Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [117]
As soon as he arrived back in Zurich, Schrödinger recounted Bohr's 'really remarkable' approach to atomic problems in a letter to Wilhelm Wien. 'He is completely convinced that any understanding in the usual sense of the word is impossible', he told Wien. 'Therefore the conversation is almost immediately driven into philosophical questions, and soon you no longer know whether you really take the position he is attacking, or whether you really must attack the position that he is defending.'74 Yet despite their theoretical differences, Bohr and 'especially' Heisenberg had behaved 'in a touchingly kind, nice, caring and attentive manner', and all 'was totally, cloudlessly amiable and cordial'.75 Distance and a few weeks had made it seem less of an ordeal.
A week before Christmas 1926, Schrödinger and his wife travelled to America, where he had accepted an invitation from the University of Wisconsin to give a series of lectures for which he would receive the princely sum of $2,500. Afterwards he criss-crossed the country, giving nearly 50 lectures. By the time he arrived back in Zurich in April 1927, Schrödinger had turned down several job offers. He had his eye on a far greater prize, Planck's chair in Berlin.
Having been appointed in 1892, Planck was due to retire on 1 October 1927 to an emeritus professorship. Heisenberg, 24, was too young for such an elevated position. Arnold Sommerfeld had been first choice, but at 59, he decided to stay in Munich. It was now either Schrödinger or Born. Schrödinger was appointed as Planck's successor and it was the discovery of wave mechanics that had clinched it. In August 1927, Schrödinger moved to Berlin and found someone there who was just as unhappy with Born's probabilistic interpretation of the wave function as he was – Einstein.
Einstein had been the first to introduce probability into quantum physics in 1916 when he provided the explanation for the spontaneous emission of light-quanta as an electron jumped from one atomic energy level to another. Ten years later, Born had put forward an interpretation of the wave function and wave mechanics that could account for the probabilistic character of quantum jumps. It came with a price tag that Einstein did not want to pay – the renunciation of causality.
In December 1926, Einstein had expressed his growing disquiet at the rejection of causality and determinism in a letter to Born: 'Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the "old one". I, at any rate, am convinced that He is not playing at dice.'76 As the battle lines were being drawn, Einstein was unwittingly the inspiration for a stunning breakthrough, one of the greatest and profoundest achievements in the history of the quantum – the uncertainty principle.
Chapter 10
UNCERTAINTY IN COPENHAGEN
As Werner Heisenberg stood in front of the blackboard, with his notes spread out on the table before him, he was nervous. The brilliant 25-year-old physicist had every reason to be. It was Wednesday, 28 April 1926, and he was about to deliver a lecture on matrix mechanics to the famed physics colloquium at Berlin University. Whatever the merits of Munich or Göttingen, it was Berlin that Heisenberg rightly called 'the stronghold of physics in Germany'.1 His eyes scanned the faces in the audience and settled on four men sitting in the front row, each with a Nobel Prize to his name: Max von Laue, Walter Nernst, Max Planck, and Albert Einstein.
Any nerves at this 'first chance to meet so many famous men' quickly subsided as Heisenberg, by his own reckoning, presented 'a clear account of the concepts