Alfred Landé

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Alfred Landé (13 December 1888–30 October 1976) was a German-American physicist known for his contributions to quantum theory. He is responsible for the Landé g-factor and an explanation of the Zeeman Effect.

[edit] Life and Achievements

Alfred Landé was born on 13 December 1888 in Elberfeld, Germany.

In the year 1913 Landé became an assistant of David Hilbert in Göttingen. Here he also came in close contact with Max Born. In physics, it was the time of the Bohr atom model. The leaders of Goettinger science included many greats that Landé was to come in contact with including David Hilbert, Small, Edmund Landau, Carl Runge, Ludwig Prandtl (the founder of the aerodynamics), among others. Also Niels Bohr and Hendrik Lorentz visited Goettingen frequently.

Landé obtained his Ph.D. two weeks prior to the start of the First World War. He joined the Red Cross and served for two years on the eastern front before being invited by Max Born to join him at the Artillery Testing Commission, one of the few scientific sections of the army. Apart from their work on artillery location by sound ranging, they began to examine the cohesive forces and the compressibility of crystals. This work led to the unexpected result that the electron trajectories in atoms were not at all like planetary orbits, a conception to which science at that time held as a fundamental idea.

The spatial structure of the atom intensively employed Landé for the next seven years. In 1916, Arnold Sommerfeld had begun to apply the new atomic theory to form a general quantization rule. Landé's work over cubic and tetrahedral electron trajectories ("cube atoms") became of great interest to Sommerfeld, Peter Debye and Bohr. But at the beginning of 1919 Landé unexpectedly turned to spectroscopy even though the continuation of the study of the spatial orientation of the atoms was the most pressing problem of the time.

Here the Frankfurt period of Alfred Landé begins which is perhaps the most important period of his life from the scientific point of view. The work from this time made him a continuing figure in science.

Landé turned to the problem of atoms with several electrons, in particular to the simplest case, the spectrum of helium. The spectroscopy of helium had been examined experimentally by Friedrich Paschen, but there did not exist a theoretical interpretation. The spectrum showed non-combining single and double (actually triplet, as it turned out later) terms so that it seemed as if helium was made of two different substances which we know today are related to spin (physics).

Although the main thrust of Landé's work was afflicted with errors still the work contained several new important ideas, among other things the rule of vector addition of two quantum-mechanical angular momenta J1 and J2, such ideas were later confirmed by Quantum Theory.

The short time interval of three to four months, from December 1920 until April 1921 in Frankfurt ended with the discovery of the well-known Landé g-formula and an explanation for the anomalous Zeeman Effect. The Landé g-factor is now defined through mJ the magnetic quantum number.

During 1925, Ralph Kronig the discoverer of electron spin was working as an assistant to Landé.

In the autumn of 1929 Landé was invited to Ohio State University in Columbus, in order to hold a set of lectures. After a second stay 1930/31 in Columbus, Ohio, he decided to establish himself in the United States. Landé was forerunner of a phase of new interpretation of quantum theory, from which concrete physical statements about experimentally verifiable facts can be made. This happened, after the first phase of the interpretation of the theory with well-known discussions between De Broglie, Schroedinger, Bohr and Einstein who opted provisionally in favor of the Bohr view as to where a solution seemed to lead. It is undisputed that an important deep problem lie with quantum mechanics at that time, because otherwise there would not have been new efforts to fathom the nature of the quantum-mechanical truth. The renewed interest expressed itself in new experiments with new technical methods, on individual quantum systems, individual atoms, electrons and photons.

Interestingly though after 1950, and actually up until his death, Landé turned energetically against the Copenhagen interpretation of quantum theory, very much as Einstein did, based upon Landé's perception that the Uncertainty Principle was unacceptable.

Alfred Landé died on 30 October 1976 in Columbus, Ohio.

[edit] References

• A Landé, Foundations of Quantum Theory, a study in Continuity and Symmetry, Yale and Oxford University Presses, 1955.
• A Landé, From Dualism to Unity in Quantum Physics, Cambridge University Press, 1960.
• A Landé, New Foundations of Quantum Mechanics, Cambridge University Press, 1962.
• Paul Forman, Alfred Landé and the anomalous Zeeman Effect, 1919-1921, Historical Studies in the Physical Sciences, Vol. 2, 1970, 153-261.
• Perspectives in Quantum Theory Essays in Honor of Alfred Landé (edited by Yourgraw and van der Merwe), 1971, MIT Press, Dover Publications 1979: ISBN 0-486-63778-6
• Selected Scientific Papers of Alfred Landé, (edited by Barut and van der Merwe), Reidel, 1988, 557 pages.