A long-term program of computer simulations to study how galaxies form, evolve and cluster in one specific and very successful theory will be continued. The galaxy distribution traces the structure of the universe on the largest scales accessible to observation; it reflects both the processes which generated irregularities on the cosmos and the nature of its material contents. Most of the universe appears to be in an unknown "dark" component, which may be an entirely new form of matter, a relic of the very early history of the Big Bang. Computer simulations of cosmic evolution based on this assumption lead to galaxy clustering which agrees well with that observed. They suggest that our Universe may contain enough "cold dark matter" that it will eventually stop expanding and recollapse. Such simulations can be "observed" in the same way as the real Universe, allowing a very direct comparison between theory and observation. The research will involve studies of interactions between close pairs of galaxies to see whether such pairs always merge into a single system. Finally, the extent of the distribution of dark matter around individual spiral galaxies will be estimated. Even if the theoretical premises of the cold dark matter theory turn out to be false, this program will deepen our understanding of the structure and origin of galaxies and galaxy clusters.
