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We received a letter from one of our readers with a question about Einstein's Theory of Relativity:
曾经有位读者来信询问了这样一个关于爱因斯坦“相对论”的问题：
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?
一旦时间的速度减缓，我们将接近光速，如果外星飞船以光速飞行，那不是需要更长的时间才能到达目的地吗？
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.
事实上，没有任何以低速运转的物体可以达到光速，但从理论上来说，我们能够与光速无限接近。
So to keep things simple, let's say the flying saucers move atjust under light speed.
简单来说，我们假设宇宙飞碟以仅次于光速的速度飞行。
Let's also say that their planet, Zork, is a hundred light years from Earth.
再假如，外星人的星球为“卓克”星球，距离地球一百光年，
How long does it take them to get from Zork to Earth?
他们从“左克”星球到达地球需要多长时间呢？
Just over one hundred years.
仅需要一百年多点儿。
Now here's the tricky part.
可是棘手的问题出现了。
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.
既然外星飞碟的飞行速度相对我们来说如此之快，对他们而言，时间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.
地球上的一百年仅相当于他们的数秒钟而已。
Notice, though, that there's no going back.
值得注意的是，这一切却是不可逆转的。
Their fellow aliens on Zork who didn't take the near-light speed trip are all one hundred years older now, too!
因为在“卓克”星球，那些没有踏上近光速飞行之旅的同类们也将一百岁了。
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.
如果我们的“左克”星球来访者抵达后立即掉头返回，当他们到达自己的星球，那也已经是两百年以后了。
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.
如果人类真能制造出那样的飞船，事实是对于那些近光速飞行的人来说时间的速度会变慢，但那不会使得飞船本身的速度加快或减慢。
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.
正因为如此，探险家们可能在他们的有生之年到达遥远的外星球，但是请注意，这个有生之年仅仅是他们的，而不是与留在地球的其他人共享的。
