Microcanonical Ensemble - Connection With Liouville's Theorem

Connection With Liouville's Theorem

We have

(the curly bracket is Poisson bracket) since is a function of H. Therefore, according to Liouville's theorem (Hamiltonian) we get

In particular, is time-invariant, that is, the ensemble is a stationary one.

Alternatively, one can say that since the Liouville measure is invariant under the Hamiltonian flow, so is the measure .

Physically speaking, this means the local density of a region of representative points in phase space is invariant, as viewed by an observer moving along with the systems.

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