The '''Relativistic cosmology''' or, more precisely, the general-relativistic theory of [[cosmology]] started in 1922 with the remarkable work of A. Friedmann, who solved the Einstein's [[gravitational field equations]] and found that they allow for non-static cosmological solutions presenting an [[expanding universe]]. An extension of the A.Friedmann models was carried out by [[Georges-Henri Lemaître|G.Lemaître]], who considered universes with zero energy-momentum but with a non-zero [[cosmological constant]].<ref>{{cite web |title=Cosmological Relativity: A New Theory OF Cosmology|author=Silvia Behar and Moshe Carmeli (Department of Physics, Ben Gurion University )|publisher=Intrn. Journal Theor. Physics|year=2000|issue=39 (1375)|url=http://arxiv.org/pdf/astro-ph/0008352.pdf|accessdate=July 7, 2013}}</ref> | The '''Relativistic cosmology''' or, more precisely, the general-relativistic theory of [[cosmology]] started in 1922 with the remarkable work of A. Friedmann, who solved the Einstein's [[gravitational field equations]] and found that they allow for non-static cosmological solutions presenting an [[expanding universe]]. An extension of the A.Friedmann models was carried out by [[Georges-Henri Lemaître|G.Lemaître]], who considered universes with zero energy-momentum but with a non-zero [[cosmological constant]].<ref>{{cite web |title=Cosmological Relativity: A New Theory OF Cosmology|author=Silvia Behar and Moshe Carmeli (Department of Physics, Ben Gurion University )|publisher=Intrn. Journal Theor. Physics|year=2000|issue=39 (1375)|url=http://arxiv.org/pdf/astro-ph/0008352.pdf|accessdate=July 7, 2013}}</ref> |