Three years ago, researchers created a light pulse that appeared to defy nature's fundamental speed limit—it traveled faster than the speed of light in a vacuum. If it were possible to transmit information at such speeds, Einstein's theory of relativity would be in tatters, and the principle of causality—the idea that cause must always come before effect—would go out the window. With a faster-than-light telephone, you could place a call back in time and tell your parents not to conceive you, for example. Now physicists (and everyone vexed by time-travel paradoxes) can breathe a sigh of relief. A recent series of experiments by experimental physicist Dan Gauthier of Duke University confirm that the earlier result was a kind of illusion; information cannot outrun light's fastest pace.
The ruckus began in 2000, when physicist Lijun Wang of the NEC Research Institute in Princeton, New Jersey, and his colleagues beamed a pulse ...
