Harry Potter and his pals Ron and Hermione have been scooting undetected around Hogwarts for years beneath the invisibility cloak that Harry got from his murdered father, but now an international team of theoretical physicists suggests that muggles, or nonwizards, might someday make a cloak of their own. Reporting last week in the journal Science, physicists J.B. Pendry of Imperial College London and David Smith and David Schurig of Duke University described a way to make high-tech "metamaterials" that can funnel light around an object and make it invisible. Metamaterials, assemblages of small artificial bits of patterned metal films, can...