E3S Web of Conferences.
EDP Sciences.
Vol. 56.
2018.
Being periodically under gravitational force field, collisionless ideal gas in a rectangular parallelepiped performs the non-equilibrium irreversible Poincare cycles. We prove, that for any initial probability distribution density this system irreversibly tends to the Maxwell distribution on the velocities, and uniform distribution on the coordinates. © 2018 IEEE.