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Timothy Clifton

Gravity, Entropy, and Cosmology: In Search of Clarity - 3 views

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    This paper is by David Wallace (a philosopher in Oxford, not the novelist). The idea seems to be to talk through some of the statements that are made about the treatment of entropy in gravitation. I found this to be a useful exercise, and there are some interesting thoughts in here, even if the cosmology is a bit hit and miss. In particular he points out that the formation of structure in the Universe does not necessarily imply that gravitational fields in the Universe have to carry large amounts of entropy at late times.
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    Potentially simple question alert: what is the entropy associated with a gravitational field? Is there a statistical physics (ie, about disorder vs order) interpretation to whatever thermodynamic integral is implied by Eintein's equations?
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    Good question. So far the only compelling definitions of gravitational entropy have been in stationary space-times (those that admit a time-like Killing vector). There are various suggestions for how to define entropy in other situations, most notably Penrose's Weyl curvature hypothesis, but nothing concrete has yet emerged.
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    Is there not a definition of gravitational entropy from the holographic principle?
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