Many physicists shunned Heisenberg after the war. Bohr tried to be at least cordial. Slowly, Heisenberg worked his way back into the scientific community, eventually becoming director of the Max Planck Institute in Munich. Einstein was long gone by then. Pauli died suddenly in 1958, Bohr in 1962. Heisenberg died in Munich in 1976.
ACKNOWLEDGMENTS
I owe a great debt to the numerous authors who over the years have sifted through the history of quantum mechanics in far more detail than I was able to, and whose work I have relied on enormously in writing my own account. I particularly acknowledge the efforts of Abraham Pais and David Cassidy. Of course they and others are not to be held responsible for any errors or idiosyncrasies in my version of history.
I could not have researched this book without the use of the Niels Bohr Library of the Center for History of Physics, at the American Institute of Physics in College Park, Maryland. Many thanks to the always helpful staff there. I am also grateful to have had easy access and helpful assistance from the Library of Congress, the libraries of the University of Maryland and George Mason University, and the Smithsonian’s Dibner Library of the History of Science and Technology at the National Museum of American History. (And thanks to Mary Jo Lazun for putting me on to that last one.)
I had an enjoyable and illuminating conversation about the EPR paper with Abner Shimony of Boston University. Ralph Cahn helped me out with some of the translation from German.
My agent, Susan Rabiner, encouraged (I might even say pushed) me to work out more clearly what this book was about before I started writing it, and without her help, as always, the project would never have got off the ground. The acute editorial eye of Charlie Conrad at Doubleday made the book slimmer, sharper, and more purposeful than it would otherwise have been. Many thanks to both.
For moral support, especially in the uncertain early stages of putting this project together, I thank Peggy Dillon.
NOTES
In these notes I have not attempted to annotate every scrap of information in the text. Details of the participants’ lives and works come generally from the works cited in the bibliography, the Dictionary of Scientific Biography edited by C. C. Gillispie being the default reference for lesser characters.
For my understanding of the emergence of quantum theory, I relied heavily on the three books by Abraham Pais cited in the bibliography. Cassidy’s biography of Heisenberg and Dresden’s of Kramers were also useful, as was the lengthy introduction by van der Waerden to his compilation of important papers. The multivolume history by Mehra and Rechenberg I made less use of, only because it goes into far more technical detail than I needed for my telling of the story.
The AHQP interviews are the invaluable oral histories recorded as part of the Archives for the History of Quantum Physics, a joint project, begun in 1960, of the American Philosophical Society and the American Physical Society. (See www.amphilsoc.org/library/guides/ahqp for more details.) I consulted transcriptions of these interviews at the Niels Bohr Library of the Center for History of Physics, at the American Institute of Physics in College Park, Maryland. Most of the AHQP interviews, even of non-native English speakers, were conducted in English, whence the occasional awkwardness of some of the phrasing.
Wherever possible I tried to find the original German sources for remarks quoted in the text, and my translations are therefore sometimes a little different from versions published elsewhere in English.
Bohr, CW, refers to Bohr, Collected Works.
1: Irritable Particles
“a walking catalogue”: Remark is by Edward Parry, a future arctic explorer, quoted by Patrick O’Brian in Joseph Banks: A Life (Chicago: University of Chicago Press, 1987), 300.
Charles Darwin, before he was married: N. Barlow, ed., The Autobiography of Charles Darwin (London: Collins, 1958), 103–4.
In June 1827, Brown began a study: I have mixed here Brown’s words and observations from his two famous papers in the Philosophical Magazine 4 (1828): 161 and 6 (1829): 161.
“The motion of most of these animalcules”: From a letter from Leeuwenhoek to Henry Oldenburg, secretary of the Royal Society, Sept. 7, 1674, in C. Dobell, ed., Antony van Leeuwenhoek and His “Little Animals” (New York: Dover, 1960), 111.
“Brown’s new thing”: George Eliot, Middlemarch, ch. 17; Nelson 2001, 9, was my source for this reference.
It’s strangely difficult: See J. Delsaulx, Monthly Microscopical Journal 18 (1877): 1; and J. Thirion, Revue des Questions Scientifiques 7 (1880): 43.
“une trépidation constante et caractéristique”: L.-G. Gouy, Comptes Rendus 109 (1889): 102.
