Guiding light around an object as if through empty space, surveyed in PURSUE Release 06 record DOW-UAP-D122, Invisibility Cloaking: Theory and Experiments, a Defense Intelligence Reference Document of 2 March 2010 (DIRDs).
The paper reports other groups’ work and no experiment of its own: two independent theories published on 25 May 2006, the first cloaking device, for microwaves, in October 2006, built from split-ring resonators, and about a thousand papers since. Its central argument is a limit. A cloak built by coordinate transformation works for one frequency only, because light would have to travel infinitely fast at its inner lining, so information-carrying wave packets cannot be hidden. Cloaks built on non-Euclidean geometry could in principle work across a broad band, but they delay light, and their presence could in principle be sensed. It concludes that perfect cloaking is impossible, that microwave cloaks are within reach of present technology, that optical cloaking devices do not yet exist, and that the greatest challenge is imagination, not technology.
A companion survey in the release, on metamaterials for aerospace, does not discuss cloaking (Negative-Index Metamaterials). Another paper, on vacuum engineering, lists a sudden cloaking or blinking out, consistent with strong gravitational lensing, among the possible side effects of engineered spacetime around a craft, as a consequence of its physics and not a report of anything seen.
Connections
DIRDs · PURSUE · Negative-Index Metamaterials · Defense Warning Office