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.
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