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The universe began its cosmic life in a big bang nearly fourteen billion years ago, and has been expanding ever since.
宇宙的生命从大爆炸开始，将近140亿年前，一直膨胀扩大至今日。
But what is it expanding into? That's a complicated question.
但它是在膨胀成为什么呢？这是一个复杂的问题。
Here's why: Einstein's equations of general relativity describe space and time as a kind of inter-connected fabric for the universe.
以下是原因：爱因斯坦的广义相对论方程把空间和时间描述为一种相互连结的宇宙的构造。
This means that what we know of as space and time exist only as part of the universe and not beyond it.
这意味着我们所知道的空间和时间只作为宇宙的一部分而存在，并不存在于宇宙之外。
Now, when everyday objects expand, they move out into more space.
当日常生活中的物体膨胀，它们会占据更多空间。
But if there is no such thing as space to expand into, what does expanding even mean?
但如果并不存在额外的空间去膨胀，那膨胀到底意味什么？
In 1929, Edwin Hubble's astronomy observations gave us a definitive answer.
1929年，爱德文·哈勃的天文观测给了我们明确的答案。
His survey of the night sky found all faraway galaxies recede, or move away, from the Earth.
他对夜空的调查发现了所有遥远的星系会朝着远离地球的方向移动。
Moreover, the further the galaxy, the faster it recedes.
此外，越遥远的星系，后退移动的就越快。
How can we interpret this? Consider a loaf of raisin bread rising in the oven.
这该怎么理解？想象一块葡萄干面包在烤箱中膨胀。
The batter rises by the same amount in between each and every raisin.
每颗葡萄干之间的面糊膨胀的量是相同的。
If we think of raisins as a stand-in for galaxies, and batter as the space between them,
如果我们想象葡萄干是星系，面糊是它们之间的空间，
we can imagine that the stretching or expansion of intergalactic space will make the galaxies recede from each other,
我们可以想象星际空间的拉伸或膨胀会让星系远离彼此，
and for any galaxy, its faraway neighbors will recede a larger distance than the nearby ones in the same amount of time.
而且对于任何一个星系，在相同时长里，它远处的邻居会比更近的邻居移动更长的距离。
Sure enough, the equations of general relativity predict a cosmic tug-of-war between gravity and expansion.
果不其然，广义相对论的公式预测会有一场重力和扩张的较量。
It's only in the dark void between galaxies where expansion wins out, and space stretches.
只有在星系之间黑暗空虚的空间中扩张才会胜出，于是这些空间会膨胀。
So there's our answer. The universe is expanding unto itself.
这就是我们的答案。宇宙正在扩张到自己上。
That said, cosmologists are pushing the limits of mathematical models to speculate on what, if anything, exists beyond our spacetime.
即便如此，宇宙学家正在探索数学模型的极限，来推测什么（如果有的话）存在于我们的时空之外。
These aren't wild guesses, but hypotheses that tackle kinks in the scientific theory of the Big Bang.
这不是胡猜乱想，而是科学假设针对宇宙大爆炸科学理论的漏洞。
The Big Bang predicts matter to be distributed evenly across the universe, as a sparse gas
大爆炸理论预测物质会均匀的分布在宇宙中，以一种稀薄的气体存在
but then, how did galaxies and stars come to be?
那么，星系和星体是怎么形成的呢？
The inflationary model describes a brief era of incredibly rapid expansion
暴胀理论描述了一段短暂的快速扩张时期，
that relates quantum fluctuations in the energy of the early universe, to the formation of clumps of gas that eventually led to galaxies.
把早期宇宙中能量的量子波动联系到了气体团的形成，最终形成星系。
If we accept this paradigm, it may also imply our universe represents one region in a greater cosmic reality that undergoes endless, eternal inflation.
