A metamaterial sends rays of
light cascading around a ball,
rendering it invisible, in this schematic.
David Schurg
Xiang Zhang remembers the day he recognized that something extraordinary was happening around him. It was in 2000, at a workshop organized by DARPA (the Defense Advanced Research Projects Agency) to explore a tantalizing idea: that radical new kinds of engineered materials might enable us to extend our control over matter in seemingly magical ways.
The goal at hand, changing how objects interact with light, seemed at first blush to be routine; people had been manipulating visible light with mirrors and lenses and prisms nearly forever. But Zhang, a materials scientist then at the University of California at Los Angeles, knew those applications were limited. Based overwhelmingly on a single material, glass, the technologies were restricted by the laws of optics described in standard physics texts. The engineers in the room hoped to smash through those barriers with materials and technologies never conceived of before. The proposals included crafting what amounts to an array of billions of tiny relays; in essence, the relays would capture light and send it back out. Depending on the specific design of the array, the light would be bent, reflected, or skewed in different ways.
What could you do with a tool like that? An amazing amount, Zhang soon discovered. For one thing, you could render objects invisible. You see something, after all, when light bounces off it, creating the reflections that enter your eye and form an image on your retina. If you could direct light to flow smoothly around the object like water flowing past a rock in a stream, there would be no reflection, no rays entering your eye, and nothing to see—not even a shadow.
Harry Potter’s invisibility cloak inevitably arises as an example of the power of such materials, but invisibility is just the start. Every tool based on the interaction of electromagnetic waves with objects, from modems and MRIs to radios and radar, could have their powers extended, altered, enhanced.
One version of the technology might lead to superfast optical computers, which store and process information using light. Another version might obliterate the line between the large things we can see and the small things we cannot. Instead of an invisibility cloak, imagine the reverse: a supermicroscope that would let you view vanishingly small objects such as individual strands of DNA. Such a tool could turbocharge biological research, advance computer chip manufacture, revolutionize education, and usher in an age of near-magical nanotechnology. The potential is so vast that Zhang and his colleagues have struggled for ways to sum it up.
The laws of refraction, which govern how light bends, were codified by the great Arab physicist Ibn Sahl in A.D. 984 and updated by the Dutch mathematician Willebrord Snellius in 1621. For almost four centuries these laws had been passed down from generation to generation unquestioned, like the laws of gravity. Suddenly it seemed possible to Zhang that you could stretch the law of refraction to its limits because you could make light bend in any direction you liked—including the exact opposite of the way glass and every other natural material bends it.
It was like learning that you could make a form of water that flowed uphill. Thomas Zentgraf, who works in Zhang’s new lab at the University of California at Berkeley, puts it this way: “Imagine that you were raised in a world in which the only color was red. Then one day someone discovers blue.”
At that DARPA conference, Zhang was only beginning to appreciate the hues and tints and shades. He realized the magnitude of the coming change when, during one conference session, a Defense Department scientist handed him a copy of an article. The man’s eyes were dancing, and he had a broad smile. “Take a look at this,” he said. Zhang started reading the paper, written by a professor in Hong Kong who was pursuing similar research but with a twist: Instead of light, he was working with acoustics. Sound is a kind of wave totally different from light, yet the principles were the same. In a flash Zhang saw that the concepts swirling around him were basic, universal new rules about how humans could control and manipulate the world. Right then he knew how he would be spending the next several years of his life.
“It was a very exciting moment,” he says, with a scientist’s penchant for understatement.
That moment was the culmination of the iconoclastic work of John Pendry, a physicist from Imperial College London. Back in the 1990s, Pendry, an expert in condensed-matter physics with a special interest in electromagnetism, was consulting with Marconi Materials Technology. The British company manufactured a radiation-absorbing carbon material that could hide battleships from radar detection but didn’t know the physics of how it worked. Could Pendry find out?
