1. WH, PB, p. 93.
2. L. Weickmann, “Nachruf auf Otto Wiener,” SAW, MPK, Berichte, 79 (1927) 107-123.
3. Wentzel to Sommerfeld, 26 May 1927 (SN).
4. Note from Ulrich, dated 31 May 1932, on letter of Debye to Saxon Culture Ministry, 26 May 1932 (“Physikalisches Institut der Universitat Leipzig,” vol. 2, 1929-1939, SStA, Ministerium fur Volksbildung, 10230/27). Depictions of the history of Leipzig physics have been assembled in “Sektion Physik der Karl-MarxUniversitat 150 Jahre nach der Griindung des Physikalischen Instituts in Leipzig,”
Wissenschaftliche Zeitschrift der Karl-Marx-Universitat Leipzig, mathematischnaturwissenschaftliche Reihe, 34 (1985): 1, 1-87; and in Martin Franke, “Zu den Bemuhungen Leipziger Physiker urn eine Profilierung der physikalischen Instituts der Universitat Leipzig im zweiten Viertel des 20. Jahrhunderts,” NTM-Naturwissenschaft, Technik, Medizin, 19 (1982), 68-76.
5. Floor plans in Otto Wiener, “Das Physikalische und das TheoretischPhysikalische Institut,” Festschrift zur Eeier des 500jahrigen Bestehens der Universitat Leipzig, vol. 4, part 2 (Leipzig: Hirzel, 1909), pp. 24-69.
6. Debye to Ministerialrat von Seydewitz, 19 Sep 1927, and Debye to Notgemeinschaft, 20 Jul 1928 (DP).
7. WH to his parents, 5 and 9 Nov 1927.
8. WH to his parents, 13 Dec 1927, and Akten des Rentamtes (UA Leipzig).
9. WH to his parents, 9 Nov 1927.
10. Sommerfeld to WH, 15 Nov 1927 (SN).
11. WH to his parents, 7 May [1928], and Wentzel to Sommerfeld, 12 May 1928 (SN). The three students were Peierls, Eckart, and Houston, an American visitor.
12. WH to his parents, 27 Jun [1928].
13. In the same period, the total number of Reich university students increased by 20 percent; the number of first-year physics students in Leipzig went from 1 to 14. Data derived from V ierteljahrshefte zur Statistik des Deutschen Reiches, 37 (1928), 38 (1929), 39 (1930).
14. Debye to Staatsministerium, 27 Feb 1931 (note 4, Physikalisches Institut).
15. As a result, overcrowding in physics became common. Wien’s successor in Munich, Walther Gerlach, reported that about 1000 students attended his lectures in a hall seating 525. This prompted a student delegation to complain “in the most irate form.” Gerlach to Rector of Universitat Munchen, 16 May 1930 (Acta des K. Akademischen Senats, Das physikalische Cabinet betr., UA Munchen).
16. List compiled by Dr. Michael Eckert, to whom I am grateful for a copy.
17. The establishment and maintenance of this network is indicated by the travels of the assistants and students and by the correspondence of their teachers, especially WH to Pauli, 1 Aug [1929].
18. Interview with Friedrich Hund, Gottingen, April 1981; and interview with Hund by the Project for History of Solid State Physics, Deutsches Museum, Munich, 1982. According to Hund’s “Wissenschaftliches Tagebuch” (Deutsches Museum), he accepted the call to Leipzig on February 4, 1929, then left for the United States about the same time Heisenberg did. A photograph of the two in Chicago is extant. Hund returned to Leipzig by the start of the summer semester in May 1929 in order to run the teaching program while Heisenberg stayed abroad until the fall.
19. C. I. Zahn to S. A. Goudsmit, 24 Feb 1933 (PWB, vol. 2, p. 148).
20. WH to Mansel Davies, 16 Jan 1970, published in Mansel Davies, “Peter Joseph Wilhelm Debye,” Royal Society of London, Biographical memoirs, 16 (1970), 175-232, on 221.
21. Interview with Hund, April 1981. However, Guido Beck later told Peierls that he actually picked up the pastries. Rudolf Peierls, Bird of passage: Recollections of a physicist (Princeton: Princeton University Press, 1985), p. 32.
22. WH to Bohr, 23 Jul 1928 (BSC 11, 2).
23. WH to his mother, 25 Nov [1928] and 6 Dec 1928.
24. WH to his parents, 27 Jun 1928 and 16 Oct [1928].
25. Felix Bloch, “Reminiscences of Heisenberg and the early days of quantum mechanics,” Physics today, 29:12 (December 1976), 23-27, on 27.
