.” Bernstein 1973, 89, emphasis in the original. Einstein finished his work on general relativity when he was 36, but his initial step, what he called his “happiest thought” about the equivalence of gravity and acceleration, came when he was 28. Max Planck was 42 when, in Dec. 1900, he gave his lecture on the quantum.
18
. Einstein to Heinrich Zangger, Aug. 11, 1918; Clive Thompson, “Do Scientists Age Badly?,”
, Aug. 17, 2003. John von Neumann, a founder of modern computer science, once claimed that the intellectual
powers of mathematicians peaked at the age of 26. One study of a random group of scientists showed that 80 percent did their best work before their early forties.
19
. Einstein to Maurice Solovine, Apr. 27, 1906.
20
. Aphorism for a friend, Sept. 1, 1930, AEA 36-598.
21
. Einstein to Hendrik Lorentz, June 17, 1916; Miller 1984, 55–56.
22
. Einstein, “Ether and the Theory of Relativity,” speech at University of Leiden, May 5, 1920, CPAE 7: 38.
23
. Einstein to Karl Schwarzschild, Jan. 9, 1916.
24
. Einstein, “Ether and the Theory of Relativity,” speech at University of Leiden, May 5, 1920, CPAE 7: 38.
25
. Greene 2004, 74.
26
. Janssen 2004, 22. Einstein made this clearer in his 1921 Princeton lectures, but also continued to say, “It appears probable that Mach was on the right road in his thought that inertia depends on a mutual action of matter.” Einstein 1922a, chapter 4.
27
. Einstein, “Ether and the Theory of Relativity,” speech at University of Leiden, May 5, 1920, CPAE 7: 38.
28
. Einstein, “On the Present State of the Problem of Specific Heats,” Nov. 3, 1911, CPAE 3: 26; the quote about “really exist in nature” appears on p. 421 of the English translation of vol. 3.
29
. Robinson, 84–85.
30
. Holton and Brush, 435.
31
. Lightman 2005, 151.
32
. Clark 202; George de Hevesy to Ernest Rutherford, Oct. 14, 1913; Einstein 1949b, 47.
33
. Einstein, “Emission and Absorption of Radiation in Quantum Theory,” July 17, 1916, CPAE 6: 34; Einstein, “On the Quantum Theory of Radiation,” after Aug. 24, 1916, CPAE 6: 38, and also in
18 (1917). See Overbye, 304–306; Rigden, 141; Pais 1982, 404–412; Folsing, 391; Clark, 265; Daniel Kleppner, “Rereading Einstein on Radiation,”
(Feb. 2005): 30. In addition, in 1917 Einstein wrote a paper on the quantization of energy in mechanical theories called “On the Quantum Theorem of Sommerfeld and Epstein.” It shows the problems that the classical quantum theory encountered when applied to mechanical systems we would now call chaotic. It was cited by earlier pioneers of quantum mechanics, but has since been largely forgotten. A good description of it and its importance in the development of quantum mechanics is Douglas Stone, “Einstein’s Unknown Insight and the Problem of Quantizing Chaos,”
(Aug. 2005).
