Affiliation:
1. Department of Physics, University of Wales, Swansea, Singleton Park, Swansea, SA2 8PP, UK
Abstract
The existence of time machines, understood as space–time constructions exhibiting physically realised closed timelike curves (CTC's), would raise fundamental problems with causality and challenge our current understanding of classical and quantum theories of gravity. In this paper, we investigate three proposals for time machines which share some common features: cosmic strings in relative motion, where the conical space–time appears to allow CTC's; colliding gravitational shock waves, which in Aichelburg–Sexl coordinates imply discontinuous geodesics; and the superluminal propagation of light in gravitational radiation metrics in a modified electrodynamics featuring violations of the strong equivalence principle. While we show that ultimately none of these constructions creates a working time machine, their study illustrates the subtle levels at which causal self-consistency imposes itself, and we consider what intuition can be drawn from these examples for future theories.
Publisher
World Scientific Pub Co Pte Lt
Subject
Astronomy and Astrophysics,Nuclear and High Energy Physics,Atomic and Molecular Physics, and Optics
Cited by
13 articles.
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