We come now to the critical part of the theory. In my view the origin and the necessity for the electromagnetic field lie in the following justification. The components \(\psi_{1},\psi_{2}\) are, in fact, not uniquely determined by the tetrad but only to the extent that they can still be multiplied by an arbitrary “gauge-factor” \(e^{i\lambda}\) of absolute value 1. The transformation of the \(\psi\) induced by a rotation of the tetrad is determined only up to such a factor. In the special