(1900-1958) Austrian-born Swiss Theoretical Physicist, Quantum Theorist, Particle Physicist
Wolfgang Pauli was one of the pioneering generation of 20th-century physicists who discovered and refined the basic principles of atomic behavior as revealed by the laws of quantum mechanics. His most far-reaching contributions flowed from his insight that no two electrons in an atom can occupy the same energy state. Enunciated in 1925, the Pauli exclusion principle, as it came to be called, explained numerous phenomena on both the atomic and nuclear levels and garnered Pauli the 1945 Nobel Prize in physics. He is also famous for his 1930 prediction of the existence of the neutrino, a particle without charge or mass, which was discovered almost 30 years later.
Wolfgang Pauli was born in Vienna on April 25, 1900. His father, a physician and professor of chemistry at the University of Vienna, was of Jewish origin but had his son baptized a Catholic. His godfather was the famous Austrian physicist ernst mach. A precocious high school student in Vienna, Wolfgang entered the University of Munich in 1918, having already mastered both special and general relativity. Encouraged by his professor, the eminent arnold johannes wilhelm sommerfeld, Pauli wrote the first comprehensive monograph on the subject, a 200-page work, which prompted albert einstein himself to observe, “Whoever studies this mature and grandly conceived work might not believe that its author is a twenty-one year old man.” The Munich years were formative for Pauli. It was then that he was exposed to ideas far stranger than those he had found in Einstein’s work. As he would later recall, “I was not spared the shock, which every physicist accustomed to the classical way of thinking experienced when he came to know Niels Bohr’s basic postulate of quantum theory for the first time.”
He formed a lifelong friendship with werner heisenberg, whose uncertainty principle would add the notion of nondeterminacy to the startling picture of nature emerging from quantum mechanics in the 1920s. Their long and copious correspondence would later be published, providing a wealth of insights into one of the most exciting periods in the history of physics. Pauli received a doctorate in 1922 for a thesis, supervised by Sommerfeld, on the quantum theory of ionized molecular hydrogen.
That same year he went to Gottingen as an assistant to max born but soon moved to Copenhagen to study with niels henrik david bohr; there he began, in his own words, “a new phase of my scientific life.” When he returned to Germany in 1923, accepting a position at the University of Hamburg as a lecturer, his exposure to Bohr’s work on the structure of the atom and the problems that work was encountering had become the focus of his research.
Bohr’s model of the atom, modified by Som-merfeld, proposed that the electrons of an atom are arranged in groups, which have different mean distances from the nucleus and are each characterized by three quantum numbers, which describe the rotation of the electron around the nucleus. Problems with the model arose when these numbers failed to account for magnetic anomalies in matter. Pauli solved the problem by adding a fourth quantum number to the three already in use (n, l, and m). This number, s, would represent the electron’s rotation around an axis through its own center of gravity, what came to be called spin, and would have two possible values: +1/2 or -1/2. Building on this hypothesis, in 1925, he enunciated his Pauli exclusion principle, which stated that no two electrons in the same atom could have the same values for their four quantum numbers. One of these quantum numbers describes one of the two possible directions for the electron’s intrinsic spin. Thus, two electrons that are in the same energy level as described by the other three quantum numbers are differentiated from each other because they have opposite spins. The exclusion principle proved essential not only in explaining atomic structure: by uncovering the significance of ordering elements by their atomic number, it provided an explanation for the periodic table of the elements.
Pauli’s important work led to his appointment, in 1928, as professor of experimental physics at the Federal Institute of Technology, Zurich, a position he would hold for the rest of his life. During the years before World War II, Pauli developed the institute into a vibrant international center for physical research. At the beginning of his Zurich years he made another major contribution in his prediction of a new elementary particle: the neutrino. Pauli’s hypothetical particle was offered as a solution to the dilemma posed by the observation that electrons appeared to be emitted in a continuous stream whereas theory called for a discontinuous spectrum. Pauli accounted for this discrepancy by proposing that the emission of an electron in beta decay is accompanied by the production of an unknown particle. Because Pauli’s particle had neither charge nor mass, the model explained why it had never been detected. It was enrico fermi who in 1934 confirmed Pauli’s view and dubbed the new particle the neutrino. Two years before Pauli’s premature death, on December 15, 1958, in Zurich, his prediction was experimentally validated by the American physicists frederick reines and Clyde L. Cowan, who recognized neutrinos by their impact with sub-nuclear particles in mineral water.
Wolfgang Pauli discovered the fact that no two electrons in an atom can occupy the same energy state. Known as the Pauli exclusion principle, it explained numerous phenomena on both the atomic and the nuclear level.
Pauli left Europe when hostilities broke out and spent the war years in the United States, at the Institute for Advanced Study, Princeton. He acquired both Swiss and U.S. citizenship and spent his later years in Princeton and in Zurich.
An intuitively gifted scientist, universally respected by colleagues such as Bohr and Heisen-berg, who relied on his advice, Pauli was also a lifelong student of the great Swiss psychoanalyst Carl Gustav Jung. When his brief first marriage failed in 1929, Pauli underwent analysis with Jung and later continued corresponding with him. In 1952, Jung and Pauli coauthored The Explanation of Nature and the Psyche, which discusses the influence of Jungian archetypes on the work of the great astronomer Johannes Kepler.
