Edwin Thompson Jaynes, an innovative figure in many fundamental aspects of theoretical physics, died on April 30, 1998 in St. Louis, Missouri.

Born on July 5, 1922 in Waterloo, Iowa, Ed Jaynes grew up in Parkersburg, Iowa, attended nearby Cornell College, and received a B.A. in Physics from the University of Iowa in 1942. His father died when he was very young, but left a large library and a piano, legacies that stimulated a lifelong involvement with learning and music. After graduation, Ed was engaged with microwave theory and applications, first at the Sperry Gyroscope Company and then, as a U.S. Navy officer, at the Naval Research Laboratory in Washington, D.C. Upon discharge from the Navy, he moved to California, worked for a summer in the group designing the first linear electron accelerator, and enrolled as a graduate student at UC-Berkeley. In 1947 he transferred to Princeton University, where he completed a Ph.D. thesis in 1950 on ferroelectricity under the direction of Eugene Wigner. A modified version of this thesis was published by Princeton University Press as the inaugural volume of the Investigations in Physics book series.

Ed spent the next decade at Stanford in the Microwave Laboratory and the Department of Physics. In 1960 he accepted a senior faculty appointment at Washington University, St. Louis, where, with few interruptions, he remained for the rest of his life. Jaynes became Wayman Crow Professor of Physics in 1975. He spent productive sabbatical years at the University of Wyoming and at St. John's College, Cambridge University, the home of one of his intellectual heros, Sir Harold Jeffreys. Following a heart attack, Ed retired in 1992. As his health allowed, he continued to work toward the completion of several books and manuscripts. For a time he also continued his engagement with conference series in probability theory and statistical methods, where he was in great demand as a speaker.

Ed's searching mind ranged widely over many disciplines within and outside physics. However, his major contributions lie essentially in four areas: applied classical electrodynamics; information theory and statistical mechanics; quantum optics and neoclassical radiation theory; and probability theory and statistical inference. Much of this work was controversial and in some cases remains so today. All of it has the mark of an extraordinary intellect seeking new foundations for our understanding of nature.

In 1957 Ed published his first two papers interpreting statistical mechanics in terms of information theory. The Gibbs probability distribution was derived from a principle of maximum entropy subject to constraints representing prior knowledge. Statistical mechanics was thus viewed as a form of statistical inference based partial information, rather than a physical theory. Published by Physical Review against the advice of a referee, this approach spurred a continuing debate between ``subjectivists'' and ``objectivists.'' Over the years, Jaynes' view has gained many adherents, not least because of the opportunities it opens in nonequilibrium statistical mechanics and in manifold applications of the maximum entropy principle outside physics.

Ed's vastly influential synthesis of the ideas and results of Laplace, Bayes, Jeffreys, Cox, and Shannon into a consistent modern framework of probabilistic reasoning is a natural outgrowth of this striking early work. A series of beautifully composed and argued papers on this subject and on information-theoretic statistical mechanics was published in conference proceedings volumes -- it was commonplace for mainstream journals to reject Ed's manuscripts. Among these is the classic ``How the Brain Does Plausible Reasoning,'' originally a 1959 Stanford Microwave Laboratory Report. Jaynes' impact on the field of statistical inference has been enormous and has been summarized in Probability & Physics: Essays in Honor of Edwin T. Jaynes, edited by W. T. Grandy, Jr. and P. W. Millonni and published by Cambridge University Press in 1993. Ed left us a virtually complete book manuscript entitled Probability Theory: The Logic of Science, a monumental contribution which, on-line and in preprint form, has already become one of the most widely studied books in science. His writings expose the foundations of ``the calculus of inductive reasoning'' with a clarity and elegance that will continue to enlighten and delight his readers for many generations to come.

Ed insisted that some of the thorniest conceptual problems faced in physics, notably in statistical physics and quantum theory, arise from a mistaken identification of probabilities as physical quantities rather than as representations of the available information on a system -- a confusion between what is ontological and what is epistemological. Like Einstein, he was repelled by the Copenhagen interpretation of quantum mechanics and what he viewed as an incursion of mysticism into science. His dissatisfaction with quantum mechanics, with the uncertainty principle and with the divergences arising in quantum electrodynamics, spurred him to reformulate QED to avoid quantization of the electromagnetic field. His first work on neoclassical radiation theory, published with Fred Cummings in 1963, is probably his most cited and most notorious paper. Whatever the final fate of Ed's campaign to excise the ghostly demons of quantum physics, there is no doubt that it stimulated many advances of technique and understanding in the early days of quantum optics. Certainly, the Jaynes-Cummings model remains as one of the most useful soluble models in all of physics.

Ed was a superb lecturer, a compelling and inspiring teacher. Every lecture was a new creation, reflecting his own evolving understanding of science. He attracted many of the best students; with his continuing guidance, many have themselves become leaders in their fields.

In his social interactions, Ed could be rather shy, but he was a generous and open-hearted person. For many years, he hosted in his large home a weekly gathering of faculty, students, and their families. He was a gifted pianist, and impromptu musical performances on his splendid grand piano highlighted many of these occasions. Ed also enjoyed having faculty and student colleagues join him for outings at his rural Ozarks farm. Those who participated in these activities have fond remembrances of the freshness, intellectual excitement, and iconoclastic pleasure that we felt when we were in Ed's good company. 
 

With the passing of Edwin Jaynes, science has lost a uniquely provocative mind always ready to challenge our understanding of the deepest issues. His colleagues have lost a wise and trusted friend who will be greatly missed.

John W. Clark
Richard E. Norberg
G. Larry Bretthorst
Washington University
St. Louis, Missouri