The Validity of the mean-field approximation is tested in the spinodal
region by comparing the predictions of the Boltzmann-Nordheim-Vlasov
(BNV) equation for an expanding classical system to the exact solution
given by Classical Molecular Dynamics. The two solutions show, outsid
e the critical region, the same isentropic behaviour, but largely diff
er inside. The exact solution enters deeply inside the spinodal region
and remains there, while the BNV solution enters and after some time
goes back. For the BNV solution, we test in particular the effects of
the collision term, of a surface term added to the mean-field and Bolt
zmann-Langevin type of fluctuations.