Perhaps the most important recent result in cosmology is the development of a cosmological standard model that explains a remarkable variety of observational phenomena in the Universe. In this model, small initial fluctuations in density existed near the Big Bang, perhaps generated via quantum fluctuations. Between that time and the present, 13.8 billion years later, these small fluctuations developed into the rich observed structure that characterizes the current Universe: galaxies with a wide range of sizes, masses, luminosities, and appearance; groups and gigantic clusters of galaxies, and a vast, complex cosmic web of gas and galaxies connecting the largest clusters. The evolution of this cosmic structure is determined in principle by the well-known laws of gravity, hydrodynamics, and relativity; but solving these equations has been an immense challenge.
Over the past four decades Simon White, together with an exceptional group of collaborators and students, has developed N-body computer simulations as a new tool of extraordinary power, yielding fundamental insights into cosmic structure formation. The recent “Millennium simulation” captures with great precision the time evolution of cosmic structure between 10 million years after the Big Bang to the present, with over 10,000 million particles representing dark matter distributed in a cube of 2.2 billion light years on a side. In post-processing of this simulation, White, Springel and their colleagues also added models of the small-scale physical processes that govern the evolution of normal matter within the dark matter halos. The formation of stars in galaxies results from a competition between gas cooling and the ejection of matter from the galaxies through the action of supernovae and massive black holes. These semianalytic methods were first proposed by White and Frenk in 1991, and their current predictions for galaxy properties match a remarkable variety of observations, such that such simulations are beginning to approach the age-old dream of “creating the Universe in a computer”.