# Wolfgang Pauli

## (1900 - 1958)

Pauli was born in Vienna, Austria on August 25, 1900. Pauli attended the Döblinger Gymnasium in Vienna, graduating with distinction in 1918. Only two months after graduation, he published his first paper, on Einstein's theory of general relativity.

He attended the Ludwig-Maximilian University of Munich, where he received his doctorate in July 1921 for a thesis on the quantum theory of ionised molecular hydrogen. During his time at the University of Munich, Pauli was requested to review relativity for the *Encyklopaedie der mathematischen Wissenschaften*, a German encyclopedia. It was praised by Einstein; published as a monograph, it remains a standard reference on the subject to this day.

He spent a year at the University of Göttingen as the assistant to Max Born (Nobel Prize recipient in 1954), and the following year at what became the Niels Bohr Institute for Theoretical Physics in Copenhagen. From 1923 to 1928, he was a lecturer at the University of Hamburg. During this period, Pauli was instrumental in the development of the modern theory of quantum mechanics. In particular, he formulated the exclusion principle and the theory of nonrelativistic spin.

In 1928, he was appointed Professor of Theoretical Physics at the Federal Institute of Technology in Zurich, Switzerland. He held visiting professorships at the University of Michigan in 1931, and the Institute for Advanced Study at Princeton in 1935.

The German annexation of Austria in 1938 made Pauli a German citizen, which became a difficulty with the outbreak of the Second World War in 1939. Pauli moved to the United States in 1940, where he was Professor of Theoretical Physics at Princeton. After the war, Pauli became a naturalized citizen of the United States in 1946 before returning to Zurich, where he remained for the rest of his life.

In 1945, Pauli received the Nobel Prize in Physics for his "decisive contribution through his discovery in 1925 of a new law of Nature, the exclusion principle or Pauli principle." He had been nominated for the prize by Einstein.

In 1958, Pauli was awarded the Max Planck medal. In that same year, he fell ill with pancreatic cancer. Pauli died on December 15, 1958.

### Scientific Career

Pauli made many important contributions in his career as a physicist, primarily in the subject of quantum mechanics. He seldom published papers, preferring lengthy correspondences with colleagues (such as Bohr and Heisenberg, with whom he had close friendships.) Many of his ideas and results were never published and appeared only in his letters, which were often copied and circulated by their recipients. Pauli was apparently unconcerned that much of his work thus went uncredited. The following are the most important results for which he has been credited:

In 1924, Pauli proposed a new quantum degree of freedom to resolve inconsistencies between observed molecular spectra and the developing theory of quantum mechanics. He formulated the Pauli exclusion principle, perhaps his most important work, which stated that no two electrons could exist in the same quantum state. Uhlenbeck and Goudsmit later identified this degree of freedom as electron spin.

In 1926, shortly after Heisenberg published the matrix theory of modern quantum mechanics, Pauli used it to derive the observed spectrum of the hydrogen atom. This result was important in securing credibility for Heisenberg's theory.

In 1927, he introduced the Pauli matrices as a basis of spin operators, thus solving the nonrelativistic theory of spin. This work influenced Dirac in his discovery of the Dirac equation for the relativistic electron.

In 1930, he proposed the existence of a hitherto unobserved neutral and massless particle, in order to explain the continuous spectrum of beta decay. In 1934, Fermi incorporated the particle, which he called a neutrino, into his theory of radioactive decay. The neutrino was first observed experimentally in 1959.

In 1940, he proved the spin-statistics theorem, a critical result of quantum mechanics which states that particles with half-integer spin are fermions, while particles with integer spin are bosons.

**Sources:** Wikipedia. Picture courtesy of: Fermi National Accelerator Laboratory