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 Planck-scale 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.
Physical Review D
- Pub Date:
- May 2003
- Spacetime topology causal structure spinor structure;
- Fundamental problems and general formalism;
- General Relativity and Quantum Cosmology
- Minor corrections and additions