Time travel is a familiar subject of science fiction and fantasy stories, from H.G. Wells to Rod Serling to Hot Tub Time Machine. But could time travel ever be possible in real life? And, if so, how would humans even handle a technology with such great capacity for destruction?

　　时空旅行一直是科幻小说和奇幻故事中被津津乐道的话题，从科幻作家赫伯特·乔治·威尔斯到编剧罗德·瑟林再到科幻喜剧《热浴盆时光机》，应有尽有。但时空旅行究竟能否在现实生活中真正实现?如果真的可以实现，若人类用这种拥有强大能力的科技去破坏或毁灭这个世界，又将如何应对?

　　Some scientists say time travel is theoretically possible, at least if you want to jump ahead to the future, but don’t start saving up for a time machine just yet. As physicist Paul Davies explained for CNN in 2013, "Over a century ago, Albert Einstein showed that time is intrinsically elastic, capable of being stretched or shrunk by motion."

　　一些科学家认为时空旅行从理论上是可以实现的，可能未来真的你能够一下子去往将来你想去的时间阶段。但是也不要从现在开始就抱有希望，想着攒钱在将来买一台时光机。正如物理学家保罗·戴维斯于2013年在CNN(美国有线电视新闻网络)中所解释的那样：“一百年以前，埃尔伯特·爱因斯坦证明：时间从本质上来讲是具有弹性的，能够受运动影响而扩展或伸缩。”

　　Essentially the closer you’re going to the speed of light, the slower time moves. "Fly to the star Vega, 25 light years away, and back again at 99% of the speed of light, and when you return to Earth in 2062, you will have experienced only seven years’ travel time in the spacecraft. In effect, you will have leaped 42 years into Earth’s future," Davies wrote.

　　从本质上来讲，你的速度越是接近光速，时间移动地相对也就越慢。戴维斯写道：“假如你想要飞到二十五光年之外的织女星，然后再以99%光速的速度回到地球。当你回到地球，时间大约在2062年，这仅仅相当于你在宇宙飞船内停留7年的时间。换句话说，你将跨越了42年的时间跳到了地球的未来时空。”

　　So if you were to, theoretically, take a trip in a super-fast spaceship, you might feel (and look) as though only a few years had passed, but when you arrived back on Earth, decades would have passed and all your friends and family would be dead and gone. Time travel!

　　从理论上来讲，如果你乘着超快速宇宙飞船去太空旅行，你将会感觉到时间过得很慢，可能仅仅过了几年的时间。但当你回到地球之后，实际上地球上已经过了几十年的时间，你的家人或朋友很可能已经不在人世了。这就是所谓的时间旅行。

　　But what about going backwards? Could it ever be possible to pop back in time and stop bad things from happening and good people from dying? Theoretically, if you were to travel faster than the speed of light, you would be moving backwards in time, according to one hypothesis LiveScience reported.

　　那么如果想要回到过去呢?有没有可能使人类回到过去，从而阻止那些不好的事情发生，使那些善良的人们免于死亡?根据《生活科学》中曾提出的一个假说，从理论上来讲，只有当你运动的速度能够超越光速，你才有可能引起时光倒流，回到过去。

　　But most scientists believe that nothing can actually travel faster than light, and, if you could go back in time, messing with the past would create all kinds of unsolvable paradoxes, like the Grandfather Paradox (what if you went back in time and killed your grandpa?!).

　　但大多数科学家都认为没有任何物体的运动速度可以超越光速。并且，如果人类能够回到过去，和过去纠缠不清，就可能引发一系列不易解决的问题和矛盾。比如“祖父悖论”，即如果你通过时间旅行回到过去，在你母亲出生之前杀死了你的外祖父，娶了你的外祖母，那么你自己到底是谁?

　　Although some theories have attempted to propose workarounds for these inconvenient time-travel problems, it remains a pretty widely held belief that traveling backwards in time isn’t possible for us humans. After all, as physicist Stephen Hawking said in his book A Brief History of Time, "If time travel is possible, where are the tourists from the future?"

　　尽管一些理论已经尝试着为这些复杂的时空旅行问题提供了一些替代解决办法，但大多数意见还是认为回到过去时人类不可能实现的一个梦想。毕竟，正如著名物理学家斯蒂芬·霍金在他的《时间简史》中提到的那样：“如果时空旅行可能实现，那些从未来穿梭到现今世界的旅行者们又在哪里呢?”

（编辑：何莹莹）