Magazine article The Futurist

The Perils of Time Travel

Magazine article The Futurist

The Perils of Time Travel

Article excerpt

Using gravitational slingshots, spacecraft may be able to visit the past. But should they?

The idea that it might be possible to travel back and forth in time has been a staple of fiction ever since H.G. Wells published The Time Machine back in 1895. However, is it conceivable that time travel might actually be possible in the near future?

Maybe. Princeton physicist J. Richard Gott published a paper in 1991 claiming that a pair of cosmic strings could open a route into the past. A cosmic string is a theoretical object that is literally a crack in spacetime--long, thin, and with a massive density of trillions of tons per square inch. Because of the enormous gravitational pull of such a string, spacetime in its vicinity would be very strongly curved. Since space and time are interwoven (thus spacetime), such curvature affects time as well as space. If cosmic strings exist, they must travel through the universe at velocities approaching the speed of light. Under such circumstances they should be capable of producing some very dramatic effects.

When Gott looked at the equations of general relativity to see what they said about spacetime in the vicinity of a single cosmic string, he found that it would offer no possibility of time travel. But when he began to consider what would happen if two cosmic strings happened to hurtle past one another in opposite directions, things changed. He found that, if a spaceship looped around the strings along a certain trajectory, it could travel into the past without exceeding the speed of light. The spaceship would follow a path that brought it back to its starting point, arriving before it had left. For a brief moment, the same spaceship would exist twice--one of them from the present and the other from the future.

Needless to say, Gott's results created a certain amount of consternation in the theoretical-physics community. Although cosmic strings were only theoretical objects, there is good reason for believing they might exist. Furthermore, Gott's calculations had been relatively straightforward. He had apparently shown that, under the right conditions, general relativity did allow travel into the past. However, numerous scientists, including British astrophysicist Stephen Hawking, came out with their own calculations proving just the opposite. …

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