The term Big Bang has three related meanings. It refers to the observable facts of the evolution of the universe. It is also a cosmological model in which the universe has been expanding for around 13.7 billion years (13.7 Ga), starting from a tremendously dense and hot state. The term is also used in a narrower sense to describe the fundamental 'fireball' that erupted at or close to time t=0 in the history of the universe. Georges Lemaître, a Catholic priest from Belgium, proposed "hypothesis of the primeval atom" in 1927; this is considered to be the first published version of the Big Bang.
Time-viewer downloads of the Big Bang event were not popular among the general population. The events that created the universe were almost impossible to comprehend to non-cosmologists, despite the best efforts of the editors. The 1968 motion picture 2001: A Space Odyssey, even with its aged special effects, was regarded as more exciting than seeing the actual Big Bang.