Technical Note: Does General Relativity Permit Superluminal Travel?

K. D. Olumn (2015), JBIS, 68, pp.214-216

Refcode: 2015.68.214

Abstract:
Is it possible to send a spacecraft faster than the speed of light via wormholes or “warp drive” in general relativity? Einstein’s equations allow any spacetime if the appropriate matter source is available, but superluminal travel requires “exotic” sources whose energy density is negative. In particular, such a source would have to violate the self consistent achronal averaged null energy condition. No violations of this condition are known, and there are some reasons to suppose that it cannot be violated. If that is so, then superluminal travel is impossible in semiclassical gravity.