Note 23 — ON THE THEORY OF RELATIVITY

E.g. the surface of a sphere cuts a finite volume out of space, but particles sliding on the surface nowhere encounter boundaries or barriers. This is a three-dimensional analogon to the four-dimensional space-time manifold of Minkowski. It does not mean that the universe is enclosed by a spherical shell, as was supposed by the ancients. We cannot form a picture of the corresponding result in the four-dimensional continuum in which, according to the general theory of relativity, we live.