  We demonstrate, by numerical simulations, that the dynamics of nuclear matter
mean field inside the spinodal region is chaotic. Spontaneous symmetry-breaking
- no explicit fluctuating term is considered - occurs leading to wild
unpredictable density fluctuations. A proper recipe to calculate an average
Lyapunov exponent in this multidimensional phase space is introduced. The
latter is calculated for different values of the density in order to
characterize in a quantitative way the chaotic and regular regions. It is
argued that the mean field chaoticity can be the main mechanism of the nuclear
multifragmentation occurring in the intermediate energy reactions.
