Tuesday, May 14, 2013

Time travel: Can it really be done?

Ever since H. G. Wells' trailblazing novel "The Time Machine," time travel has been a staple of science fiction. The idea of traveling through time is deeply fascinating: you get into a machine, press a few buttons, and step out not just somewhere else, but "somewhen" else. It's easy to imagine, but can it really be done?

Yes it can, at least in a limited sense. Over a century ago, Albert Einstein showed that time is intrinsically elastic, capable of being stretched or shrunk by motion. Fly from London to New York and back, and you will leap a split second into the future of stay-at-home Londoners. The effect can easily be measured using atomic clocks and involves only billionths of a second -- too brief for a person to notice, and hardly the stuff of "Doctor Who" television series-style adventures.

But time stretching can be magnified by increasing the speed. Close to the speed of light (about 300,000 kilometers per second), time warps become startling. Fly to the star Vega, 25 light years away, and back again at 99% of the speed of light, and when you return to Earth in 2062, you will have experienced only seven years travel time in the spacecraft. In effect, you will have leaped 42 years into Earth's future.