如果我们接受这个理论，它也可能意味我们的宇宙代表了一个永远在膨胀的更大的宇宙现实中的一个区域。
We know nothing of this speculative inflating reality,
关于这个推测的在膨胀的现实，我们什么也不了解，
save for the mathematical prediction that its endless expansion may be driven by an unstable quantum energy state.
除了数学上预测了这无尽的膨胀可能是由一种不稳定的量子能级所导致。
In many local regions, however, the energy may settle by random chance into a stable state, stopping inflation and forming bubble universes.
不过，在很多局部的区域中，这种能量可能会随机的安定下来，进入稳定的状态，停止膨胀并形成多个泡泡宇宙。
Each bubble universe -- ours being one of them -- would be described by its own Big Bang and laws of physics.
每一个泡泡宇宙--我们的宇宙也是其中一个--会有自己的大爆炸和物理定律。
Our universe would be part of a greater multiverse,
我们的宇宙会是一个更大的多重宇宙的一部分，
in which the fantastic rate of eternal inflation makes it impossible for us to encounter a neighbor universe.
它极速的膨胀使得我们不可能与其他宇宙相遇。
The Big Bang also predicts that in the early, hot universe, our fundamental forces may unify into one super-force.
大爆炸理论还预测了在高温的早期宇宙中，我们的4种基本力可能统一成一股超级力。
Mathematical string theories suggest descriptions of this unification,
数学的弦理论描述了这个统一的过程，
in addition to a fundamental structure for sub-atomic quarks and electrons.
还有亚原子的夸克和电子的基本结构。
In these proposed models, vibrating strings are the building blocks of the universe.
在这些被提出的模型中，振动的弦是组成宇宙的基本单元。
Competing models for strings have now been consolidated into a unified description,
曾经相互竞争的弦理论模型现在已经巩固成了一个统一的描述，
and suggest these structures may interact with massive, higher dimensional surfaces called branes.
并指出这些结构可能与叫做膜的高维度平面相互影响。
Our universe may be contained within one such brane,
我们的宇宙可能存在于一个这样的膜之中，
floating in an unknown higher dimensional place, playfully named "the bulk," or hyperspace.
漂浮在一个未知的高纬度空间，叫做“体宇宙”，或超空间。
Other branes -- containing other types of universes -- may co-exist in hyperspace,
其他膜--包含其他类别的宇宙--可能会共同存在于超空间，
and neighboring branes may even share certain fundamental forces like gravity.
相邻的膜甚至可能会共有一些基本力，比如重力。
Both eternal inflation and branes describe a multiverse,
永恒膨胀和膜都描述了一个多重宇宙，
but while universes in eternal inflation are isolated, brane universes could bump into each other.
但永恒膨胀中的宇宙是孤立的，而膜宇宙可能会相撞。
An echo of such a collision may appear in the cosmic microwave background
这样的碰撞产生的回声会出现在宇宙微波背景辐射，
a soup of radiation throughout our universe, that's a relic from an early Big Bang era.
早期大爆炸遗留下来的遍及我们宇宙的辐射。
So far, though, we've found no such cosmic echo.
不过，至今为止，我们没有找到这样的宇宙回声。
Some suspect these differing multiverse hypotheses may eventually coalesce into a common description, or be replaced by something else.
有些人怀疑这些不同的多重宇宙假设可能最终会聚合成一个共同的描述，或者被其他理论所替代。
As it stands now, they're speculative explorations of mathematical models.
目前来说，它们仅是对数学模型的推测性的探索。
While these models are inspired and guided by many scientific experiments,
虽然很多科学实验启发或引导了这些模型，
there are very few objective experiments to directly test them, yet.
目前只有很少的客观实验可以直接测试这些模型。
Until the next Edwin Hubble comes along, scientists will likely be left to argue about the elegance of their competing models...
在下一个爱德文·哈勃到来之前，科学家们很可能会继续争论相互竞争的模型的美妙简洁性...
and continue to dream about what, if anything, lies beyond our universe.
并继续梦想着，什么（如果有的话）存在于我们的宇宙之外。
