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One of the things we assume to be fundamental about the universe is that it's the same in all directions.
我们认为宇宙的基本特征之一是它各个方向都是一样的。
That means that over large scales, matter is spread out pretty evenly, things look more or less the same in every direction, and you'll never find a corner of space with its own laws of physics.
这意味着，在大尺度上，物质分布得相当均匀，事物在各个方向上看起来多多少少都是一样的，你永远找不到一个有自己物理定律的空间角落。
And considering the universe is such an impossibly huge thing to explore, it’s comforting to think that somehow, fundamentally, it’s pretty simple.
考虑到宇宙大到不可能被探索，想到它在某种程度上，从根本上说，是相当简单的，还挺令人欣慰。
It all sticks to the same rules.
整个宇宙都遵循同样的规则。
So you don’t have to explore the whole thing to understand it.
所以你无需探索整个宇宙才能理解它。
This notion is called the cosmological principle.
这个概念被称为宇宙学原理。
But there’s no law, exactly, that says the universe has to be that way.
但并没有确切的定律，说宇宙必须如此。
So, what if it weren't uniform?
那么，如果它不是相同的呢?
The main problem is that it would mean there’s only so much we can learn about the universe by looking at it from our little perch in the Milky Way.
主要的问题是，这意味着我们只能从银河系这个小小的栖息处来观察它，对宇宙的了解非常有限。
For example, fundamental laws like general relativity— which deals with gravity— assume that the universe is homogeneous.
例如，像广义相对论这样处理引力的基本定律假设宇宙是同质的。
If it’s not, it would mean we might not understand gravitational interactions in other parts of space as well as we think we do.
如果不是，那就意味着我们可能不像我们认为的那样了解宇宙其他部分的引力相互作用。
And our models of cosmology, which describe how the universe began and evolved, might not be as accurate as we think, either, if the forces that push and pull aren’t the same in every direction.
我们的宇宙学模型描述了宇宙是如何起源和演化的，可能也没有我们想象的那么精确，如果推动和拉动的力量在每个方向上并不都是一样的。
In short, we tend to assume that studying small chunks of the universe tells us about what it’s like as a whole, and if that weren’t true, it would limit what we can ever know.
简而言之，我们倾向于假设，研究宇宙的一小部分可以让我们知道它的整体是什么样子，如果事实并非如此，它将会使我们的认知受限。
Thankfully, there are a lot of reasons to believe that it is uniform.
值得庆幸的是，有很多理由相信它是相同的。
One of the strongest pieces of evidence comes from the cosmic microwave background, a faint glow of radiation from the Big Bang that fills all of space.
最有力的证据之一来自宇宙微波背景，来自充满整个宇宙的宇宙大爆炸的微弱辐射。
Back in those first moments, the universe consisted of just free electrons and nuclei in an extremely hot plasma, along with a bunch of light particles, or photons.
在那些最初的时刻，宇宙是由极热的等离子体中的自由电子和原子核组成，还有一束光粒子，或者说光子。
In denser areas, photons had to work against the pull of gravity as they radiated outward, and that cost them some energy.
在密度更大的区域，光子向外辐射时必须抵抗重力的牵引，这就消耗了一些能量。
So the energy of the radiation was directly tied to how densely packed particles were in the region it came from.
所以辐射的能量直接与它所在区域的粒子密度有关。
And we can actually still see that radiation today— that’s the cosmic microwave background.
今天我们仍然可以看到辐射，那就是宇宙微波背景。
Which means it’s one of the most direct ways we have of looking at the conditions just after the birth of the universe.
这意味着这是我们观察宇宙诞生后的情况最直接的方法之一。
Of course, that was 13.8 billion years ago, but other studies have found that the cosmological principle seems to have held up as the universe evolved.
当然，那是138亿年前的事了，但其他研究发现，宇宙原理似乎在宇宙演化的过程中得到了支持。
For example, the Sloan Digital Sky Survey created an enormous, three-dimensional map of the universe in greater detail than we’d ever seen,
例如，斯隆数字天空勘测计划绘制了一张巨大的三维宇宙地图，其细节之详细是我们从未见过的，
and it showed that, no matter which way you look, the distribution of galaxies is extremely similar on large scales.
它表明，无论你从哪个角度看，星系的分布在大范围内都是极其相似的。
So together, these two lines of evidence make a pretty strong case for the cosmological principle!
所以，这两方面的证据加在一起，为宇宙学原理提供了强有力的支持!
But even though the universe seems to be homogeneous, and cosmological principle seems to hold, the case isn’t totally closed— because there’s still no proof that it has to be that way.
但是，即使宇宙似乎是同质的，宇宙原理似乎也能成立，也不能妄下定论——因为仍然没有证据表明它必须得是如此。
And, of course, scientists are always testing their assumptions.
当然，科学家们总是在验证他们的假设。
In the last decade, studies have actually raised some doubts about the cosmological principle.
