  The formation of complex nonuniform phases of nuclear matter, known as
nuclear pasta, is studied with molecular dynamics simulations containing 51200
nucleons. A phenomenological nuclear interaction is used that reproduces the
saturation binding energy and density of nuclear matter. Systems are prepared
at an initial density of 0.10fm$^{-3}$ and then the density is decreased by
expanding the simulation volume at different rates to densities of 0.01
fm$^{-3}$ or less. An originally uniform system of nuclear matter is observed
to form spherical bubbles ("swiss cheese"), hollow tubes, flat plates
("lasagna"), thin rods ("spaghetti") and, finally, nearly spherical nuclei with
decreasing density. We explicitly observe nucleation mechanisms, with
decreasing density, for these different pasta phase transitions. Topological
quantities known as Minkowski functionals are obtained to characterize the
pasta shapes. Different pasta shapes are observed depending on the expansion
rate. This indicates non equilibrium effects. We use this to determine the best
ways to obtain lower energy states of the pasta system from MD simulations and
to place constrains on the equilibration time of the system.
