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One thing that humans simply cannot stop doing is trying to figure out where we came from and why we exist. That's, like, Our Big Thing.
人类一直无法停止探索我们的起源以及存在的原因，就好像这才是大事。
That, and getting really inventive with fried foods, but that's a subject for another channel.
除了这件事之外，我们还在创新快餐食物方面颇有建树，不过这是另一个讨论范畴了。
Philosophers and fry cooks are still working on those questions, but science can at least answer one thing: when the universe began.
很多哲学家和快餐大师依然在研究这些问题，但科学至少能肯定一件事：宇宙是什么时候开始的。
And right now, we're pretty confident that it all happened around 13.8 billion years ago with the Big Bang.
而如今，我们十分坚信，宇宙大约于138亿年前随着宇宙大爆炸的出现而萌生。
Figuring that out hasn't been easy, and our estimates could still get better,
得出这个结论并不容易，而且我们的估测还能更多更准，
but thanks to some useful tools and a lot of math, we're off to a really good start.
不过多亏了一些有用的工具和大量的数学计算，我们实现了良好的开始。
To calculate the age of the universe, astronomers use two main tools, or pieces of evidence.
为了计算宇宙的年龄，天文学家们主要使用了两种工具，或者说证据。
The first is pretty intuitive: They look for old stuff. For the most part, that means looking at really faraway stuff.
证据之一是凭直觉获得的：他们寻找普通的东西，大多数时候，这种方法基本上都是在观测十分遥远的物体。
See, the universe has been expanding ever since the Big Bang, so the very oldest objects have been hurtling away from the Earth for billions of years.
毕竟宇宙自大爆炸发生以来就一直在延伸，所以最古老的物体向远离地球的方向疾驰了数十亿年了。
And based on how far an object is, astronomers can get a rough idea of how old it is.
所以，根据某个物体距离地球的远近，天文学家就能大致得出该物体的年龄。
So far, using photos, like ones from the Hubble Space Telescope, researchers have been able to find clusters of stars as old as 13.2 billion years!
目前为止，通过使用照片，比如通过哈勃太空望远镜获得的照片，研究人员得以发现年龄高达132亿年的星团。
But they don't know the stars are old just by looking at them.
不过，他们无法通过观测这些星团来得知其中恒星的具体年龄。
To figure it out, they have to take into account some of the cool, weird ways that light behaves.
为了得知这一点，他们必须考虑到光的一些冷门、怪异的行为方式。
See, as the universe expands, it also stretches the light waves traveling through it.
毕竟随着宇宙的膨胀，穿梭于其中的光波也会随之而延伸。
So if a star is moving away from Earth, its light will be stretched and have a longer wavelength by the time it gets to us.
所以，如果一颗恒星逐渐远离地球，那么它所发出的光波也会延伸，并且在其发出的光波抵达地球时，其波长要比一开始更长。
This is called redshift. By seeing how stretched, or redshifted, a star's light is,
这种现象叫做红移，通过观测某颗恒星的光波是如何实现延伸，或者说，如果发生红移的，
and doing some math, astronomers can get a rough idea of how far and how old a star is.
再加上数学计算的辅助，天文学家就能大致知道这颗恒星距离地球有多远以及其年龄有多大。
But that isn't the only tool they use, because even though we can detect some faraway objects,
但这并不是他们使用的唯一一种工具，因为即便我们能探测到一些遥远的物体，
others are still really difficult to observe over those large distances.
还是会有一些物体由于距离地球很远而很难对其进行观测。
Mostly, this just tells us that the universe has to be at least 13.2 billion years old.
基本上，这种情况都让我们得出这样一个结论：宇宙至少有132亿年的历史。
To refine the estimate, astronomers also use measurements about the expansion of the universe itself.
为了使该估测更加准确，天文学家还对宇宙本身的膨胀进行了测量。
We've known the universe was expanding since the late 1920s, but understanding how it's expanding is what's especially useful.
