* Early Ideas: The idea that the universe was expanding was first proposed by Georges Lemaître in 1927. He was a Belgian priest and physicist who studied the work of Edwin Hubble.
* Hubble's Observations: Edwin Hubble, an American astronomer, made observations in the 1920s that showed galaxies were moving away from each other. This observation provided strong support for an expanding universe.
* The Big Bang Theory: While Lemaître proposed an expanding universe, it was George Gamow and his colleagues in the 1940s who formalized the theory into what we know as the Big Bang. They predicted the existence of cosmic microwave background radiation (CMB), a faint afterglow from the Big Bang.
* Discovery of the CMB: In 1964, Arno Penzias and Robert Wilson accidentally discovered the CMB, providing crucial evidence for the Big Bang theory.
So, while the Big Bang theory developed over time, the key contributors were Georges Lemaître, Edwin Hubble, George Gamow, and Arno Penzias and Robert Wilson. Their work and discoveries led to the theory we know today.
