Anders Olof Gunnar Källén (13 February 1926 – 13 October 1968) was a Swedish

theoretical physicist Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain, and predict natural phenomena. This is in contrast to experimental physics, which uses experi ...

and professor at

Lund University Lund University () is a Public university, public research university in Sweden and one of Northern Europe's oldest universities. The university is located in the city of Lund in the Swedish province of Scania. The university was officially foun ...

, known for his work on correlation functions in

quantum field theory In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines Field theory (physics), field theory and the principle of relativity with ideas behind quantum mechanics. QFT is used in particle physics to construct phy ...

. He died at the age of 42 as a result of a plane crash.

Biography

Anders Olof Gunnar Källén was born in 1926 in

Kristianstad Kristianstad ( , ) is a Urban areas in Sweden, city and the seat of Kristianstad Municipality, Scania County, Sweden with 41,198 inhabitants in 2023. Since the 1990s, the city has gone from being a garrison town to a developed commercial city, ...

, Sweden. His father, Yngve Källén, was a teacher of physics and mathematics, and together they published a paper on the theory of relativity. Gunnar's brother was the embryologist . Källén earned his doctorate at Lund in 1950 working with Torsten Gustafson, who was in close correspondence with

Wolfgang Pauli Wolfgang Ernst Pauli ( ; ; 25 April 1900 – 15 December 1958) was an Austrian theoretical physicist and a pioneer of quantum mechanics. In 1945, after having been nominated by Albert Einstein, Pauli received the Nobel Prize in Physics "for the ...

. He worked at

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...

's theoretical division from 1952 to 1957, which, at that time, was situated at the Institute for Theoretical Physics of the University of Copenhagen, later to be named

Niels Bohr Institute The Niels Bohr Institute () is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics, and biophysics. Overview The institute was foun ...

. Afterwards he worked at Nordita from 1957 to 1958, and then began a professorship at Lund University. Källén's research focused on

and

elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. The Standard Model presently recognizes seventeen distinct particles—twelve fermions and five bosons. As a c ...

physics. His developments included the so-called

Källén–Lehmann spectral representation The Källén–Lehmann spectral representation, or simply Lehmann representation, gives a general expression for the (time ordered) two-point function of an interacting quantum field theory as a sum of free propagators. It was discovered by Gun ...

of correlation functions in quantum field theory, and he made contributions to

quantum electrodynamics In particle physics, quantum electrodynamics (QED) is the Theory of relativity, relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quant ...

, especially in renormalization. He also worked with the axiomatic formulation of quantum field theory, which led to contributions to the theory of functions of several complex variables, and collaborated on the Pauli–Källén equation. The

Källén function The Källén function, also known as triangle function, is a polynomial function in three variables, which appears in geometry and particle physics. In the latter field it is usually denoted by the symbol \lambda. It is named after the theoretical ...

, as well as the Källén–Yang–Feldman formalism and the Källén-Sabry potentials are named after him.

Plane crash

Källén was an avid pilot, who, being fascinated by flying from his childhood on, started taking lessons in 1964. He was flying a

Piper PA-28 Cherokee The Piper PA-28 Cherokee is a family of two-seat or four-seat light aircraft built by Piper Aircraft and designed for flight training, air taxi and personal use.Plane and Pilot: ''1978 Aircraft Directory'', pages 62–64. Werner & Werner Corp, ...

Arrow from

Malmö Malmö is the List of urban areas in Sweden by population, third-largest city in Sweden, after Stockholm and Gothenburg, and the List of urban areas in the Nordic countries, sixth-largest city in Nordic countries, the Nordic region. Located on ...

to CERN when his plane crashed during an

emergency landing An emergency landing is a premature landing made by an aircraft in response to an emergency involving an imminent or ongoing threat to the safety and operation of the aircraft, or involving a sudden need for a passenger or crew on board to term ...

Hanover Hanover ( ; ; ) is the capital and largest city of the States of Germany, German state of Lower Saxony. Its population of 535,932 (2021) makes it the List of cities in Germany by population, 13th-largest city in Germany as well as the fourth-l ...

, Germany in 1968. His two passengers, one of them his wife, survived the crash. Many years after his death,

Cecilia Jarlskog Cecilia Jarlskog (born in 1941) is a Swedish theoretical physicist, working mainly on elementary particle physics. Jarlskog obtained her doctorate in 1970 in theoretical particle physics at the Technical University of Lund. She is known for her ...

edited the book ''Portrait of Gunnar Källén: A Physics Shooting Star and Poet of Early Quantum Field Theory'' (Springer, 2013) with 9 invited contributors, all of whom had a personal acquaintance with Källén. The book consists mainly of testimonies by Källén's colleagues.

Steven Weinberg Steven Weinberg (; May 3, 1933 – July 23, 2021) was an American theoretical physicist and Nobel laureate in physics for his contributions with Abdus Salam and Sheldon Glashow to the unification of the weak force and electromagnetic inter ...

, whose first published physics paper was motivated by Källén, wrote one of the book's chapters. The chapter deals with Källén's research and is the written version of a 2009 lecture by Weinberg. (lecture recorded on February 13, 2009)

Bibliography

*G. Källén, ''Quantenelektrodynamik'', Handbuch der Physik (Springer-Verlag, Berlin, 1958) *G. Källén, ''Elementary Particle Physics'' (Addison-Wesley, Reading, Massachusetts, 1964) *G. Källén, ''Quantum Electrodynamics'' (Springer-Verlag, Berlin, 1972)
2013 pbk reprint

Biography

Plane crash

Bibliography

References

Further reading