ScienceNow: Physicists and electrical engineers around the world are pushing hard to make materials that twist a fundamental law of optics and bend light the "wrong way." Such "left-handed" materials could be used to make lenses that focus light much more tightly than ordinary lenses can, as well as other novel devices. But a critical aspect of the current approach won't work because it violates the principle that cause must precede effect, one theorist argues.