Are Causality Violations Undesirable?
Abstract
Causality violations are typically seen as unrealistic and undesirable features of a physical model. The following points out three reasons why causality violations, which Bonnor and Steadman identified even in solutions to the Einstein equation referring to ordinary laboratory situations, are not necessarily undesirable. First, a spacetime in which every causal curve can be extended into a closed causal curve is singularity free—a necessary property of a globally applicable physical theory. Second, a causalityviolating spacetime exhibits a nontrivial topology—no closed timelike curve (CTC) can be homotopic among CTCs to a point, or that point would not be causally well behaved—and nontrivial topology has been explored as a model of particles. Finally, if every causal curve in a given spacetime passes through an event horizon, a property which can be called “causal censorship”, then that spacetime with event horizons excised would still be causally well behaved.
 Publication:

Foundations of Physics
 Pub Date:
 November 2008
 DOI:
 10.1007/s1070100892549
 arXiv:
 arXiv:grqc/0609054
 Bibcode:
 2008FoPh...38.1065M
 Keywords:

 General relativity;
 Differential geometry;
 Spacetime topology;
 General Relativity and Quantum Cosmology;
 Mathematics  Algebraic Topology;
 Mathematics  Differential Geometry
 EPrint:
 Accepted in October 2008 by Foundations of Physics. Latex2e, 6 pages, no figures. Presented at a seminar at the Universidad Nacional Autonoma de Mexico. Version 2 was cowinner of the QMUL CTC Essay Prize