Complex sentence: Since the 1980s, the prevailing cosmological model for the universe, the big-bang theory, was envisioned by a Roman Catholic priest, Monsignor Georges Lemaître in the 1930s.
Split into simpler sentences: Since the 1980s, the big-bang theory is the prevailing cosmological model for the universe. It was envisioned by a Roman Catholic priest, Monsignor Georges Lemaître in the 1930s.