In December 1954, Einstein gave the final legacy for his theory of general relativity (he died in April 18, 1955 at the age of 76). AKA theory of gravity, in the preface to the 5th edition of the Meaning of Relativity, he made the following statement: For the present edition I have completely revised the “Generalization of Gravitation Theory” under the title “Relativistic Theory of the Non-symmetric Field.” For I have succeeded - in part in collaboration with my assistant B. Kaufmann – in simplifying the derivations as well as the form of the field equations. The whole theory becomes thereby more transparent, without changing its content.

His concluding remarks: This does not seem to be in accordance with a continuum theory, and must lead to an attempt to find a purely algebraic theory for the description of reality. But nobody knows how to obtain the basis of such a theory. This final remark together with his need of an assistant suggested that Einstein was still deficient in modern algebra of group theory and matrix theory. He never completely realized that tensors are equivalent to matrices and complex elements matrices have been used extensively in quantum mechanics: Pauli spin matrices, Dirac spinors, and Penrose twistors. Many of these abstract constructions are very similar to Einstein’s own z-values of free parameters consistent with the system of field equations. Unknowingly, Einstein was looking for a system with z-value of zero. This corresponds to nonzero noncomplex, or non-imaginary real matrices, in other words, positive definite values of matrix elements.