Note 120 — Chapter XXXIV · THE FINITENESS OF THE UNIVERSE

It is of interest to note that in an alternative presentation of the cylindrical universe Einstein does not make use of the term at all. He confines himself to studying under what conditions a cloud of cosmic dust could cause the universe to be cylindrical, hence to be stable. The novelty of the procedure consists in taking into consideration a certain pressure (not a hydrostatic pressure) which physicists have been led to discuss but which as yet remains unexplained. We refer to the internal pressure which prevents an electron from exploding under the mutual repulsions of its various parts, all of which are charged with negative electricity. This pressure has been called the Poincaré pressure; it is thought to be responsible for atomicity, but its nature is highly enigmatic. Under this new treatment of the problem, the mysterious cohesive pressure takes the place of in our former equations. Einstein then shows, as before, that for the universe to be cylindrical, hence stable, a connection must exist between this mysterious pressure and the average density of matter throughout the universe, hence also between the pressure and the universal curvature. In this respect, at least, a slight advance in our understanding of the binding pressure of matter appears to have been obtained (see Chapter XXXVI). Furthermore, the connection between the density of matter and the internal pressure is easier to understand than that between and the curvature of the universe; although, of course, and are one and the same, so that, as before, it is matter that creates the spatio-temporal universe.