Let's Do the Time Warp Again

But the paradox problem does not bother David Deutsch, a theoretical physicist at Oxford University. Deutsch dislikes the violent aspect of the grandfather paradox, which he says is only confused "by the issue of human conflict that people put into the story to make it more interesting." Deutsch has instead created a gentler paradox.



In this experiment, a person watches a time machine to see whether a copy of himself emerges on, say, Tuesday. If it does not, on Wednesday he journeys back in time one day-emerging from the time machine on the same Tuesday when he had not emerged before. The experiment can be reversed: If, in the opposite scenario, he does emerge on the Tuesday, he simply waits until Wednesday and chooses not to get in the time machine. In either case, a paradox is created: The time traveler is there on Tuesday and not there at the same time-a phenomenon that, intriguingly, echoes some of the fundamental mysteries of particle behavior at the quantum level.




Indeed, Deutsch reaches into quantum mechanics for an explanation of the paradox. He is a leading proponent of the many worlds theory, in which multiple new universes are triggered by each quantum event. If two subatomic particles collide, for example, one of the particles does not go either right or left, but rather it goes right in one universe and left in another universe that is instantly created in the so-called multiverse. In the Deutsch experiment, one universe contains the lab in which the experimenter did not journey back, another the lab in which he did: paradox resolved.



In any case, a hundred years after the Special Theory of Relativity, time travel is theoretically possible, and therefore theoretically in the future of human development. So the big question is: When will we have a machine to test the theories? Wormhole engineering doesn't offer much promise, since it involves near-light-speed travel, antigravity, and the like. But Paul Davies is hopeful. He says we would begin by sending a particle, rather than a human being, back in time to test the paradoxes. Emerging theories about the nature of gravitation already suggest, he says, that "it might be possible to reconfigure space-time with energies that could be accessible by the next-generation of particle accelerator." If so, "We're talking about more like 100 years," Davies says, "than about who knows how many years."




> Reported by Peter Kobel