Gravitational instability of vacuum and the cosmological problem

It is shown that, with the account of the gravitational interaction, the physical vacuum can spontaneously partially 'dissociate' into particles and antiparticles without violation of any conservation laws. Possible cosmological significance of this effect is discussed. A 'vacuum cosmological model' is formulated, in which vacuum is taken as the initial state of the Metagalaxy. A generalization of the classical cosmological Einstein equations is made which allows one to take into account phenomenologically the effect of gravitational instability of vacuum.