The Strangest Man
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21 Postcard from Dirac to his parents, 27 July 1926, DDOCS.
22 Letter to Dirac from Fermi, Dirac Papers 2/1/3 (FSU).
23 Greenspan (2005: 135); Schücking (1999: 26).
24 Letter to Dirac from his mother, 2 October 1926, Dirac Papers 1/3/6.
25 Mott (1986: 42).
Chapter eight
1 Wheeler (1998: 128–9). On 24 April 1932, Jim Crowther wrote of hearing a similar anecdote from Bohr over afternoon tea (Book I of Crowther’s notes from his meeting with Bohr, pp. 99–100 [SUSSEX]).
2 Book I of Crowther’s notes from his meeting with Bohr, 24 April 1932, pp. 96–101, SUSSEX. See also the article on Dirac by John Charap in The Listener, 14 September 1972, pp. 331–2.
3 Book I of Crowther’s notes from his meeting with Bohr, p. 99, SUSSEX. 4 Dirac (1977: 134).
5 Bohr’s words (Nicht um zu kritisieren aber nur um zu lernen) are quoted in Dirac (1977: 136).
6 Postcard from Dirac to his parents, 1 October 1926 (DDOCS).
7 Letter from Dirac to James Wordie, 10 December 1926, STJOHN; Dirac (1977: 139).
8 The phrase ‘liked the sound of his own voice’ is taken from the letter John Slater wrote to John Van Vleck on 27 July 1924, John Clarke Slater papers APS. See also Cassidy (1992: 109).
9 Crowther notes, p. 99, SUSSEX.
10 The wave is what is known mathematically as a complex function, which means that the wave at any point has two parts: one real, the other imaginary. The ‘size’ of the wave at any point, related to both parts, is called its modulus. According to Born, the probability of detecting the quantum in a tiny region near a point is related to the square of the modulus of the wave.
11 Pais (1986: 260–1).
12 Heisenberg (1967: 103–4).
13 Interview with Oppenheimer, AHQP, 20 November 1963.
14 Weisskopf (1990: 71).
15 Interview with Dirac, AHQP, 14 May 1963, p. 9.
16 Garff (2005: 308–16, 428–31).
17 Interview with Monica Dirac, 3 May 2006.
18 Quoted in Garff (2005: 311); interview with Dirac, AHQP, 14 May 1963, p. 9.
19 Møller (1963).
20 Dirac had also seen the need for the function when he was studying Eddington’s The Mathematical Theory of Relativity (1923). On page 190, Eddington uses non- rigorous mathematics, and he drew attention to this in a footnote, which Dirac read. This was an example of the case where the delta function is needed to make some sense of a scientific equation which would otherwise be mathematically unintelligible. See interview with Dirac, AHQP, 14 May 1963, p. 4.
21 Interview with Dirac, AHQP, 6 May 1963, p. 4.
22 Heaviside (1899: Sections 238–42).
23 Lützen (2003: 473, 479–81).
24 Interview with Heisenberg, AHQP, 19 February 1963, p. 9.
25 Dirac (1962), report of the Hungarian Academy of Sciences, KFKI-1977-62.
26 Letter from Einstein to Conrad Habicht, 24 December 1907, see Pais (1982: 441).
27 Dirac mentioned this in a press release issued by Florida State University on 24 November 1970; Dirac Papers, 2/6/9 (FSU).
28 Letters to Dirac from his mother, 19 November, 26 November, 2 December, 9 December 1926, Dirac Papers, 1/3/6 (FSU).
29 It is possible that Charles wrote other letters to Dirac. If so, Dirac did not keep them – uncharacteristically, as he appears to have kept most of his family correspondence. Moreover, the frequent letters from Dirac’s mother often send messages from his father, indicating that his father was communicating to his son via her, a common arrangement in family correspondence of this type.
