标题: 时间旅行 Traveling in time [打印本页] 作者: davy10 时间: 2011-3-22 17:22 标题: 时间旅行 Traveling in time
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 planet 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 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.
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 crucial12 experiment. They used two atomic clocks, synchronized13 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 nanoseconds14 slower than the other clock. The experiment was replicated15 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.
So, time is warped--and this opens up the possibility that we might be able to somehow manipulate16 it as a mode of travel one day.Already one scientist has published a paper in which he detailed how to build a time machine.
If it were possible, however, it would present some pretty knotty paradoxes17... For example, what if someone or something traveled back in time and changed the ensuing18 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 stranded19 21st century beings?
