Wolfgang Pauli




AMERICAN THEORETICAL PHYSICIST
1900–1958

Wolfgang Ernst Pauli was born in Vienna, Austria, where his father, regarded as one of the founders of colloid chemistry, was employed at the University of Vienna. His godfather was Ernst Mach, a famous physicist, philosopher, and one of the founders of logical positivism; he had a significant influence on Pauli's thinking. In high school Pauli was an outstanding student with a special talent for mathematics and physics. His parents fostered Pauli's appetite for science by hiring a private tutor. The tutor was so successful that within twelve months of beginning his studies at the University of Munich in 1918, Pauli had submitted three original papers on the theory of relativity to a leading physics periodical; all were published before his twentieth birthday.

Pauli received his doctorate in 1921 for theoretical work on the hydrogen molecule ion. He then became an assistant to Max Born at Göttingen. While at Göttingen, Pauli met Niels Bohr, who invited him to work for a year with his group in Copenhagen, Denmark. Once there, Pauli began work on the problem of the anomalous Zeeman effect (how the energy levels of a multielectron atom are split in a magnetic field), work that he continued when in 1923 he moved to a new position at the University of Hamburg. By 1924 he had decided that the current model of atomic structure used by Bohr, which assumed only two numbers and which allowed many electrons to have identical quantum numbers, needed to be modified. He also found that the currently accepted idea that it was the magnetic moment of the core of the atom that was responsible for the splitting of the electron energy levels of the outer electrons, was incorrect. Instead, Pauli proposed a new model that had as its consequence his famous exclusion principle .

The new model had its origins in a new classification of electron levels published in 1924 by Edmond C. Stoner, an English physicist at the University of Leeds who was an expert on the magnetic properties of matter. This classification divides the electrons of an atom into electronic shells using three quantum numbers (n, k1, k2). The first two number are the same as those used by Bohr, and the third one, the inner quantum number k2, was chosen so that twice the sum of the individual k2 numbers became the number of electrons in a subgroup. It was Pauli's genius that allowed him to extend this classification by adding a fourth quantum number (m1), which could have only two values (+1/2 and −1/2). As a result, Pauli was able in 1925 to arrive at the first statement of his exclusion principle, that stated that there cannot be two or more equivalent electrons in an atom for which in strong fields the values of all quantum numbers n, k1, k2, and m1 are the same. Initially, Pauli rejected the notion that the two-valuedness of m1 was due to spin, but after discussing the matter of electron spin with fellow physicists Samuel Goudsmit and George Uhlenbeck, he accepted the idea. The term "exclusion principle" had its origin in Pauli's insistence on each electron having a unique set of quantum numbers. This requirement immediately solved many problems in the interpretation of observed atomic spectra, because it prevented many lines that, according to prior theories, should be seen but never were, to become forbidden.

In 1928 Pauli became professor of theoretical physics at the Federal Institute of Technology, Zurich; largely through his efforts it became a leading center for research in theoretical physics. In 1931 he observed that when an electron was emitted from a nucleus, a loss of energy occurred that could not be explained by then-current theories. He proposed that it was due to the existence of another particle which carried no charge and had very low mass. The American physicist Enrico Fermi named this particle the "neutrino"; it was eventually discovered some twenty-five years later.

During World War II Pauli worked at the Institute for Advanced Studies at Princeton in New Jersey; he then returned to Zurich, where he died in 1958.

SEE ALSO Bohr, Niels ; Fermi, Enrico .

John E. Bloor

Bibliography

McMurray, Emily J., ed. (1995). Notable Twentieth-Century Scientists. Detroit: Gale Research.

Peierls, Rudolf E. (1959). "Wolfgang Ernst Pauli." In Biographical Memoirs of Fellows of the Royal Society, Vol. 5, pp. 175–192. London: Royal Society.

Internet Resources

"Wolfgang Pauli and Modern Physics." Available from http://www.ethbib.ethz.ch/exhibit/pauli .



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