Harry Potter's Invisibility Cloak Is Possible, Studies Say

[Rhiannon]

May 26 (Bloomberg) -- The creation of an invisibility cloak like the one used by Harry Potter in J.K. Rowling's books is theoretically possible, scientists said in two studies published by the online Science Express journal.

The key to making an object invisible is to surround it with a cloak made of ``metamaterials'' that are engineered to bend light around an object, continuing on the other side in the same direction as before, Ulf Leonhardt, author of one of the studies, said in a telephone interview. Sound waves, which have a longer wavelength than light, can be distorted in such a way, and light bends naturally in mirages, for instance, he said.

``All one has to do is enhance this bending effect and control it better,'' said Leonhardt, Professor of theoretical physics at the University of St. Andrews in Scotland. ``We've given recipes of how to do this. You have to control structures that are smaller than the wavelength of light -- less than half a micrometer,'' he said. A micrometer is a millionth of a meter.

The authors of the papers set out mathematical requirements for a theoretical metamaterial, that could achieve invisibility. Applications include protecting structures from vibrations, sound and seismic waves, improving wireless communications, seeing through obstructions, and hiding objects, David Schurig, a scientist at Duke University, North Carolina, and co-author of the second paper, said in a statement.

``The cloak would act like you've opened up a hole in space,'' another co-author, David Smith, professor of electrical and computer engineering at Duke, said in the statement. ``All light or other electromagnetic waves are swept around the area, guided by the metamaterial to emerge on the other side as if they had passed through an empty volume of space.''

`Broadband Cloak'

The cloaking device posited by the Duke scientists and the paper's third co-author, Professor John Pendry at Imperial College London, would cover the entire light spectrum and other lines of force, such as magnetic fields, Imperial said in an online statement.

``Ours would be a broadband cloak,'' Pendry said in the statement. ``There would be no communication between the object that is cloaked and the outside world.''

Translating the math into a metamaterial that works isn't easy, Leonhardt said, describing his proposal as more ``modest'' than Pendry's.

``If you relax the requirement of perfection in the invisibility, we can have much more modest requirements of the material,'' he said. ``If you're happy with a slight haze, or even things you can't really perceive with the naked eye, but you can with instruments,'' then it's easier to make, he said.

`Spacewarp'

The two Duke scientists are now working on building the proposed material, and the first device would be a few millimeters across, according to Imperial College. When built, a final theoretical device would have just the same effects as the magical cloak in J.K. Rowling's books, the British school said.

``Just as in the Harry Potter film, nobody would be able to see an object if it was cloaked, as it's in a spacewarp, and that's exactly what our stuff would do,'' Pendry said.

The two papers, ``Controlling Electromagnetic Fields'' by Pendry, Schurig and Smith, and ``Optical Conformal Mapping,'' by Leonhardt, were published yesterday by Science Express, the online advance publication of the journal Science. The Duke/Imperial research was supported by the U.S. Defense Advanced Research Projects Agency.

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