Invisibility is a property that would clearly have to arise at the atomic level, via Maxwell’s equations, and hence would be exceedingly difficult, if not impossible, to duplicate using ordinary means. To make a solid boy like Harry Potter invisible, you would have to liquefy him by boiling, crystallize him, heat him again, and then cool him, all of which would be quite an accomplishment, even for a wizard.
But what if you could control the index of refraction at will, so that, for instance, it changed continuously from point to point in the glass? If a beam of light could create its own path—slithering around an object’s atoms like a snake—and exit the material along the same line it entered, then the object could be invisible. To do this, however, the object would need to bend light in unorthodox ways, which would require using a medium with a negative index of refraction, and that’s exactly what every optics textbook for decades said was impossible. Yet in 2006, researchers at Duke University’s Pratt School of Engineering in Durham, North Carolina, and at Imperial College London successfully defied conventional wisdom and made objects that were “invisible” to microwave radiation—by manipulating refraction.
The scientists designed a kind of metamaterial: a substance that has optical properties not found in nature. Nathan Myhrvold, former chief technology officer at Microsoft, says metamaterials “will completely change the way we approach optics and nearly every aspect of electronics. . . . [They] can perform feats that would have seemed miraculous a few decades ago.”
The metamaterial, made by the Duke University engineers, relied upon tiny implants that forced electromagnetic waves to bend in unorthodox ways. Tiny electric circuits were embedded in a concentric series of bands arranged rather like the coils of an electric oven. Those implants—a mixture of ceramic, Teflon, fiber composites, and metal—made it possible to channel the path of microwave radiation in a specific way around the device. A small copper cylinder inside the device was undetectable to microwave radiation. But it did cast a minuscule shadow. True invisibility requires eliminating all reflections and shadows.