After years of research, "perfect" invisibility cloaks are finally a reality— at least so long as you are a tiny cylinder.
In 2006, the development of metamaterials resulted in a working example of a cloaking device, an essential accoutrement for young wizards and evil Klingon generals alike. Practical complexities, however, meant the material offered no more than a "simplifying approximation" of the desired functionality.
Now, however, researchers Nathan Landy and David R. Smith have described a "perfect" implementation in A full-parameter unidirectional metamaterial cloak for microwaves, a new study published by Nature: "Here, we design and experimentally characterize a two-dimensional, unidirectional cloak that makes no approximations to the underlying transformation optics formulation, yet is capable of reducing the scattering of an object ten wavelengths in size. We demonstrate that this approximation-free design regains the performance characteristics promised by transformation optics."
In other words, the cloaked object is completely invisible, unlike previous attempts in which reflections were visible: good enough for the Predator's interstellar hunting trips, but not for the Center for Metamaterials and Integrated Plasmonics in Durham, N.C.
While this is the first successful demonstration of the original 2006 paper's claims, that's not to say that there'll be practical implementations any time soon. The effect still only worked when viewed from one direction, and on a perfectly cylindrical object.