In cosmology, a static universe (also referred to as stationary, infinite, static infinite or static eternal) is a cosmological model in which the universe is both spatially and temporally infinite, and space is neither expanding nor contracting. Such a universe does not have so-called spatial curvature; that is to say that it is 'flat' or Euclidean. A static infinite universe was first proposed by English astronomer Thomas Digges (1546–1595). In contrast to this model, Albert Einstein proposed a temporally infinite but spatially finite model as his preferred cosmology during 1917, in his paper Cosmological Considerations in the General Theory of Relativity. After the discovery of the redshift-distance relationship (deduced by the inverse correlation of galactic brightness to redshift) by American astronomers Vesto Slipher and Edwin Hubble, the astrophysicist Georges Lemaître interpreted the redshift as evidence of universal expansion and thus a Big Bang, whereas Swiss astronomer Fritz Zwicky proposed that the redshift was caused by the photons losing energy as they passed through the matter and/or forces in intergalactic space. Zwicky's proposal would come to be termed 'tired light'—a term invented by the major Big Bang proponent Richard Tolman. The Einstein universe During 1917, Albert Einstein added a positive cosmological constant to his equations of general relativity to counteract the attractive effects of gravity on ordinary matter, which would otherwise cause a static, spatially finite universe to either collapse or expand forever. This model of the universe became known as the Einstein World or Einstein's static universe. This motivation ended after the proposal by the astrophysicist and Roman Catholic priest Georges Lemaître that the universe seems to be not static, but expanding. Edwin Hubble had researched data from the observations made by astronomer Vesto Slipher to confirm a relationship between redshift and distance, which forms the basis for the modern expansion paradigm that was introduced by Lemaître. According to George Gamow this caused Einstein to declare this cosmological model, and especially the introduction of the cosmological constant, his "biggest blunder". Einstein's static universe is closed (i.e. has hyperspherical topology and positive spatial curvature), and contains uniform dust and a positive cosmological constant with value precisely , where is Newtonian gravitational constant, is the energy density of the matter in the universe and is the speed of light. The radius of curvature of space of the Einstein universe is equal to The Einstein universe is one of Friedmann's solutions to Einstein's