2: Entropy Strives Toward a Maximum
“this phenomenon seems to have barely attracted”: L.-G. Gouy, Comptes Rendus 109 (1889): 102.
“We may regard the present state”: Laplace’s famous statement, from his 1812 Théorie Analytique des Probabilités, can be found in J. H. Weaver, ed., The World of Physics (New York: Simon & Schuster, 1987), vol. 1, 582.
“The observed motions of very small particles”: Lindley, 212; the remark is from Boltzmann’s reply to criticism by E. Zermelo.
“it is possible that the motions to be discussed here”: A. Einstein, Annalen der Physik 17 (1905): 549.
“the scientific synthesis commonly called Unity”: Adams, 431.
3: An Enigma, a Subject of Profound Astonishmentd
“but Radium denied its God”: Adams, 381.
“Radioactivity is an atomic property”: Pais 1986, 55, quoting an 1898 paper by the Curies and G. Bémont.
“The spontaneity of the radiation is an enigma”: Quinn, 159, quoting the Curies’ report to the International Congress, Paris, 1900.
“I have never had a student with more enthusiasm”: From the Rutherford collection at Cambridge University Library, MS. Add. 7653:PA.296.
What Rutherford and Soddy proposed: E. Rutherford and F. Soddy, Philosophical Magazine 4 (1902): 370 and 569.
The atom might have internal components: A. Debierne, Annales de Physique 4 (1915): 323; a similar proposal is by F. A. Lindemann, Philosophical Magazine 30 (1915): 560.
4: How Does an Electron Decide?
Thinking hard, his features slack: J. Franck AHQP interview.
Bohr had difficulty with English manners: Sources for Bohr’s time at Cambridge are the AHQP interviews with Niels and Margrethe Bohr; Bohr’s letters in Bohr, CW, vol. 1; and Pais 1986, 194–95.
“quite the most incredible event in my life”: E. de Andrade, Rutherford and the Nature of the Atom (New York: Doubleday, 1964), 11. These much-cited words are said to be from a lecture by Rutherford, but no further details are given. Eve, 197, has Rutherford making a comparison to a rifle bullet bouncing off a sheet of paper.
the idea of energy quanta: Bohr AHQP interview.
“no attempt at a mechanical foundation”: Bohr, CW, vol. 2, 136.
“Yes, I have looked at it”: Lord Rayleigh’s remark to his son, R. J. Strutt, given by Strutt, Life of John William Strutt, Third Baron
Rayleigh (Madison: University of Wisconsin Press, 1968), 357.
“There appears to me one grave difficulty”: Rutherford to Bohr, March 20, 1913, Bohr, CW, vol. 2, 583.
“The statistical law is nothing but the Rutherford law of radioactive decay”: Pais 1991, 191, quoting a 1916 paper by Einstein. The simple thought experiment analyzed here by Einstein was remarkably productive. In this paper he also proved that as well as spontaneous emission of light by atoms in excited states, there must be a process of so-called stimulated emission, in which the probability for an atom to emit a quantum of light is enhanced by the external presence of radiation of the same frequency. This observation, half a century later, became the theoretical basis for masers and lasers.
“That business about causality”: Einstein to Born, Jan. 27, 1920, Born, Born, and Einstein, Briefwechsel.
5: An Audacity Unheard Of in Earlier Times
“randomly chosen numbers”: Harald to Niels Bohr, autumn 1913, Boh
r, CW, vol. 1, 567.
“all nonsense…just a cheap excuse”: This and Born’s remark are from Landé’s AHQP interview.
“unquestionably a great achievement”: Sommerfeld to Bohr, Oct. 4, 1913, Bohr, CW, vol. 2, 603.
“It is the custom in Germany”: Pais 1991, 165, from a 1961 interview not in the AHQP collection.
“Bohr confirmed to me”: Heisenberg 1989, 40.
“I do not believe I have ever read anything with more joy”: Bohr to Sommerfeld, March 19, 1916, Bohr, CW, vol. 2, 603.
“almost like a second father”: Rutherford Memorial Lecture 1958, Bohr, CW, vol. 10, 415.
“I am at present myself most optimistic”: Bohr to Rutherford, Dec. 27, 1917, Bohr, CW, vol. 3, 682.
“play games with their symbols”: Eve, 304.
“as long as German science can continue in the old way”: Heilbron, 88.
