Thursday, January 5, 2012

Short Sharp Science

Cut-and-splice time cloak makes events disappear

David Shiga, reporter
dv499069.jpg(Image: Digital Vision/Getty Images)

Want to steal money from a safe and get away with it? Your best bet is a time cloak, a device that can hide an event in time, making it appear as if it never happened.
The possibility of such a device was suggested in 2010 by a team led by Martin McCall of Imperial College London. Now the notion has been put into practice, with the first demonstration of a time cloak by a team led by Moti Fridman of Cornell University in Ithaca, New York.
Before any bank robbers out there get too excited, it's important to note that the event in question was the passage of a beam of light, and that the researchers only cloaked a section of it for 5 trillionths of a second.
Nonetheless, it's an intriguing idea that may have more prosaic applications, such as hiding traffic passing through fibre optic cables to help prevent eavesdropping. So how do time cloaks work?
It may help to cast your mind back to invisibility cloaks, which hide objects (albeit tiny ones) in space. These work via a metamaterial that bends light around an object, making the object appear as if it isn't there. If you were filming a movie of a scene including a cloaked object, the object would be invisible in every frame.
A time cloak on the other hand, is like cutting some frames out of a movie and then splicing it back together again. An entire scene could now be missing from the movie, rather than just a specific object.
To demonstrate this, Fridman's team passed a beam of light through lenses that can compress or stretch out a light signal in time. A clever arrangement allowed them to do the equivalent of cutting frames from a movie and splicing it back together. They created a time gap in the light beam a few trillionths of a second long, then seamlessly stitched the rest of the beam back together so that anyone recording it would not notice it had been tampered with.
It's fun to speculate how one might take advantage of such a device. "Negative and positive depends on your point of view," Fridman told the Toronto Star. "But when you're talking about cloaking the first thing that comes to mind is, you want to hide something, you want to deceive."
But anything highly imaginitive will require improving the device to allow it to produce longer gaps in time than 5 trillionths of a second. "It is not enough time to steal a painting from a museum," Fridman told The Washington Post.

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