26. Quoted in Bernhard Schweitzer, Die Universitat Leipzig 1409-1959 (Tubingen:
J. C. B. Mohr, 1960), pp. 13-14.
27. Interview with C. F. von Weizsacker, 30 Apr 1982.
28. WH to his parents, 25 Feb 1930.
29. Interview with Hund, Gottingen, April 1981.
30. Hans Driesch, Lebenserinnerungen (Basel: Ernst Reinhardt Verlag, 1951), p. 200.
31. Gerhard Ritter, Carl Goerdeler und die deutsche Widerstandsbewegung (Stuttgart: Deutsche Verlagsanstalt, 1954).
32. Draft of nomination, 23 May 1930 (DP), and SAK, MPK, Bericbte, 82 (1930).
33. WH, “Uber Energieschwankungen in einem Strahlungsfeld,” delivered 9 January 1931 (HCW A2, 116-131).
34. Hund, note 29, and Weizsacker, note 27.
35. The early development of quantum field theory and its history to the present are subjects still requiring much research. Summaries of this history, from which this chapter has benefited, include Pais, Inward-, MR 4; Joan Bromberg, “Dirac’s quantum electrodynamics and the wave-particle equivalence,” in History of twentieth century physics, ed. C. Weiner (New York: Academic Press, 1977), pp. 147-157; Olivier Darrigol, “Les debuts de la theorie quantique des champs (1925-1948),” doctoral dissertation, Universite de Paris I (Pantheon-Sorbonne), 1982.
36. Dirac, PRS, 114 (1927), 243-265 and 710-728. Studies of Dirac’s life and work, along with more detailed discussions of the physics presented here, have been provided in Helge Kragh, Dirac: A scientific biography (New York: Cambridge University Press, 1990), as well as in the works cited in note 35.
37. Commuting variables obey the rule AB = BA, or AB — BA = 0, for example,
4 X 3 = 3 X 4.
38. Indicated in WH to Pauli, 23 Feb 1927, the same letter in which he first presented to Pauli his notions on uncertainty.
39. WH to Pauli, 4 Apr 1927.
40. Jordan and Pauli, ZB, 47 (1928), 151-173.
41. Indicated in Pauli to Dirac, 17 Feb 1928.
42. WH to Pauli, 23 Feb 1927.
43. Presented on 1 Feb 1928.
44. Dirac, PRS, 117 (1928), 610-624. For details, see Kragh, note 36, and the works in note 35.
45. Jordan and Wigner, ZP, 47 (1928), 631-651.
46. Pauli to Dirac, 17 Feb 1928.
47. The dilemma of negative energies was made worse by Oskar Klein’s 1929 paradox, in which negative energy states must be taken into account in the scattering of an electron by a barrier.
48. Dirac delivered his lecture (probably in English) entitled “Uber die Quantentheorie des Elektrons” on 22 Jun 1928. Conference program in Debye to Fermi, 9 Jun 1928 (DP). It was published in PZ, 29 (1928), 561-563 and 712. Heisenberg reported a long discussion with Dirac in Leipzig in WH to Jordan, 25 Jun 1928 (Nachlass Jordan, SPK).
49. Pauli to Bohr, 16 Jun 1928.
50. WH to Pauli, 3 May 1928.
51. Sommerfeld, Nwn, 15 (1927), 825-832. A fuller account of the electron theory of metals in this period is provided by L. Hoddeson, G. Baym, and M. Eckert, “The development of the quantum-mechanical electron theory of metals: 1928-1933 ” Reviews of modern physics, 59 (1987), 287-327.
52. Bloch completed his dissertation, entitled “Uber die Quantenmechanik der Eletronen in Kristallgittern,” on 2 Jul 1928, indicated in “Promotionen,” (file MI,
UA Leipzig). Heisenberg’s and Debye’s opinions are in “Promotionsakten” (UA Leipzig). Bloch published a version of the dissertation in ZP, 52 (1928), 555-600.
53. Peierls recalls his work in Leipzig in Peierls, note 21, pp. 32-40.
54. WH to Pauli, 3 May 1928.
55. Heisenberg s earlier efforts and his contributions to the theory of ferromagnetism are discussed in Hoddeson et al., note 51, pp. 304-311.
56. WH, “Zur Theorie des Ferromagnetismus,” ZF, 49 (1928), 619-636, rec. 20 May 1928 (HCW Al, 580-597).
57. WH to Pauli, 31 Jul 1928.
58. WH, “Fortschritte in der Theorie des Ferromagnetismus,” Metallwirtscbaft, 9 (1930), 843-844 (HCW B, 167-168).
59. Papers by WH and Pauli in Probleme der modemen Pbysik. Arnold Sommerfeld zum 60. Geburtstag gewidmet von seinen Schiilem, ed. Peter Debye (Leipzig: Hirzel, 1928); WH’s paper reprinted in HCW B, 100-108.
60. Pauli to Bohr, 16 Jan [1929]; Pauli to O. Klein, 18 Feb 1929; WH to Jordan, 22 Jan [1929] (Nachlass Jordan, SPK).
61. WH and Pauli, “Zur Quantendynamik der Wellenfelder” ZF, 56 (1929), 1-61, rec. 19 Mar 1929 (HCW A2, 8-68); WH and Pauli, “Zur Quantentheorie der Wellenfelder, II” ZF, 59 (1930), 168-190, rec. 7 Sep 1929 (HCW A2, 69-91). Their theory is also discussed in the works cited in note 35.