30 Letter to Dirac from his father, 22 December 1926, Dirac Papers, 1/1/7 (FSU).
31 Letter to Dirac from his mother, 25 December 1926, Dirac Papers, 1/3/6 (FSU).
32 Mehra (1973: 428–9).
33 Postcard from Dirac to his parents, 10 January 1927, DDOCS.
34 Slater (1975: 135).
35 Elsasser (1978: 91).
36 Born (2005: 88).
37 ‘The deepest thinker’: Dirac (1977: 134).
38 ‘The most remarkable scientific mind…’: Crowther notes, p. 21, SUSSEX. The ‘logical genius’ comment is in the interview with Bohr, AHQP, 17 November 1962, p. 10.
39 Both quotes from the Crowther notes, p. 97, SUSSEX.
40 ‘PAM Dirac and the Discovery of Quantum Mechanics’, Cornell colloquium, 20 January 2003, available at http://arxiv.org/PS_cache/quant-ph/pdf/0302/ 0302041v1.pdf (accessed 24 September 2007).
Chapter nine
1 Bird and Sherwin (2005: 62).
2 Bernstein (2004: 23).
3 Bird and Sherwin (2005: 65).
4 The address of the Carios’ home was Giesmarlandstrasse 1. See interview with Oppenheimer, AHQP, 20 November 1963, p. 4.
5 Michalka and Niedhart (1980: 118).
6 Frenkel (1966: 93).
7 Interview with Gustav Born, 6 April 2005.
8 Frenkel (1966: 93).
9 Weisskopf (1990: 40).
10 Bird and Sherwin (2005: 56, 58).
11 See Frenkel (1966: 94) for a reference to the practice of Mensur in Göttingen. See also Peierls (1985: 148).
12 Interview with Oppenheimer, AHQP, 20 November 1963, p. 6.
13 Interview with Oppenheimer, AHQP, 20 November 1963, p. 11.
14 Delbrück, M. (1972) ‘Homo Scientificus According to Beckett’, available at http://www.ini.unizh. ch/~tobi/fun/max/delbruckHomoScientificusBecket1972.pdf, p. 135 (accessed 13 May 2008).
15 Greenspan (2005: 144–6).
16 Elsasser (1978: 71–2).
17 Letter from Raymond Birge to John Van Vleck, 10 March 1927, APS.
18 Elsasser (1978: 51).
19 Frenkel (1966: 96).
20 Delbrück (1972: 135).
21 Wigner (1992: 88).
22 Mill’s comment is in Mill (1873: Chapter 2).
23 Interview with Oppenheimer, AHQP, 20 November 1963, p. 11.
24 During his time in Göttingen, Dirac successfully applied his theory to the light emitted by atoms when they make quantum jumps, apparently after discussions with Bohr. See Weisskopf (1990: 42–4).
25 Letter from Pauli to Heisenberg, 19 October 1926, reprinted in Hermann et al. (1979). See also Beller (1999: 65–6); Cassidy (1992: 226–46).
26 Heisenberg (1971: 62–3).
27 Heisenberg demonstrated that the principle also applied to energy and time and to other pairs of quantities known technically as ‘canonically conjugate variables’.
28 This was a popular walk with students. See, for example, Frenkel (1966: 92). On 5 April 1927, Dirac referred to the walk in a postcard of the path to his parents (DDOCS).
29 Lecture by Dirac, 20 October 1976, ‘Heisenberg’s Influence on Physics’: Dirac Papers, 2/29/19 (FSU); see also the interview with Dirac, AHQP, 14 May 1963, p. 10.
30 See the article on complementarity in French and Kennedy (1985), e.g. Jones, R.V. ‘Complementarity as a Way of Life’, pp. 320–4; see also the illustration of Bohr’s coat of arms, p. 224.
31 Interview with Dirac, AHQP, 10 May 1969, p. 9.
32 Eddington (1928: 211). This book is an overview of the latest ideas in physics based on a series of lectures he gave between January and March 1927.
