Explanation

Edwin Hubble's observations of galaxies moving away from each other, encapsulated in Hubble's Law, were crucial in suggesting that the universe is expanding.

This observation strongly supported the idea that the universe had a singular, hot, dense origin.

Georges Lemaître, in 1927, was the first to propose the idea of the universe expanding from a "primeval atom," a concept that would later form the basis of the Big Bang theory.