A magazine of forecasts, trends, and ideas about the future
September-October 2007 Vol. 41, No. 5
| World Trends | & Forecasts |
Technology
Finding Invisibility
European researchers pursue bending of
light to cloak
By Patrick Tucker
In April 2007, a group of computer scientists from Purdue University debuted a rudimentary "optical cloaking" design that would, if constructed, render objects invisible. Now, a group of European mathematicians has created a model proving that submarines, airplanes, and other large objects can be "cloaked" even at close range. The breakthrough heralds an important step forward in science's bold march toward an unseeable future.
"A cloak, such as the one worn by the Harry Potter character, is not yet possible, but it is a good example of what we are trying to move towards," says Sébastien Guenneau of the University of Liverpool. "Using this new computer model we can prove that light can bend around an object under a cloak and is not diffracted by the object. This happens because the meta-material that makes up the cloak stretches the metrics of space, in a similar way to what heavy planets and stars do for the metrics of space-time in Einstein's general relativity theory."
While an invisibility cloak may sound like an exotic, far-off concept, the physics of invisibility play out in nature quite commonly, such as when a desert horizon seems to vanish, or when shallow water distorts the position of objects beneath it like fish. This occurs because rays of light--composed of photons--bend depending on the atomic properties of the objects they are encountering.
The Purdue University engineers' "cloak" design uses a layered, cylindrical arrangement of nano-needles radiating outward from a spoke, resembling a round hairbrush, to bend light around the object being cloaked. The design is effective only for one wavelength, so the object would be invisible from far away, and only if it remained perfectly still.
Guenneau, along with Frédéric Zolla and André Nicolet from the University of Marseille, have proven that even with single-wavelength invisibility, objects at close range can disappear.
"Until now, it was not clear whether photons--particles that make up all forms of light--can split and form new waves when the light source is close to the object. If we use ray optic techniques--where light travels in beams--photons break down at close range and the object does not appear invisible. If we study light as it travels in waves, however, invisibility is maintained," says Guenneau.
The breakthrough will not lead to an actual invisibility cloak for a person any time soon, he says, because metamaterials--the building block of any invisibility device--by their nature only work for one wavelength. "So, no worries, the invisibility cloak is not for tomorrow or the day after, but in the very far future--more than a decade," Guenneau predicts.
While limited in application, the single-wavelength cloaking technology could still make soldiers invisible to night-vision goggles, which operate at just one wavelength. Vladimir Shalaev of the Purdue team expressed hope that such technology could one day hide objects with a fixed shape, like submarines or airplanes. Guenneau is more interested in non-military uses of cloaking technology. "In terms of civil applications, we can imagine scientists observing animals in the wild without being seen," he says.
Sources: University of Liverpool, Liverpool L69 3BX United Kingdom. Web site www.liv.ac.uk. Birck Nanotechnology Center, Purdue University, 1205 West State Street West Lafayette, Indiana 47907. Website www.nano.purdue.edu .To order the print edition of the September-October 2007 issue of THE FUTURIST or to become a member of the World Future Society ($49 per year).
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