從科幻作家赫伯特·喬治·威爾斯到編劇羅德·瑟林再到科幻笑劇《熱浴盆時間機》，時空旅遊一向是科幻小說和奇異故事中熟習的主題。但時空旅遊畢竟可否在實際生存中真正實現?假如真的可以實現，那末人類將如那邊理一項具有如斯偉大損壞力的技巧呢?
一些科學家以為，時空旅遊從理論上是可以實現的，最少假如你想去往未來照樣可以的。然則也不要從如今開端就攢錢買一台時間機。正如物理學家保羅·戴維斯於2013年在CNN中所說明的那樣：“一百年曩昔，埃爾伯特·愛因斯坦證實：時光從實質上來說是具備彈性的，可以或許受活動影響而擴大或壓縮。”
從實質上來說，你的速率越是靠近光速，時光挪動地相對於也就越慢。戴維斯寫道：“如果你想要飛到二十五光年以外的織女星，然後再以99%光速的速率回到地球。那末當你回到地球時，約莫已是2062年了，這僅僅相稱於你在宇宙飛船內逗留7年的時光。換句話說，你將超過了42年的時光，來到了地球的將來時空。”
從理論上來說，假如你乘著超快速宇宙飛船去太空旅遊，你大概會感到到時光僅僅過了幾年。不外當你回到地球以後，現實上幾十年已經由去了，你的家人或同夥極可能已不在人間了。這便是所謂的時空旅遊!
那末假如想要回到曩昔呢?有無大概令人類回到曩昔，從而阻攔那些欠好的工作產生，使那些仁慈的人們免於滅亡?依據《生存科學》中曾提出的一個假說，從理論上來說，只有當你活動的速率可以或許超出光速，你才有大概引發時間倒流，回到曩昔。
但大多半科學家都以為，沒有任何物體的活動速率可以超出光速。而且，假如人類可以或許回到曩昔，和曩昔扳纏不清，就大概激發一系列不容易辦理的題目和抵觸。好比“祖父悖論”。
只管一些理論已試下著為這些龐雜的時空旅遊題目供給了一些替換辦理方法，但大多半看法照樣以為回到曩昔是人類弗成能實現的一個妄想。究竟，正如有名物理學家斯蒂芬·霍金在他的《時光簡史》中提到的那樣：“假如時空旅遊大概實現，那些從將來穿梭到當今天下的旅遊者們又在那邊呢?”
【參考譯文】
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?
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."
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.
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!
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.
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.
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?"
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