FNWI --- IMAPP Department of Astrophysics
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news:typical_universes_and_their_entropy [2014/11/21 16:26] (current)
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 +------------ ​  ​Quantum Gravity Seminar ​ ------------
 +WHEN:  Tuesday, Oct 14, 14.00h
 +WHERE: ​ HG00.058
 +SPEAKER: ​ **Julian Barbour** (College Farm)
 +TITLE: **Typical Universes and their Entropy**
 +ABSTRACT: It is shown in ArXiv:​1409.0917 (PRL 13/10/14; JB, T Koslowski,
 +and F Mercati) that a gravitational arrow of time arises solely by
 +virtue of the law of gravity and does not require any special initial
 +condition. Building on the methods of that paper, we have created a framework
 +of gravitational statistical mechanics for dynamically closed universes. It
 +allows us to create a theory of initial conditions for the universe and in
 +principle establish whether we live in a typical universe. We are also able to
 +define an initial and current gravitational entropy of the universe. I will
 +explain the basic ideas of our theory using the Newtonian N-body problem.
 +Contrary to present ideas, our results suggest that the gravitational entropy
 +of our universe was maximal at the big bang and has been decreasing ever
 +since. This reflects the long-recognized negative specific heat of a self-
 +gravitating system and is not necessarily in conflict with the standard second
 +law, which applies to iasolated subsystems of the universe. General relativity
 +shares the key structural features that underlie N-body theory, so our results
 +should extend to Einstein gravity.