“now work with an audacity unheard of in earlier times”: Pais 1991, 88, quoting a 1910 paper by Planck.
Robert A. Millikan carefully measured the photoelectric effect: Millikan, Physical Review 8 (1916): 355; quotations are from pp. 388 and 383, respectively.
6: Lack of Knowledge Is No Guarantee of Success
“a stronger personality than was the Catholic priest”: Von Meyenn and Shucking; remark is from a letter from Pauli to Carl Jung, March 31, 1953.
Pauli wanted to hew strictly to the experimental data: Heisenberg AHQP interview.
“conscience of physics”: This was a widely known sobriquet for Pauli, mentioned by Enz and many others. I haven’t been able to pin down who said it first.
“Munich was in a state of utter confusion”: Heisenberg 1971, 8.
“a downright amazing specimen”: Sommerfeld to J. von Gietler, Jan. 14, 1919; quoted by Enz, 49.
“What we are listening to nowadays”: Sommerfeld’s preface to the first edition of his Atombau und Spektrallinien (Braunschweig: F. Vieweg and Sohn, 1919).
Pauli referred to Sommerfeld…as a hussar colonel: Heisenberg 1971, 24, and AHQP interview.
“A kind of market place to exchange views”: Heisenberg AHQP interview.
“it’s much easier to find one’s way”: Heisenberg 1971, 26.
“My original wish to study mathematics”: Heisenberg 1989, 108.
“if someone were to say that I had not been a Christian”: Cassidy 1992, 13.
“when our families had long since eaten their last piece of bread”: For Heisenberg’s youthful life in Munich, see Heisenberg 1971, ch. 2, and AHQP interview.
“the cocoon in which home and school protect the young”: Heisenberg 1971, 1.
“such a temporary style of life”: From ch. 14 of Doctor Faustus, in the recent translation by John E. Woods (New York: Vintage International, 1999).
“In that case you are completely lost to mathematics”: Heisenberg 1971, 16.
“I have grasped the theory with my brain”: Heisenberg 1971, 29.
As Landé put it many years later: Landé AHQP interview.
“It works fine, but the foundation of it is quite unclear”: Sommerfeld to Einstein, Jan. 11, 1922, Einstein and Sommerfeld, Briefwechsel.
“damn it, I can see that it’s right”: Heisenberg AHQP interview.
7: How Can One Be Happy?
Einstein and Bohr subsequently exchanged little mash notes: Einstein to Bohr, May 2, 1920; Bohr to Einstein, June 20, 1920; Bohr, CW, vol. 3, 634.
“each one of his sentences revealed a long chain of underlying thoughts” and following remarks: Heisenberg 1971, 38–39.
the correspondence principle “cannot be expressed in exact quantitative laws”; Pais…comments mysteriously that “it takes artistry to make practical use of the correspondence principle.” Segrè explains that it amounted to saying, “Bohr would have proceeded in this way”: Pais 1986, 247, quoting a book by H. A. Kramers and H. Holst and following with his own remark; Segrè, 125.
“generalities and matters of taste…very interesting”: Cassidy 1992, 130; from a letter from Heisenberg to his parents.
“young Pauli is very stimulating”: Born to Einstein, Nov. 29, 1921, Born, Born, and Einstein, Briefwechsel.
“I was, from the beginning, quite crushed by him”: Born AHQP interview.
“I was so impressed by the greatness of his conception”: Born 1968, 30.
“quite different; he was like a little peasant boy when he came”: Born AHQP interview.
“I always thought mathematics was cleverer than we are”: Ibid.
“Born was very conservative in some ways”: Heisenberg AHQP interview.
“How can one be happy”: Pauli, Science 103 (1946): 213.
“some of us had begun to feel”: Heisenberg 1971, 35.
8: I Would Rather Be a Cobbler
“Dr. Nils Bohr” and subsequent comment: New York Times, Nov. 7 and 16, 1923.
“This remarkable agreement between our formulas and the experiments”: A. H. Compton, Physical Review 21 (1923): 483.
no one in Germany read the Physical Review: Heisenberg AHQP interview.
“Bohr is Allah and Kramers is his prophet”: A widely reported remark; see Enz, 36.
a story unearthed only recently: Dresden, 292.
Slater said how thrilled he was: Pais 1991, 235.
“We will assume that a given atom”: From the BKS paper, included in van der Waerden.
