Pascual Jordan (1963)
|Born||18 October 1902
Hanover, German Empire
|Died||31 July 1980
Hamburg, West Germany
|Institutions||Technical University Hanover|
|Doctoral advisor||Max Born|
|Doctoral students||Jürgen Ehlers, Engelbert Schücking|
|Known for||Quantum mechanics, quantum field theory, matrix mechanics, Jordan algebra, Nazi political affiliation|
|Notable awards||Max Planck Medal (1942), Carl Friedrich Gauß Medal (1955)|
(Ernst) Pascual Jordan (18 October 1902 – 31 July 1980) was a theoretical and mathematical physicist who made significant contributions to quantum mechanics and quantum field theory. He contributed much to the mathematical form of matrix mechanics, and developed canonical anticommutation relations for fermions. While the Jordan algebra he invented is no longer employed in quantum mechanics, it has found other mathematical applications.
Family history 
An ancestor of Pascual Jordan named Pascual Jorda was a Spanish nobleman and cavalry officer who served with the British during and after the Napoleonic Wars. Jorda eventually settled in Hanover, which in those days was a possession of the British royal family. The family name was eventually changed to Jordan (pronounced in the German manner, "YOUR-dunn"). A family tradition dictated that the first-born son in each generation be named Pascual.
Jordan enrolled in the Hanover Technical University in 1921 where he studied an eclectic mix of zoology, mathematics, and physics. As was typical for a German university student of the time, he shifted his studies to another university before obtaining a degree. Göttingen University, his destination in 1923, was then at the very zenith of its prowess and fame in mathematics and the physical sciences. At Göttingen Jordan became an assistant first to mathematician Richard Courant and then to physicist Max Born.
Scientific work 
|This section requires expansion. (January 2011)|
Together with Max Born and Werner Heisenberg Jordan was co-author of an important series of papers on quantum mechanics. He went on to pioneer early quantum field theory before largely switching his focus to cosmology before World War II.
Jordan devised a type of non-associative algebras, now named Jordan algebras in his honor, in an attempt to create an algebra of observables for quantum mechanics and quantum field theory. Today, von Neumann algebras are employed for this purpose. Jordan algebras have since been applied in projective geometry and number theory.
In 1966, Jordan published the 182 page work Die Expansion der Erde. Folgerungen aus der Diracschen Gravitationshypothese (The expansion of the Earth. Conclusions from the Dirac gravitation hypothesis) in which he developed his theory that, according to Paul Dirac's hypothesis of a steady weakening of gravitation throughout the history of the universe, the Earth may have swollen to its current size, from an initial ball of a diameter of only about 7,000 kilometres (4,300 mi). This theory could explain why the ductile lower sima layer of the Earth's crust is of a comparatively uniform thickness, while the brittle upper sial layer of the Earth's crust had broken apart into the main continental plates. The continents having to adapt to the ever flatter surface of the growing ball, the mountain ranges on the Earth's surface would, in the course of that, have come into being as constricted folds.
Political activities 
Jordan enlisted in the Luftwaffe in 1939 and worked as a weather analyst at the Peenemünde rocket center, for a while. During the war he attempted to interest the Nazi party in various schemes for advanced weapons. His suggestions were ignored because he was considered "politically unreliable," probably because of his past associations with Jews (in particular: Courant, Born, and Wolfgang Pauli) and "Jewish Physics".
Wolfgang Pauli declared Jordan "rehabilitated" to the authorities some time after the war, allowing him to regain academic employment after a two-year period and then recover his full status as a tenured professor in 1953. Jordan went against Pauli's advice, and reentered politics after the period of denazification came to an end under the pressures of the Cold War. He secured election to the Bundestag standing with the conservative Christian Democratic Union. In 1957 Jordan supported the arming of the Bundeswehr with tactical nuclear weapons by the Adenauer government, while the Göttinger 18 (which included Born and Heisenberg) issued the Göttinger Manifest in protest. This and other issues were to further strain his relationships with his former friends and colleagues.
Selected works 
- Born, M.; Heisenberg, W.; Jordan, P. (1925). "Zur Quantenmechanik". Zeitschrift für Physik 34 (1): 858. Bibcode:1925ZPhy...34..858B. doi:10.1007/BF01328531.
- Born, M.; Heisenberg, W.; Jordan, P. (1926). "Zur Quantenmechanik. II". Zeitschrift für Physik 35 (8–9): 557. Bibcode:1926ZPhy...35..557B. doi:10.1007/BF01379806.
- Jordan, P.; von Neuman, J.; Wigner, E. (1934). "On an Algebraic Generalization of the Quantum Mechanical Formalism". Annals of Mathematics 35 (1): 29–64. doi:10.2307/1968117. JSTOR 1968117.
- "Max Born and the quantum theory". Retrieved 2009-07-01.
- [dead link]
- Silvan S. Schweber, QED and the Men Who Made It: Dyson, Feynman, Schwinger, and Tomonaga, Princeton: Princeton University Press, 1994, xxviii + 732 pages, ISBN 0-691-03327-7.
- Die Wissenschaft, vol. 124. Friedrich Vieweg & Sohn, Braunschweig 1966
- Heinz Haber: "Die Expansion der Erde" [The expansion of the Earth]. Unser blauer Planet [Our blue planet]. Rororo Sachbuch [Rororo nonfiction] (in German) (Rororo Taschenbuch Ausgabe [Rororo pocket edition] ed.). Reinbek: Rowohlt Verlag. 1967 . pp. 48, 52, 54–55. "Nehmen wir einmal an, dass die Erde, als ihre Bildung vor Jahrmilliarden im Wesentlichen abgeschlossen war, einen Durchmesser von nur 7000 Kilometern gehabt hat. So groß war damals vermutlich das Maß der Schwerkraft, dass sie bis auf diesen Durchmesser zusammengepresst wurde. Die Oberfläche einer Kugel dieser Ausmaße entspricht der Gesamtoberfläche aller heutigen Kontinente. Damals war die Kruste der Erde zumindest vorübergehend in einem glutflüssigen Zustand, und so hat sich eine einheitliche Kruste gebildet, wobei eine etwa 5 bis 10 Kilometer dicke Basaltschicht unter einer etwa 30 Kilometer dicken Granitschicht zu liegen kam." [p. 54] English: "Let us assume that the Earth, when its formation was, altogether, completed, billions of years ago, had a diameter of only 7000 kilometers. Gravitation was probably as strong, then, that the Earth was pressed together to a ball of such a diameter. The surface of a ball of such measures tallies with the overall surface of all the continents of today. At that time, the Earth's crust was, at least temporarily, in a molten state. Thus, there formed a regular crust, a layer of basalt of about 5 to 10 km thickness finding its position under an about 30 km thick layer of granite."
- Bernstein (2005)
- Bert Schroer (2003). "Pascual Jordan, his contributions to quantum mechanics and his legacy in contemporary local quantum physics". arXiv:hep-th/0303241 [hep-th].
Further reading 
- Schroer, B. (2011). "Pascual Jordan's legacy and the ongoing research in quantum field theory". European Physical Journal H 35 (4): 377. arXiv:1010.4431. Bibcode:2010EPJH...35..377S. doi:10.1140/epjh/e2011-10015-8.