[1008.1127] Closed timelike curves and causality violation
|Authors:||Francisco S. N. Lobo|
|Abstract:||The conceptual definition and understanding of time, both quantitatively and qualitatively is of the utmost difficulty and importance. As time is incorporated into the proper structure of the fabric of spacetime, it is interesting to note that General Relativity is contaminated with non-trivial geometries which generate closed timelike curves. A closed timelike curve (CTC) allows time travel, in the sense that an observer that travels on a trajectory in spacetime along this curve, may return to an event before his departure. This fact apparently violates causality, therefore time travel and it's associated paradoxes have to be treated with great caution. The paradoxes fall into two broad groups, namely the consistency paradoxes and the causal loops. A great variety of solutions to the Einstein field equations containing CTCs exist and it seems that two particularly notorious features stand out. Solutions with a tipping over of the light cones due to a rotation about a cylindrically symmetric axis and solutions that violate the energy conditions. All these aspects are analyzed in this review paper.|
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I liked this review of closed timelike curves (CTCs) and time travel in general relativity. The presentation is easy to follows, but has sufficient technical details to appreciate what is really going on. Especially interesting was the analysis showing how generic CTCs are in rotating axisymmetric solutions, and the examples of spacetimes with CTCs without exotic matter.