The origin of black hole entropy

In this thesis properties and the origin of black hole entropy are investigated from various points of view. First, laws of black hole thermodynamics are reviewed. In particular, the first and generalized second laws are investigated in detail. It is in these laws that the black hole entropy plays key roles. Next, three candidates for the origin of the black hole entropy are analyzed: the D-brane statistical-mechanics, the brick wall model, and the entanglement thermodynamics. Finally, discussions are given on semiclassical consistencies of the brick wall model and the entanglement thermodynamics and on the information loss problem.