Physics

Big Idea: Physicists Carve a Niche in Time

Physicists routinely baffle reporters, but for once things went the other way. Alexander Gaeta was sitting in his Cornell University office in the fall of 2010 when a reporter called to ask his opinion of a strange new paper in the Journal of Optics: What did he think about the claim that it might be possible to create a time cloak, a device that would render events undetectable?
Gaeta was caught off guard. He was still grappling with the invisibility cloak, a wild idea that turned into reality in 2006, when physicists demonstrated that a class of synthetic materials could bend light completely around an object. (Think of water in a stream flowing around a rock.) Without light bouncing off the object, it would essentially disappear.
But creating a time cloak–something that could hide not just an object but an event–is even more ambitious. Rather than just rerouting the rays of light striking an object, a time cloak would have to deflect all the light beams influenced by the object as it moves through space. The time cloak would, in essence, create an interval during which all information about what an object is doing disappears.
Although Gaeta had not heard of the time-cloak study until that phone call, he dove into it as soon as the reporter sent it over. The author, theoretical physicist Martin McCall of Imperial College London, proposed splitting a light beam into two segments moving at different speeds. As one fragment built a lead on the other, a gap of complete darkness would open up between them. Anything happening within that gap, McCall reasoned, would be impossible to detect, since there would be no light to scatter. Then, to complete the trick, McCall proposed bringing those two segments back together so that by the time the beam of light reached an observer, there would be no way to detect that the gap ever existed...