Faster than a speeding light beam

By Jeff Hecht in Boston EINSTEIN’S cosmic speed limit may not be absolute after all. When the overall energy level in space is negative, it should be possible to travel faster than light, a physicist claims. The special theory of relativity, which holds that nothing can travel faster than light, has confounded hopes of interstellar travel. But now Ken Olum of Tufts University in Medford, Massachusetts, has found a possible way. Olum compared the transit times of signals following various paths. If light passes through space containing mass, gravity will delay it slightly. “If you only have positive mass, you can only make delays,” says Olum. To make the signal travel faster than light, the mass needs to be less than zero. “You’ve got to have negative mass, which is equivalent to negative energy,” he says. No one knows whether negative energy can exist on a large scale, but it can exist in small regions. Seemingly empty space contains so-called virtual particles with both positive and negative energy, which add to zero. Placing two metal plates close to each other excludes some positive-mass virtual particles from the intervening space, leaving a slight excess of negative energy. This pulls the plates inward, a phenomenon called the Casimir effect. However, Olum, whose works appears in Physical Review Letters (vol 81, p 3567), admits that there’s a complication. As yet,
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