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Telescopes, you may have heard, are time machines.
大家可能听说过，望远镜就是时光机。
Because light has a speed limit, the deeper into space we look, the older the signal we receive.
因光有速度限制，所以观察太空越远，收到的信号就越久远。
The oldest light we can see is called the Cosmic Microwave Background, and it comes from when the universe was less than 400,000 years old.
我们所能观测到的最久远的光是宇宙微波背景，它来自于宇宙诞生不到40万年的时候。
And while that's great and all, it also means there are 400 thousand years of history we can't study using traditional methods.
虽然这段时间已经够短，但对我们来说，这40万年的历史依然是我们通过传统方法无法研究的。
That's why astronomers are so interested in finding techniques that don't rely on light.
因此，天文学家希望找到某种手段，不依赖光的手段。
And luckily for them, and us, there are some other waves out there that could reveal the universe when it was a teeny tiny fraction of a second old.
所幸，宇宙中存在其他的波，可以解密宇宙诞生没多久的时光。
I'm talking about gravitational waves.
我说的波就是引力波。
Over a century ago, Albert Einstein taught us that mass deforms the fabric of spacetime, kind of like how a bowling ball deforms a trampoline.
一个多世纪以前，阿尔伯特·爱因斯坦让我们了解到质量会让时空变形，这就有点像保龄球让弹簧垫变形一样。
But he also predicted that accelerating mass would cause space itself to ripple, like the surface of a pond.
但爱因斯坦还预测了一件事：质量的加速会引起宇宙的波动，就像水池表面的涟漪。
And back in 2015, we directly detected these gravitational waves for the first time.
2015年的时候，我们首次对引力波进行了直接的监测。
That was thanks to a pair of black holes spiraling inward and merging with one another.
这要感谢一对黑洞，这对黑洞盘旋着向内，彼此交融。
But technically, lots of things in space can cause gravitational waves.
但从技术层面来讲，太空中的很多事物都会引起重力波。
And if we think of spacetime like the surface of a lake, all of these astronomical events are like raindrops, whose gravitational waves interfere with one another and generate a kind of noise.
如果我们将时空看作一个湖面，那么所有的天文事件都像是雨点，它们的引力波会干扰彼此，并产生噪音。
Theoretically, we could someday pick apart that noise to study specific events.
从理论上来说，我们有一天可以通过这噪音来研究特定的一些事件。
But what's maybe even more interesting is that, beneath that noise, space is actually filled with evidence of other, older gravitational waves.
但可能更有趣的是：隐藏在这噪音背后的宇宙实际上充满了其他更为久远的引力波存在的证据。
And those waves could teach us about the birth of the universe itself.
这些引力波可以让我们了解宇宙诞生的情况。
Waves from way back then are called primordial gravitational waves, and there are a few proposed sources for them.
那时候的波名作原始引力波，这种引力波可能有几种来源。
According to many cosmologists, some were generated by the formation and merger of still-hypothetical primordial black holes.
很多宇宙学家认为，一些引力波之所以形成是因为存在假设中的原始黑洞，这些黑洞的合并和形成生发出了引力波。
These objects would act like regular black holes, but would be less massive, and may have sprung up from pockets of super dense matter in the very early universe.
这些物体的行为看起来像常规的黑洞，但质量却小很多。而且可能是从宇宙初期一些密度极大的物质中生发出来的。
Other primordial gravitational waves could have been generated by the formation of various particles as the universe cooled down.
其他原始引力波可能是因为宇宙降温期间各种粒子形成而产生的。
The ultimate primordial waves though, weren't caused by stuff in space, they were made by space itself.
不过，原始引力波并不是由宇宙里的物质引起的，而是由宇宙本身产生的。
They come from a hypothetical period in the universe's history called inflation.
他们来自于宇宙暴胀期这个假设时期。
It's the time a tiny fraction of a second after the Big Bang, around 10-32 to 10-36 seconds, when most cosmologists believe the universe expanded way faster than the speed of light.
这个时期紧接着宇宙诞生而发生，大概在10-32至10-36秒之间。宇宙学家认为，在此期间，宇宙暴胀的速度比光速快。
For the record, this wouldn't break the law that says nothing can travel faster than the speed of light, because that law only applies to matter in space, not to space itself.
补充一下，这并不会违背任何事物的速度都无法超过光速的定律，因为这一规律只适用于宇宙里的物质，而并非宇宙本身。
Regardless, inflation still isn’t set in stone.
当然了，暴胀的说法并非定论。
There are definitely alternative interpretations for what could have happened back then.
对于以前发生的事情，当然还有别的解释。
Gravitational waves are predicted in these alternative hypotheses, too, but detecting primordial waves will hopefully give cosmologists the data they need to pin down what actually happened.
引力波也在替代假说中做了预测。不过，检测原始波有希望为宇宙学家带来一些数据，他们需要这些数据才能确定发生了什么。
For example, they could use the amplitude of the waves to help define how fast everything expanded, the energy involved in inflation, and exactly when and for how long it happened.
