SCHUCKING AND VON MEYENN REPLY: Yes, indeed, it was at the Solvay Conference in 1930 that Bohr reminded Einstein of his elevator. How the wrong date crept into our manuscript baffles us still.
Kurt Gottfried is surprised that Pauli thought of Dirac as a formalist. Dirac was a formalist. He wrote in 1931: “The most powerful method of advance that can be suggested at present is to employ all the resources of pure mathematics in attempts to perfect and generalize the mathematical formalism that forms the existing basis of theoretical physics, and after each success in this direction, to try to interpret the new mathematical features in terms of physical entities.” 1
We disagree with Gottfried’s characterization of the Pauli equation for the electron as merely an elegant restatement of a Heisenberg–Jordan paper. Paul Ehrenfest wrote on 25 March 1931 about the Pauli equation: “This work has become very important. It has opened the way to Dirac’s ingenious work on the spin-electrons and probably also to Heisenberg’s famous work about the helium spectrum.” 2 Pauli introduced spinors into quantum mechanics and thus—in hindsight—made the step from two to four components not such a giant leap.
We agree with Gottfried that the golden rule 3 is due to Dirac. When Pauli derived this equation using Dirac’s time-dependent perturbation theory, he analyzed its domain of validity using the uncertainty relation for time and energy that he had first pointed out in a letter to Heisenberg. Apparently, Pauli and Heisenberg 4 had first thought that Dirac had “gemogelt” (cheated) in its derivation.
We both cherish Dirac’s beautiful physics, but his approach to theory was different from Pauli’s or Heisenberg’s. By praising Galileo, one does not demean Kepler.
On Dirac’s comment about Schrödinger, we stand corrected. Luis Boya also may have a point on vacuum degeneracy. But Pauli’s crucial role in the Heisenberg theory still needs clarification. There are 144 letters from the correspondence between Pauli and Heisenberg in 1957 and 1958, up to 30 pages in length, which still await analysis.
With regard to the early history of quantum field theory, we agree that much more could be said about it, and we refer Boya to Tian Yu Cao. 5 For the history of nuclear magnetism, we suggest that Boya might consult Hendrik Casimir. 6
Boya remarks that Heisenberg “never tried using his newborn matrix mechanics to solve for the hydrogen spectrum.” On 3 November 1925 Heisenberg wrote to Pauli: “After your first letter, I had also tried at once the calculation in three dimensions and was busy just this afternoon with the evaluation of the last equations and the elimination of the many possible mistakes in calculation when the postman entered and made my work superfluous.” 7 The postman had brought Pauli’s three-dimensional calculation for the H-atom. We believe that Boya underrates the role Pauli played in the dialogue with Heisenberg and that a careful reading of their correspondence supports our view. Freeman Dyson, with his unique insight into physics and the ways of physicists seems to agree with our assessment.
Finally, we thank Gottfried, Boya, and Dyson for their comments.
