Wednesday, 17 November 2010

Space-time cloak can edit history

One of the central planks of science-fiction, the invisibility cloak, has taken one step closer to becoming reality, according to extraordinary new research revealed today in the Journal of Optics. And it isn't just matter it can render invisible, but entire tracts of history.

The "space-time cloak" is a device conceived by Martin McCall, an optical physicist at Imperial College London. It generates a pocket in reality in which actions can be concealed. Unlike "standard" invisibility cloaks, which bend light around an object, a space-time cloak would open up a time gap in the light by controlling its speed through optical fibres, and then seal it again to hide all traces of activity within the gap.

"I realised that it may be possible to use metamaterials to bend light rays in both space and time, not just in space," says Martin McCall, in Nature. "This would add a new dimension to the invisibility cloak - literally."

"You could imagine a burglar using a space-time cloak to create an invisible corridor leading to a safe," says McCall. With the cloak turned on, the burglar could run through this corridor, open the safe, steal the contents, shut the safe and escape, while any security camera trained on the safe would just show a continuous image of a locked door at every point in time, explains McCall. "The dastardly event would have been edited from history," he says.

Nature go on to explain that the key feature of the proposed space-time cloak is that its refractive index - the optical property that governs the speed of light within a material - is continually changed, pulling light rays apart in time. When the leading edge of a light wave hits the cloak, the material is manipulated to speed up the light, but when the trailing edge hits, the light is slowed down and delayed. "Between these two parts of the light, there will be a temporal void - a space in which there will be no illuminating light for a brief period of time," explains McCall.

McCall hopes that a fibre-optic cloak creating a space-time void around 30 centimetres long, to hide actions taking place over a few nanoseconds, could be built within the next year.


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