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

Timothy Clifton on 11 Nov 11This 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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Timothy Clifton on 15 Nov 11Good question. So far the only compelling definitions of gravitational entropy have been in stationary spacetimes (those that admit a timelike 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.

David Marsh on 12 Dec 11Is there not a definition of gravitational entropy from the holographic principle?