THE BOLTZMANN MEDAL

Presentation by Edouard Brezin
Chairman, IUPAP C3 Commission on Statistical Physics

Samuel Edwards: Boltzmann Medallist 1995

The work of Prof. Sir Sam Edwards provides a cornerstone to the modern theory of disordered systems. he was instrumental in bringing quantum field theory into statistical physics; he simulated -- and was at the forefront of -- a new understanding of the statics and dynamics of polymeric systems, and he co-founded the subject of spin glasses.

Edwards' work has been marked by a series of deep physical insight into difficult problems, coupled with major technical innovations, many of which have become a standard tool for workers in polymer theory and condensed matter physics. He introduced quantum field theory, in its formulation in terms of functional integrals, to condensed matter physics. This led him in 1965 to model polymer chains as continuous flexible curves with point-like repulsions; this has now become standard but it has been clearly as very novel and important idea. The self-consistent field formalism to study screening effects in many chain systems was also a very important step. This led to the first quantitative theories of polymer absorbtion and remains the method of choice for studies of concentrated solutions and melts; new predictions still flow from it, 25 years after its introduction.

A second major series of contributions has concerned systems with quenched disorder. In a seminal collaboration with P.W. Anderson, the replica method was discovered in the context of spin glasses, magnetic systems with quenched random interactions, which are clearly the prototype of new states of matter and of many problems in which disorder leads to "frustation" of the ordered state.

Edwards studied the effects of chain entanglements in rubbery materials and introducted the idea of a "tube" around a particular molecule, representing the topological constraints of its neighbors. This led to a reformulation of the theory of rubber elasticity based on the replica method. The impact of this work on subsequent theories of quenched disorder has been profound and far reaching: for instance much of neural network theory descends from it.

A third major area of impact has been in predicting the dynamics and viscoelastic properties of dense polymer systems. these phenomena are now systematically understood in terms of tubes models of polymer entanglement. Edwards' idea of this tube was eessential for PG de Geenes' work on "reptation", the snake-like motion of a chain in the medium, explicitly visualized nowadays in the experimental settings of S. Chu with optical tweesers. It was Edwards who had the insight to apply reptation directly to polymer melts, in a brillant series of papers with Doi, in which the concept of reptation is scrutinized, formalized and worked out in all its consequences. This leads to predictions of such scope and importance that has taken the polymer science community a decade or more to assimilate them. Let us quote also the work of Doi and Edwards on the dynamics of entangled rod-like molecules.

Over the past decade Prof. Edwards has made several major contributions to the theory of aggregated granular matter. In 1982 he gave the first theoretical treatment of interfacial structure and roughness in granular materials, which became a new field of study. He was able there to take up ideas which he had developed in turbulence around 64 and he gave the first accurate description in this context, of the strong coupling fixed poin in the Kardar-Parisi-Zhang equation, which is in fact a generatlization of the earlier Edwards-Wilkinson model for randomly moving interfaces.

Let me briefly describe the various steps which have marked Prof. Edwards' career. Educated in Cambridge (UK) and Harvard, where he made his PhD under the supervision of Julian Schwinger, Prof. Edwards started as a member of the Institute for Advanced Study in Princeton, then took a position at Birmingham University in 53, became a Professor of theoretical physics at Manchester University in 63, and at Cambridge in 72, the Cavendish Professor for theoretical physics in 84. Prof. Edwards has held various governmental positions: Chairman of the SRC 73-77, Chairman of the Defense Scientific Council 77-80, Chief Scientific Adviser of the Department of Energy 83-88. Prof. Edwards has been the Vice-President of the Royal Society, of the Institute of Physics, the President of the Institute of Mathematics; he is a foreign member of the french Academie des Sciences, and he has received a number of international awards and honorary degrees. let me also mention that Prof. Edwards has been actively militant in favour of human rights, in particular at the time of the former Soviet Union.

This Boltzman medal goes therefore to a scientist of exceptional vision which has allowed him to identify and fruitfully apply methods of seemingly unrelated fields to other areas. This has allowed him to make important contributions to some of the most outstanding and significant problems in statistical physics over more than 30 years.