Lande, Alfred (physicist)


(1888-1976) German/American Theoretical Physicist, Quantum Theorist

Alfred Lande was a theoretical physicist best known for discovering the g-formula, which relates the ratio of the magnetic moment of an atom to the angular momentum of the electric current loops that generate it. This fundamental discovery enabled physicists to determine the fine as well as the superfine structure of the optical and X-ray spectra of atomic systems.

Lande was born on December 18, 1888, in Elberfeld, in the Rhine region of Germany. Lande’s father served as deputy head of the provincial government in Duesseldorf for a time. The family was a cultured one, imbuing him with a deep love of music. His early fascination with science encompassed cosmology, the study of crystals and minerals, chemistry, and electricity. His superiority in mathematics and physics led his high school teachers to consider him something of a prodigy. He studied at the Universities of Marburg and Gottingen, where he became an assistant to the great mathematician David Hilbert. He went on to earn his Ph.D. at the University of Munich in 1914, working under arnold johannes wilhelm sommerfeld, an influential and revered member of the community of European-born physicists who produced the quantum revolution in the first third of the 20th century. Unlike Sommerfeld and other visionary physicists, who regarded the new quantum theory and its wave-particle duality as a radical paradigm shift, however, Lande tried to understand the quantum mystery as a gap in classical mechanics.

When World War I began, Lande enlisted for service with the Red Cross and worked in a hospital for a few years. Later max born, one of the pioneers of quantum mechanics, managed to have him transferred to one of the few scientific sections of the army, a weapons development center in Berlin, where he worked under Born on sound detection methods. The two physicists did not confine their collaboration to war-related research, but moved into the abstract domain of the new quantum theory. Together they reached the conclusion that niels henrik david bohr’s 1913 quantum mechanical model of the atom, which was limited to electron orbits moving in the same plane (in analogy to the solar system), was inadequate, since they found evidence that the electron orbits must be inclined toward each other. They published a paper stating these results, which were experimentally justified in 1918, arousing widespread interest and controversy in the physics community.

The following year Lande became a lecturer at the University of Frankfurt, where he would remain until 1922. This would be one of the most important periods of his scientific life. He visited Bohr at his institute in Copenhagen to discuss the Zeeman effect, the splitting of spectral lines in an intense magnetic field, which had been discovered by pieter zeeman, in 1897. He was able to pursue this issue further, when, in 1922, he was appointed associate professor of theoretical physics at the University of Tubingen, then the most renowned center for atomic spectroscopy in Germany. That year he married Elisabeth Grunewald, with whom he would have two sons, Arnold and Carl.

In 1923, Lande became famous for publishing a formula (known as the g-formula) expressing a factor known as the Lande splitting factor as a function of the quantum numbers of the stationary state of the atom. The Lande splitting factor determined the ratio of the magnetic moment of an atom to its intrinsic angular momentum, measured in quantum units of Bohr magnetons, which equals eh/4nmc, where e is the charge on an electron, h is the Planck constant, m is the electron rest mass, and c is the speed of light. On the basis of this fundamental discovery physicists were able to determine the fine and superfine structures of the optical and X-ray spectra of atomic systems. Lande went on to collaborate with Louis Paschen and others to analyze in great detail the fine structure of the line spectra and the further splitting of the lines under the action of magnetic fields of increasing strength. He formulated the laws obeyed by the frequencies and intensities of the lines in terms of the sets of spectroscopic quantum numbers, which could take on either integral or half-integral values.

As the Nazi regime was rising to power in 1931, Lande, who had visited Columbus, Ohio, in 1929 and 1930, left Germany for the United States and became a professor of theoretical physics at Columbus State University. He remained there for the rest of his life. His son Arnold became a surgeon in Minneapolis, and his son Carl became a professor of politics at the University of Kansas.

Despite his many significant contributions to the quantum theory of atomic structure, to the very end of his career Lande remained opposed to the wave-particle duality interpretation of quantum mechanics. In support of this conservative point of view he claimed Today, after endless repetition, a dual nature of matter may seem as obvious and indisputable to the experts as the immobility of the earth seemed to Galileo’s learned colleagues who refused to look through his telescope because it might make them dizzy.

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