Who is credited with creating the "Big Bang Theory"?

Georges Lemaître is credited with creating the Big Bang theory.

The Belgian priest, physicist, and mathematician proposed the “hypothesis of the primeval atom,” arguing that the universe began from an extremely dense initial state and has been expanding. His 1927 work connected Einstein’s general relativity with the observed recession of galaxies, making him the first to formulate the modern expanding-universe model.

The credit is sometimes blurred because Alexander Friedmann had earlier published mathematical solutions describing an expanding universe, while Edwin Hubble supplied important observational evidence. Lemaître’s distinctive contribution was interpreting those equations and observations as evidence for a universe with a finite beginning. The name “Big Bang” came later: astronomer Fred Hoyle used the phrase during a 1949 BBC radio broadcast, originally as a dismissive label.

Another common mix-up is George Gamow, whose later work developed hot Big Bang physics and nucleosynthesis. In 1965, the discovery of the cosmic microwave background by Arno Penzias and Robert Wilson provided powerful evidence supporting the model Lemaître had pioneered.