| Time's Up on Time Travel |
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20 May 2005, for Science Perhaps the best experimental evidence yet against the feasibility of going back in time is that no one from the future showed up at a convention on time travel on 7 May at the Massachusetts Institute of Technology (MIT). The gathering sprang from a late-night idea of MIT graduate student Amal Dorai, who read in a comic strip that only one such meeting would be needed because any future time travelers could attend. Theoretical physicist Alan Guth of MIT filled in roughly 500 conventioneers on the leading proposals for time travel. The best that can be offered is a limited deal, he said. One scenario involves traveling through a wormhole, a tube through spacetime. By swirling one end of the hole at near the speed of light, time inside would slow down so a round trip could be made in a split second. But to keep a wormhole open would require a negative energy density-- a state seen only at the quantum level. The other proposal, said Guth, involves circling around two infinitely long cosmic strings, theorized tight wrinkles in spacetime with intense gravitational fields. In this scenario, you could return to the exact place and time you left, but you would be able to kill your departing self, creating a paradox that is at the heart of objections to time travel. Another problem is that such cosmic strings could take half the energy of the universe to create. MIT theoretical physicist Ed Farhi regretfully concluded: "It does look like the laws of physics conspire to prevent time travel." |