1 4 4 D O C U M E N T 7 8 O C T O B E R 1 9 2 7 Published in Électrons et photons: Rapports et discussions Solvay 1928, pp. 253–256. The manuscript (see Doc. 76) was sent to Jules Émile Verschaffelt on 21 November 1927, with accompanying letter Abs. 277. [1] This first sentence would naturally be translated into English as: “I must excuse myself for not having delved deeply into the essentials of quantum mechanics. Nevertheless, I would like to make some general remarks.” However, the original German (see Doc. 76) would be translated as, “Despite being conscious of the fact that I have not entered deeply enough into the essence of quantum mechanics, nevertheless I want to present here some general remarks.” (“Trotzdem ich mir des Umstandes bewusst bin, dass ich in das Wesen der Quantenmechanik nicht tief genug eingedrungen bin, will ich doch hier einige allgemeine Bemerkungen vorbringen.”) See Bacciagaluppi and Valentini 2009, p. 440. [2] Louis de Broglie. Einstein is using the expressions “De Broglie waves,” “De Broglie- Schrödinger waves,” and “Schrödinger waves” interchangeably here. For a discussion of the relation between De Broglie’s and Schrödinger’s wave mechanics, see Bacciagaluppi and Valentini 2009, chap. 11.1. [3] As noted in Bacciagaluppi and Valentini 2009, p. 440, “donne la measure” (“gives the mea- sure”) is a mistranslation of “ist massgebend” (“is responsible”) see Doc. 76. [4] As noted in Bacciagaluppi and Valentini 2009, p. 441, the “I” and “II” in this sentence appear to be the wrong way around. [5] The Bothe-Geiger experiments (Bothe and Geiger 1925a and b) demonstrated that, during Compton scattering, outgoing scattered photons and outgoing recoil electrons were produced simul- taneously for individual events, thus providing strong evidence in favor of the quantum hypothesis. See Vol. 14, Introduction, sec. VIII, for some discussion. [6] For discussions of the significance of Einstein’s argument in this paragraph, in particular with regard to the tension between locality considerations and the completeness of quantum mechanics, see Norsen 2005 and Bacciagaluppi and Valentini 2009, chap. 7.1. [7] Einstein had first raised the concern that the wave function was defined on a high-dimensional configuration space rather than on four-dimensional space-time in a letter to Lorentz (Einstein to Lorentz, 1 May 1926 [Vol. 15, Doc. 272]). Einstein continued to worry about this matter, and to flesh out his concern in more detail, over the ensuing two years see Vol. 15, Introduction, sec. IX. For some further discussion of Einstein’s objection to treating configuration space as fundamental, see also Bacciagaluppi and Valentini 2009, chap 7.3. [8] Einstein is referring to the work he had done in connection with the Indian physicist Satyendra Nath Bose (see Bose 1924 and Einstein 1924o [Vol. 14, Doc. 283]). For a discussion of the discovery and significance of Bose-Einstein statistics, see Vol. 14, Introduction, sec. X. 78. To Caesar Koch[1] [Brussels,] Freitag. [28 October 1927] Lieber Onkel! Ich danke Dir sehr für Deine herzliche Einladung. Ich habe es noch nicht früher gethan, weil ich warten wollte, bis ich Dir meine Antwort präzis angeben könnte. Aber nun ist es höchste Zeit und ich weiss immer noch nicht, wann meine Sitzun- gen fertig sind.[2] Ich komme morgen Samstag im Laufe des Nachmittags oder