cosmology

Branch of astronomy that deals with the structure and evolution of the universe as an ordered whole. Cosmologists construct ‘model universes’ mathematically and compare their large-scale properties with those of the observed universe.

Modern cosmology began in the 1920s with the discovery that the universe is expanding, which suggested that it began in an explosion, the Big Bang. An alternative – now discarded – view, the steady-state theory, claimed that the universe has no origin, but is expanding because new matter is being continually created.