Out of Sight

First, a disclaimer: Invisibility cloaks like Harry Potter's are nowhere near becoming reality. Nor has anyone unearthed proof that the infamous Philadelphia experiment—in which U.S. Navy scientists in 1943 supposedly made a destroyer and its crew vanish—really took place. Stygian crystals, said to confer invisibility in Star Wars films and books, remain figments of writers' imaginations. And not one invisibility shield yet exists, not even a mouse-size one, as best anyone can tell.

The reality is this: Scientists have recently been doing some deep thinking about how light and matter interact. As a result, even some practical-minded physicists and engineers have embraced the notion that humankind's long-held desire to make a person or an object invisible may no longer be just the stuff of fantasy.

"In principle, it's possible to make cloaking devices," contends theoretical physicist Ulf Leonhardt of the University of St. Andrews in Scotland, speaking for a growing number of researchers. In recent studies, several teams have proposed rigid shells or walls—invisibility shields—that would interact with electromagnetic radiation in new ways. As a result, observers could, in essence, look right through those shields and the objects they enclose.

While none of the strategies has yet been tested experimentally, experimental physicist David Schurig of Duke University in Durham, N.C., predicts that he and his colleagues will demonstrate such a device that can render, say, a toaster-size object invisible to radar in less than 6 months.

"What differs from science fiction," says experimental physicist David R. Smith, who heads the Duke team, is that those authors "imagine a field in space that does this. We do it by creating a material that directs the light around the thing being cloaked."

The new strategies also differ from the military's current stealth technologies for planes, boats, and armored vehicles. Whereas those objects have equipment and surface coatings that absorb or deflect radar signals, the envisioned invisibility devices would cancel electromagnetic waves from the object or route radar or light signals around it.

Although some of the new schemes might apply only to objects already too small to be seen with the naked eye, others may be suitable for ordinary, human-scale items. However, no theorist has yet proposed a shield that drapes and folds like a cloak—à la Harry Potter.

Out of Sight