C. MØLLE R ON THE CRISI S IN THE THEORY OF GRAVITATIO N AND A POSSIBLE SOLUTION

It is now generally believed that Einstein's beautiful theory of gravitation under special cir-cumstances leads to inconsistent results. In fact, according to this theory a well-defined physical system may after a finite time pass over into an unphysical state, where the metric is singular and consequently the notions of space and time lose their physical meaning. This inconsistenc y calls for a generalized theory of gravitation for macroscopic matters which is free of singularitie s and at the same time retains all the satisfactory features of Einstein ' s theory. It is shown that such a generalization may possibly be obtained by assuming that the fundamental gravitationa l variables are, not the metric tensor, but the components of a tetrad field from which the metri c of space-time can be derived uniquely. In a tetrad theory of gravitation the basic principles o f Einstein's theory are still valid exactly, first of all the principle of general relativity, the principl e of equivalence, and the fusion of gravity and mechanics. Such a theory also leads to a more satisfactory solution of the energy problem