The prehistory to Schrödinger's activity in unifed field theory

Unification is one of those long-standing quests of science. A superior point of view allows one to recognize connections and to uncover common roots. In the theory of general relativity Einstein succeeded in achieving a superior point of view in an especially impressive manner. By extension of the theory of special relativity he was able to comprehend gravitation in the geometrization of the space-time-continuum. After the success of this process of geometrization, the inclusion and unification of the electromagnetic field and possibly other fields could be considered to be a particularly important goal.

A few years after the discovery of general relativity, Weyl (1918) had already tried a fundamental extension of the framework of the theory in order to include electromagnetism as well. His attempt was based on the idea of gauge in variance–a concept which was to emerge 30 years later as a cornerstone of the modern theories of unification. Nevertheless, no agreement with observed facts could be reached by his concept of the path-dependence of a displaced length.

Whereas Weyl's generalization consisted in placing a connection of lengths beside the connection of directions given by the metric, Eddington (1923) followed a different course in considering the connection of directions as an a priori property of the manifold. In this case the metric becomes a deduced quantity.