# Infeld, Leopold

# Infeld, Leopold

(*b.*Cracow, Poland, 20 August1898; *d.* Warsaw, Poland, 15 January 1968)

*theoretical physics.*

Infeld was the son of Salomon and Ernestyna Infeld, his father being a merchant in the leather business. Against his will Leopold was sent to a commercial school. He became interested in the theory of relativity as a student of physics at the Jagiellonian University in Cracow. In 1920 he went to Berlin for eight months, where he met Einstein and worked on his doctoral dissertation, which was devoted to the problem of light waves in general relativity. In 1929 Infeld was given an appointment at the University of Lvov. After a short visit to Leipzing in 1932, he undertook research on spinor analysis in Riemannian spaces, a spinor being a mathematical concept used to describe particles possessing intrinsic angular momentum (spin). In a paper published in 1933, Infeld and Bartel LL. van der Waerden showed how spinor calculus can be extended to take into account the influence of gravitation on spinning particles.

As a fellow of the Rockefeller Foundation, from 1933 to 1934, Infeld spent over a year in Cambridge, England. He gave there a new interpretation of a theory of nonlinear electrodynamics and, together with Born, worked on how to describe particles and quanta within that theory, which is now known as the Born-Infeld theory. In 1936, at Einstein’s suggestion, Infeld was offered a fellowship at the Institute for Advanced Study in Princeton. He accepted it and, at Princeton from 1936 to 1938, joined Einstein in research on the problem of motion of heavy bodies according to the theory of general relativity. Together with Banesh Hoffmann, they laid the foundations of a new approximation method, today known as the EIH (Einstein-Infeld-Hoffmann) method. The method is well suited for the solution, within the framework of general relativity, of all problems related to the motion of slowly moving, gravitating bodies. One of the principal results is that the motion of bodies, described by singularities of the field, is determined by the equations of the gravitational field. In this respect, general relativity differs considerably from other physical theories, where the equations of motion usually have to be postulated separately.

Questions connected with the motion of bodies, such as the problem of gravitational radiation and the structure of sources, dominated the subsequent scientific activity of Infeld and his students. Infeld showed that gravitational radiation is strongly inhibited by the nature of Einstein’s equations, and he simplified the derivation of post-Newtonian corrections to the motion of celestial bodies. These results are collected in *Motion and Relativity* (1960), a unique book on this subject, written by Infeld in collaboration with Jerzy Plebański.

At the end of Infeld’s stay in Princeton, he wrote with Einstein *The Evolution of physics* (1938), today a widely read book on modern Physics for the layman. Later, at the University of Toronto (1938-1950), Infeld had many students and did research in several fields: he developed the factorization method of solving differential equations and, in collaboration with Alfred Schild, he formulated a new approach to relativistic cosmology, based on the similarity of propagation of light in cosmological models and in flat space. During the war, he worked on waveguides and antennas for a Canadian defense project. While in Canada, Infeld wrote *Whom the Gods Love* (1948) a biographical novel about Evariste Galois.

After a short visit to Poland in 1949, Infeld left Canada and, in the fall of 1950, returned to Warsaw to become professor at the university. He subsequently played a leading role in the development of theoretical physics in his country, becoming director of the new Institute of Theoretical Physics at the university and heading the theoretical division of the Institute of Physics of the Polish Academy of Sciences. Within a short time Infeld gathered around himself a large group of young physicists, whow he inspired with enthusiasm for scientific research and encouraged in new domains of physics and new approaches to science teaching.

Infeld’s own research during the Warsaw period was devoted mostly to the classical theory of fields. But he also followed with fascination the rapid development of other areas of physics and encouraged Polish students to do theoretical work in nuclear, “high-energy, and solid-state physics.”

In recognition of his achievements, Infeld was awarded the highest distinctions by the Polish government. He was a member not only of the Polish Academy of Sciences but of several other academies. His activities were never restricted to the domain of science alone. Infeld did a great deal for international scientific cooperation, for physics in Poland, and especially for theoretical physics in Warsaw. His feeling of responsibility for the world prompted him to sign the Einstein-Russell appeal that gave birth to the Pugwash movement, in which he became very active.

## BIBLIOGRAPHY

I. Original Works. Infeld published more than 100 scientific papers and several books; a comprehensive list of his scientific writings may be found in *General Relativity and Gravitation*, I (1970), 191-208. In addition to the books mentioned in the text, Infeld wrote *Albert Einstein* (New York, 1950), a book describing Einstein’s main ideas in simple terms.

II. Secondary Literature. Infeld’s *Quest* (New York. 1941) is an autobiography written in Canada and covering the period until 1939. *Szkice z przeszlości* (“Sketches From the Past”) and *Kordian i ja* (“Kordian and I”), both published in Warsaw in 1965 and 1968, respectively, are two autobiographical books written in Polish by Infeld during the last years of his life. The former has also been published in German as *Leben mit Einstein* (Vienna, 1969).A third book, *W siuzbie cesarza i fizyki*, is in preparation.

Andrzej Trautman

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