‘Speed of Light’ Redefined

Researchers at the University of Rochester have pushed light so far forward it goes into reverse. And as if that weren’t hard enough to grasp, the backward-moving pulse of light travels faster than the speed of light.

Robert Boyd, the M. Parker Givens Professor of Optics, has taken what was once just a mathematical oddity—negative speed—and shown it working in the real world.

Boyd sent a burst of laser light through an optical fiber, first splitting it into two so one pulse could travel alongside unencumbered as a reference. The peak of the pulse traveling through the fiber emerged from the end of the fiber before the peak entered the front, and well ahead of the peak of the reference pulse.

“I’ve had some of the world’s experts scratching their heads over this one,” Boyd says. “It’s weird stuff.”