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We're used to thinking of space as the emptiness in which things happen, like an empty warehouse ready to be filled,
我们一直认为空间是个会有事情发生的虚无空间，就像一个准备被填满的空房子
or a theater stage on which the events of the Universe play out.
或是像一个发生着各种事情的舞台。
But General Relativity predicts that space is not just emptiness, it's a physical, dynamic thing,
但是广义相对论预言空间并不是一片虚无，它是一个有形的、动态的事物，
and that prediction has been borne out by many, many experiments.
并且这个预测已经被很多很多的实验证明了。
Space can bend because of matter and energy, curving the paths of objects that move inside of it.
由于物质和能量的作用，空间可以弯曲，影响着物体在其中移动的路径。
It can ripple with gravitational waves. And it can expand, creating more and more space in space.
它可以因重力波影响而震动，也可以膨胀，在两个物件之间创造出更多的空间。
All of these seemingly different phenomena can be described by one idea: curvature of space or spacetime.
所有这些看似不同的现象都可以用一个概念来描述：空间或时空曲率。
In flat regions of spacetime, like, if there's no energy or matter nearby, objects traveling along parallel paths stay along parallel paths.
在时空的平坦区域，例如没有能量或物质的附近，沿平行路径运动的物体就会停留在平行路径上。
In positively curved regions of space, like near planets or black holes, parallel paths converge,
在曲度为正的时空，比如星球或黑洞附近，平行路径会向彼此靠近,
and in negatively curved regions of space parallel paths or even paths pointed at each other diverge.
而在曲度为负的时空，平行路径，甚至是相互指向彼此的路径都会互相远离。
But what about space as a whole? If space is positively curved everywhere,
但如果把整个时空视为一个整体呢？如果空间的每处曲度都为正,
then there's only one shape space can be: a giant hyperspace-potato.
那么就只可能有一种形状的空间：一个巨大的超空间的球体。
If you went in one direction for long enough, eventually you'd end up in the same place you started.
如果你向着一个方向前进，那么你最终还会回到原点。
If space is flat everywhere, its shape could be simple: just extend out straight to infinity.
如果空间是平坦的，那么其形状就很简单：无限延伸的平面。
Or it could loop around in a periodic way, like in some video games.
或者它可以进行周期性循环，就像一些游戏一样。
And if space is negatively curved everywhere, sports would be impossible. So which is it?
如果时空整体曲度为负，那么有些体育运动就不可能进行。所以到底是哪一种呢？
There are basically two ways to measure the large-scale curvature of the Universe.
测量整个宇宙曲度的方法大体上有两种。
One is to measure the angles inside of triangles. If the space is flat, the angles will add up to 180 degrees.
一种是测量三角形的内角。如果空间是平的，那么内角和即为180度。
But if the space is curved, those angles will add up to more or less than 180 degrees depending on the type of curvature.
但如果空是曲的，那三角形的内角和一定大于180度或小于180度，这取决于曲度。
Cosmologists have done the equivalent of measuring our Universe's triangles by looking at a picture of the early Universe,
宇宙学家进行了类似的实验，通过观察早期宇宙的图像，
and studying the spatial relationship between different points on that picture.
研究图中不同点之间的空间关系来测量我们宇宙的三角形。
The second way to measure curvature is to measure the thing that causes space to curve in the first place:
第二种测量曲度的方法是测量造成时空扭曲的主因：
the density of energy and matter throughout the Universe. Which cosmologists have also measured.
宇宙中物质和能量的密度。宇宙学家也对此进行了测量。
It turns out that in both cases, measurements show the Universe to be pretty much flat (within 0.4% margin of error).
结果表明，在这两种情况下，测量结果显示宇宙几乎是平的（误差范围在0.4%以内）。
But before you get disappointed that we don't live in a cool cosmic hyper-potato, let me tell you one big problem:
在你为我们不是生活在球形宇宙中而失望之前，先让我告诉你一个大问题：
The fact that we live in a flat Universe appears to be a GIGANTIC, COSMIC-LEVEL COINCIDENCE.
我们生活在一个平坦的宇宙，这其实是一个天大的巧合。
If the Universe had just a little bit more mass and energy, space would have curved one way.
如果宇宙有多一点点的质量和能量，空间就会向一个方向弯曲。
And if it had just a little bit less mass and energy, space would have curved the other way.
如果宇宙少一点点的质量和能量，空间就会朝着另一个方向弯曲。
But we seem to have just the right amount to make space perfectly flat as far as we can tell.
但我们的宇宙拥有刚刚好的质量和能量，让我们的空间保持平坦。
This perfect amount is the equivalent of five hydrogen atoms per cubic meter of space, on average.
这完美的量就相当于平均每一立方米内有5粒氢原子。
Does big empty parts of space make up for all the atoms we have crammed in here around us.
又大又空的空间部分能弥补我们周围的原子吗？
If instead there were six hydrogen atoms per cubic meter of space on average, or four,
如果平均每一立方米内有6粒或4粒氢原子,
the entire Universe would have been a lot more curved or a lot less.
那么整个宇宙将会更加弯曲或平坦。
And we so far have no idea why our universe has the mass energy density it does.
到目前为止，我们还不知道为什么我们的宇宙有着恰到好处的质量能量密度。
When it comes to the curvature of the universe, our knowledge falls flat.
当谈到宇宙曲率时，我们的知识是贫乏的。