33 Eddington (1928: 209–10).
34 Dirac (1977: 114).
35 Dirac Papers, 2/28/35 (FSU). The seminar took place on 30 October 1972. See Farmelo (2005: 323).
Chapter ten
1 Interview with Oppenheimer, AHQP, 20 November 1963, p. 5.
2 Greenspan (2005: 137).
3 Goodchild (1985: 20). Even if Dirac did not write these words, he agreed with their sentiment; see interview with von Weizsächer, AHQP, 9 June 1963, p. 19.
4 Dirac (1977: 139); Greenspan (2005: 141).
5 Greenspan (2005: 142), and von Meyenn and Schücking (2001: 46). The student was Otto Heckmann. Boys Smith’s comment is from a conversation with his former colleague at St John’s College, Cambridge, Peter Goddard, 5 July 200
6.
6 Information on scholarship from Angela Kenny, archivist, Royal Commission for the Exhibition of 1851 (e-mail, 10 December 2007).
7 Letter from Dirac to James Wordie, 28 February 1927, STJOHN.
8 Letter to Dirac from his mother, 28 June 1928, Dirac Papers, 1/3/8 (FSU).
9 Greenspan (2005: 145).
10 Greenspan (2005: 146).
11 Letter to Dirac from his mother, 7 April 1927, Dirac Papers, 1/3/7 (FSU).
12 Letter to Dirac from his mother, 20 May 1927, Dirac Papers, 1/3/7 (FSU).
13 Letter to Dirac from his mother, 6 January 1927, Dirac Papers, 1/3/7 (FSU).
14 Letter to Dirac from his mother, 10 February 1927, Dirac Papers, 1/3/7 (FSU).
15 Letter to Dirac from his mother, 20 May 1927, Dirac Papers, 1/3/7 (FSU).
16 Letter to Dirac from his mother, c. 26 March 1927, Dirac Papers, 1/3/7 (FSU).
17 Flo enjoyed the company of several men in her classes and even put Dirac in touch with one of them, a German-speaking insurance clerk Mr Montgomery (‘Monty’). Letter to Dirac from his mother, 18 March 1927, Dirac Papers, 1/3/7 (FSU).
18 These recollections were given to Richard Dalitz in the 1980s.
19 Letter from Dirac to Manci Balázs, 7 April 1935, DDOCS.
20 Letter from Dirac to Manci Balázs, 17 June 1936, DDOCS.
21 Their address was 173 Huntingdon Road. Fen (1976: 161); Boag et al. (1990: 78).
22 The conference was held at L’Institut de Physiology Solvay au Parc Léopold, from 24 to 29 October 1927.
23 Letter from John Lennard-Jones (of Bristol University) to Charles Léfubure (Solvay official), 9 March 1928, SOLVAY.
24 See http://www.maxborn.net/index.php? page=filmnews (accessed 13 May 2008).
25 Heisenberg (1971: 82–8); interview with Heisenberg, AHQP, 27 February 1963, p. 9. The location of the hotel is specified in a letter to Dirac from the conference administrator on 3 October 1927: Dirac Papers, 2/1/5 (FSU).
26 Dirac (1982a: 84).
27 Interview with Heisenberg, AHQP, 27 February 1963, p. 9.
28 Heisenberg (1971: 85–6).
29 In the early 1850s, the Punch humorist Douglas Jerrold quipped about the controversial feminist writer Harriet Martineau, ‘There is no God, and Harriet Martineau is her prophet.’ See A. N. Wilson (2002), The Victorians, London: Hutchinson, p. 167.
30 Dirac Papers, 2/26/3 (FSU).
31 Dirac (1977: 140).
32 Dirac (1977: 141).
Chapter eleven
1 Menu from College records, STJOHN.
2 Crowther (1970: 39) and Charap (1972).
3 Interviews with Dirac, AHQP, 1 April 1962, p. 15; 7 May 1963, pp. 7–8.
4 Dirac gave contradictory accounts of the goal he was pursuing at that time. In one account, he stated that he was seeking the answer to the question ‘How could one get a satisfactory relativistic theory of the electron?’ (Dirac 1977: 141). In another account, he says that ‘my dominating interest was to get a satisfactory relativistic theory of a particle, of the simplest possible kind, which was presumably a spinless particle.’ Dirac wrote the latter words on a single sheet of paper headed ‘Sommerfeld Atombau un Spektralinen II 539.18’ in Dirac Papers, 2/22/15 (FSU). I prefer to use the 1977 account as it is the nearest thing we have to a carefully prepared history of Dirac’s thinking in his own hand.
