Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [129]
In the middle of April 1927, as he worked on formulating a consistent interpretation of quantum mechanics within the conceptual framework provided by complementarity, Bohr sent a copy of the uncertainty paper to Einstein at Heisenberg's request. In the accompanying letter he wrote that it was a 'very important contribution to the discussion of the general problems of quantum theory'.71 In spite of their ongoing and often heated arguments, Bohr informed Einstein that 'Heisenberg shows in an exceedingly brilliant manner how his uncertainty relations may be utilized not only in the actual development of quantum theory, but also for the judgement of its visualizable content'.72 He went on to outline some of his own emerging ideas that would throw light on 'the difficulties of the quantum theory [that] are connected with the concepts, or rather with the words that are used in the customary description of nature, and which always have their origin in the classical theories'.73 Einstein, for some unknown reason, chose not to reply.
If he was hoping to elicit a response from Einstein, then Heisenberg must have been disappointed when he returned to Copenhagen after spending Easter in Munich. It was a much-needed break from the constant pressure to yield to Bohr's interpretation. 'So I have come to be in a fight for the matrices and against the waves', Heisenberg wrote to Pauli on 31 May, the very day his 27-page paper appeared in print. 'In the ardour of this struggle I have often criticized Bohr's objections to my work too sharply and, without realizing or intending it, have in this way personally wounded him. When I now reflect on these discussions, I can very well understand that Bohr was angry about them.'74 The reason for such contrition was that two weeks earlier, he had finally admitted to Pauli that Bohr was right.
The scattering of gamma rays into the aperture of the hypothetical microscope was the basis of the uncertainty relation for momentum and position. 'Thus the relation pqh indeed comes out naturally, but not entirely as I had thought.'75 Heisenberg went on to concede that 'certain points' were easier to handle using Schrödinger's wave description, but he remained utterly convinced that in quantum physics 'only discontinuities are interesting' and they could never be emphasised enough. It was still not too late to withdraw the paper, but it was a step too far. 'All results of the paper are correct after all,' he told Pauli, 'and I am also in agreement with Bohr concerning these.'76
As a compromise, Heisenberg added a postscript. 'After the conclusion of the foregoing paper,' it began, 'more recent investigations of Bohr have led to a point of view which permits an essential deepening and sharpening of the analysis of quantum-mechanical correlations attempted in this work.'77 Heisenberg acknowledged that Bohr had brought to his attention crucial points that he had overlooked – uncertainty was a consequence of wave-particle duality. He closed by thanking Bohr, and with the publication of the paper, months of wrangling and 'gross personal misunderstandings', though not entirely forgotten, were firmly pushed aside.78 Whatever their differences, as Heisenberg said later, 'all that mattered now was to present the facts in such a way that despite their novelty they could be grasped and accepted by all physicists'.79
'I am very ashamed to have given the impression of being quite ungrateful', Heisenberg wrote to Bohr in the middle of June, not long after Pauli had visited Copenhagen.80 Two months later, still full of remorse, he explained to Bohr how he reflected 'almost every day on how that came about and am ashamed that it could not have gone otherwise'.81 Future job prospects had been a major determining factor in the rush to publish. When he turned down the Leipzig professorship in favour of Copenhagen, Heisenberg was certain that if he continued producing 'good papers',