自上世纪20年代以来，我们就知道，宇宙是不断膨胀的，但尤其有用的并不是这一点，而是：宇宙是如何膨胀的。
Knowing how fast it's happening and how that speed is changing really allows researchers to work backwards from right now,
我们得知道宇宙膨胀的速率有多快，以及其速率变化是怎样的，只有这样，研究人员才能从当前的工作进行倒推，
to find out exactly when the universe was a tiny seed of everything.
才能得知宇宙最初开始于何时。
It's basically like how a forensic scientist can study an explosion site and tell you when the bomb went off.
这就好比，法医要先勘测爆炸现场，才能得出炸弹是何时爆炸的结论。
Just with a much bigger bomb in this case. Two major discoveries have helped us understand this expansion.
只不过，宇宙大爆炸的规模要比爆炸现场的规模大很多而已，有两个重大发现帮助我们理解了宇宙膨胀的过程。
The first was type Ia supernovas, which form from the explosion of a tiny white dwarf star and some other stellar companion.
第一个发现是Ia超新星，它是由体型不大的白矮星及其附近一些近距恒星爆炸形成的。
In 2011, a team of scientists won a Nobel prize for using them to prove that the universe's expansion is getting faster.
2011年，一组科学家通过Ia超新星证明了宇宙膨胀的速度是不断变快的，该发现使他们获得了诺贝尔奖。
These supernovas are extremely bright, and their brightnesses are all pretty uniform, so one of them will look a lot like any other.
Ia超新星亮度极大，而且亮度十分统一，所以他们中的每个都与其他所有超新星非常相似。
This makes them really good for calculating distances, or what astronomers call standard candles.
它们的这个特性使其成为计算距离的好帮手，天文学家称其为标准烛光。
Since we know what their brightnesses should be at any given distance,
既然我们可以根据这种超新星的距离得知其亮度，
whether it's a million or a billion light-years away, they're easy to use in measurements.
无论它们距离地球有100万光年还是10亿光年，那么无论怎样都很容易就能用于测量中。
And after years of measurements, astronomers noticed that the redshifts for these supernovas was a lot smaller than they should've been for galaxies so far away.
经过多年的测量，天文学家发现，Ia超新星发生的红移现象要比理论上的小很多，毕竟这些星系离地球有这么远呢。
That means that, sometime after the supernovas emitted their light, they actually got farther from Earth than expected.
也就是说，Ia超新星发出光线后的，他们距离地球的距离实际上比预期的更远。
That could only be explained by a universe that's expanding faster as the years go on, although we aren't positive what's causing that to happen.
对于这一点，唯一能解释的说法就是：宇宙是随着时间不断膨胀的，虽然我们也不知道膨胀的原因是什么。
But it has helped us understand when the Big Bang happened.
但该结论帮助我们推算出了大爆炸发生的时间。
Before we knew that the expansion of the universe was accelerating, our calculations about its age could be pretty inaccurate.
在人类得知宇宙膨胀的速度是不断加快的之前，我们对于宇宙年龄的计算相当的不准确。
Astronomers used to assume a constant rate of expansion, so if you're working backwards from our current rate, you'd get a universe that's way too young.
天文学家以前一直以为宇宙膨胀的速度是恒定的。按照这种结论，要是用当前的速率回推，宇宙的年龄就太小了。
Or, if you picked a bad standard candle, you'd get inaccurate measurements, too.
或者，如果以一个亮度未知的天体作为标准烛光，也会得到不精确的计算结果。
For instance, Hubble's original calculations from the 1920s used a type of star called a Cepheid variable as the standard candle,
比如，上世纪20年代，哈勃最初的计算用了一种名为造父变星的恒星作为标准烛光的常量，
and that suggested the universe was about 2 billion years old, which is definitely not right. Science is a process.
计算结果是：宇宙的年龄是20亿年，这当然不对，但科学是一步一步来的。
Still, type Ia supernovas aren't the only way we've studied how the universe is expanding.
不过，Ia超新星并非人类研究宇宙膨胀的唯一方法。
The other way we've figured out the rate of expansion is with the Cosmic Microwave Background, or CMB,
我们发现宇宙膨胀速率的另一种方法与宇宙微波背景(CMB)有关，
which is the energetic glow left over from the Big Bang.
