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Symmetry 2010, 2(2), 582-608; doi:10.3390/sym2020582

Broken Time Translation Symmetry as a Model for Quantum State Reduction

T.C.M. Group, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
Received: 22 December 2009 / Revised: 22 March 2010 / Accepted: 22 March 2010 / Published: 1 April 2010
(This article belongs to the Special Issue Symmetry Breaking Phenomena)
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The symmetries that govern the laws of nature can be spontaneously broken, enabling the occurrence of ordered states. Crystals arise from the breaking of translation symmetry, magnets from broken spin rotation symmetry and massive particles break a phase rotation symmetry. Time translation symmetry can be spontaneously broken in exactly the same way. The order associated with this form of spontaneous symmetry breaking is characterised by the emergence of quantum state reduction: systems which spontaneously break time translation symmetry act as ideal measurement machines. In this review the breaking of time translation symmetry is first compared to that of other symmetries such as spatial translations and rotations. It is then discussed how broken time translation symmetry gives rise to the process of quantum state reduction and how it generates a pointer basis, Born’s rule, etc. After a comparison between this model and alternative approaches to the problem of quantum state reduction, the experimental implications and possible tests of broken time translation symmetry in realistic experimental settings are discussed.
Keywords: spontaneous symmetry breaking; unitarity; quantum state reduction spontaneous symmetry breaking; unitarity; quantum state reduction
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Van Wezel, J. Broken Time Translation Symmetry as a Model for Quantum State Reduction. Symmetry 2010, 2, 582-608.

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