The death of the universe

宇宙之死—Renée Hlozek

翻译人员: Minglei Wang 校对人员: Bighead Ge

Looking up at the night sky,

仰望夜空，

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

我们为其永无止境的广阔而感到惊讶。

But what will the sky look like

然而数十亿年前的天空

billions of years from now?

又会是什么样子的呢 ？

A particular type of scientist,

有一种科学家，

called a cosmologist,

被称为宇宙学家，

spends her time thinking about that very question.

她们就专门思考这样的问题。

The end of the universe is intimately linked

宇宙的尽头

to what the universe contains.

与其自身的构成有着密切的联系。

Over 100 years ago,

一百多年前，

Einstein developed the Theory of General Relativity,

爱因斯坦提出了广义相对论，

formed of equations that help us

帮助我们以方程的形式

understand the relationship

来理解

between what a universe is made of

宇宙的组成

and its shape.

和其形状之间的关系。

It turns out that the universe

结果表明

could be curved like a ball or sphere.

宇宙可能是呈球状或半球状的曲线。

We call this positively curved or closed.

我们称之为正弯曲或正关闭。

Or it could be shaped like a saddle.

或者它也可能呈马鞍形。

We call this negatively curved or open.

我们称之为负弯曲或负开放。

Or it could be flat.

又或者它也可能是扁平状。

And that shape determines

这样不同的形状决定着

how the universe will live and die.

宇宙将会怎样存在和灭亡。

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

如今我们认为宇宙最接近扁平状。

However, the components of the universe

然而组成宇宙的各个部分

can still affect its eventual fate.

同时也会影响其最终的命运。

We can predict how the universe

我们能够预测宇宙如何

will change with time

随着时间而发生改变，

if we measure the amounts or energy densities

这需要我们对目前组成宇宙的

of the various components in the universe today.

各要素的数量及其能量密度进行测量。

So, what is the universe made of?

那么，宇宙是由什么构成的呢？

The universe contains all the things that we can see,

宇宙中包含着我们肉眼所能看到的一切，

like stars, gas, and planets.

比如恒星、气体和行星。

We call these things ordinary or baryonic matter.

我们称这些为普通物质或重子物质。

Even though we see them all around us,

尽管它们就在我们的周围，

the total energy density of these components

但这些组成部分的总能量密度

is actually very small,

却十分渺小，

around 5% of the total energy of the universe.

它们仅占整个宇宙总能量的5%左右。

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

那么现在我们就来探讨组成宇宙另外95%的部分是什么。

Just under 27% of the rest

其他近27%的

of the energy density of the universe

宇宙能量密度

is made up of what we call dark matter.

是由暗物质构成的。

Dark matter is only very weakly interacting with light,

暗物质与光的相互作用很弱，

which means it doesn't shine or reflect light

也就是说暗物质本身并不发射或反射光线，

in the way that stars and planets do,

这与其他恒星和恒星不同，

but, in every other way,

但从其它方面来讲，

it behaves like ordinary matter --

暗物质与普通物质是相似的—

it attracts things gravitationally.

暗物质通过重力吸引物体。

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

事实上，我们唯一能够探测暗物质的方法

is through this gravitational interaction,

就是通过暗物质与其它物质的重力相互作用，

how things orbit around it

比如物体如何围绕暗物质运行

and how it bends light

或暗物质如何扭曲光线

as it curves the space around it.

使其周围空间呈显曲线状。

We have yet to discover a dark matter particle,

目前我们还没能发现一块暗物质颗粒，

but scientists all over the world are searching

但全世界的科学家们都在探索

for this elusive particle or particles

这个或这些神秘的物质

and the effects of dark matter on the universe.

以及它对宇宙所产生的影响。

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

可是这样的组成结构还是未能达到100%。

The remaining 68%

剩余68%的

of the energy density of the universe

宇宙能量密度

is made up of dark energy,

来自于暗能量，

which is even more mysterious than dark matter.

