A Proof of the Gao-Wald Theorem

About apparent superluminal drives in generic gravity theories

A result due to gao and wald suggests that warp drives in general relativity (gr) are unlikely for matter satisfying both the null energy and the nullgeneric conditions.An independent proof of this result is presented by use of the raychaudhuri equation, and avoiding several technical complications described along the text.Some consequences of these affirmations are discussed at last section, in particular their potential use in problems of causal theories.