文档介绍：3、Traveling in Time
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 and there are now scientists looking into it as a serious scientific proposal, at least at a theoretical1 level.
Many science-fictional2 ideas from the past have subsequently became scientific realities. Take space exploration3, for example. In the 1950s this was just a fantastical idea that few people would have dreamt could actually happen. Now it's such a part of modern life that the latest blastoff4 of a spacecraft, or the discovery of a new often doesn't even make the national news.
Time travel is clearly a trickier5 proposition than space travel,though. And prior to Einstein, it would have been deemed6 utterly7 impossible! That's because the old idea about time was that it was like a cosmic8 metronome9 keeping a regular and constant beat throughout the universe. And it was thought to move in one direction only (this is the idea of “ time's arrow”--time can go forwards but never backwards).
However, what physicists now know is that time is rather more flexible than the old “ Clockwork10 Universe” ideas they had it. And it was Albert Einstein who set the cat among the pigeons11.
Put simply, Einstein's idea was that every