cosmology

The branch of astronomy concerned with the origin, properties and evolution of the universe. Physical cosmology is about making observations that give information on the universe as a whole, and theoretical cosmology establishes models that aim to describe the observed properties of the universe in mathematical terms. Cosmology in the broadest sense spans physics, astronomy, philosophy and theology because it aims to assemble a world picture explaining why the universe has the properties it has. Ancient cosmologies were simple pictorial models and myths. Greek cosmology sought to build a mathematical model of the motion of the planets. Modern cosmology is firmly rooted in the laws of physics and the constructs of mathematics. Modern observational cosmology aims to provide data on the universe at large through studies of the distribution of matter at great distances, the velocities of galaxies as a function of their distances from us, and the cosmic background radiation. Examples of cosmological investigations are radio source counts, which can in principle show whether the universe is evolving; the measurement of the redshifts and distances of the furthest galaxies, which gives information on the rate of expansion at great distances; measuring the isotropy of the background radiation to see whether the universe is uniform in all directions. Theoretical cosmology is normally based on the General Relativity theory. Over large distances, gravitation is the dominant force affecting matter and it therefore controls the large-scale structure of the universe. General Relativity is able to describe the relationships between space, time, matter and gravitation; the equations of General Relativity can, in mathematical terms, describe a huge variety of universes. Assumptions such as the cosmological principle are used to restrict the range of models. In practice, the steady-state theory and Big Bang theory have been the major areas of study in the last fifty years. It is now generally accepted that the observational evidence strongly supports a Big Bang cosmology.