时空穿梭

If you could travel in time, where would you go?

Perhaps you would watch an original performance of a Shakespeare play in Elizabethan England? What about hanging out with Laozi in the Spring and Autumn period? Or maybe you'd voyage far ahead of the present day to see what the future holds.

The possibility of time travel is indeed tantalising. Stories exploring the subject have been around for hundreds of years. Perhaps the best known example is science fiction novella The Time Machine, written by HG Wells in 1895, about a contraption that transports people into the far future.

But could time travel actually be possible?

Some scientists say yes, in theory.

They propose using cracks in time and space called 'wormholes', which could be used as shortcuts to other periods. Einstein's theory of relativity allows time travel in extreme circumstances. And British physicist Stephen Hawking says you could travel into the future with a really fast spaceship – going at nearly the speed of light. Though building such a spaceship would of course be no simple task.

Even if you could travel into the past, there is something called the 'grandfather paradox'. It asks what would happen if a time traveller were to go back in time and kill their own grandfather; and therefore prevent themselves from being born.

If the time traveller wasn't born, how would he travel back in time?

And would you really like to visit the future? In HG Wells's book, the main character travels into distant time where he arrives at a beach and is attacked by giant crabs. He then voyages 30 million years into the future where the only living thing is a black blob with tentacles.

If that's what's in store, maybe we are better just living in the present day after all.