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我们如何知道宇宙在加速? – 译学馆
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我们如何知道宇宙在加速?

How Do We Know The Universe Is ACCELERATING?

The universe is expanding.
宇宙正在膨胀
If you zoom out far enough, you’ll find that everywhere in the universe is moving
在大视角下 你会发现宇宙万物都在
away from everywhere else.
远离着彼此
But once you know the universe is expanding, you might wonder if it’s going to keep expanding
但当你知道宇宙在膨胀 你可能会想它是否会
somehow, or eventually stop and crunch in on itself because of the attractive force of gravity.
以某种方式继续膨胀 或在引力作用下停止膨胀甚至收缩
Well, all you have to do is point your telescope at a distant galaxy, measure how fast it’s
你只需用你的天文望远镜观察远处星系
moving away from us, wait about a million years, and then do the same thing again to
测量其远离我们的速度 百万年后 再做一遍
see if the galaxy is moving faster or slower than before.
来检测星系移动速度是变快还是变慢了
But if you don’t have a million years to spare, here’s what you do.
但若你没有百万年时间 你可以这样做
You look at different galaxies.
你可以观察不同星系
Because light takes time to reach us, when we look at a galaxy far, far away, we see
因为光抵达需要时间 当我们望向遥远星系
it as it was a long time ago.
我们看到的是它的过去
So looking at a bunch of galaxies different distances away is kind of a rough proxy for
观察大量星系不同远离速度是观察单一星系
looking at the same one at different times.
不同时间远离速度的粗略替代方案
The light from the stars in a distant galaxy can tell us two basic things.
从遥远恒星而来的光告诉我们两个基本事实
First, its speed: light from anything moving away from you becomes redder in color (kinda
其一 我们可以根据红移现象推测其速度
like how police sirens get lower in pitch when moving away).
(红移现象与多普勒效应相似)
This redshifting of light tells us exactly how fast stars are moving away from us.
红移程度可以告诉我们恒星远离的确切速度
If the light from a star is 5 percent redder than it should be, it means the star is moving
若光比原来红了五度 意味着恒星在
away from us at 5 percent the speed of light.
以光百分之五的速度远离我们移动
Light can also tell us how far away a star (and thus its parent galaxy) is.
其二 我们可以推测恒星离我们的距离
When you’re driving at night, you can tell how far away a motorcycle is by comparing
在晚上开车时 如果你刚好在摩托车正前方
how bright its headlight seems to you, to how bright it would be if you were right in front of it.
可以通过比较其车头灯亮度来推测自身与它的距离
The same trick works with stars.
对恒星也一样
There’s a rare kind of supernova explosion that’s like a standard interstellar headlight
有种罕见的超新星爆炸 像标准的星际信号
– it’s about 5 billion times brighter than our sun, and, crucially, it’s very
它大约比太阳亮五十亿倍 关键的是
consistent in its brightness.
光亮能持续很长时间
These only happen a few times in a galaxy every thousand years, but there are enough
一个星系几千年才有几次
galaxies in the universe that, if you look closely at a wide enough patch of sky, it’s
但宇宙里有足够多星系 你若仔细观察
possible to see a dozen of them go off in a month.
能够在一个月中看到几十次
By comparing the brightness as seen here on Earth with how bright we know each of them
通过比较在地球上的亮度和其原始亮度
should be, we can work out how far away each supernova is.
我们可以计算出超新星的距离
The dimmer its light, the farther away it is.
亮度越暗 距离越远
So the color of a type Ia supernova tells us how fast it’s moving away from us, and
超新星光的颜色告诉我们其远离速度
its brightness is like a ruler, telling us how far away it is – or, because light takes
其亮度告诉我们它离我们的距离
time to get here, how long ago we’re measuring its speed.
或者说 我们能测量其过去的速度
By measuring the speed of different supernovae at different distances – different
测量不同时间不同距离超新星的不同速度
times in the past – we can plot the expansion of the universe over time.
我们可以绘制宇宙膨胀的坐标图
A straight line means the universe is expanding at a constant rate, a curve means it’s speeding
直线代表恒速 曲线代表变速
up or slowing down.
包括加速和减速
For a long time we thought the line was straight, or slightly curved in the slowing down direction.
我们长时间认为速度线是直的 或略微减速的曲线
But when astronomers finally looked carefully at supernova in super-distant galaxies, they
但当天文学家仔细观察遥远星系的超新星
discovered, to their surprise, that the universe is expanding faster now than it was long ago.
他们惊讶发现 宇宙膨胀速度比以往快
The universe’s expansion is accelerating!
宇宙在加速膨胀
p.s.
附言
We have a few basic ideas for why the universe is accelerating, but we still don’t really
我们有一些基本假设 但都不确信
know why it’s happening.
其发生的真正原因
One of the simplest and most popular ideas is that there’s an everywhere-permeating
最通俗也最流行的假说是无处不在的
vacuum energy with negative pressure which we’ve never detected in any way other than
产生排斥力的能量 我们至今没有检测到
by measuring the expansion of the universe… so we call it dark energy.
而是通过事实推测出来 故称其为暗能量
Thanks to the Wide Field Infrared Survey Telescope project at NASA Goddard Space Flight Center
感谢美国宇航局戈达航天局飞行中心广域红外探测望远镜项目
and the Space Telescope Science Institute for supporting this video.
以及天文科学协会对本视频的支持
WFIRST is planned to launch in the mid-2020s, and will, among other things, allow us to
WFIRST将在20年代中叶建成
see a much wider swath of the sky at Hubble-like resolutions and even farther distances, and
它将比哈勃望远镜看得更宽更远
thus hunt for more supernovas many billions of light years away.
并且可以探索几十亿光年外的超新星
That’ll help us understand whether the acceleration of the universe is different in different
这能帮助我们更好理解在不同地方
parts of the universe or whether it has changed over time, which should help us figure out
宇宙膨胀速度的不同和其是否会随时间改变
what exactly dark energy is.
也将更好帮助我们探索暗能量之谜

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视频概述

宇宙加速膨胀已经家喻户晓,但这困扰科学家百年的问题,究竟最后是通过什么方法来解决的呢?现在对这问题的研究又到了什么程度了呢?这将会在本期视频进行讲解,一起来探索这宇宙的奥秘吧!

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收集自网络

翻译译者

林木小

审核员

审核员 V

视频来源

https://www.youtube.com/watch?v=tXkBfkeJJ5c

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