1.1 Preface
This historical review of classical unified field theories consists of two parts. In the first, the development
of unified field theory between 1914 and 1933, i.e., during the years Einstein lived and worked in Berlin, will
be covered. In the second, the very active period after 1933 until the 1960s to 1970s will be
reviewed. In the first version of Part I presented here, in view of the immense amount of material,
neither all shades of unified field theory nor all the contributions from the various scientific
schools will be discussed with the same intensity; I apologise for the shortcoming and promise to
improve on it with the next version. At least, even if I do not discuss them all in detail, as many
references as are necessary for a first acquaintance with the field are listed here; completeness
may be reached only (if at all) by later updates. Although I also tried to take into account
the published correspondence between the main figures, my presentation, again, is far from
exhaustive in this context. Eventually, unpublished correspondence will have to be worked
in, and this may change some of the conclusions. Purposely I included mathematicians and
also theoretical physicists of lesser rank than those who are known to be responsible for big
advances. My aim is to describe the field in its full variety as it presented itself to the reader at the
time.
The review is written such that physicists should be able to follow the technical aspects of the papers
(cf. Section 2), while historians of science without prior knowledge of the mathematics of general relativity
at least might gain an insight into the development of concepts, methods, and scientific communities
involved. I should hope that readers find more than one opportunity for further in-depth studies concerning
the many questions left open.
I profited from earlier reviews of the field, or of parts of it, by Pauli ([246
], Section V); Ludwig [212]; Whittaker ([414], pp. 188–196);
Lichnerowicz [209]; Tonnelat ([356], pp. 1–14); Jordan ([176], Section III); Schmutzer ([290],
Section X); Treder ([183], pp. 30–43); Bergmann ([12], pp. 62–73); Straumann [334, 335];
Vizgin [384, 385];
Bergia [11]; Goldstein and Ritter [146]; Straumann and O’Raifeartaigh [240]; Scholz [292], and
Stachel [330]. The section on Einstein’s unified field theories in Pais’ otherwise superb book presents the
matter neither with the needed historical correctness nor with enough technical precision [241]. A recent
contribution of van Dongen, focussing on Einstein’s methodology, was also helpful [371]. As
will be seen, with regard to interpretations and conclusions, my views are different in some
instances. In Einstein biographies, the subject of “unified field theories” – although keeping
Einstein busy for the second half of his life – has been dealt with only in passing, e.g., in the
book of Jordan [177], and in an unsatisfying way in excellent books by Fölsing [136] and by
Hermann [159]. This situation is understandable; for to describe a genius stubbornly clinging
to a set of ideas, sterile for physics in comparison with quantum mechanics, over a period of
more than 30 years, is not very rewarding. For the short biographical notes, various editions of
J. C. Poggendorff’s Biographisch-Literarischem Handwörterbuch and internet sources have been used (in
particular [1]).
If not indicated otherwise, all non-English quotations have been translated by the author; the original
text of quotations is given in footnotes.
