Cosmology has a "Standard Model", which includes the Big Bang, Inflation, and Dark Matter. Using this framework, Physical cosmologists are beginning to understand how structures form, how the action of gravity amplifies initially tiny perturbations, giving rise to galaxies, stars and ultimately our own planet. My research uses as a tool computer simulation codes (running on parallel computing facilities established in the Physics department) which evolve model universes forwards in time, subject to the laws of Physics which have been included: gravity, gas dynamics, radiative cooling and so on. Our analytical theories of how astrophysical processes take place can be checked with these numerical experiments, which also provide predictions to be compared with observational data. I study the Universe both at high and low redshift, using this approach, looking at structure traced by galaxy clusters, galaxies, and intergalactic gaseous filaments seen as absorption features in the spectra of quasars. By working closely with observational astrophysicists at CMU I aim to make use of the enormous quantities of data from new telescopes, satellites and surveys. Our Universe is the ultimate physics laboratory, and these new data contain information which will constrain not only our theories of structure formation within the Universe, but also the physical processes and parameters which govern its global evolution.