Theory of Expanding Universe
Einstein (1915) and General Relativity, in 1917 uses the
cosmological constant to get a static universe solution
(�Greatest blunder of my career.�)
de Sitter, Friedman, and Lemaitre follow, with more
solutions covering a variety of situations, including no
matter, closed universes, and expanding universes (and this
is all before Hubble found and expanding universe)
Cosmological constant was handy, however, for reconciling
Hubble�s universe age with the age of Earth, and handy
today in reconciling otherwise conflicting data.