1888-1925

Russian mathematician and astrophysicist best known for his mathematical model of an expanding universe. Albert Einstein's 1917 static model of the universe required an arbitrary "cosmological constant" to explain why the universe does not collapse. Friedmann argued that Einstein's model was inconsistent with general relativity. He discarded the cosmological constant and demonstrated that expansion or contraction of the universe was due solely to gravity. Friedmann models or universes laid the foundation for "big bang" theories.