Are Causality Violations Undesirable? Article

First Online: 29 October 2008 Received: 11 January 2008 Accepted: 21 October 2008 DOI :
10.1007/s10701-008-9254-9

Cite this article as: Monroe, H. Found Phys (2008) 38: 1065. doi:10.1007/s10701-008-9254-9 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 space-time 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 causality-violating space-time 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 space-time passes through an event horizon, a property which can be called “causal censorship”, then that space-time with event horizons excised would still be causally well behaved.

Keywords General relativity Differential geometry Spacetime topology In honor of the retirement from Davidson College of Dr. L. Richardson King, an extraordinary teacher and mathematician. An earlier version (gr-qc/0609054v2 ) was selected as co-winner of the CTC Essay Prize set by Queen Mary College, University of London. The views expressed in this paper are those of the author and should not be attributed to the International Monetary Fund, its Executive Board, or its management. This paper was not prepared using official resources. Comments are appreciated from anonymous referees and from participants in seminars at the Universidad Nacional Autónoma de México and Davidson College.

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Authors and Affiliations 1. International Monetary Fund Washington USA