Quantum mechanics near closed timelike lines

David Deutsch
Phys. Rev. D 44, 3197 – Published 15 November 1991
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Abstract

The methods of the quantum theory of computation are used to analyze the physics of closed timelike lines. This is dominated, even at the macroscopic level, by quantum mechanics. In classical physics the existence of such lines in a spacetime imposes "paradoxical" constraints on the state of matter in their past and also provides means for knowledge to be created in ways that conflict with the principles of the philosophy of science. In quantum mechanics the first of these pathologies does not occur. The second is mitigated, and may be avoidable without such spacetimes being ruled out. Several novel and distinctive (but nonparadoxical) quantum-mechanical effects occur on and near closed timelike lines, including violations of the correspondence principle and of unitarity. It becomes possible to "clone" quantum systems and to measure the state of a quantum system. A new experimental test of the Everett interpretation against all others becomes possible. Consideration of these and other effects sheds light on the nature of quantum mechanics.

  • Received 9 April 1991

DOI:https://doi.org/10.1103/PhysRevD.44.3197

©1991 American Physical Society

Authors & Affiliations

David Deutsch

  • Oxford University Mathematical Institute, 24-29 St. Giles, Oxford OX1 3LB, England

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Issue

Vol. 44, Iss. 10 — 15 November 1991

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