Structure formation and many-body problem with a special-purpose computer

Abstract

In the universe there are a diversity of structures of large and small scales. On the other hand, the universe began with a thermal equilibrium state as evidenced by the black body spectrum of the cosmic background radiation. Emergence of structures or information from the thermal equilibrium state awaits for interpretations. They are given for different strata of structures. For the largest region, where the expansion of the universe played an essential role, the maximum possible entropy, which corresponded to thermal equilibrium state, increased with the expansion of the universe so rapidly that the entropy production due to irreversible processes fell behind. For a smaller scale the spatial structure appears as a result of segregation of lower entropy region from higher entropy region, which is promoted by the gravothermal catastrophe. These two were studied with gaseous models, but there are collisionless systems such as large star clusters and galaxies. Though the phase mixing takes place in such systems, there are no entropy production except due to that by coarse graining. Using large N-body simulations the implication of the violent relaxation is critically discussed. The structures originated from collision and merging of galaxies and the evolution of cluster of galaxies are discussed as examples of structure formation through the collisionless evolution. Such problems await for further large simulations. In August 1992 we initiated a tera-flops special-purpose computer project.