The father of the Big Bang theory was a Belgian priest, Georges Lemaitre. At https://phys.org/news/2023-01-lost-video-georges-lematre-father.html … there is a link to a 20 minute video interview of Lemaitre. It goes back to 1964. In the video Lemaitre discusses the beginning of the universe and his hypothesis of the primordial atom. The idea the universe expanded from a simple point. He first proposed the concept in 1931 and it evolved into Big Bang theory over time, so beloved of mainstream. Lemaitre, and others, provided the mathematical framework.