"Universe" is a word derived from the Old French univers, which in turn comes from the Latin roots unus ("one") and versus (a form of vertere, "to turn"). Based on observations of the observable universe, physicists attempt to describe the whole of space-time, including all matter and energy and events which occur, as a single system corresponding to a mathematical model.

The currently-accepted theory of the universe's formation is the Big Bang model, which describes the expansion of space-time from a gravitational singularity. The universe underwent a rapid period of cosmic inflation that flattened out nearly all initial irregularities. Thereafter the universe expanded and became steadily cooler and less dense. Minor variations in the distribution of mass resulted in fractal segregation into features that are found in the current universe; such as clusters of galaxies. Status OK.