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Light's Hidden Holdup: Reflected laser beams loiter a little

Physicists in France have timed the tiny pause between the arrival of light at a reflective surface and its departure from that surface. Ever since Newton made the suggestion, theorists have been aware that incoming light slightly overshoots some surfaces before bouncing away, but no one could time that excursion, until now.

"We all think of [reflection] as instantaneous, but it takes a little time," says Albert Le Floch of the University of Rennes 1, leader of the team that made the measurement.

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