比如，他们可以通过波的振幅来助力确定事物膨胀的速度、参与暴胀的能量以及爆炸何时发生、持续了多久。
And through other methods, they could learn how consistent that inflation was across the whole universe.
通过其他一些方法，他们可以了解暴胀是怎样持续出现在整个宇宙的。
Of course, before we can figure out any of that, we have to actually detect these waves.
当然了，在我们弄清楚这些之前，我们还是要先检测这些引力波。
And we do have a few options. First, there's the indirect method of detection, which comes from looking at the Cosmic Microwave Background.
而且我们确实有几个选项可以选择。首先，有一种间接的检测方法，来自于观测宇宙微波背景。
According to the math, gravitational waves older than the CMB would have influenced what it looks like.
数学告诉我们：引力波产生的时间早于宇宙微波背景能产生影响之前。
Specifically, they would have caused a certain spiral pattern in the light that cosmologists call B-mode polarization.
具体来说，它们会在光中引发某种螺旋图样，宇宙学家将其称之为B模偏振。
We can already detect a different kind of polarization in the CMB, called E-mode, and scientists are investigating the B-mode kind.
我们已经能在宇宙微波背景中探测到一种不同的偏振了，这种偏振就是E模偏振。而科学家正在研究的是B模偏振。
But it's hard because it's a way weaker effect, and these signals can also come from things like dust in the Milky Way.
但这很难，因为这种效应更为若，而且这些信号也可能来自于银河系中的灰尘。
The other option, of course, is to just try to directly detect primordial gravitational waves, using equipment similar to what we've used to detect the waves from black hole mergers.
另一个选择当然是直接探测原始引力波了。这过程要用到设备，这设备与我们用来探测黑洞吞并所产生的波的设备相同。
Right now, to detect those events, we mainly use interferometers like LIGO, which send laser pulses down two perpendicular arms.
现在，为了探测这些活动，我们主要用到了激光干涉引力波天文台（LIGO）这样的干涉仪。干涉仪可以发送激光脉冲。
If a gravitational wave passes through the system, it will compress or stretch things, meaning one laser beam will have to travel farther than the other.
如果一个引力波穿越这个系统，就会导致物体压缩或者伸展，也就是说，一道激光束必须要比另一道快才行。
Unfortunately, none of our current interferometers is sensitive enough to detect primordial waves, but there are future projects in the works.
不幸的是，当前的干涉仪灵敏度都不足以探测到原始波，但未来的项目已经在筹备中了。
The main one is LISA, which will work roughly the same way as LIGO, except in space.
主要的项目是空间天线激光干涉仪（LISA），它的工作原理与LIGO差不多，但在太空里是不一样的。
It'll consist of three spacecraft, arranged in a triangle and separated by millions of kilometers, and it's scheduled to launch in 2034.
它将由3个宇宙飞船组成，分布在一个三角形中，相隔数百万公里，预计2034年起飞。
The other direct detection method uses dense, spinning objects called pulsars.
另一个直接的探测方法是用密度大的旋转物体——脉冲星。
They shoot out beams of radiation as they rotate, which can hit Earth at really regular intervals.
脉冲星旋转时会释放出大量辐射，辐射会定期抵达地球。
But if a gravitational wave passed through the space between the pulsar and Earth, that interval would change.
但如果一道引力波穿过脉冲星和地球之间的空间，辐射抵达地球的频率就会改变。
And astronomers would be able to use details about the wave's signal to figure out if they came from primordial or recent sources.
天文学家就能通过有关这道波信号的细节来弄清楚它们是来自于原始引力波还是最近的引力波。
Still, figuring out what “normal” means is complicated, because even if pulsars are known for being predictable, there are still other factors that can affect how fast they rotate.
不过，弄清楚“常规的东西”是很复杂的，因为即便脉冲星可预测性很强，但依然有其他因素可以影响它们的转速。
And it's going to take time for scientists to pin down a model that's good enough to use pulsars effectively.
科学家需要一段时间才能确定出一个足够精良的模型，从而有效利用脉冲星。
But once we find those elusive primordial waves, it will mean big things for astronomy.
一旦能发现这些难以捉摸的波，天文学就将发生巨大变革。
We'll be able to figure out more about inflation, and see back further than we ever have before.
我们就能弄清楚暴胀，就能观测到宇宙里更远的地方。
And with more research, we're getting closer and closer to understanding the moment our universe's story began.
随着研究的推进，我们就能越来越多地了解到宇宙初期的情况。
Thanks for watching this episode of SciShow Space!
感谢收看本期的节目！
If you want to learn more about other tools we could use to study the universe, you can watch our episode about the Cosmic Neutrino Background after this.
如果您想了解有关我们研究宇宙其他工具的话，可以观看有关宇宙微波背景的那一集。
