Physicists have drawn up blueprints for a cloaking device that could, in theory, render objects invisible.
Light normally bounces off an object’s surface making it visible to the human eye. But John Pendry and colleagues at Imperial College London, UK, have calculated that materials engineered to have abnormal optical properties, known as metamaterials, could make light pass around an object as so it appears as if it were not there at all.
Metamaterials are exotic composites made of electronic components such as wires and inductors that can be engineered to precisely control the way light travels through them.
Pendry’s team has drawn up plans for a spherical metamaterial structure that would render an enclosed object invisible. “The theory tells us the material properties we need at each point,” says team member David Smith, from Duke University in North Carolina, US. “The challenge is to match those theoretical requirements in the actual material, point-by-point.”
Other designs for invisibility cloaks have been drawn up in the past. One idea is to calculate exactly how an object scatters light and design a surrounding material to exactly cancel this out.
But such cloaking devices could not be used for more than one object. “Using our method you can hide different objects under the same cloak, or move around within the cloak, and remain hidden,” says Pendry.
However, Pendry’s team’s design could currently only work at wavelengths larger than visible light. Designing a cloaking device for visible wavelengths could be tricky as it would involve creating nanoscale metamaterials. “At these levels it is far more difficult to control the metal’s properties,” says Smith. Nonetheless, he believes that optical cloaking devices could be become a reality within the next decade.
Will Stewart, an independent optics expert at the University of Southampton, UK, is less convinced. He believes that it may prove too difficult to overcome these problems within such a timeframe. “It’s great fun and a lovely idea, but I don’t think it can literally be taken and applied to make an optical cloak,” he says.
But Stewart says the approach could work well with a narrow band of wavelengths and could, for example, shield an object from radar. Pendry’s team is, in fact, working on just such a device made from millimetre-sized metal units, which they hope to complete within a year.
“It looks like Star Trek was right,” Stewart