Wolfgang Pauli

Austrian-born Swiss physicist

• Born: April 25, 1900; Vienna, Austria-Hungary
• Died: December 15, 1958; Zurich, Switzerland

Pauli’s discovery of the exclusion principle, which asserts the individuality of electrons, revolutionized atomic physics. He is also responsible for the electron theory of metals, which led to the development of transistors, and for proposing the existence of neutrinos.

Primary field: Physics

Specialty: Theoretical physics

Early Life

Wolfgang Ernst Pauli was born in Vienna, Austria-Hungary. His father, also named Wolfgang, was a distinguished professor of colloid physics at the University of Vienna. Although Pauli received his formal education in the Viennese school system, he was also informally instructed by his father. Pauli proved to be proficient in higher mathematics. Inspired by Albert Einstein’s theory of relativity, he studied classical physics in preparation for a career as a physicist.

When he was nineteen, Pauli enrolled at the University of Munich. His mentor at this time was Arnold Sommerfeld, the most prestigious teacher of theoretical physics in Germany. Under Sommerfeld’s supervision, Pauli acquired the analytical skills that he was to put to good use years later. At the age of twenty, Pauli was assigned the task of submitting an article on relativity theory for the Encyklopädie der mathematischen Wissenschaften (Encyclopedia of mathematical knowledge). Pauli’s article became a 250-page monograph that is both an informative introduction to relativity theory and a history of the mathematical foundations of the theory.

In 1921, Pauli became an assistant in theoretical physics at the University of Göttingen. Not only did he meet the noted physicists Max Born and James Franck, who were teaching there at the time, but also he came into personal contact with physicist Niels Bohr, who delivered a series of lectures there in 1922. Pauli was particularly impressed with Bohr’s attempts to explain why electrons in an atom are distributed in definite groups throughout the atom’s structure instead of clustering within the shell closest to the nucleus.

Life’s Work

After obtaining his doctorate, Pauli immediately initiated the projects from which emerged his most significant hypothesis. In 1922, Pauli tried to explain why the spectrum lines of atoms do not always split into three lines when exposed to a strong magnetic field. After spending considerable time probing this phenomenon, known as the Zeeman effect, Pauli postulated that the quantum properties of the atomic core were permanent. This theory had far-reaching consequences, both for Pauli’s own research and for the field of physics in general, because it suggested that every electron could be described by quantum numbers. Pauli was not any closer to solving the Zeeman effect a year later, when he went to the University of Hamburg as an assistant in theoretical physics. Soon after his arrival there, he was promoted to the position of assistant professor, and he spent the next few months reexamining the standard explanations for the anomalous splitting of the spectrum lines.

In 1925, Pauli’s research culminated in an argument that he proposed in an article in Zeitschrift für Physik (Journal of physics). In this article, he stated that a new quantum theoretic property of the electron was necessary before the Zeeman effect could be properly understood. The publication of this opinion gave him the resolve he needed to complete his research into the phenomenon. That same year, Pauli discovered the final clue to the problem’s solution in a paper by the British physicist Edmund Stoner. By way of explaining Stoner’s rule, Pauli developed his famous exclusion principle, which states that no two electrons can have the same energy in an atom. Pauli’s description of the exclusion principle in the Handbuch der Physik (Encyclopedia of Physics, 1958) in 1926 paved the way for the development of mathematically consistent quantum mechanics through research conducted by Werner Heisenberg, Paul A. M. Dirac, and Erwin Schrödinger.

Pauli left Hamburg in 1928 to assume a position as professor of theoretical physics at the Federal Institute for Technology in Zurich, Switzerland, which became his home for the next twelve years. Together with his friend George Wentzel, a professor at the University of Zurich, Pauli taught a seminar for many years in which all areas of theoretical physics were discussed. During his first ten years in Zurich, he was fortunate enough to have students such as R. Kronig, Rudolf Peierls, H. B. G. Casimir, and V. F. Weisskopf as his assistants, all of whom later went on to become prominent physicists.

While Pauli was in Zurich, he produced one of his most important theories, the neutrino hypothesis. In a letter that he wrote to Lise Meitner in 1930, he reported that a neutron is emitted along with an electron when certain subatomic particles decay. Although Enrico Fermi later christened this neutron the “neutrino,” it is also referred to in some circles as the “Paulino,” since Pauli made this observation before Sir James Chadwick had discovered the neutron in the nucleus. Pauli published his proposal in the report of the Solvay Congress in 1933.

Much of Pauli’s research in this period was also devoted to the development of relativistic quantum electrodynamics in an effort to explain the infinite self-energy of the electron. This work led Pauli into a study of wave mechanics. In an article Pauli wrote for Handbuch der Physik in 1933, he expanded the scope of wave mechanics to include not only a single particle but also the interaction of an indefinite number of particles.

In the late 1930s, Pauli’s work began to take him away from Zurich. Between 1935 and 1936, he was appointed visiting professor of theoretical physics at the Institute for Advanced Study in Princeton, New Jersey. Then, in 1940, the Institute for Advanced Study once again summoned him to Princeton, largely because of the Nazi invasion of Norway and Denmark. In 1945, while he was still a temporary member of the institute’s faculty, Pauli received a Lorentz Medaille and, later, the Nobel Prize in Physics.

In 1946, at the end of the war, Pauli returned to Zurich with his wife, Franciska, whom he had married in April 1934. He spent the remainder of his life in a heavily forested area called Zollikon, where he often took long walks. During this time, he also became a Swiss citizen.

In the last years of his life, Pauli began to reflect seriously on the meaning of scientific activity; this new interest manifested itself in a number of essays, lectures, and a book coauthored with Carl Jung, Natureklärung und Psyche (1952; The Interpretation of Nature and the Psyche, 1955). He even looked to Chinese philosophy for answers. Actually, though, Pauli had hoped all along that physics would reveal the harmony between God and nature. Pauli became seriously ill in December 1958, and he died on December 14.

Impact

Pauli’s research laid the foundation for a new physics at the same time that it was shaking the very foundation of the old. His exclusion principle demonstrated the individuality of electrons and thus solved the problem posed by the Zeeman effect, which had puzzled physicists since Pieter Zeeman first observed it in 1892. The principles of relativistic quantum electrodynamics, which had been the focus of much of Pauli’s work, were finally accepted after twenty years of skepticism and inquiry. Pauli’s discovery of the neutrino set the stage for further investigations by Chadwick and Fermi. Finally, his hypothesis for the permanence of quantum numbers permitted the development of a periodic table.

Bibliography

Enz, Charles P. No Time to Be Brief: A Scientific Biography of Wolfgang Pauli. New York: Oxford UP, 2002. Print. Chronicles Pauli’s life and the evolution of his thinking. Also provides a detailed analysis of Pauli’s scientific contributions.

Miller, Arthur I. Deciphering the Cosmic Number: The Strange Friendship of Wolfgang Pauli and Carl Jung. New York: Norton, 2009. Print. Examines the friendship and collaboration between the physicist and the psychoanalyst, providing insight into Pauli’s inner life and preoccupations.

Straumann, N. “Wolfgang Pauli and Modern Physics.” Space Science Review 148 (2009): 25–35. Print. Offers a brief biography and introduction to Pauli’s scientific career, describing his discovery of the exclusion principle.