Google on Tuesday celebrated the 124th birth anniversary of Belgian astronomer Georges Lemaître with a doodle. Lemaître, who was a professor of physics, is believed to be the first to have theorised that the universe is expanding.

Lemaître is also credited with proposing what is now known as the Big Bang theory – which says that the universe began with an explosion of a single particle.

Born in 1894, Lemaître was a Belgian Catholic priest who proposed that the universe began as a single primordial atom, which he referred to as the ‘Cosmic Egg’. His thesis was based on calculations derived from Einstein’s theory of General Relativity. Einstein, however, dismissed Lemaitre’s work, saying, “Your calculations are correct, but your physics is atrocious.” Two years later, Einstein accepted Lemaître’s calculations.

A paper published by Lemaître in 1927 theorising that the universe was expanding was substantiated by American astronomer Edwin Hubble’s observations, which were published in 1929. Lemaître accurately estimated the numerical value that astronomers have come to call the Hubble constant – a unit of measurement that describes the universe’s rate of expansion.

Lemaître trained in physics at Cambridge, Harvard and Massachusetts Institute of Technology.