Traveling in Time
You cannot change the laws of physics …… but could physics actually enable us to travel through time？
It might sound crazy， but according to Einstein's theories， there's no logical reason why time travel isn't possible――and there are now scientists looking into it as a serious scientific proposal， at least at a theoretical1 level.
Many science-fictional2 ideas from the past have subsequently became scientific realities. Take space exploration3， 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 blastoff4 of a spacecraft， or the discovery of a new planet often doesn't even make the national news.
Time travel is clearly a trickier5 proposition than space travel，though. And prior to Einstein， it would have been deemed6 utterly7 impossible！ That's because the old idea about time was that it was like a cosmic8 metronome9 keeping a regular and constant beat throughout the universe. And it was thought to move in one direction only （this is the idea of " time's arrow"――time can go forwards but never backwards）。
However， what physicists now know is that time is rather more flexible than the old " Clockwork10 Universe" ideas they had it. And it was Albert Einstein who set the cat among the pigeons11.
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.
Einstein's theories about time and space were revolutionary. He became a celebrity――and not just in scientific circles. It's only since he published his theories that scientists have been able to demonstrate that space and time really behave the way he said they did.
In 1971， after Einstein's death， two scientists were able to carry out a crucial12 experiment. They used two atomic clocks， synchronized13 them， and placed one on a plane， while the other stayed in the same location on Earth. The plane then flew around the world for 80 hours. According to Einstein's theory， the clock on the plane would be expected to have lost time， due to being in motion over 80 hours compared to the clock on the ground. When they brought the clocks together and made a comparison， the clock on the plane was indeed a few nanoseconds14 slower than the other clock. The experiment was replicated15 in 1996 with advanced technology， and it was proved again――with an even bigger time difference this time. Which proves that not only is time " warp-able" ， but Einstein was arguably the greatest thinker the world has ever seen.
So， time is warped――and this opens up the possibility that we might be able to somehow manipulate16 it as a mode of travel one day.Already one scientist has published a paper in which he detailed how to build a time machine.
If it were possible， however， it would present some pretty knotty paradoxes17…… For example， what if someone or something traveled back in time and changed the ensuing18 future？ And have you heard the one about the time traveller who dots back and forward in time and by means of various medical technologies is able to be his own father AND mother？！ And besides， if time travel is possible， where are all the people from the future――surely they'd want to come and meet us poor stranded19 21st century beings？
時間旅行
你無法改變物理學定律……但是物理學能否使我們在時間中旅行呢？
這聽上去或許像個癡想。但是根據愛因斯坦的理論，時間旅行在邏輯上不是不可能的。現在科學家正把它視為一個嚴肅的科學命題，至少在理論上如此。
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。
與太空旅行相比，時間旅行很顯然是一個更為復雜的命題。在愛因斯坦之前，這個想法肯定會被認為是無稽之談！這是因為傳統上人們認為時間就如同一個巨大的節拍器，在宇宙空間中持續著同一種節奏，而且只沿著一個方向運動。（這就是"時間箭"的概念，即時間一直向前永不后退。）
但是物理學家現在所知道的事實是："精確宇宙"觀念并不正確，時間其實是可伸縮的。而正是艾伯特?愛因斯坦掀起了這一軒然大波。
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，它只能參照其他物體才能得以體現。換句話說，萬物皆相對。
愛因斯坦關于時間和空間的理論具有革命性。他成了名人，而且不僅局限于科學界。正是從他的理論發表以后，科學家才得以有機會證實時空規律確實如其所述。
愛因斯坦去世后，1971年，兩名科學家完成了一項重要實驗。他們使用兩個原子鐘，將時間調成一致。其中一個被放在飛機上，而另一個則置于地球上的原來地方。隨后飛機環繞全球飛行了80個小時。按照愛因斯坦理論，相對于地面上的時鐘，飛機上的時鐘會因為80個小時的運動而減少時間。當他們將兩個時鐘拿到一起比較時，飛機上的時鐘確實較另一只慢了幾毫微秒。1996年，科學家用先進的技術重復了同樣的實驗，也證實了該理論，時間差距甚至更大了。這一實驗不僅驗證了時間的可扭曲性，還證明愛因斯坦可能是人類史上最偉大的思想家。
所以說，時間是可彎曲的。這也使我們或許有朝一日有可能利用它作為某種形式進行旅行。有一位科學家已經發表了一篇論文，詳細地描述如何建造一部時間機器。
然而，如果這一切成為可能的話，那么將會出現一些非常令人困惑的邏輯混亂……比如，如果某人或某物逆時間旅行并改變隨之發生的情況，那會發生什么情況呢？又比如說，你是否曾聽說過這樣的事情――一位時間旅行者在時間隧道中穿梭往返，利用各種醫學技術使自己成為自己的父親和母親？還有，如果時間旅行成為可能，未來的所有人都會在哪里呢？他們肯定想來見見我們這些滯留在21世紀的可憐人。
注釋：
1.theoretical adj.理論上的
2.science-fictional adj.科學幻想小說的
3.exploration n.探險，探測
4.blastoff n.（火箭、導彈、宇宙飛船等）發射
5.tricky adj.難對付的，需慎重對待的
6.deem vt.認為，視為，相信
7.utterly adv.完全地，徹底地
8.cosmic adj.宇宙的，無比巨大的
9.metronome n.節拍器
10.clockwork adj.有規律的
11.set the cat among the pigeons （英口）引起麻煩（或紛擾）
12.crucial adj.至關重要的
13.synchronize vt.校準，
14.nanosecond n.毫微秒
15.replicate vt.重復
16.manipulate vt.使用
17.paradox n.有明顯的矛盾特點的事
18.ensue vi.接踵而來
19.stranded adj.未得到幫助的
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