Which theory was the natural beginning of the big bang theory?

Answer 1

Perhaps you mean the Friedmann Theory - Alexander Alexandrovich Friedmann is best known for his pioneering theory that the universe was expanding, governed by a set of equations he developed from Albert Einstein's equations of general relativity, showing that the Universe might be expanding in contrast to the static Universe model advocated by Einstein at that time. From these equations he postulated three Friedmann models describing positive, zero and negative curvature respectively. This dynamic cosmological model of general relativity would come to form the standard for both the Big Bang and Steady State theories.

However it was Georges Lemaître, a Belgian physicist and Roman Catholic priest, who, in 1927, independently used Friedmann's equations to propose that the inferred recession of the spiral nebulae (per Edwin Hubble's discovery of 1924) was due to the expansion of the Universe. As such, the Jesuit priest Georges LeMaitre was credited with being the first to mathematically detail a cosmological study now known as the Big Bang.