Quantum inequalities do not forbid spacetime shortcuts
Abstract
A class of spacetimes (comprising the Alcubierre bubble, Krasnikov tube, and a certain type of wormhole) is considered that admits “superluminal travel” in a strictly defined sense. Such spacetimes (they are called “shortcuts” in this paper) were suspected to be impossible because calculations based on “quantum inequalities” suggest that their existence would involve Planckscale energy densities and hence unphysically large values of the “total amount of negative energy” E^{}_{tot}. I argue that the spacetimes of this type may not be unphysical at all. By explicit examples I prove that (1) the relevant quantum inequality does not (always) imply large energy densities, (2) large densities may not lead to large values of E^{}_{tot}, and (3) large E^{}_{tot} being physically meaningless in some relevant situations does not necessarily exclude shortcuts.
 Publication:

Physical Review D
 Pub Date:
 May 2003
 DOI:
 10.1103/PhysRevD.67.104013
 arXiv:
 arXiv:grqc/0207057
 Bibcode:
 2003PhRvD..67j4013K
 Keywords:

 04.20.Gz;
 04.20.Cv;
 Spacetime topology causal structure spinor structure;
 Fundamental problems and general formalism;
 General Relativity and Quantum Cosmology
 EPrint:
 Minor corrections and additions