評論
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We received a letter from one of our readers with a question about Einstein's Theory of Relativity:
曾經有位讀者來信詢問了這樣一個關于愛因斯坦“相對論”的問題：
Since time slows down the closer you get to the speed of light, if alien spaceships could travel atlight speed, wouldn't they take longer to get places?
一旦時間的速度減緩，我們將接近光速，如果外星飛船以光速飛行，那不是需要更長的時間才能到達目的地嗎？
Well, nothing that starts at a lower speed can ever make it to light speed, but theoretically you can come as close as you want.
事實上，沒有任何以低速運轉的物體可以達到光速，但從理論上來說，我們能夠與光速無限接近。
So to keep things simple, let's say the flying saucers move atjust under light speed.
簡單來說，我們假設宇宙飛碟以僅次于光速的速度飛行。
Let's also say that their planet, Zork, is a hundred light years from Earth.
再假如，外星人的星球為“卓克”星球，距離地球一百光年，
How long does it take them to get from Zork to Earth?
他們從“左克”星球到達地球需要多長時間呢？
Just over one hundred years.
僅需要一百年多點兒。
Now here's the tricky part.
可是棘手的問題出現了。
Since the aliens on board the ship traveled so fast relative to us, time slowed to a crawl for them relative to the way it passed for us on Earth.
既然外星飛碟的飛行速度相對我們來說如此之快，對他們而言，時間的速度就如同爬行一般。
In a hundred years' Earthtime, the zippy aliens may have only aged a few seconds.
地球上的一百年僅相當于他們的數秒鐘而已。
Notice, though, that there's no going back.
值得注意的是，這一切卻是不可逆轉的。
Their fellow aliens on Zork who didn't take the near-light speed trip are all one hundred years older now, too!
因為在“卓克”星球，那些沒有踏上近光速飛行之旅的同類們也將一百歲了。
If our Zorkian visitors turned right around and flew home again, when they got there, they would find it was now two hundred years later.
如果我們的“左克”星球來訪者抵達后立即掉頭返回，當他們到達自己的星球，那也已經是兩百年以后了。
If humanity ever does build such awesome ships, the fact that time slows down for near-lightspeed travelers won't make the ships themselves go any faster or slower.
如果人類真能制造出那樣的飛船，事實是對于那些近光速飛行的人來說時間的速度會變慢，但那不會使得飛船本身的速度加快或減慢。
It will, however, make itpossible for explorers to go to distant stars in their own lifetimes-just not in the lifetimes of anyone they left behind.
正因為如此，探險家們可能在他們的有生之年到達遙遠的外星球，但是請注意，這個有生之年僅僅是他們的，而不是與留在地球的其他人共享的。
