The researcher who introduced the concept of negative-index-of-refraction metamaterials in 2000 is now positing that materials with a variable refractive index could enable such fantastic applications as a Harry Potteresque "invisibility cloak." Sir John Pendry, a physicist at Imperial College in London, predicted six years ago that metals could be engineered to make electrical fields behave oppositely to normal, yielding negative-index-of-refraction metamaterial composites. Since his prediction, such metamaterials have been created and demonstrated from gigahertz to optical frequencies. Now Pendry has teamed with Duke University EEs David Schurig and David Smith to predict that both the electrical and the magnetic properties of an inhomogeneous composite with embedded nanoparticles could be altered to create a variable-index-of-refraction material. They postulate that such a material could adapt at the nanoscale to conceal what's under it by preventing electromagnetic energy from entering an area. Light hitting the material would "flow" around it and continue, undistorted, on the other side. The material thus would neither reflect light nor cast a shadow.