所谓宇宙微波背景，就是大爆炸留下的极具能量的辐射。
Well, it's not wildly energetic, it comes in at 2.7 Kelvin, or about -270 degrees Celsius.
不过，宇宙微波背景各处都极具能量：其初始温度是2.7开，大约是270摄氏度。
But it's not 2.7 Kelvin everywhere you look! And that's super useful to us!
但并非各处都是2.7开哦！这一点对我们非常有用！
Those temperature variations can tell us about the movement of objects and the densities of gases in the universe,
我们能从温度的变化得知宇宙中物体的运动以及气体的密度，
both of which are used in calculating the universe's rate of expansion.
而物体的运动和气体的密度都可以用来计算宇宙的膨胀速率。
And along with type Ia supernovas, these studies have allowed us to get a much more precise picture of how the universe has been growing since it began.
关于宇宙微波背景的发现和Ia超新星的发现，都让我们得以更精确地得知宇宙产生以来经历了怎样的变化。
That's let us zero in on our current age estimate: 13.8 billion years.
假设现在将宇宙的年龄统一估定为138亿年。
And our observations are just going to get better from here on out!
以这个估定值为基础，我们的观测进展会越来越多。
We think 13.8 billion is pretty solid, but don't be surprised if you hear that number change a little bit as we make better observations.
我们认为138亿是个固定值，但如果您听说这个数字有所变化也不要惊奇，那是因为我们的观测又有了新进展。
It just means we're getting better at science. And speaking of CMB,
这只是表明，我们的科学越来越进步了，而提到宇宙微波背景，
Brilliant.org has a lesson in their astronomy unit that covers even more of what that background radiation has taught scientists about the universe.
Brilliant.org的一个天文学单元里也有关于它的课程，其中讲解了更多关于：通过宇宙微波背景辐射，科学家对宇宙了解到了什么。
And it's really fun, because each question makes you an active problem solver.
课程非常有趣，因为其中的每一个发问都能让您积极地解决问题。
So let's see if we learned anything from everything I was just telling you about.
那么，这里我也来检测一下您是否通过我今天的讲解学到了什么。
I'm going to take the quiz here in the studio, but Brilliant.org also set up a link so that you can test your knowledge at home for free.
我将在演播室里进行一个小测验，而Brilliant.org会通过一个链接来让您在家就能免费检测自己的知识学习情况。
You can find that at brilliant.org/SciShowSpaceCosmology.
您可以在brilliant.org/SciShowSpaceCosmology进行测验。
So like all Brilliant quizzes, this one opens with giving you more information about how to solve these problems.
跟其他所有Brilliant推出的测试一样，这个测试也是公开的，旨在为您提供更多的知识，让您可以解决这些问题。
This quiz kind of starts with explaining the CMB a little bit more before we dive into answering questions about it,
测验开头会稍微介绍一下宇宙微波背景是什么东西，然后才开始提问。
and one of the things that I love about Brilliant is that it's not just text-based, that you're working with, you have amazing images like this map.
而我钟爱Brilliant的一个原因就是：它并不是只是回答问题而已，您还会在上面看到有这样令人惊奇的地图。
Not only do they help me understand the problem that I'm trying to solve,
这些内容不仅帮助我理解了我想解决的问题，
but they give context to everything that they're talking about in this quiz, and that helps me make more sense of it,
也给了我测验中讨论问题的背景知识，可以帮助我弄懂整件事情。
but also retain that information over the long run and be excited about it.
同时也能将这些知识作为我的长期储备，一提起它们就能想到这些知识。
So check out the quiz for yourself, and let us know how you do in the comments below.
所以，大家也来测验一下自己吧，可以将测验的情况在评论里告诉我哦！
This quiz is totally free for you to play with, so have at it.
测验是完全免费的，不妨小试牛刀。
And the first 200 to sign up at brilliant.org/scishowspace will get 20% off of their annual Premium subscription, and be supporting SciShow Space, so thank you!
最先注册brilliant.org/scishowspace的200名用户不仅是对我们节目的大力支持，也可以减免20%的订阅费哦！谢谢大家！