“utters his opinions like one perpetually groping”: Pais 1991, epigraph.
“You could never pin Bohr down”: Rosenfeld AHQP interview.
“Quite artificial”: Pauli to Bohr, Oct. 2, 1924, Bohr, CW, vol. 5,418.
“I would rather be a cobbler”: Einstein to Born, April 29, 1924, Born, Born, and Einstein, Briefwechsel.
“Can you explain to me what the BKS theory was?”: Born AHQP interview.
“It seems to me the most important question is this”: Pauli to Bohr, Feb. 21, 1924, Pauli, Briefwechsel.
9: Something Has Happened
At Heisenberg’s oral exam in July: Heisenberg AHQP interview.
Born…published a paper calling for a new system of “quantum mechanics”: The paper, titled “Quantum Mechanics,” is included in van der Waerden.
Rutherford, no lazybones, commended Bohr: Pais 1991, 261, quoting a letter from Rutherford to Bohr, July 18, 1924.
“right now physics is very confused once again”: Pauli to R. Kronig, May 21, 1925, in Pauli, Briefwechsel. Ironically, this lament from Pauli came at about the time of his most memorable achievement in physics. Thinking further on the half-quantum number that Landé and Heisenberg had devised for certain atomic transitions, Pauli concluded that it must correspond to a certain Zweideutigkeit (ambiguity or two-valuedness) in the electron itself. In effect, he proposed a fourth quantum number, intrinsic to the electron rather than a property of electron orbits, which could take one of two values. Pauli was then led to his famous exclusion principle, which states that each electron in an atom is specified by a unique combination of the four quantum numbers, so that no two electrons can occupy the same state. A little later, Pauli’s Zweideutigkeit was interpreted by S. Goudsmit and G. Uhlenbeck as the spin of the electron, which comes in half values when compared to the orbital angular momentum any electron can possess. In this tortuous way, it turns out that Heisenberg’s half quantum was not so far off the mark after all.
“Now everything is in Heisenberg’s hands”: F. C. Hoyt AHQP interview.
“was always a perfect gentleman”: Heisenberg AHQP interview.
“completely shocked…I got quite furious”: Ibid.
“Things always go very oddly with him”: Pauli to Bohr, Feb. 11, 1924, Pauli, Briefwechsel.
“The idea suggested itself”: Heisenberg 1958, 39.
“Well, something has happened”: This and other details of Heisenberg’s stay on Helgoland come mainly from his AHQP interview.
he had written what he called a “crazy paper”: This is Born’s recollection from his AHQP interview of what Heisenberg said.
“formal and feeble”: Heisenberg to Pauli, July 9, 1925, Pauli, Briefwechsel.
“looks very mystical”: Born to Einstein, July 15, 1925, Born, Born, and Einstein, Briefwechsel.
“As Kramers has perhaps told you”: Heisenberg to Bohr, Aug. 31, 1925, Bohr, CW, vol. 5, 366.
“An attempt is made to obtain foundations”: Heisenberg, Zeitschrift für Physik 33 (1925): 879, translated in van der Waerden.
“has given me new joie de vivre”: Pauli to R. Kronig, Oct. 9, 1925, Pauli, Briefwechsel.
“Heisenberg has laid a large quantum egg”: Einstein to Ehrenfest, Sept. 20, 1925, quoted by Dresden, 51.
10: The Soul of the Old System
The fog has begun to lift: Moore, 187, quotes a letter from Einstein to P. Langevin, in which he said, “Er hat eine Ecke des grossen Schleiers gelüftet,” literally, “He [de Broglie] has lifted a corner of the great veil.” But Schleier can also mean atmospheric haze, and the verb lüften is perhaps better rendered as “dispel,” hence my looser translation.
“whitecaps” of an underlying wave field: Moore, 187, quoting a 1926 paper by Schrödinger.
“a late erotic outburst in his life”: Moore, 191; the remark is by Hermann Weyl.
“the concept of your paper shows real genius” and “I am convinced that you have made a decisive advance”: Einstein to Schrödinger, April 16 and 26, 1926, Przibram.
“I know you are fond of tedious and complicated formalism”: Born 1978, 218.
“awfully clever of Heisenberg”: Born AHQP interview.
“the immediate task is to save Heisenberg’s mechanics”: Pauli to Kronig, Oct. 9, 1925, Pauli, Briefwechsel.
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