Butsuri
Online ISSN : 2423-8872
Print ISSN : 0029-0181
ISSN-L : 0029-0181
Researches
Arrow of Time in Quantum Mechanics
Naomichi Hatano
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2017 Volume 72 Issue 6 Pages 408-414

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Abstract

The arrow of time is a big and long-standing problem of physics. It refers to a situation in which one phenomenon is more often observed than its time-reversal counterpart as time goes by. We pinpoint the instance at which the arrow of time appears in microscopic quantum mechanics. We first show that the Schrödinger equation, despite that it is time-reversal symmetric, can harbor eigenstates that break time-reversal symmetry. The eigenstates always appear as a pair of those which are time reversal to each other, namely decaying and growing eigenstates. We next show that the decaying eigenstates excel in the initial-state problem for t>0, whereas the growing ones dominate in the terminal-state problem for t<0. This explains why a two-state atom in a radiation field always decays as in the theory of the Einstein coefficients.

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© 2017 The Physical Society of Japan
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