Time evolution of a bose system passing through the critical point

Kinetics of Bose condensation of an ideal Bose gas and of the classical Bose gas of hard spheres is considered. Deviations from the equilibrium state are not assumed to be small. An analytic solution for the problem of an ideal Bose gas is found and the role of collisions between the Bose particles themselves is discussed qualitatively. It is shown that Bose condensation is a slowing down process which can be completed at → infinity while the formation of the high energy tail of distribution function is relatively fast. It is further shown that performing the measurements near the singularities of thermodynamic functions one should wait for quite a long time even in the case of an ideally performed experiment in which all the technical difficulties are avoided. The data extracted from experiments confirm these conclusions qualitatively. (B.G.)