Until the 20th century, virtually all scientists and philosophers, including those who were not theists, believed the universe to be eternal. They thought nothing had caused or created it, because it had always existed.
In 1927, Georges Lemaitre challenged this belief when he hypothesized that the universe began with the detonation of a “primordial atom” of infinite density. Lemaitre’s idea was ridiculed as a transparent attempt to place the first book of the Bible, Genesis, on technical grounding. But Lemaitre persisted, submitting a testable prediction. If his theory was correct, it would also mean the galaxies were rushing away from one another. This idea too, was ridiculed - until 1929 when Edwin Hubble stunned the scientific world by presenting evidence that our universe was, in fact, expanding.