Entropy of eternal black holes 1 Erik

The entropy of a quantum-statistical system which is classically approximated by a general stationary eternal black hole is studied by means of a microcanonical functional integral. This approach opens the possibility of including explicitly the internal degrees of freedom of a physical black hole in path integral descriptions of its thermodynamical properties. If the functional integral is interpreted as the density of states of the system, the corresponding entropy equals calS = AH/4− AH/4 = 0 in the semiclassical approximation, where AH is the area of the black hole horizon. The functional integral reflects the properties of a pure state.