What are gravitational waves? - Amber L. Stuver

譯者: chenching teng 審譯者: Helen Chang

At about six o'clock in the morning on September 14, 2015,

2015 年 9 月 14 早上六點左右

scientists witnessed something no human had ever seen:

科學家們觀察到 一個從沒有人看過的現象：

two black holes colliding.

兩個黑洞的碰撞

Both about 30 times as massive as our Sun,

兩者的個別質量都有太陽的 30 倍

they had been orbiting each other for millions of years.

它們已經互轉幾百萬年了

As they got closer together,

隨著彼此越來越接近

they circled each other faster and faster.

轉動的速度也越來越快

Finally, they collided and merged into a single, even bigger, black hole.

最後互撞並融合成了一個更大的黑洞

A fraction of a second before their crash,

在它們互撞前的幾分之一秒

they sent a vibration across the universe at the speed of light.

釋出以光速橫跨宇宙的波動

And on Earth, billions of years later,

數十億年後在地球上

a detector called the Laser Interferometer Gravitational Wave Observatory,

名為「雷射干涉引力波 天文臺」的探測器

or LIGO for short,

它簡稱為 LIGO

捕捉到了這個波動

picked it up.

The signal only lasted a fifth of a second

這個訊號長度只有五分之一秒

and was the detector's first observation of gravitational waves.

是這個探測器第一個觀察到的重力波

What are these ripples in space?

這些太空裡的漣漪是什麼呢？

The answer starts with gravity,

答案必須從萬有引力 （gravity）開始說起

the force that pulls any two objects together.

也就是將兩樣物體拉到一起的力量

That's the case for everything In the observable universe.

這適用於宇宙中所有可觀測的東西

You're pulling on the Earth, the Moon, the Sun, and every single star,

你拉著地球、月亮、太陽 甚至是每顆星星

and they're pulling on you.

而它們也拉著你

The more mass something has, the stronger its gravitational pull.

物體的質量越大，引力也越大

The farther away the object, the lower its pull.

物體距離越遠，引力也越小

If every mass has an effect on every other mass in the universe,

如果每個質量體都會影響 宇宙中的其他質量體

no matter how small,

無論影響有多小

then changes in gravity can tell us about what those objects are doing.

那麼引力的改變 就能告訴我們那些物體的行動

Fluctuations in the gravity coming from the universe

來自宇宙的引力波動

are called gravitational waves.

稱之為重力波 (gravitational wave)

Gravitational waves move out from what caused them,

重力波從波源處向外傳遞

like ripples on a pond,

就像水池裡的漣漪一樣

getting smaller as they travel farther from their center.

隨著離圓心越遠而變小

But what are they ripples on?

但是漣漪的介質是什麼呢？

When Einstein devised his Theory of Relativity,

當愛因斯坦提出相對論時

he imagined gravity as a curve in a surface called space-time.

他將重力想像成 在「時空」表面上的弧形

A mass in space creates a depression in space-time,

空間中的質量體會使時空產生凹陷

and a ball rolling across a depression will curve

而當球滾過，那個凹陷便會彎曲

like it's being attracted to the other mass.

就像是被其他質量體吸引了一樣

The bigger the mass,

質量體越大

the deeper the depression and the stronger the gravity.

凹陷越深，引力也越大

When the mass making the depression moves, that sends out ripples in space-time.

當造成凹陷的質量體移動了

漣漪就在時空裡向外傳遞

這就是重力波

These are gravitationl waves.

What would a gravitational wave feel like?

重力波的感覺像是什麼呢？

If our bodies were sensitive enough to detect them,

如果我們的身體敏感到能偵測它們

we'd feel like we were being stretched sideways

我們會感覺像是被橫向伸展開來

while being compressed vertically.

同時也被縱向壓縮了

And in the next instant,

而在下一個瞬間

stretched up and down while being compressed horizontally,

被縱向伸展也同時橫向壓縮

sideways,

橫向伸展

then up and down.

再縱向伸展

This back and forth would happen over and over

重力波穿過你身體時

as the gravitational wave passed right through you.

伸展和壓縮不斷來回反覆發生

But this happens on such a minute scale that we can't feel any of it.

但這些改變幅度太小 以至於我們感受不到

So we've built detectors that can feel it for us.

因此建造了探測器幫助我們觀測它

That's what the LIGO detectors do.

這就是 LIGO 探測器的功能

And they're not the only ones.

而那並不是唯一一個

There are gravitational wave detectors spread across the world.

世界各地都有重力波探測器

These L-shaped instruments have long arms,

這些 L 形的儀器有著長臂

whose exact length is measured with lasers.

用雷射來精確測量臂長

If the length changes, it could be because gravitational waves are stretching

如果長度改變了

很有可能是重力波在伸展、壓縮手臂

and compressing the arms.

Once the detectors feel a gravitational wave,

一旦探測器感受到重力波

scientists can extract information about the wave's source.

科學家們可以獲取波源資訊

In a way, detectors like LIGO are big gravitational wave radios.

某種程度上

像 LIGO 這樣的探測器 就是個大型重力波收音機

Radio waves are traveling all around you, but you can't feel them

無線電波總是在你周遭穿梭

但你感受不到 也聽不見它們載著的音樂

or hear the music they carry.

It takes the right kind of detector to extract the music.

必須要藉由正確的探測器來擷取出音樂

LIGO detects a gravitational wave signal,

LIGO 探測重力波訊號

which scientists then study for data about the object that generated it.

並由科學家們研究產生波的物體數據

They can derive information, like its mass and the shape of its orbit.

他們可以從中獲得資訊 像是它的質量或運行軌道的形狀

We can also hear gravitational waves by playing their signals through speakers,

我們也可藉由揚聲器播放它們的訊號 而「聽見」重力波

just like the music a radio extracts from radio waves.

就像由收音機 從無線電波中取得的音樂一樣

So those two black holes colliding sounds like this.

那兩個黑洞的碰撞聽起來像這樣

Scientists call this slide whistle-like noise a chirp,

科學家們稱這如滑哨般的雜音為啁啾

and it's the signature of any two objects orbiting into each other.

而這是來自任何互繞兩物體的簽章

The black hole collision was just one example

黑洞碰撞

只是重力波能帶給我們的其中一個例子

of what gravitational waves can tell us.

Other high-energy astronomical events will leave gravitational echoes, too.

其他高能量天文現象也會帶來重力迴波

The collapse of a star before it explodes in a supernova,

像是一顆星球在超新星爆炸前塌陷

or a very dense neutron stars colliding.

或是高密度中子星的碰撞

Every time we create a new tool to look at space,

每一次我們創造出新的工具看向外太空

we discover something we didn't expect,

我們總發現一些從沒預期過的事

something that might revolutionize our understanding of the universe.

一些可能使我們對宇宙認知 產生革命性變化的事

LIGO's no different.

LIGO 也是如此

In the short time it's been on,

它出現的短短期間內

LIGO's already revealed surprises,

LIGO 已經揭露了一些驚喜

like that black holes collide more often than we ever expected.

像是比預期中更頻繁發生的黑洞碰撞

It's impossible to say, but exciting to imagine,

雖然沒辦法肯定

但光是想著就令人振奮

what revelations may now be propagating across space

有哪些等著被揭露的真相 可能正在橫越太空

towards our tiny blue planet and its new way of perceiving the universe.

朝著我們的迷你藍色星球

帶給我們看待宇宙的全新角度