万物简史 第20期:如何营造一个宇宙(12)

I should say that everything is just right so far. Inthe long term, gravity may turn out to be a little toostrong, and one day it may halt the expansion ofthe universe and bring it collapsing in upon itself,till it crushes itself down into another singularity,possibly to start the whole process over again.

我要说，到目前为止，一切都恰到好处。从长远来说，引力也许会变得稍强一点;有朝一日，它可能阻止宇宙膨胀，让自己将自己压瘪，最后坍缩成又一个奇点，整个过程很可能重新开始。

On the other hand it may be too weak and the universe will keep racing away forever untileverything is so far apart that there is no chance of material interactions, so that the universebecomes a place that is inert and dead, but very roomy. The third option is that gravity isjust right—"critical density" is the cosmologists' term for it—and that it will hold the universetogether at just the right dimensions to allow things to go on indefinitely. Cosmologists in theirlighter moments sometimes call this the Goldilocks effect—that everything is just right. (For therecord, these three possible universes are known respectively as closed, open, and flat.)

另一方面，引力也许会变得过弱，那样的话，宇宙会永远地膨胀，直到一切都互相远离，不再可能发生实质性的相互作用，于是宇宙就成为一个非常空旷呆滞而又没有生命的地方。第三种可能是，引力恰如其分--就是宇宙学所谓的"临界密度"--它把宇宙控制在一个恰当的范围，使事物永远继续下去。宇宙学家有时轻浮地把这称之为"金发姑娘效应"--一切都处于恰如其分的状态。(需要说明的是，这三种可能出现的宇宙分别叫做封闭式宇宙、开放式宇宙和扁平式宇宙。)

Now the question that has occurred to all of us at some point is: what would happen if youtraveled out to the edge of the universe and, as it were, put your head through the curtains?Where would your head be if it were no longer in the universe? What would you find beyond?

大家迟早会想到一个问题，那就是，假设你来到宇宙边缘，把头伸出帘幕，那会发生什么?你的头会在什么地方(要是它不再是在宇宙里的话)?你会看到对面是什么?

The answer, disappointingly, is that you can never get to the edge of the universe. That's notbecause it would take too long to get there—though of course it would—but because even if youtraveled outward and outward in a straight line, indefinitely and pugnaciously, you would neverarrive at an outer boundary. Instead, you would come back to where you began (at whichpoint, presumably, you would rather lose heart in the exercise and give up).

回答是令人失望的：你永远也到不了宇宙的边缘。倒不是因为去那里要花很长时间--虽然没错儿，的确要花很长时间--而是因为，即使你沿着一条直线往外走，不停地坚持往外走，你也永远到不了宇宙的边缘。恰恰相反，你会回到起始的地方(到了这种地步，你很可能会灰心丧气，放弃这种努力)。

The reason for this is that the universe bends, in a way we can't adequately imagine, inconformance with Einstein's theory of relativity (which we will get to in due course). For themoment it is enough to know that we are not adrift in some large, ever-expanding bubble.

其原因是，按照爱因斯坦的相对论(我们届时将会讲到)，宇宙是弯曲的。至于怎么弯曲，我们也不大能想像出来。眼下，你只要知道，我们并不是在一个不断膨胀的大气泡里飘浮，这就足够了。

Rather, space curves, in a way that allows it to be boundless but finite. Space cannot evenproperly be said to be expanding because, as the physicist and Nobel laureate StevenWeinberg notes, "solar systems and galaxies are not expanding, and space itself is notexpanding." Rather, the galaxies are rushing apart. It is all something of a challenge tointuition. Or as the biologist J. B. S. Haldane once famously observed: "The universe is notonly queerer than we suppose; it is queerer than we can suppose."

确切点说，空间是弯曲的，恰好使其无限而又有限。恰当地说，甚至不能说空间在不断膨胀，这是因为，正如诺贝尔奖获得者、物理学家史蒂文·温伯格指出的："太阳系和星系不在膨胀，空间本身也不在膨胀。"倒是星系在飞速彼此远离。这对直觉都是一种挑战。生物学家J.B.S.霍尔丹有一句名言："宇宙不仅比我们想像的要古怪，而且比我们可能想像的还要古怪。"