The German Genius

Research Council, but Germany and Austria were excluded. Not until 1925 and the Locarno Pact was this rule relaxed but even then German and Austrian scientists turned down the olive branch. The frost existed on more informal levels too—Germans were banned from international science conferences, they were not offered visiting fellowships, and their research was not incorporated into the leading journals. Notably, the Solvay Conferences of physicists were without German participation until 1923. 1
    At much the same time, a new organization was established in the Weimar Republic, the Assistance Fund for German Science, which brought together the universities, the academies, and the Kaiser Wilhelm Societies. While the financial and organizational situation thus slowly improved, problems began to emerge at more personal levels. Einstein began to experience anti-Semitism and he was not the only one. Richard Willstätter had won the Nobel Prize for Chemistry in 1920 for his work on the understanding of chlorophyll but, before that, in World War I, he had invented a triple-layered gas-mask, and as a result had been awarded the Iron Cross. Yet he found Munich, where he was professor, so anti-Semitic that in 1924 he resigned his position. 2
    Out of this unenviable situation, however, something rather striking occurred. The period between 1919 and 1932 would become the golden age of physics, particularly theoretical physics, and although it was very much an international effort, the centers of gravity in those years were three institutes, in Copenhagen, Göttingen, and Munich.
    Niels Bohr’s Institute of Theoretical Physics had opened in Copenhagen in January 1921, quickly followed, in 1922, by the award of a Nobel Prize. Just before World War I, Bohr had explained how electrons orbit the nucleus only in certain formations, which married atomic structure to Max Planck’s notion of quanta. But, in the same year that he was awarded the Nobel Prize, Bohr also explained the fundamental links between physics and chemistry, showing that successive orbital shells could contain only a precise number of electrons, and introduced the idea that elements that behave in a similar way chemically do so because they have a similar arrangement of electrons in their outer shells, which are the ones most used in chemical reactions.
    T HE A DVENT OF Q UANTUM W EIRDNESS
     
    One of the international galaxy of physicists who studied at Copenhagen was the Swiss-Austrian Wolfgang Pauli. In 1924 Pauli was a pudgy twenty-three-year-old, prone to depression when scientific problems defeated him. One problem in particular had set him prowling the streets of the Danish capital. 3 It arose from the fact that no one just then understood why all the electrons in orbit around the nucleus didn’t just crowd in on the inner shell. This is what should have happened, with the electrons emitting energy in the form of light. What was known by now, however, was that each shell of electrons is arranged so that the inner shell always contains just one orbit, whereas the next shell out contains four. Pauli’s contribution was to show that no orbit could contain more than two electrons. Once it had two, an orbit was “full,” and other electrons were excluded, forced to the next orbit out. This meant that the inner shell (one orbit) could not contain more than two electrons, and that the next shell out (four orbits) could not contain more than eight. This became known as Pauli’s exclusion principle, and part of its beauty lay in the way it expanded Bohr’s explanation of chemical behavior. Hydrogen, for example, with one electron in the first orbit, is chemically active. Helium, however, with two electrons in the first orbit, is virtually inert (i.e., that orbit is “full” or “complete”).
    The next year, 1925, the center of activity moved for a time to Göttingen. Before World War I, British and American students regularly went to Germany to complete their studies, and Göttingen was a frequent stopping-off place. Bohr gave a lecture there in 1922 and was taken to task by a young student who corrected a point in his argument. Bohr, being Bohr, hadn’t minded. “At the end of the discussion,” said Werner Heisenberg later, “he came over to me and asked me to join him that afternoon on a walk over the Hain Mountain.” 4 It was more than a stroll, for Bohr invited the young Bavarian to Copenhagen where they set about tackling yet another problem of