在过去的十年里，其实有研究提出了一些关于宇宙学原理的疑问。
For example, in 2011, researchers published a study based on supernovas, bright explosions of stars that let us see deep into the universe.
例如，2011年，研究人员发表了一项基于超新星的研究，超新星是恒星的明亮爆炸，让我们能够看到宇宙深处。
By measuring the distances to supernovas and how fast they seem to be moving away from us, astronomers can estimate how fast the universe is expanding.
通过测量到超新星的距离以及它们远离我们的速度，天文学家可以估算出宇宙膨胀的速度。
Incredibly, this study found that, in some directions, supernovas appeared to be receding faster than in other directions, implying that the universe was expanding unevenly.
令人难以置信的是，这项研究发现，超新星在某些方向上似乎比其他方向后退得更快，这意味着宇宙的膨胀是不均匀的。
In other words, it suggested that the universe is not the same in every direction— exactly the opposite of what the cosmological principle says.
换句话说，它表明宇宙在各个方向上都是不一样的——这与宇宙学原理所说的完全相反。
Then, in 2014, another team of researchers made another unusual discovery.
2014年，另一组研究人员又有了一个不同寻常的发现。
They were studying quasars, the compact areas surrounding supermassive black holes at the centers of galaxies.
他们研究的是类星体，即星系中心特大质量黑洞周围的致密区域。
Quasars are extremely bright, and like supernovas, they let us see into the distant universe.
类星体非常明亮，就像超新星一样，它们能让我们看到遥远的宇宙。
By studying them, scientists found that, across billions of light-years, many different quasars seemed to be rotating around axes that lined up with each other. Which is bizarre.
通过对它们的研究，科学家们发现，在数十亿光年的范围内，许多不同的类星体似乎都在绕着彼此对齐的轴旋转。很奇怪哈。
Because if there’s nothing special about one direction or another, you’d expect that quasars that have nothing to do with each other would just rotate around random axes.
因为如果各个方向没有什么不同，那么那些彼此没有任何关系的类星体只会绕着随机的轴旋转。
The implication that the universe had a preferred axis went directly against the cosmological principle.
宇宙有一个优先轴，这直接违背了宇宙学原理。
Which was potentially a really big deal.
这可是件大事。
Like the supernova study, it implied that the universe was anisotropic, meaning it has different properties in different directions.
就像超新星的研究一样，它暗示了宇宙是各向异性的，这意味着它在不同的方向上有不同的特性。
But as the saying goes, extraordinary claims require extraordinary evidence, and the cosmological principle hasn’t gone down the drain yet.
但俗话说，非凡的主张需要非凡的证据，而宇宙学原理还没有被抛弃。
In a 2016 study, researchers considered how a preferred axis would have shaped the early universe and looked for telltale signs like spirals or gravitational waves in the cosmic microwave background.
在2016年的一项研究中，研究人员考虑了优先轴是如何形成早期宇宙的，并在宇宙微波背景中寻找螺旋或引力波等信号。
And they didn’t find anything.
他们什么也没找到。
What’s more, all of the anisotropies different studies have found seem to be related in direction.
更重要的是，所有不同研究发现的各向异性似乎在方向上有联系。
So the authors suggested that they have to do with the way we observe the universe, rather than a problem with the cosmological principle.
因此，作者认为，这与我们观察宇宙的方式有关，而不是宇宙学原理的问题。
It’s still not proven, though, so astronomers are continuing to look for evidence that either confirms or defies our expectations.
尽管它还没有被证实，天文学家们仍在继续寻找证实或违背我们预期的证据。
And even though the cosmological principle seems to have stood the test of time, it’s important to keep checking.
尽管宇宙学原理似乎经受住了时间的考验，但继续检验仍然很重要。
Because anytime we study the universe, we’re going into it with some assumptions— and sometimes the concepts that seem the most intuitive and obvious are the ones keeping us from unlocking even deeper truths.
因为任何时候我们研究宇宙，都是带着一些假设去做的——有时那些看起来最直观、最明显的概念恰恰也是那些阻止我们揭示更深层真理的概念。
Thanks for watching this episode of SciShow Space!
感谢收看本期《太空科学秀》!
And a special thanks to our President of Space, SR Foxley.
特别感谢我们的太空总裁，SR Foxley。
SR is one of the awesome people who support SciShow through Patreon, and it’s thanks to patrons like him that we can keep making science education free on the internet.
SR是通过Patreon支持《科学秀》的了不起的人之一，感谢像他这样的赞助人，我们才能继续在互联网上免费提供科学教育。
If you’re interested in supporting what we do or learning more about our wonderful patron community, head on over to Patreon.com/SciShow.
如果你有兴趣支持我们所做的事情，或者想了解更多关于我们奇妙的赞助人社区的信息，请登录Patreon.com/SciShow。
