The Big Bang theory explains that the universe expanded from a very high density and high temperature state – a ‘singularity’ associated with the Big Bang. Measurements indicate that this moment happened about 13.8 billion years ago, which is seen as the age of the universe.
No single person discovered the Big Bang. Several scientists have put forward models that explain a range of phenomena e.g. expanding universe, cosmic microwave background.
The British astronomer Fred Hoyle is believed to have said the term “Big Bang” on a BBC radio programme in 1949.