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Time travel is clearly a trickier proposition than space travel, though. Put simply, Einstein's idea was that every object in the universe has it's own “time”, and these vary as objects move. The faster an object moves, the slower its time is, compared to the time of a slower moving object. The extreme situation would be if an object could move as fast as the speed of light, its time would be completely halted. But whatever an object--or person's--time is, it's only evident in contrast to other objects. In other words, it's all relatives.

與太空旅行相比，時間旅行很顯然是一個更為復雜的命題。簡而言之，愛因斯坦的觀點就是，宇宙中每一物體都有其自身的“時間”，并隨其運動的不同而不同。物體運動越快，其時間越慢(與運動較慢的物體相比而言)。最極端的假設是，如果一個物體運動達到光速，那么其時間就會完全停止。但無論一個物體或者一個人的時間為何，它只能參照其它物體才能得以體現。換句話說，萬物皆相對。

Many science-fictional ideas from the past have subsequently became scientific realities. Take space exploration, for example. In the 1950s this was just a fantastical idea that few people would have dreamt could actually happen. Now it's such a part of modern life that the latest blastoff of a spacecraft, or the discovery of a new planet often doesn't even make the national news.

以前科學小說中提出的很多想法已經變成了科學的現實。拿太空探險來說，50年代，這只不過是一種科學狂想，很少人相信有一天會變成現實。可是現在它已成為現代生活的一個組成部分，以至于一次最新的宇航器發射或者一個新行星的發現已不再列為國內新聞。

Relevant link：

2012公共英語二級考試每日一練（8月20日）

（責任編輯：中大編輯）

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