Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [94]
In the middle of writing his dazzling review of relativity, it was Pauli who steered Heisenberg away from Einstein's theory and towards the quantum atom as a more fertile area of research in which to make his name. 'In atomic physics we still have a wealth of uninterpreted experimental results,' he told Heisenberg; 'nature's evidence in one place seems to contradict that in another, and so far it has not been possible to draw an even halfway coherent picture of the relationship involved.'10 It was likely, thought Pauli, that everyone would still be 'groping about in a thick mist' for years to come.11 As Heisenberg listened, he was inexorably drawn into the realm of the quantum.
Sommerfeld soon assigned Heisenberg a 'little problem' in atomic physics. He asked him to analyse some new data on the splitting of spectral lines in a magnetic field and to construct a formula that replicated the splitting. Pauli warned Heisenberg that Sommerfeld hoped that deciphering such data would lead to new laws. It was an attitude that for Pauli bordered on 'a kind of number mysticism', but then he admitted, 'no one has been able to suggest anything better'.12 The exclusion principle and electron spin still lay in the future.
Heisenberg's ignorance of the accepted rules and regulations of quantum physics allowed him to tread where others, wedded to a more cautious and rational approach, feared to. It enabled him to construct a theory that appeared to explain the anomalous Zeeman effect. Having dismissed an earlier version, Heisenberg was relieved when Sommerfeld sanctioned the publication of his latest effort. Although it was later shown to be incorrect, his first scientific paper brought Heisenberg to the attention of Europe's leading physicists. Bohr was one of those who sat up and took notice.
They first met in Göttingen in June 1922 when Sommerfeld took some of his students to hear Bohr's series of lectures on atomic physics. What struck Heisenberg was how precise Bohr was in his choice of words: 'Each one of his carefully formulated sentences revealed a long chain of underlying thoughts, of philosophical reflections, hinted at but never fully expressed.'13 He was not alone in sensing that Bohr reached his conclusions more by intuition and inspiration than by detailed calculations. At the end of the third lecture, Heisenberg rose to point out some difficulties that remained in a published paper that Bohr had praised. As people began to mingle after the question-and-answer session, Bohr sought out Heisenberg and asked the twenty-year-old if he would like to accompany him on a walk later that day. Their hike to a nearby mountain lasted some three hours, and Heisenberg later wrote 'that my real scientific career only started that afternoon'.14 For the first time, he saw 'that one of the founders of quantum theory was deeply worried by its difficulties'.15 When Bohr invited him to Copenhagen for a term, Heisenberg suddenly saw his future as one 'full of hope and new possibilities'.16
Copenhagen would have to wait. Sommerfeld was due to go to America and in his absence had arranged for Heisenberg to study with Max Born in Göttingen. Although he looked 'like a simple farm boy, with short fair hair, clear bright eyes, and a charming expression', Born quickly discovered that there was much more to him than met the eye.17 He was 'easily as gifted as Pauli', Born wrote to Einstein.18 When he returned to Munich, Heisenberg finished his doctoral thesis on turbulence. Sommerfeld had chosen the topic to broaden his knowledge and understanding of physics. During the oral examination his inability to answer simple questions, such as the resolving power of a telescope, almost cost him his doctorate.