Big Bang and possible ends to the universe, illustration. The term Big Bang describes the initial expansion of all the matter in the universe from an infinitely compact state 13.7 billion years ago (top left). Matter formed and coalesced into the galaxies, which are observed to be moving away from each other. Background radiation in the universe is considered a remnant of the Big Bang. The 'Big Crunch' is a postulated possible end to the universe, where the expansion of the universe slows and reverses as all space and matter contracts to form a new singularity (lower right). Two other possible ends are also shown here: an infinite expansion (a 'Big Rip', lower centre), and an equilibrium with slow heat death (bottom right).