了解宇宙是如何运行的（2010）

How the Universe Works S10E05

Part 2 Aug. 5, 2022, 5:05 p.m.

我们得到一个年龄……
we get an age...
138.2亿年
13.82 billion years.
工作完成了!
Job finished!
但这并不是板上钉钉的事
But it's not quite
a slam dunk.
这个数字必须经过验证
The figure must be verified.
我们不会使用单一的技术
We don't make
a single measurement
进行单一的测量
using a single technique.
我们通过多种技术进行多种测量
We make multiple measurements
via multiple techniques.
另一组科学家
Another group
of scientists use
使用了一种完全不同的方法
a totally different method
来计算宇宙的年龄
to calculate
the age of the cosmos,
他们测量我们在宇宙中可以看到的物体
measuring objects
that we can see
以确定它们离我们有多远
in our universe to determine
how far away they are and how
以及随着宇宙膨胀它们离我们有多快
fast they're moving away from
us as the universe expands.
最直接、最精确的测量方法
The most direct and most
accurate measurements
是视差法
are using what is known
as parallax.
视差是在两个不同的位置
Parallax is the apparent shift
in an object relative
观察物体时，物体相对于背景的
to the background
when it's viewed
明显偏移
from two different locations.
所以如果我用一只眼睛看着我的拇指，然后闭上它
So if I look at my thumb with
one eye, and then I close it
接着用另一只眼睛看，看起来我的拇指在动
and look at the other eye,
it looks like my thumb moves.
如果我把拇指移近我的脸
If I move my thumb
closer to my face,
那么它来回移♥动♥的距离就会改变
then the distance it moves
back and forth changes.
它似乎更来回移♥动♥地更多
It appears to move back
and forth more.
当我们将拇指相对脸部
That parallax difference
as we move the thumb closer
移近或移远时
and farther from the face
视差差就是我们测量与远处物体距离的方式
is the way we measure
distances to distant objects.
利用视差
Using parallax,
we can measure
我们可以测量到银河系中被称为造父变星的
the distance to bright stars
called cepheids
明亮恒星的距离
in the Milky Way.
南斯:造父变星的亮度
NANCE: Cepheids
are stars that burn 100,000
是太阳的10万倍
times brighter than our sun,
所以它们非常亮，而且它们有脉动,这意味着
so they're extremely bright,
and they pulsate, meaning they
它们在一段固定的时间内会变亮或变暗
get brighter and dimmer over
a regular time period.
以相同频率脉动的
Cepheids that pulsate at
造父变星具有相同的亮度
the same rate have
the same brightness.
它们被称为标准蜡烛
They're known
as a standard candle.
标准蜡烛是一种标准
A standard candle is something
that is a standard, meaning
意思是我们知道它本身有多亮
we know how intrinsically
bright it is.
所以我们要做的就是
So all we have to do
is measure
测量我们在地球上看到的亮度
the brightness that we appear
to perceive on Earth,
然后算出距离
and then you solve
for the distance.
想象一下，如果你在街上
So imagine that
you're on the street.
沿着街道往前看
By looking down the street,
你会发现街灯会随着距离越来越远
you'll see that the street
lights get dimmer and dimmer
亮度越来越暗
the farther away they are,
但那不是它们本身的亮度
but that's not
their intrinsic brightness.
它们的固有亮度是相同的
Their intrinsic brightness
is the same.
所以通过观察离你最远的星体有多暗
So by seeing how faint
the farthest away ones are,
你就能知道它们离你有多远
you can understand how far
away they are from you.
我们可以用标准蜡烛
We can use
standard candles to measure
来测量到更远恒星的距离
the distance to stars
farther away.
但有一个大问题——在整个宇宙中
But there's a big problem --
throughout the universe,
存在着一种竞争，即一方要将物体推开的膨胀
there's a competition between
the expansion pushing things
和另一方要将物体拉到一起的引力
apart and gravity pulling
things together.
在银河系中
In the Milky Way,
有非常多的物质，所以引力占了上风
there's so much matter
that gravity wins.
即使观察我们附近的星系
Even looking at galaxies in
our neighborhood,
膨胀也是很小的
the expansion is tiny,
但在不同星系的宇宙尺度上
but at cosmic scales of very
different galaxies,
物质更分散，膨胀获得胜利
matter is more spread out,
and expansion wins,
所以我们测量远距离时只须考虑膨胀
so we can only measure expansion
over massive distances.
当我们开始测量物体的距离
The way we start to measure
distances to things that
越来越远时
are farther and farther away
使用我们称之为距离阶梯的方法
is to use something we call
the distance ladder.
南斯:我们观察到的每一类物体
NANCE: Each category of object
that we observe
都在这个梯子的一个单独的梯级上
is on a separate rung
of this ladder.
测量到第一梯级的距离
Measuring the distance to one
will then inform us how far
就能知道第二梯级和第三梯级的距离
away the second rung is
and then the third rung.
所以每一级都取决于前一级
So each rung depends on
the previous rung, and from
把这些加在一起，我们就可以开始测量
stacking these together, we can
start to measure things very,
离我们很远很远的东西
very far away from us.
利用视差来测量银河系中的造父变星
Using parallax
to measure cepheid stars in
给了我们一个基准
the Milky Way
gives us a benchmark.
然后我们可以用它们的标准亮度
We can then use
their standard brightness
来测量其他星系中的造父变星
to measure cepheids
in other galaxies.
下一个梯级是更亮的标准烛光
The next rung is a brighter
standard candle called
称为1A型超新星
<关于1A型超新星详见第九季第五集：白矮星的诅咒>
Type 1A supernovas.
在更远的星系中也能看到它们
They can be seen
in galaxies farther away.
最后，我们可以测量来自遥远椭圆星系的光
Finally, we can measure light
from distant elliptical
通过观察光的红移程度
<红移解释起来文字比较多，想了解就百度吧>
galaxies, and by looking
at how red the light is,
我们可以计算出它们离我们有多快
we can work out how fast
they're moving away from us.
这三种情况分别一个接一个给出了
So those three things
give us the nearby universe,
附近的宇宙、较远的宇宙，以及非常遥远的宇宙的
the somewhat far away universe,
and the very distant universe,
距离测算方法
rung by rung.
2021年3月
March 2021.
科学家们测量了来自63个
Scientists measure
the light from 63
巨大椭圆星系的光
giant elliptical galaxies,
这是距离阶梯中最远的阶梯
the farthest rung of
the distance ladder.
他们希望获得迄今为止
They hope to get the most
accurate measurement of
最精确的哈勃常数测量值，以及宇宙的
the Hubble constant to date
and a precise age
精确年龄
for the universe.
根据他们的计算
Their calculations make
the universe
宇宙的年龄为133亿年