5 Farmelo (2002a: 133).
6 See the notes for Dirac’s lectures in the 1970s and 1980s: 2/28/18–2/29/52 (FSU).
7 Huxley’s 1870 Presidential Address to the British Association for the Advancement of Science in Huxley (1894). Dirac uses similar words: ‘The originator of a new idea is always rather scared that some development may happen which will kill it’ (1977: 143).
8 Interview with Dirac, AHQP, 7 May 1963, p. 14; Dirac (1977: 143).
9 Letter from Darwin to Bohr, 26 December 1927 (AHQP).
10 Interview with Rosenfeld, AHQP, 1 July 1963, pp. 22–3.
11 Mehra (1973: 320).
12 The talented young physicist Rudolf Peierls remarked that, even after a few days studying the equation, ‘I have begun to have an inkling of what it deals with, but I haven’t understood a single word.’ Letter from Peierls to Hans Bethe, 4 May 1924, quoted in Lee (2007b: 33–4).
13 Florida State University Bulletin, 3 (3), 1 February 1978.
14 Slater (1975: 145).
15 Postcard from Darwin to Dirac, 30 October 1929, Dirac Papers, 2/1/9 (FSU).
16 Dirac gave courses on quantum mechanics in the Michaelmas and Lent terms of 1927–8 and was paid £100 for the pair: see the letter from the Secretary to the Faculty of Mathematics, 16 June 1927, Dirac Papers, 2/1/4 (FSU).
17 Crowther later affirmed that he had left the Communist Party by 1950, but it is not clear when he left it. I thank Allan Jones for this information.
18 Clipping, annotated by Charles Dirac, in Dirac Papers, 1/12/5 (FSU).
19 The Times, 5 October 1931, p. 21. This well-briefed article was written by a journalist who appears to have succeeded in persuading Dirac to speak about his work.
20 ‘Mulling over the Universe with Paul Dirac’, interview by Andy Lindstrom, Tallahassee Democrat, 15 May 1983.
21 Letter to Dirac from his mother, 26 January 1928, Dirac Papers, 1/3/8 (FSU). See also postcard from Dirac to his parents, 1 February 1928 (DDOCS).
22 See the entry for Bishop Whitehead in Crockford’s Clerical Dictionary, 1947, p. 1,416. See also Billington Harper (2000: 115–26, 129–33, 293–5). The quoted description of Mrs Whitehead is on p. 145. I thank Oliver Whitehead and the late David Whitehead, grandsons of Isabel Whitehead, for the information in the description of Isabel Whitehead’s home.
Chapter twelve
1 Kojevnikov (1993: 7–8).
2 Peierls (1985: 62–3).
3 Kojevnikov (2004: 64–5).
4 Letter from Tamm to his wife, 4 March 1928, in Kojevnikov (1993: 7).
5 ‘The tulip fields are all in flower now’: postcard from Dirac to his parents, 29 April 1928 (DDOCS). ‘[Leiden] is below sea level and there are nearly as many canals as streets’: postcard from Dirac to his parents, 29 June 1927 (DDOCS).
6 Letter from Tamm to his wife, undated, Kojevnikov (1993: 8).
7 Casimir (1983: 72–3).
8 Brown and Rechenberg (1987: 128).
9 Letter from Heisenberg to Pauli, 31 July 1928, in Kronig and Weisskopf (1964).
10 Peierls (1987: 35). In this account, Peierls remembers going to the theatre, but it seems from his letter to Dirac of 14 September 1928 (Lee [2007: 50]) that they went to the opera. I am grateful to Professor Olaf Breidbach for his comments on early twentieth-century Prussian politesse.
