At Mercier’s institute Lemaître learned to differentiate between two levels of existence, between the beginning of the physical world in a temporal sense and metaphysical questions of existence: “We may speak of this event [the disintegration of the primeval atom] as of a beginning. I do not say a creation. Physically everything happens as if it was really a beginning, in the sense that if something has happened before, it has no observable influence on the behavior of our universe….Any pre-existence of our universe has a metaphysical character.”
