Perturbative superluminal censorship and the null energy condition
Abstract
We argue that ``effective'' superluminal travel, potentially caused by the tipping over of light cones in Einstein gravity, is always associated with violations of the null energy condition (NEC). This is most easily seen by working perturbatively around Minkowski spacetime, where we use linearized Einstein gravity to show that the NEC forces the light cones to contract (narrow). Given the NEC, the Shapiro time delay in any weak gravitational field is always a delay relative to the Minkowski background, and never an advance. Furthermore, any object travelling within the lightcones of the weak gravitational field is similarly delayed with respect to the minimum traversal time possible in the background Minkowski geometry.
 Publication:

General Relativity and Relativistic Astrophysics
 Pub Date:
 November 1999
 DOI:
 10.1063/1.1301601
 arXiv:
 arXiv:grqc/9908023
 Bibcode:
 1999AIPC..493..301V
 Keywords:

 04.20.Gz;
 03.30.+p;
 Spacetime topology causal structure spinor structure;
 Special relativity;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 5 pages. Uses AIP proceedings style (aipproc.sty). To appear in the Proceedings of the Eighth Canadian Conference on General Relativity and Relativistic Astrophysics. (McGill University, Montreal, June 1999). To be published by AIP Press