EINSTEIN, Albert. Autograph manuscript on gravitational theory, in German, [Berlin, November 1920]. 3 pages, 4to, one page on blank side of a typed letter to Einstein, a working manuscript, closely written and with numerous revisions and interlinear additions; with a TLS of Einstein's secretary Ilse Einstein, presenting the manuscript at Einstein's request to his friend Hans Mühsam, Berlin, 1 December 1920, 1 page, 4to.
Nineteen-twenty marks an important turning point in Einstein's career. Previously, he had been seeking a field theory in which the fabric of space-time, represented by the metric field, is reduced to matter (which in the late 1910s was widely believed to be constructed out of electromagnetic fields satisfying some non-linear generalization of Maxwell's equations); henceforth, Einstein pursued the search for a deeper field theory that would unify the metric field and the electromagnetic field without reducing one to the other. Einstein's manuscript reply to Reichenbächer forcefully defends this change in direction.
The lot comprises three parts. First, and most important, is the draft manuscript of the paper by Einstein for the December 1920 issue of Die Naturwissenschaften, in response to a paper by Ernst Reichenbächer in the same issue, entitled "To What Extent Can Modern Gravitational Theory Be Established without Relativity?" Also present is the cover letter from Einstein's secretary, stepdaughter and love interest Ilse Einstein, presenting the manuscript to Hans Mühsam to be sold for the benefit of Jewish charities. Finally, the first of two pages of a letter from Einstein to Vilhelm Bjerknes, 12 November 1920, is present (used for one page of Einstein's draft).
Einstein's romantic interest in Ilse Einstein is documented by a letter from her to Georg Nicolas, May 22, 1918, which is included as Doc. 545 in Vol. 8 of the Einstein edition. This letter reveals that when Einstein and Elsa Lowenthal-Einstein, Ilse's mother, began discussions about marriage--while Einstein was seeking a divorce from his first wife, Mileva Maric--the discussion in the Einstein household turned to the possibility of Einstein marrying Ilse instead. The story is recounted in Dennis Overbye's biography, pp.342-346.
Einstein's article was rapidly set in type and the manuscript returned immediately to Einstein, for on 1 December it was presented to Dr. Mühsam to be used "for the purposes of Jewish philanthropy." The Berlin physician was a close friend of the Einsteins during the Berlin years (in Pais's opinion Mühsam was Einstein's closest confidant during this period). He apparently was one of those who played a role in arousing Einstein's support for and interest in the Zionist movement. A few months later, Einstein made his first visit to America, with Chaim Weizmann, to raise funds for building the Hebrew University in Jerusalem.
The manuscript is interesting for Einstein's exceptionally clear response to what even today is a common objection to his equivalence principle. Reichenbächer points out that in general one cannot transform a gravitational field away except in very small regions. Einstein uses the mature formulation of the equivalence principle in a paper on the foundations of general relativity of 1918 to make it clear that this criticism completely misses the mark. The key point, Einstein explains, is the insight that the equality of inertial and gravitational mass shows that inertial and gravitational effects are of the exact same nature (Wesensgleich) and that they thus must be represented by the same structure, which in Einstein's theory is the metric field. Full relativity of motion would be obtained if this metric field could be completely reduced to matter. Motion of material objects with respect to the field can then be seen as a façon de parler about the purely relative motion of these material objects themselves, since the metric field would then just be an epiphenomenon of matter. Einstein makes it clear in his reply to Reichenbächer that the latter requirement is not all that important to him anymore.
The letter to Bjerknes (on the verso of which one page of the manuscript is written) contains an eloquent statement of the reason Einstein had grown disenchanted with Mach's principle. He writes: "I must confess that I am no longer a supporter of mechanical analogies in the explanation of forces acting at a distance, on the argument that the electromagnetic field has turned out to be more fundamental than ponderable masses" ("Ich muss gestehen, dass ich kein Anhänger der mechanischen Analogien zur Erklärung der Fernkräfte mehr bin, aus dem Grunde, weil sich das elektro-magnetische Feld als fundamentaler herausgestellt hat als die ponderable Masse"). This makes it clear that by 1920, Einstein had come to the realization that Mach's principle was tacitly based on an antiquated 19th century particle ontology. In the field ontology that had taken its place with the success of the electrodynamics of Faraday, Maxwell and Lorentz, it made no sense to demand that one field, the metric field, be reduced to another, the electromagnetic field.
Albert Einstein, "Prinzipielles zur allgemeinen Relativitätstheorie." Annalen der Physik 55 (1918): 241-244 (Doc. 4 in Janssen et al. 2002). Albert Einstein, "Antwort auf vorstehende Betrachtung." Die Naturwissenschaften 8 (1920): 1010-1011. (Doc. 49 in Janssen et al. 2002).
Michel Janssen, Robert Schulmann, Jozsef Illy, Christoph Lehner, and Diana Kormos Buchwald (eds.), The Collected Papers of Albert Einstein. Vol. 7. The Berlin Years: Writings, 1918-1921. Princeton: Princeton University Press, 2002.
Dennis Overbye, Einstein in Love. A Scientific Romance. New York: Viking, 2000.
Ernst Reichenbächer, "Inwiefern lässt sich die moderne Gravitationstheorie ohne die Relativität begründen?" Die Naturwissenschaften 8 (1920): 1008-1010.