萬物簡史 第20期:如何營造一個宇宙(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.

我要說，到目前為止，一切都恰到好處。從長遠(yuǎn)來說，引力也許會變得稍強(qiáng)一點(diǎn);有朝一日，它可能阻止宇宙膨脹，讓自己將自己壓癟，最后坍縮成又一個奇點(diǎn)，整個過程很可能重新開始。

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，引力也許會變得過弱，那樣的話，宇宙會永遠(yuǎn)地膨脹，直到一切都互相遠(yuǎn)離，不再可能發(fā)生實(shí)質(zhì)性的相互作用，于是宇宙就成為一個非常空曠呆滯而又沒有生命的地方。第三種可能是，引力恰如其分--就是宇宙學(xué)所謂的"臨界密度"--它把宇宙控制在一個恰當(dāng)?shù)姆秶?，使事物永遠(yuǎn)繼續(xù)下去。宇宙學(xué)家有時輕浮地把這稱之為"金發(fā)姑娘效應(yīng)"--一切都處于恰如其分的狀態(tài)。(需要說明的是，這三種可能出現(xiàn)的宇宙分別叫做封閉式宇宙、開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?

大家遲早會想到一個問題，那就是，假設(shè)你來到宇宙邊緣，把頭伸出簾幕，那會發(fā)生什么?你的頭會在什么地方(要是它不再是在宇宙里的話)?你會看到對面是什么?

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：你永遠(yuǎn)也到不了宇宙的邊緣。倒不是因?yàn)槿ツ抢镆ê荛L時間--雖然沒錯兒，的確要花很長時間--而是因?yàn)?，即使你沿著一條直線往外走，不停地堅(jiān)持往外走，你也永遠(yuǎn)到不了宇宙的邊緣。恰恰相反，你會回到起始的地方(到了這種地步，你很可能會灰心喪氣，放棄這種努力)。

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，按照愛因斯坦的相對論(我們屆時將會講到)，宇宙是彎曲的。至于怎么彎曲，我們也不大能想像出來。眼下，你只要知道，我們并不是在一個不斷膨脹的大氣泡里飄浮，這就足夠了。

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."

確切點(diǎn)說，空間是彎曲的，恰好使其無限而又有限。恰當(dāng)?shù)卣f，甚至不能說空間在不斷膨脹，這是因?yàn)?，正如諾貝爾獎獲得者、物理學(xué)家史蒂文·溫伯格指出的："太陽系和星系不在膨脹，空間本身也不在膨脹。"倒是星系在飛速彼此遠(yuǎn)離。這對直覺都是一種挑戰(zhàn)。生物學(xué)家J.B.S.霍爾丹有一句名言："宇宙不僅比我們想像的要古怪，而且比我們可能想像的還要古怪。"