎曲光線周圍的空間

as it curves the space around it.

導致光線本身的彎曲

We have yet to discover a dark matter particle,

我們尚未發現暗物質粒子

but scientists all over the world are searching

但是全世界的科學家都在尋找

for this elusive particle or particles

這種難以捉摸的粒子

and the effects of dark matter on the universe.

以及暗物質對整個宇宙的影響

But this still doesn't add up to 100%.

但暗物質和普通物質 並不是宇宙的全部

The remaining 68%

宇宙能量密度

of the energy density of the universe

剩下的 68％

is made up of dark energy,

是由暗能量組成的

which is even more mysterious than dark matter.

它比暗物質來得更為神秘

This dark energy doesn't behave

這種暗能量並不表現得

like any other substance we know at all

像我們所知道的任何一種物質

and acts more like anti-gravity force.

而是表現得更像反重力力量

We say that it has a gravitational pressure,

我們稱這一特性為“重力壓力”

which ordinary matter and dark matter do not.

這是普通物質和暗物質所沒有的

Instead of pulling the universe together,

和我們所預計的

as we would expect gravity to do,

重力會令宇宙收縮恰恰相反

the universe appears to be expanding apart

宇宙似乎在

at an ever-increasing rate.

以倍增的速率膨脹開來

The leading idea for dark energy

暗能量的主導思想

is that it is a cosmological constant.

是著是一個宇宙常數

That means it has the strange property

那也就意味著它有個奇怪的特性

that it expands as the volume of space increases

也就是隨著它膨脹，宇宙空間擴大

to keep its energy density constant.

來保持能量密度守恆

So, as the universe expands

因此

as it is doing right now,

隨著宇宙當下的膨脹

there will be more and more dark energy.

會有越來越多的暗能量

Dark matter and baryonic matter,

而另一方面

on the other hand,

暗物質和普通物質

don't expand with the universe

並不會隨著宇宙而膨脹

and become more diluted.

而會變得更加稀釋

Because of this property

由於宇宙常數的

of the cosmological constant,

這一特性

the future universe will be more and more dominated

宇宙在未來

by dark energy,

會進一步由暗能量主導

becoming colder and colder

變得越來越冷

and expanding faster and faster.

膨脹得越來越快

Eventually, the universe will run out of gas

最終，宇宙會耗盡

to form stars,

用以形成恒星的氣體

and the stars themselves will run out of fuel

而恒星本身會耗盡燃料

and burn out,

並且熄滅

leaving the universe with only black holes in it.

宇宙最後只剩下黑洞

Given enough time,

隨著時間進一步流逝

even these black holes will evaporate,

甚至這些黑洞都會蒸發

leaving a universe that is completely cold and empty.

令宇宙最終完全變得寒冷而空洞

That is what we call the heat death of the universe.

這也就是我們所說的“宇宙熱寂”

While it might sound depressing

儘管這一理論聽上去讓人十分鬱悶

living in a universe

我們所生活的宇宙

that will end its lifetime cold

將以寒冷和毫無生機的狀態

and devoid of life,

迎來自己的結局

the end fate of our universe

但是我們的宇宙最終的命運

actually has a beautiful symmetry

其實也與它炎熱，炙烈的開端

to its hot, fiery beginning.

有著對稱之美

We call the accelerating end state

我們將宇宙加速終結的狀態

of the universe a de Sitter phase,

稱為“德西特階段”

named after the Dutch mathematician

是以一位荷蘭數學家

Willem de Sitter.

威廉德西特來命名的

However, we also believe

然而，我們也相信

that the universe had another phase

宇宙在誕生初期

of de Sitter expansion

有著另一個

in the earliest times of its life.

“德西特膨脹”階段

We call this early period inflation,

我們稱之為初期階段膨脹

where, shortly after the Big Bang,

在大爆炸之後

the universe expanded extremely fast

宇宙以極快的速度

for a brief period.

在一段很短的時期膨脹

So, the universe will end

所以，宇宙基本上將會

in much the same state as it began,

以它的初始狀態終結

accelerating.

初生時加速膨脹 終了時加速收縮

We live at an extraordinary time

我們生活在宇宙的生命中

in the life of the universe

一個極其不凡的時間段

where we can start to understand

期間，我們能夠開始

the universe's journey

理解宇宙的生命旅程

and view a history

透過茫茫蒼穹中

that plays itself out on the sky

我們可見的蛛絲馬跡

for all of us to see.

來觀察宇宙的歷史