), but with
which yields a closed spherical, space-time extension. We thus obtain a four-dimensional spherical Riemann space-time as a possible model of the universe. From these equations we may also deduce
, which shows us that
is proportional to the curvature of the universe.
Inasmuch as in any case the universe, whether finite or infinite, is certainly of huge proportions, its curvature must be practically insignificant. We may infer, therefore, that