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Published on Feb 10, 2017
Erik Curiel Ludwig-Maximilians-Universität How Thermodynamical Are Black Holes?
Abstract: Serious problems have been raised about the idea that black holes "really are thermodynamical objects", for instance: that the Zeroth Law for black holes, constancy of surface gravity, is not equivalent to the deepest formulation of the Zeroth Law for ordinary thermodynamics, transitivity of equilibrium; that black-hole area is neither an extensive nor an additive quantity, as ordinary thermodynamical entropy is; that a lack of a general, localized expression for gravitational energy makes it difficult to construct a thermodynamical internal (or free) energy for black holes; that Hawking radiation is not generated by internal degrees of freedom of a horizon, as blackbody radiation is for normal thermodynamical systems, but rather by scattering of an external field; and several more along the same lines. The fundamental concern is that the mere fact that the relevant black-hole quantities satisfy formal analogues of the Laws of ordinary thermodynamics does not by itself guarantee that enough of the structure of ordinary thermodynamics is thereby recovered. There is much more to thermodynamics, after all, than just the four Laws. Transitivity of equilibrium, for instance, normally grounds the construction of the state space of an ordinary thermodynamical system, the arguments that isolated systems spontaneously approach equilibrium, and many other fundamental features of ordinary thermodynamics. I argue in this talk that enough of these problems can be answered in our current state of our knowledge to warrant relying, at least provisionally, on the hypothesis that black holes can meaningfully be treated as thermodynamical objects.
Ben Bar-Or Institute for Advanced Studies Stellar Dynamics around a Massive Black Hole