The assumption of molecular chaos says the velocities of two colliding particles are uncorrelated and also independent of time. Boltzmann actually used this assumption in his formulation of the H-theorem. Loschmidt objected Boltzmann's argument by arguing that the time-reversibility of microscopic dynamics will in no way leads to a macroscopically irreversible process. The wikipage claimed that it is the molecular chaos assumption, which ignores the correlation of particle velocities, that introduced asymmetry in the microscopic dynamics which leads to the time arrow in H-theorem.
so my question is: why the velocities of the colliding particles are still correlated?