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Have you ever daydreamed about traveling through time, perhaps fast forward in the centuries and seeing the distant future?
你曾白日夢過穿越時空嗎？或者穿越到幾百年之后及看到遙遠未來？
Well, time travel is possible, and what's more, it's already been done.
讓我告訴你，穿越時空是有可能的。而且，還有的是。它已經被實現了。
Meet Sergei Krikalev, the greatest time traveler in human history.
謝爾蓋克里卡列夫是人類歷史上最偉大的穿越時空者。
This Russian cosmonaut holds the record for the most amount of time spent orbiting our planet,
這位俄羅斯宇航員創了記錄，他是環繞地球時間最久的人，
a total of 803 days, 9 hours, and 39 minutes.
總共803天9小時39分鐘。
During his stay in space, he time traveled into his own future by 0.02 seconds.
當他在太空的時候，他時空穿越到自己的未來，且用了0.02秒。
Traveling at 17,500 miles an hour, he experienced an effect known as time dilation,
當時，他在太空時的行駛速度為每小時17500英里。他體驗了一種名為"時間膨脹"的效應。
and one day the same effect might make significant time travel to the future commonplace.
而且，終于有一天，這種效應將會讓穿越時空之時間變得更持久，成為家常便飯的事。
To see why moving faster through space affects passage of time, we need to go back to the 1880s,
如果想了解為什么加快在空間里的行駛速度會影響時間流逝的速度，我們得回到1880年，
when two American scientists, Albert Michelson and Edward Morley,
當時，兩個美國科學家，阿爾伯特·邁克爾遜和愛德華·莫雷
were trying to measure the effect of the Earth's movement around the Sun on the speed of light.
嘗試衡量地球繞太陽對光速有什么影響。
When a beam of light was moving in the same direction as the Earth, they expected the light to travel faster.
他們以為，當一束光和地球往同一個方向移動時，光的速度會更快。
And when the Earth was moving in the opposite direction, they expected it to go slower.
而且，當地球與光束作反方向移動時，光的速度會減慢。
But they found something very curious. The speed of light remained the same no matter what the Earth was doing.
但是結果并非如此，有趣的是。不管地球往哪個方向移動光的速度并沒有改變。
Two decades later, Albert Einstein was thinking about the consequences of that never-changing speed of light.
20年之后，愛因斯坦回到這個問題的結果上：光速不變。
And it was his conclusions, formulated in the theory of special relativity, that opened the door into the world of time travel.
他的結論是：他所創的“相對論”開啟了。穿越時空的大門。
Imagine a man named Jack, standing in the middle of a train carriage, traveling at a steady speed.
試想，一個名為杰克的人站在一輛火車卡中間，在穩定狀態下移動。
Jack's bored and starts bouncing a ball up and down.
杰克覺得無聊，開始在地上上下拍球。
