a cosmological theory postulating that approximately 12 billion years ago all the matter of the universe, packed into a small superdense mass, was hurled in all directions by a cataclysmic explosion. As the fragments slowed down, the galaxies and stars evolved but the universe is still expanding
Compare steady-state theory
WordReference Random House Learner's Dictionary of American English © 2025
ˈbig ˈbang ˌthe•o•ry, n. [uncountable]
WordReference Random House Unabridged Dictionary of American English © 2025- Astronomya theory that the universe began with an explosion of matter and is still expanding from the force of that explosion.
big′ bang′ the′ory, [Astron.]
- Astronomya theory that deduces a cataclysmic birth of the universe (big′ bang′) from the observed expansion of the universe, cosmic background radiation, abundance of the elements, and the laws of physics. Also called big′-bang′ mod′el. Cf. steady state theory.
- 1950–55
Collins Concise English Dictionary © HarperCollins Publishers::
'big bang theory' also found in these entries (note: many are not synonyms or translations):