Paul Lieber, Mechanical Engineering: Berkeley

	1918-1992
	Professor of Engineering Science, Emeritus

Paul Lieber was born in Baltimore, Maryland, on October 11, 1918. At the age of 12, he was sent to school in Palestine at Mikveh Israel. Established in 1870 as a school of practical agriculture, Mikveh Israel enlarged its scope in the 1930s to include a broad education and leadership training for an anticipated state of Israel.

Paul returned to Baltimore in 1936 and from 1937 to 1939 studied geophysics at Johns Hopkins University. In 1939 he transferred to the California Institute of Technology to continue his studies in geophysics, and in 1940 received an M.S. His formal education was then interrupted by World War II, and from 1940 to 1946 he worked for Douglas Aircraft Company, where he became supervisor of a flutter and dynamic analysis group.

In 1946 Lieber went to the Polytechnic Institute of Brooklyn as an assistant profesor of applied mechanics. During 1949 to 1951, while continuing to teach at the Polytechnic Institute, he completed the work for his doctoral dissertation at the California Institute of Technology and received a Ph.D. in geophysics with a minor in mathematics. He then proceeded to Renssalaer Polytechnic Institute as an associate professor of aeronautics, a position he held from 1951 to 1953. In 1953 he returned to his first interest and was promoted to professor of geophysics there. In 1956 he was appointed professor of engineering science in the Department of Mechanical Engineering here at Berkeley and remained in this position until his retirement in 1989. During the year 1957-1958 he was a Fulbright lecturer at the Technion in Haifa, Israel.

Lieber's interests were wide-ranging and led him to pursue fundamental questions in the physical and biological sciences. He had a deep appreciation of, and also a reverence for, the underlying principles of the theories of classical mechanics. This attitude influenced all of his work. Some of the

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contributions that Lieber and his collaborators made in fluid mechanics and geophysics are quantitative and empirical in nature. The bulk of his work is, however, conceptual and philosophical. He sought to identify a unifying principle by which natural processes are governed. Guided by Gauss's principle of least constraint for a mechanical system, Lieber proposed a very general principle of maximum uniformity. Despite the inherent appeal of such an all-encompassing principle, in applying it to natural phenomena, one is faced with the difficulty of ascertaining what is to be uniformized and what measure of it is to be maximized. Thus, although the principle of maximum uniformity played a central organizing role in Lieber's thinking, in a sense he was not able to bring his ideas to fruition because of the lack of an algorithmic framework for his principle. Nevertheless, Lieber's papers contain many highly original and stimulating ideas, the ramifications of which may be revealed in time.

Among Lieber's few specifically geophysical publications was a 1963 paper (with K.T. Wen) giving one of the first theoretical treatments of the propagation of earthquake surface waves in visco-elastic Earth models. In it he expresses deep appreciation to his teacher Beno Gutenberg, the distinguished professor of seismology at the California Institute of Technology. The results led Lieber to be critical of inferences from linear-elasticity theory concerning the rheological processes and properties of the deep interior of the Earth. His caution concerning nonlinear effects was later confirmed more broadly and quantitatively by others.

Although Lieber's lectures to undergraduates at times deviated considerably from the standard curriculum, his interest in fundamental questions attracted a number of outstanding graduate students who wished to work with him on such problems. A good deal of what he, and they, did was not published. However, one can get some idea of his work by consulting the several papers by him and his students in the proceedings of the Seventh Symposium on Naval Hydrodynamics held in Rome in 1968.

Paul died of cancer on December 12, 1992. He is survived by his wife of forty-eight years, Bettina Vegara Lieber, five children, Michael (from an earlier marriage), Leo, Joseph, Victoria Alvarado, and Jonathon, and four granddaughters.