Hi, I was studying about the statistical ensemble theory and facing some problem to understand these concepts , I have understood that the ensemble is a collection of systems which are macroscopically identical but microscopically different . In some books they are called as systems with different initial conditions . Now when they are trying to prove the Louville's Equation concerning these elements in ensemble, they are saying that these phase points are moving . My question is what kind of movement is this ? Are they moving as a bulk ? I know that these systems can replace their position in the phase space as the time goes on . Are they assuming this movement ? My second question is, in the proof of the conservation of extension in phase space they are saying that two curves which are followed by two different elements in the ensemble can't intersect each other . Why?