Resumen de Invisibility cloaks are just an illusion
Invisibility cloaks have been a prized goal for about 10 years, ever since John Pendry and colleagues at Imperial College London proposed a way to guide light around an object using substances with exotic optical properties, called metamaterials. Ideally, these would work passively--without needing energy to be pumped in--and for all wavelengths of light. A practical cloak would have to be about as big as the object to be hidden, and would redirect light perfectly around it to meet the observer's eye on the other side. Now, Andrea Alu and Francesco Monticone at the University of Texas at Austin argue that a passive invisibility cloak large enough to hide a person, or any macroscopic object, is impossible to build.
