Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [72]
At the heart of his approach lay Bohr's belief that quantum rules apply on the atomic scale, but any conclusion drawn from them must not conflict with observations made on the macroscopic scale where classical physics rules. Calling it the 'correspondence principle' allowed him to eliminate ideas on the atomic scale that when extrapolated did not correspond to results that were known to be correct in classical physics. Since 1913 the correspondence principle had helped Bohr bridge the divide between quantum and classical. Some viewed it as a 'magic wand, which did not act outside Copenhagen', recalled Bohr's assistant Hendrik Kramers.80 Others might have struggled to wave it, but Einstein recognised a fellow sorcerer at work.
Whatever reservations there might have been at the lack of hard mathematics to underpin Bohr's theory of the periodic table, everyone had been impressed by the Dane's latest ideas and gained a greater appreciation of the problems that remained. 'My entire stay in Göttingen was a wonderful and instructive experience for me,' Bohr wrote on his return to Copenhagen, 'and I cannot say how happy I was for all the friendship shown me by everybody.'81 He was no longer feeling under-appreciated and isolated. Later that year there was further confirmation, if he needed it.
As the telegrams of congratulation landed on Bohr's desk in Copenhagen, none meant more to him than the one from Cambridge. 'We are delighted that you have been awarded the Nobel Prize', Rutherford wrote. 'I knew it was merely a question of time, but there is nothing like the accomplished fact. It is well merited recognition of your great work and everybody here is delighted in the news.'82 In the days that followed the announcement, Rutherford had never been far from Bohr's thoughts. 'I have felt so strongly how much I owe you,' he told his old mentor, 'not only for your direct influence on my work and your inspiration, but also for your friendship in these twelve years since I had the great fortune of meeting you for the first time in Manchester.'83
The other person Bohr could not help thinking about was Einstein. He was delighted and relieved that the day he received the 1922 prize, Einstein had been awarded the Nobel Prize for 1921 that had been deferred for a year. 'I know how little I have deserved it,' he wrote to Einstein, 'but I should like to say that I consider it a good fortune that your fundamental contribution in the special area in which I work as well as contributions by Rutherford and Planck should be recognized before I was considered for such an honour.'84
Einstein was on a ship bound for the other side of the world when the Nobel Prize winners were announced. On 8 October, still fearing for his safety, Einstein and Elsa had left for a lecture tour of Japan. He 'welcomed the opportunity of a long absence from Germany, which took me away from temporarily increased danger'.85 He did not return to Berlin until February 1923. The original six-week itinerary turned into a grand tour lasting five months, during which he had received Bohr's letter. He replied during the voyage home: 'I can say without exaggeration that [your letter] pleased me as much as the Nobel Prize. I find especially charming your fear that you might have received the award before me – that is typically Bohr-like.'86
A blanket of snow covered the Swedish capital on 10 December 1922 as the invited guests assembled in the Great Hall of the Academy of Music in Stockholm to watch the presentation of the Nobel Prizes. The ceremony began at five o'clock in the presence of King Gustav V. The German ambassador to Sweden received the prize on behalf of the absent Einstein, but only after winning a diplomatic argument with the Swiss over the physicist's nationality. The Swiss were claiming Einstein as one of their own, until the Germans discovered that by accepting the appointment at the Prussian Academy in 1914 Einstein had automatically become a German