Light is a nimble gymnast. It travels in many colors and frequencies. Its waves, whether long or short, can shift to be longer or shorter. Light waves change direction. They bounce. What light can’t do, on its own at least, is bend backward. In other words, it always refracts or reflects in a predictable, normal direction. Scientists seeking to make light waves do such unnatural gymnastics have failed to find any natural material that does the job. But in recent years, physicists and engineers have been experimenting with different “metamaterials,” engineered substances that inte... (p. 24)