Projective relativity theory

Independent of our investigation Einstein and Mayer (Bibl. 1930,3) have published a "unified field theory", which led to essentially the same results as ours (compare Chap. VIII). Furthermore there recently appeared several works by J.A. Schouten and D. von Dantzig (Bibl. 1931, 7 1932, 3, 4, 8, 9 1933, 1) in which the projective relativity theory was treated in different forms. It is remarkable that - in a mathematical sense - all these theories seem to converge together. One can therefore hope to find a final solution of the unification problem in this way. We say more about the limits of this solution in chap. VII. 

As the next example we take a projective covariant symmetrical tensor of second rank and index 2N. In this case we can further clarify the picture that we sketched before as the basis of projective relativity theory. 

As mentioned before it is conjectured that in projective relativity theory the coefficients gij of the conic equation are gravitational potentials and the coefficients of the hyperplane equation are electromagnetic potentials. We shall see, in fact, that the closest field equations for the 7, 3 are a combination of the classical Einstein gravitation equations and the Maxwell field equations. 

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