The Big Bang theory, which explains the origin and expansion of the universe, started with the idea proposed by astronomer Georges Lemaître in 1927. He suggested that the universe began as a single point and expanded over time. In 1931, Lemaître outlined his "hypothesis of the primeval atom," relying on Einstein's relativity laws. The theory gained further support with Edwin Hubble's observations in 1929 that galaxies are moving away from us, indicating the universe is still expanding. The Big Bang event itself, marking the start of the universe, is estimated to have happened about 13.8 billion years ago.
Note: This explanation refers to the scientific Big Bang theory about the universe's origin, not the television sitcom "The Big Bang Theory," which started airing in 2007.
