In 1971, after Einstein's death, two scientists were able to carry out a crucial experiment. They used two atomic clocks, synchronized 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 nanoseconds slower than the other clock.
爱因斯坦去世后，1971年，两名科学家完成了一项重要实验。他们使用两个原子钟，将时间调成一致。其中一个被放在飞机上，而另一个则置于地球上的原来地方。随后飞机环绕全球飞行了80个小时。按照爱因斯坦理论，相对于地面上的时钟，飞机上的时钟会因为80个小时的运动而减少时间。当他们将两个时钟拿到一起比较时，飞机上的时钟确实较另一只慢了几毫微秒。
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.
与太空旅行相比，时间旅行很显然是一个更为复杂的命题。简而言之，爱因斯坦的观点就是，宇宙中每一物体都有其自身的“时间”，并随其运动的不同而不同。物体运动越快，其时间越慢(与运动较慢的物体相比而言)。最极端的假设是，如果一个物体运动达到光速，那么其时间就会完全停止。但无论一个物体或者一个人的时间为何，它只能参照其它物体才能得以体现。换句话说，万物皆相对。