11 Born (1978: 240) and Greenspan (2005: 151–3).
12 Schücking (1999: 27).
13 Bohr nicknamed Gamow ‘Joe’ after the standard name for cowboys in western movies, which Bohr especially liked (interview with Igor Gamow, 3 May 2004). See also Reines (1972: 289–99; see pp. 280); Mott (1986: 28).
14 The only exception is the paper that Dirac co-authored with Rutherford’s student J. W. Harding, ‘Photoelectric Absorption in Hydrogen-Like Atoms’, in January 1932.
15 Gamow (1970: 14).
16 Wigner (1992: 9–15).
17 Letter from Gabriel Dirac to Manci Dirac, 5 September 1940: ‘It may interest you to know that everybody (Prof [Max] Born, Morris [Pryce] and Daddy [Paul Dirac]) says that Johnny von Neumann is the world’s best mathematician’ (DDOCS).
18 Fermi (1968: 53–9).
19 Wigner (1992: 37–43).
20 Interview with Pat Wigner, 12 July 2005.
21 Dirac wrote to his parents on 18 July 1928: ‘The woods here are full of fireflies in the evening. I have been to the top of the Harz mountains’ (DDOCS).
22 Dirac’s wife would later write to him: ‘It seems the beautiful scenery has the same effect on you as a beautiful book has on me’, 12 August 1938 (DDOCS).
23 Letter to Dirac from his mother, 12 Jul
y 1928, Dirac Papers, 1/3/8 (FSU).
24 Sinclair (1986: 32–3).
25 Letter from Dirac to Tamm, 4 October 1928, Kojevnikov (1993: 10). The conference lasted from 5 August to 20 August.
26 Brendon (2000: 241).
27 Salaman and Salaman (1986: 69). In this article, Dirac is quoted as giving 1927 as the date of the experience; this is impossible as he did not visit Russia that year.
28 He first took a boat to Constantinople (renamed Istanbul in the following year), then sailed on to Marseilles via Athens and Naples, before travelling across France and then home. He planned to arrive in Bristol on Monday, 10 September (letter from Dirac to his parents, 8 September 1928, DDOCS).
29 Letter to Dirac from his mother, 28 October 1928, Dirac Papers, 1/3/8 (FSU). A copy of the speech is in this file of the archive.
30 In mid-December, Dirac read a paper by Klein showing that the Dirac equation predicted that if a beam of electrons is fired at a barrier, more electrons will be reflected than were present in the original beam. It was as if a tennis ball struck a player’s racket and not one but several balls flew off it.
31 Howarth (1978: 156).
32 Cambridge Review, 29 November 1929, pp. 153–4. See also the rhapsodic review in the Times Literary Supplement, 24 October 1929.
33 Draft letter to Dirac from L. J. Mordell, 4 July 1928, Dirac Papers, 2/1/7 (FSU).
34 Mott (1986: 42–3).
35 Letter from Jeffreys to Dirac, 14 March 1929, Dirac Papers, 2/1/8 (FSU).
36 St John’s awarded Dirac a praelectorship in mathematical physics, which enabled him to devote himself entirely to research, apart from the presentation of his lecture course.
Chapter thirteen
1 Letter from Dirac to Oswald Veblen, 21 March 1929, LC, Veblen archive.
2 Scott Fitzgerald (1931: 459).
3 Letter from Dirac to Veblen, 21 March 1929, LC (Veblen archive).
4 Diaries of Dirac (DDOCS).
5 Fellows (1985); see the introduction (p. 4) and the conclusion.
6 Comment made by Bohr to Crowther, recorded by Crowther on 24 April 1932 in the Crowther archive, SUSSEX, Book II of his notebooks, pp. 96–7. For one of many retellings of this anecdote, see Infeld (1941: 171).