Physicists Nicolae Nicorovici from the University of Sydney, Australia, and Graeme Milton, from the University of Utah, have proposed that devices called superlenses could be used to create a type of cloaking device. Using a principle called "anomalous localized resonance," superlenses placed very close to a small object could mask its reflected light waves by resonating at the same frequency, much like how noise-canceling headphones mask sound waves by creating a sound that is at the same frequency but inverted in phase.
So what are superlenses? As they say on Mythbusters: Warning! Science Content ahead!
Anyone who has ever stared at a seemingly "broken" plant stem in a tall glass of water has experienced the laws of refraction. Light bends as it crosses a boundary from one medium (air) to another (water) and the eye is thus fooled into thinking that the submerged part of the stem is somewhere that it is not. Bending light in transparent materials has all sorts of practical applications, most notably in making lenses. From a contact lens in your eye to the focusing laser in your DVD drive, lenses are all around us.
Different materials have different indices of refraction, which is why diamonds (index 2.42) sparkle more than glass (1.66) and why cubic zirconium (2.2) is so tantalizingly close. The number indicates how much light will be bent when moving to a new medium, and also shows how much light rays slow down when moving inside said medium. The existence of materials with a negative index of refraction was first theorized in 1967 by the Russian physicist Victor Veselago, but substances able to refract visible light in this way were not actually manufactured until last year.
Light rays moving into such materials, instead of their direction being changed slightly, will be bent completely backwards. The speed of these rays will actually exceed the speed of light, although this does not violate Einstein's Theory of Relativity because only the phase of one component of this wave is moving at such a speed—one cannot send signals or any kind of information faster than the speed of light, even through these exotic materials. What negative refractive index materials are useful for is creating what is known as a superlens, a tiny lens powerful enough to view images up to ten times as small as conventional lenses. These superlenses are at the heart of the the cloaking device.
Nicorovici and Milton stress that their work is entirely theoretical at present, and the mathematics has only been worked out for small objects, such as a speck of dust. In addition, the effect would only work for one frequency of light, meaning that would-be silent assassins would have to make sure they coordinate their colors when they get dressed in the morning. Still, such technology has many potential uses, including military ones. Professor Sir John Pendry of the Imperial College in London, who helped pioneer superlenses, agrees:
"I believe their claims about the speck of dust and a certain class of objects. In the paper, they do give an instance about a particular shape of material they can't cloak. So they can't cloak everything," said Professor Pendry.
"Nevertheless, it's a very neat idea to get this aggressive response from the material to stop tiny things emitting light. Providing the specks of dust are within the cloaked area, the effect will happen."
While it may be years before practical applications of this technology appear, the potential implications are astounding. Perhaps the world of Star Trek isn't as far away as we thought after all