Wolfgang Pauli

In 1925 Pauli formulated the exclusion principle: no two electrons in an atom can have identical sets of quantum numbers, a rule that needed a new, two-valued quantum number and explains the shell structure of atoms. The Nobel Foundation awarded him the 1945 Nobel Prize in Physics 'for the discovery of the Exclusion Principle', and an Oxford physicist calls the rule crucial to understanding both the periodic table and the stability of matter, although Pauli himself admitted he could not say why it holds.

In December 1930, in an open letter 'Dear Radioactive Ladies and Gentlemen' to physicists meeting in Tübingen, Pauli proposed a 'desperate remedy' for the continuous energy spectrum of beta decay: an electrically neutral particle of spin 1/2 emitted along with the electron, which would save the conservation of energy. The Nobel Foundation's biography calls him the first to recognise the neutrino, as the particle came to be called; he held back a published account for about three years, and neutrinos were detected in 1956 by Cowan and Reines.

Pauli gave the mathematical description of electron spin in the Pauli matrices, which one reviewer says every physics undergraduate knows, and proved the relation between spin and statistics, which consolidated quantum field theory. As a student he wrote an exposition of relativity that Einstein praised in a review, and from 1928 he built at ETH Zürich one of the leading centres of theoretical physics in the world.

In December 1930 Pauli put forward the neutrino idea not in a journal but in a letter to the experimentalists meeting in Tübingen. He wrote that so far he did not dare to publish anything about it, admitted that his remedy 'may seem almost improbable', and asked them to 'scrutinize and judge'. About three years passed before the speculation appeared in print.

This is consistent with a theorist who held an unfinished idea back until others had tested it, though the letter is Pauli's own account and the three-year delay is a reviewer's reading. Perfectionism

On 17 January 1957 Pauli wrote that he did not believe 'God is a weak left-hander' and was prepared to bet a high amount that the beta-decay experiment would show a symmetric angular distribution of the electrons. Then John Blatt wrote him of the 'sudden death of parity'; on 19 January Pauli wrote to Chien-Shiung Wu that the asymmetry was 'empirically so well established', and on 27-28 January he told Victor Weisskopf that he was shocked and was already speculating on how symmetry might be restored.

This is consistent with a theorist who held a firm expectation but accepted the experimental result within days, though he went on looking for a way to restore the symmetry, and the account rests on one scholar's reading of his letters. Belief Updating

Before accepting the ETH Zürich chair, which he took up at the end of April 1928, Pauli insisted on an assistant and wrote to Ralph Kronig that the task would be 'Every time I say something, to contradict me with detailed arguments' and to animate the scientific activity with modern ideas. At Zürich he built one of the world's leading centres of theoretical physics, and a graduate student of the early 1950s remembered witnessing his strong objections at a colloquium.

This is consistent with a physicist who built disagreement into his working environment, though he was also known for sharp objections that some listeners found daunting. Conflict Tolerance