高考英语《流行话题 语境识词4500》Unit 95　Scientists Look Forward to the Past素材.docVIP

高考英语《流行话题 语境识词4500》Unit 95　Scientists Look Forward to the Past素材 Unit 95　　Scientists Look Forward to the Past　　Can time travel really be done? Physicists think that travel into future is possible. Einsteins special theory of relativity, published in 1905, predicted that time should be elastic, stretching or shrinking as an observer moves. To get a really big time leap it is necessary to travel at near the speed of light -- 300,000 km per second. At 99% of this speed, a rocket trip to a distant star and back would take 15 months, but travelers would return home to find that nearly nine years had elapsed on Earth. In effect, you would have leapt several years into Earths future.　　Gravity offers another way to slow time. On the earths surface, clocks tick a little slower than on the moon, for example. Near a neutron star or black hole, gravity is so intense that time is slowed to a crawl relative to us. These facts are accepted by almost all scientists. Traveling forwards in time has been demonstrated convincingly in experiments. But the possibility f traveling backwards in time is far more controversial. The first hint that it might be possible came in 1932, when a physicist named Stockhum investigated what might happen to an observer who orbits a rapidly spinning cylinder. He showed it was possible to travel in a closed loop and return to your starting point before you left.　　Worm holes are like black holes, with a key difference. Whereas black holes offer a one-way journey to nowhere -- fall in and you never get out -- worm holes have an exit as well as an entrance. To find whether such an idea can be taken seriously, scientists at California Institute of Technology investigated what it would take for such a short cut though space to exist. They found that if you tried to make a worm hole out of any normal form of matter, it would collapse under its own gravity and turn into a black hole. For a worm hole remain stable, it would have to be made of exotic material