Their Deepest, Darkest Discovery

"In a sense you have some negative space," Pendry said. "The light appears to go backward in space."

The first generation, metamaterial "cloaks" are not thin and flexible like Harry Potter's imagined version but are inches thick and solid, resembling canisters, making them able to hide a stationary object but not a moving person. But the science is progressing quickly, physicist Schurig said.

To make a thin, flexible metamaterial cloak, Schurig said, "is technically challenging but not fundamentally impossible." And although no cloak can yet make objects fully invisible to the human eye, he added, it may not be long before scientists can bend the visible spectrum enough to make an object hard to see.

That object might be found "if you know what you are looking for," Schurig said. "But if you're just scanning, then partial invisibility may allow something to go unnoticed."

There is a flip side to the emerging ability to manipulate light, scientists say. "Think anti-cloaking," said Shalaev, the engineering professor. "Instead of excluding light from an object, you can concentrate light in a small area."

Normally, light cannot be squeezed into a space smaller than its own wavelength, he said, but transformation optics create the possibility of accomplishing just that -- packing loads of energy into a vanishingly small space. Such beams could pack a destructive punch, or could be tamed to serve as ultrasensitive needlelike probes, able to detect even a single molecule of some substance of interest.

Pendry added a cautionary note about invisible cloaks, making a real-life distinction from the stuff of fiction: People inside them will not be able to see out. By definition, if no light is bouncing off them, none can reach their eyes, either. "You'd have to use signals other than light to communicate," Pendry said.

Asked for an example of what would work, he paused for a moment.

"You could always talk to them," he said.