Hypothetical cloaking via exotic spacetime geometry

http://arxiv.org/abs/1108.3793

In light of the surge in popularity of electromagnetic cloaking devices, we consider whether it is possible to use gravitational lensing to cloak a volume of spacetime. A metric for such a spacetime geometry is presented, and its geometric and physical implications are explained.

Several attributes of this geometry make it arguably
physically unrealizable. Firstly, the matter used to con-
struct it must violate the null (and thus the weak and
dominant) energy condition. Secondly, this geometry re-
quires an infinitesimally narrow shell of stress-energy to
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transition between interior and exterior geometries, and
it is unclear what effect allowing a transition of finite
width will have on the cloaking properties. The require-
ment for exotic energy is, however, the the same short-
coming found in traversable wormholes and warp drive
spacetimes.