 In 1917, Einstein posited a static finite universe. The finiteness was given by the choice of the 3-sphere (see section   8.2.1) and the static nature of the universe by the fact that the radius of the hypersphere did not change with time. With Friedmann (1922–24) and Lemaître (1927), Einstein’s static model would be replaced by dynamical models (to account for the empirical evidence that by 1930 led to the postulation that the universe is expanding, i.e., most galaxies, galaxy clusters, etc. are growing further apart, just as spots on an uninflated balloon grow further apart when the balloon is blown up). Such models are also among the possible solutions for Einstein’s equations and they were the source for the so-called “Big Bang” theories. But what about finiteness? The finiteness or infiniteness of the universe are not determined by Einstein’s equations, which allow for both possibilities. In his choice of the 3-sphere, Einstein was motivated by considerations that had to do with preserving a hypothesis by Mach on inertial mass and inertial motion. Friedmann and Lemaître also opted for the finiteness of the universe (we need not get into why they did so). Their dynamical models assumed a uniform distribution of matter in the universe and that space is homogeneous and isotropic. But the Friedmann-Lemaître dynamical solutions still allow for a great variety of mathematical solutions and do not settle the issue of finiteness. Our observations in what follows are restricted to such models.