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Have you ever daydreamed about traveling through time, perhaps fast forward in the centuries and seeing the distant future?
你曾白日梦过穿越时空吗？或者穿越到几百年之后及看到遥远未来？
Well, time travel is possible, and what's more, it's already been done.
让我告诉你，穿越时空是有可能的。而且，还有的是。它已经被实现了。
Meet Sergei Krikalev, the greatest time traveler in human history.
谢尔盖克里卡列夫是人类历史上最伟大的穿越时空者。
This Russian cosmonaut holds the record for the most amount of time spent orbiting our planet,
这位俄罗斯宇航员创了记录，他是环绕地球时间最久的人，
a total of 803 days, 9 hours, and 39 minutes.
总共803天9小时39分钟。
During his stay in space, he time traveled into his own future by 0.02 seconds.
当他在太空的时候，他时空穿越到自己的未来，且用了0.02秒。
Traveling at 17,500 miles an hour, he experienced an effect known as time dilation,
当时，他在太空时的行驶速度为每小时17500英里。他体验了一种名为"时间膨胀"的效应。
and one day the same effect might make significant time travel to the future commonplace.
而且，终于有一天，这种效应将会让穿越时空之时间变得更持久，成为家常便饭的事。
To see why moving faster through space affects passage of time, we need to go back to the 1880s,
如果想了解为什么加快在空间里的行驶速度会影响时间流逝的速度，我们得回到1880年，
when two American scientists, Albert Michelson and Edward Morley,
当时，两个美国科学家，阿尔伯特·迈克尔逊和爱德华·莫雷
were trying to measure the effect of the Earth's movement around the Sun on the speed of light.
尝试衡量地球绕太阳对光速有什么影响。
When a beam of light was moving in the same direction as the Earth, they expected the light to travel faster.
他们以为，当一束光和地球往同一个方向移动时，光的速度会更快。
And when the Earth was moving in the opposite direction, they expected it to go slower.
而且，当地球与光束作反方向移动时，光的速度会减慢。
But they found something very curious. The speed of light remained the same no matter what the Earth was doing.
但是结果并非如此，有趣的是。不管地球往哪个方向移动光的速度并没有改变。
Two decades later, Albert Einstein was thinking about the consequences of that never-changing speed of light.
20年之后，爱因斯坦回到这个问题的結果上：光速不变。
And it was his conclusions, formulated in the theory of special relativity, that opened the door into the world of time travel.
他的结论是：他所創的“相对论”开启了。穿越时空的大门。
Imagine a man named Jack, standing in the middle of a train carriage, traveling at a steady speed.
试想，一个名为杰克的人站在一辆火车卡中间，在稳定状态下移动。
Jack's bored and starts bouncing a ball up and down.
杰克觉得无聊，开始在地上上下拍球。
