Lemaitre (based on Hubble's observations) was the first to suggest the?

Lemaître, based on Hubble's observations, was the first to propose the idea of an expanding universe, leading to the formulation of what is now known as the Big Bang theory. He suggested that the universe began from a "primeval atom," which exploded and has been expanding ever since. This concept challenged the then-prevailing static model of the universe and laid the groundwork for modern cosmology. Lemaître's insights significantly contributed to our understanding of the origins and evolution of the cosmos.