Fans of the J.K. Rowling books will recall that everyone's favorite boy magician can vanish at will. He ducks under his magic cloak and swoosh . . . he is gone.
A prestigious journal has published two reports from scientists who have discovered how to achieve the same effect without breaking the laws of physics.
Invisibility, they argue, is a matter of diverting light around an object so all the light continues on its way instead of reflecting off the object.
The reports suggest using a thick shell of high-tech transparent material to do this.
Even when looking directly at the object, an observer would see only what was behind it.
While Harry Potter's cloak relies on supplies found only in magic marketplaces like Diagon Alley - the pelt of a "Demiguise" is apparently crucial - the scientists' cloaking device would use newly developed materials that can bend light in unexpected ways.
Scientists not involved in the work said the plans appear feasible but would require more-advanced substances than currently exist.
Still, scientists said that the work represents an important theoretical advance likely to inspire new ideas in the booming field of materials science.
"It is a fascinating concept," said Steven G. Johnson, an assistant professor at the Massachusetts Institute of Technology, in an e-mail. "But I suspect that you're unlikely to find it for sale anytime soon (except on Diagon Alley)."
The research has obvious applications for the military, which is looking for ways to improve on the stealth technology used in the B-2 stealth bomber. But the technology could also be used to protect equipment by steering radiation around it and would likely have other uses in basic scientific research, according to the scientists, whose work was published online by the journal Science.
Inspiring the new research is a type of material known as "metamaterial."
Metamaterials have special properties because they are built with internal structures small enough to interact with light or other radiation. This allows scientists to build devices that can do things, such as bending light, in ways no naturally occurring substance can.
The two reports are slightly different takes on the challenge of invisibility.
One says the cloaking device would be a thick sphere of the transparent material, with a small hollow at its center for hiding something, according to David Schurig, a physicist at Duke University who was one of three authors of that report.
Light from behind the sphere would flow through it, bend around the hollow in the center, and then continue out the front.
No light could reach the hollow or escape from it. The sphere would thus blend, virtually seamlessly, into the background.
The paper in Science describes how much light would have to be bent at each point in the device and proves that the object hidden in the center would appear to vanish.
In addition to Schurig, the paper was written by two leading figures in metamaterials research, David R. Smith of Duke University and John B. Pendry of Imperial College London.
The other paper, by theoretical physicist Ulf Leonhardt at the University of St. Andrews in Scotland, proposes a thick cylinder of the transparent material with a hole running down its center.
Leonhardt calculated how much light would need to be bent at each point in the cylinder to achieve the same effect.
His proposal might be easier to build, scientists said, but the invisibility it achieves would be less complete: An observer would always be able to see the end of the cylinder.
Researchers would likely first attempt to build cloaks that hide an object from microwave radiation, because it has a much longer wavelength than light, making it easier to construct the necessary metamaterials.
The designs suggested in Science will also probably inspire other new designs, which will in turn suggest new experiments.
"This is how the field moves forward," said Srinivas Sridhar, a metamaterials specialist who is the vice provost for research at Northeastern University.
The authors of the two reports cautioned that their proposals contain inherent flaws. They might work only at particular wavelengths of light, for example. And imperfections in the metamaterials would degrade the effect.
Another problem is that no light could enter the cloaking device, so a spy could not see out of it. |
