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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.

Time travel is clearly a trickier proposition than space travel,though. And prior to Einstein, it would have been deemed utterly impossible! That's because the old idea about time was that it was like a cosmic metronome keeping a regular and constant beat throughout the universe. And it was thought to move in one direction only .

However, what physicists now know is that time is rather more flexible than the old “ Clockwork Universe ideas they had it. And it was Albert Einstein who set the cat among the pigeons.

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 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. The experiment was replicated 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.

If it were possible, however, it would present some pretty knotty paradoxes... For example, what if someone or something traveled back in time and changed the ensuing 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 stranded 21st century beings?

（编辑：何佩琦）