这种物质比暗物质更加神秘。

This dark energy doesn't behave

这种暗能量的性质

like any other substance we know at all

与我们所熟知的其他物质完全不同

and acts more like anti-gravity force.

它更像是反重力。

We say that it has a gravitational pressure,

暗能量具有一种重力压力，

which ordinary matter and dark matter do not.

这是普通物质和暗物质所不具有的。

Instead of pulling the universe together,

宇宙并没有因为重力而向一起聚集，

as we would expect gravity to do,

这与我们所预想的不同，

the universe appears to be expanding apart

相反宇宙却似乎是在不断膨胀，

at an ever-increasing rate.

并且这种膨胀还处于一种持续增长的速度。

The leading idea for dark energy

有关暗能量的主导观点认为

is that it is a cosmological constant.

它是一个宇宙常量。

That means it has the strange property

那意味着暗能量具有一种特殊属性，

that it expands as the volume of space increases

它能够使暗能量随着宇宙体积的增长而扩大，

to keep its energy density constant.

从而使其能量密度保持不变。

So, as the universe expands

因此，随着宇宙不断膨胀，

as it is doing right now,

正如此时此刻，

there will be more and more dark energy.

暗能量也会随之不断增长。

Dark matter and baryonic matter,

然而暗物质和重子物质，

on the other hand,

从另一方面来看，

don't expand with the universe

则不会随宇宙而增长

and become more diluted.

反而他们会不断地减弱。

Because of this property

因此，由于

of the cosmological constant,

宇宙常量所具有的性质，

the future universe will be more and more dominated

未来的宇宙中更多充斥的

by dark energy,

将是暗能量，

becoming colder and colder

宇宙将会变得越来越冷

and expanding faster and faster.

其膨胀速度也会越来越快。

Eventually, the universe will run out of gas

最终，宇宙将会由于缺少气体而无法

to form stars,

形成恒星，

and the stars themselves will run out of fuel

同时恒星自身也会

and burn out,

燃烧殆尽，

leaving the universe with only black holes in it.

宇宙中留下的只会是一个个黑洞。

Given enough time,

如果经历足够的时间，

even these black holes will evaporate,

即使是这些黑洞也会消失，

leaving a universe that is completely cold and empty.

那时宇宙将会是一片寒冷空虚。

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

那就是我们所说的宇宙热寂说。

While it might sound depressing

尽管这听起来让人觉得

living in a universe

生活在宇宙之中十分沮丧，

that will end its lifetime cold

因为它将在寒冷

and devoid of life,

和了无生气中走向灭亡，

the end fate of our universe

但宇宙最终冰冷的消亡

actually has a beautiful symmetry

却完美地与其

to its hot, fiery beginning.

火热的发端相称。

We call the accelerating end state

我们称宇宙的加速最终状态为

of the universe a de Sitter phase,

德西特阶段，

named after the Dutch mathematician

这是根据荷兰数学家

Willem de Sitter.

威廉·德西特命名的。

However, we also believe

然而，我们也相信

that the universe had another phase

宇宙还存在另一个

of de Sitter expansion

德西特膨胀阶段，

in the earliest times of its life.

它发生在宇宙形成的初期。

We call this early period inflation,

我们称其为早期膨胀阶段，

where, shortly after the Big Bang,

那是在大爆炸后，

the universe expanded extremely fast

宇宙急速膨胀的

for a brief period.

短暂时期。

So, the universe will end

因此宇宙将会以

in much the same state as it began,

与其产生时相同的状态结束，

accelerating.

加速。

We live at an extraordinary time

我们生活在一个

in the life of the universe

对于宇宙生命来讲意义非凡的时代，

where we can start to understand

在在这样的时代我们能够去了解

the universe's journey

宇宙的历程，

and view a history

同时也能够去了解

that plays itself out on the sky

它那呈现在天空中

for all of us to see.

为我们每个人所展示的历史。