breakup); Pais 1982, 242; Folsing, 338.
86
. Einstein to Elsa Einstein, after Aug. 3, 1914.
87
. Einstein to Mileva Mari
, Sept. 15, 1914, contains the poisoning allegation. Many other letters in 1914 detail their struggle over money, furniture, and treatment of the children.
CHAPTER NINE: GENERAL RELATIVITY
1
. Renn and Sauer 2006, 117.
2
. The description of the equivalence principle follows the formulation that Einstein used in his yearbook article of 1907 and his comprehensive general relativity paper of 1916. Others have subsequently modified it slightly. See also Einstein, “Fundamental Ideas and Methods of Relativity Theory,” 1920, unpublished draft of a paper for
magazine, CPAE 7: 31.
Some of this chapter draws from a dissertation by one of the editors of the
Einstein Papers Project: Jeroen van Dongen, “Einstein’s Unification: General Relativity and the Quest for Mathematical Naturalness,” 2002. He provided a copy to me along with guidance and editing for this chapter. This chapter also follows the research findings of other scholars studying Einstein’s general relativity work. I am grateful to van Dongen and others who met with me and helped me on this chapter, including Tilman Sauer, Jurgen Renn, John D. Norton, and Michel Janssen. This chapter draws on their work and also that of John Stachel, all listed in the bibliography.
3
. Einstein, “The Speed of Light and the Statics of the Gravitational Field,”
(Feb. 1912), CPAE 4: 3; Einstein 1922c; Janssen 2004, 9. In his 1907 and 1911 papers, Einstein refers to it as the “equivalence hypothesis,” but in this 1912 paper, he raises it to the status of an
.
4
. Einstein, “On the Influence of Gravitation on the Propagation of Light,”
(June 21): 1911, CPAE 3: 23.
5
. Einstein to Erwin Freundlich, Sept. 1, 1911.
6
. Stachel 1989b.
7
. Record and grade transcript, CPAE 1: 25; Adolf Hurwitz to Hermann Bleuler, July 27, 1900, CPAE 1: 67; Einstein to Mileva Mari
, Dec. 28, 1901.
8
. Folsing, 314; Pais 1982, 212.
9
. Hartle, 13.
10
. Einstein to Arnold Sommerfeld, Oct. 29, 1912.
11
. Einstein, foreword to the Czech edition of his popular book
, 1923; see utf.mff.cuni.cz/Relativity/Einstein.htm. In it Einstein writes, “The decisive idea of the analogy between the mathematical formulation of the theory and the Gaussian theory of surfaces came to me only in 1912 after my return to Zurich, without being aware at that time of the work of Riemann, Ricci, and Levi-Civita. This was first brought to my attention by my friend Grossmann.” Einstein 1922c: “I realized that the foundations of geometry have physical significance. My dear friend the mathematician Grossmann was there when I returned from Prague to
