Path integrals applied to quantum gravity

Ap approach based on the path integral is applied to quantum gravity. It is shown how it leads to the notions of black hole temperature and quantum-mechanical integral entropy. A conclusion of statistical sum and entropy of the black hole based on using microcanonical ensemble is given; the system in this case is in equilibrium with the fixed quantity of energy. All possible configurations having fixed energy are considered. It is shown that in the scales of Planc length space-time can have foam-like structure. Mathematical technique for describing this structure is presented