62. J. R. Oppenheimer, ZF, 55 (1929), 725-737, rec. 6 May 1929; and Oppenheimer, PR, 35 (1930), 461-477, rec. 12 Nov 1929.
63. Bohr,/. Chem. Society London, 1932, 349-384, (BCW 6, 371-408).
64. Bohr to Dirac, 29 Aug 1930 (BSC 18, 4).
65. WH to Pauli, 20 Jul 1929.
66. WH to Bohr, 26 Feb [1930], 10 and 23 Mar 1930; Bohr to WH, 18 Mar 1930 (BSC 20, 2).
67. R. E. Peierls, ZF, 53 (1929), 255-266; and Peierls, FZ, 30 (1929), 273-274.
68. Especially, WH to Bohr, 10 Mar 1930 (BSC 20, 2).
69. WH, “Die Selbstenergie des Elektrons” ZF, 65 (1930), 4-13 (FICW A2, 106-115) on p. 4.
70. Ibid., and WH to Bohr, 26 Apr 1930 (BSC 20, 2).
71. WH to his parents, 30 May and 12 Jul 1930.
72. WH to his father, 4 Nov 1930.
73. WH to his parents, 7 Nov 1930.
74. WH to his mother, 15 Dec 1930.
75. WH to Bohr, 18 Mar 1937 (BSC 20, 2).
76. WH, “Zur Theorie der Magnetostriktion und der Magnetisierungskurve” (1931), HCW Al, 598-608; WH, “Uber die inkoharente Streuung von Rontgenstrahlen” (1931), HCW Al, 627-630; WH, “Theoretische Uberlegungen zur Hohenstrahlung” (1932), HCW A2, 250-272.
77. WH to Bohr, 27 Jul [1931] (BSC 20, 2), containing a discussion of various applications.
78. WH, “Probleme der modemen Physik” (25 Dec 1931), HCW Cl, 48-49.
79. Heisenberg, Bohr, and the route to the neutron-proton model of the nucleus have been explored in Joan Bromberg, “The impact of the neutron: Bohr and Heisenberg,” HSPS, 3 (1972), 307-341; and discussed in Laurie M. Brown and Helmut Rechenberg, “Nuclear structure and beta-decay (1932-1933),” American journal of physics, 56 (1988), 982-988, and elsewhere.
80. Bromberg, note 79, points out the importance of Heisenberg’s style for his nuclear physics. The style portrayed here differs somewhat from Bromberg’s portrayal.
81. Guido Beck returned to Leipzig from Copenhagen with a report on Bohr’s new theory of superconductivity, as indicated in WH to Bohr, 20 Jun [1932] (BSC 20, 2). But Bohr did apply the neutron to electron-neutron collision phenomena, as pointed out by Bromberg, note 79, p. 330.
82. Niels Bohr, “Atomic stability and conservation laws,” in Convegno di fisica nucleare, Ottobre 1931-IX (Rome: Reale Accademia d’ltalia, 1932), pp. 119-130.
83. WH to Bohr, 3 and 23 Feb [1932]; Bohr to WH, 24 Feb 1932 (BSC 20, 2).
84. Chadwick to Bohr, 24 Feb 1932 (BSC). Heisenberg also learned of the discovery about the same time, that is, after meeting at the ski hut.
85. WH, “Uber den Bau der Atomkerne, I” ZP, 77 (1932), 1-11, actually rec. 7 Jun 1932 (HCW A2, 197-207). Heisenberg seemed to be protecting his priority by not informing anyone in Copenhagen until June 20, 1932. When earlier announcing his arrival in Copenhagen on April 6, 1932, Heisenberg was more intrigued with a new cosmic-ray phenomenon (showers) than with the neutron. WH to Bohr, 30 Mar [1932]. He later referred only to discussions about the scattering of gamma rays by neutrons during his Easter visit in WH to Bohr, 18 Jul [1932] (BSC 20, 2), and in WH, “Uber den Bau der Atomkerne, II” (rec. 30 Jul 1932), HCW A2, 208-216.
86. WH to Bohr, 20 Jun [1932] (BSC 20, 2).
87. WH, note 85, “Uber den Bau der Atomkerne, I,” 197-198.
88. WH, note 85, “Uber den Bau der Atomkerne, II,” 216.
89. WH, “Uber den Bau der Atomkerne, III” (rec. 22 Dec 1932), HCW A2, 217-226.
90. WH, “Considerations theoretiques generates sur la structure du noyau,” report to Solvay Congress, Brussels, October 1933 (HCW B, 179-225); WH, “Die Struktur der leichten Atomkerne” (1935), HCW A2, 227-238; WH, “Bemerkungen zur Theorie des Atomkerns,” in Peter Zeeman, 1865-1935 (The Hague: Nijhoff, 1935), pp. 108-116 (HCW B, 238-246).
91. Interview with C. F. von Weizsacker, 30 Apr 1982.