Entropy and Spacetime

Dear Colleagues,

A black hole is an empty region. Anything in a black hole region cannot stay at a constant, proper distance from the center, but has to fall towards the center. In ordinary laboratory physics, we cannot regard an empty region solely as a system that forms some physical state (such as a thermal equilibrium state). Therefore, Hawking’s discovery that thermal radiation is emitted from the surfaces of black hole regions (i.e., black hole horizons) is astonishing. The black hole has to be regarded as a thermal equilibrium system. The fact that Hawking’s radiation is predicted by quantum field theory in the context of black hole spacetime implies that the black hole is a thermal equilibrium state of the underlying quantum gravity.

It is expected that the black hole is regarded as some thermal equilibrium system composed of microscopic constituents of spacetime. Such microscopic constituents should cause the black hole’s entropy. Bekenstein's proposal implies that black hole entropy is given by a quarter of the surface area of the black hole horizon (in Planck units). This is the entropy-area law of black hole. This law should include at least the following two ingredients: (1) the nature of microscopic constituents of spacetime (in other words, microstates of underlying quantum gravity), and (2) the statistical mechanical property of long range interaction systems, since gravity is a long range interaction.

This Special Issue “Entropy and Spacetime” can be a meeting place for statistical mechanics, thermodynamics, black hole, and spacetime physics. Further, both classical and quantum approaches are possible. Contributions from both gravitational and statistical physics are welcome.

Dr. Hiromi Saida
Guest Editor

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