Comments on Entropy Calculations in Gravitational Systems

Abstract

We discuss the logic of, and some puzzles in, the various approaches to thermodynamics of gravitational systems. In particular the blackhole, deSitter (dS), black hole in dS (SdS) and in Anti-deSitter SAdS backgrounds are considered. After reviewing the original calculations of Hawking and Gibbons we discuss an alternative Hamiltonian method. This justifies the lowest order Euclidean calculation but is free of the problems associated with the latter when going to higher orders. To conclude we address the sign issue in dS thermodynamics.