Pascual Jordan (b. October 18, 1902 in Hanover, Germany; d. July 31, 1980 in Hamburg, Federal Republic of Germany) was a theoretical and mathematical physicist who made significant contributions to quantum mechanics and quantum field theory.

Jordan's great-grandfather 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. His patrilineal descendants held to a tradition of naming their first-born sons Pascual, while their family name was eventually changed to Jordan (pronounced in the German manner, "YOUR-den").

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 transferred 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. Here, Jordan became an assistant to first the mathematician Richard Courant and then the physicist Max Born.

Together with Max Born and Werner Heisenberg he 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 joined the NSDAP (Nazi Party) in May 1933. The following November he joined the Sturmabteilung (SA) - the brown shirted storm troopers. He enlisted in the Luftwaffe in 1939 and worked for a while at the Peenemünde rocket center. During the war he attempted to interest the party in various schemes for advanced weapons, but these 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" (such a stigma also followed Werner Heisenberg for some time under the Nazis)(see the article Deutsche Physik).

It has been speculated that Jordan would have likely shared the 1954 Nobel Prize in Physics awarded to Max Born were it not for his membership in the Nazi party (see both J. Bernstein and B. Schroer references).

Wolfgang Pauli declared Jordan "rehabilitated" to the authorities some time after the war, allowing Jordan 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 Democrats. In 1957, Jordan came out in support for the arming of the Bundeswehr with tactical nuclear weapons by the Adenauer government, while the Göttinger 18 (which included Born, Heisenberg, and Pauli) authored the Göttinger Manifest in protest. This and other issues were to further strain his relationships with his former friends and colleagues.

The non-associative Jordan algebras are named after him. They were defined in an attempt to create an algebra of observables for quantum mechanics and quantum field theory. Today, this role is more often assumed by the von Neumann algebras. Meanwhile, Jordan algebras have seen application in projective geometry and number theory.

Jordan is sometimes confused with the French mathematician Camille Jordan and the German geodesist Wilhelm Jordan.

Selected Works

• The "Dreimännerarbeit"
  
• Jordan algebra paper with von Neumann and Wigner
  

References

• B. Schroer, "Pascual Jordan, his contributions to quantum mechanics and his legacy in contemporary local quantum physics", arXiv:hep-th/0303241
  
• J. Bernstein, "Max Born and the Quantum Theory", American Journal of Physics, 11 (2005), 999-1008).