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Identification of a Gravitational Arrow of Time

Julian Barbour, Tim Koslowski, and Flavio Mercati
Phys. Rev. Lett. 113, 181101 – Published 29 October 2014
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Abstract

It is widely believed that special initial conditions must be imposed on any time-symmetric law if its solutions are to exhibit behavior of any kind that defines an “arrow of time.” We show that this is not so. The simplest nontrivial time-symmetric law that can be used to model a dynamically closed universe is the Newtonian N-body problem with vanishing total energy and angular momentum. Because of special properties of this system (likely to be shared by any law of the Universe), its typical solutions all divide at a uniquely defined point into two halves. In each, a well-defined measure of shape complexity fluctuates but grows irreversibly between rising bounds from that point. Structures that store dynamical information are created as the complexity grows and act as “records.” Each solution can be viewed as having a single past and two distinct futures emerging from it. Any internal observer must be in one half of the solution and will only be aware of the records of one branch and deduce a unique past and future direction from inspection of the available records.

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  • Received 8 May 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.181101

© 2014 American Physical Society

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Arrow of Time Emerges in a Gravitational System

Published 29 October 2014

Study of masses interacting via gravity challenges the idea that special initial conditions are needed to give time a direction.

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Authors & Affiliations

Julian Barbour1, Tim Koslowski2, and Flavio Mercati3,*

  • 1College Farm, South Newington, Banbury, Oxon OX15 4JG, United Kingdom
  • 2University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
  • 3Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario N2L 2Y5, Canada

  • *fmercati@perimeterinstitute.ca

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Issue

Vol. 113, Iss. 18 — 31 October 2014

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