In H.G. Wells' 1895 novel, The Time Machine, a radical scientist, weary from his travels to the future and back, warns his colleagues that his story will be difficult to believe.
"I don't mind telling you the story," the Time Traveler says to his friends. "But I can't argue…Most of it will sound like lying. So be it!"
The Time Traveler's story may have sounded outrageous to his colleagues, but today physicists think Wells was onto something. In fact, according to Albert Einstein's famous equation, E = mc² , time travel is possible, at least in one direction. Going the other way — back to the past — presents a trickier challenge.
All About Einstein
This Friday, the stories of the Time Traveler, updated to suit a 21st century world, will once again be presented in a Dream Works and Warner Bros. Picture film, starring Guy Pearce. And, once again, the concept of time travel will seem far-fetched and improbable.
But physicists warn just because the feat may seem impossible, doesn't mean it is.
"We have a hard time perceiving how time can bend just like other dimensions, so Einstein's predictions seem strange," said J. Richard Gott, author of the book Time Travel in Einstein's Universe and a professor of astrophysics at Princeton University. "But this appears to be the world we live in."
Part of the "strange" world that Einstein explained in 1905 in his theory of relativity is that time and space are joined in our universe as a four-dimensional fabric known as space-time. Stranger yet is the concept that both space and time warp as mass or speed is increased.
Travel fast and time moves more slowly. Increase the mass around you to near collapsible levels and you get the same effect.
The phenomenon has already been proven, albeit at minute scales.
Slowed Clocks, Younger Particles
In 1975 Carol Allie of the University of Maryland synchronized two atomic clocks and placed one on a plane and flew it around for several hours and left the other on Earth. When the airborne clock was returned to Earth, she compared its time with the one that hadn't moved and found that time had moved a fraction of a second more slowly for the clock on board the plane.
In other experiments, scientists used particle accelerators to speed elementary particles to nearly the speed of light. They found the accelerated particles decayed slightly more slowly than ones that remained sitting in the lab.
As for the effect of mass on time, scientists have measured the ticking of atomic clocks at the top and base of skyscrapers. They found the clocks at the base — closer to the mass of Earth — ticked ever more slowly than those perched high.
Why does all this mean time travel is possible? Gott explains, the same principles that make the clocks tick slower on planes and low on Earth, should also work at extremes.
Building a Fast Ship
In The Time Machine, the traveler catapults through time by activating his hand crafted crystal and polished brass time traveling unit. Physicists believe true time travel might require something more along the lines of a very fast space ship.
By riding on a spacecraft that can travel at speeds of two hundred million meters per second, or about four hundred and fifty million miles per hour, a passenger would experience significantly slowed time.