), was sufficient.
Here we may mention that if we abandon the restriction that the law of inertia holds rigorously at infinity, hence if we abandon the condition of perfect flatness at infinity, we may build up other tensors satisfying all the remaining requirements. This can be done by adding a further tensor
(where
represents an arbitrary constant) to the left-hand side of our equation. The presence of this additional term will imply that even for very distant regions, space-time would still manifest a trace of residual spherical curvature so that the universe would close round on itself and be finite. In the first development of his theory, Einstein rejected this additional term, but the fact remains that so far as the mathematical requirements of the theory of relativity are concerned there is no reason to exclude it ab initio. At all events, we can assert that if the
term exists at all,