Adrian Nicolae Patrascioiu, a gifted theoretical physicist whose work spanned particle physics, statistical mechanics, and chaos theory, died on 2 March 2002 in Phoenix, Arizona, after a brief battle with a rare form of T-cell lymphoma.
Adrian was born on 11 December 1940 in Bucharest, Romania. While he was still in his late teens, he graduated from the Polytechnic Institute of Bucharest with a degree in electrical engineering, but soon realized that his passion was physics. In Romania in those days, one did not get second chances, so Adrian immigrated to the US in 1965 after a daring escape that involved swimming across the Adriatic Sea to Italy from what was then Yugoslavia. He obtained his PhD in physics from MIT in 1972. His thesis, written under the direction of Francis Low, dealt with Regge theory.
In 1973, Adrian moved to the Institute for Advanced Study in Princeton, New Jersey. His entire life as a scientist was characterized by his independence of spirit and unremitting search for truth. This quality was shown at an early stage in his career by his 1974 work on string theory, in which he constructed a bosonic string in noncritical (that is, fewer than 26) dimensions. Although quite prescient, this work perhaps had less impact than it might otherwise have had because “noncritical strings” are technically more complicated than their critical counterparts.
Adrian moved to the University of California, San Diego, in 1975 to take a position as a research associate. In 1977, he became an assistant professor at the University of Arizona, Tucson, where he spent the remainder of his career. As his focus shifted to gauge theories, he worked on classical solutions now called instantons and solitons. From 1977 to 1979, Adrian worked with Eldad Gildener on the contributions of instantons to energy spectra and on the effect of fermions coupled to instantons. Adrian and Gildener published a number of articles that received wide recognition.
At the end of the 1970s, Adrian became intensely concerned about the infrared problems inherent in the semiclassical treatment of instanton gases, both in Yang–Mills theory and its two-dimensional analog, the nonlinear sigma models (classical ferromagnets). His work on these instanton gases with Alain Rouet provided a complete calculation showing that these infrared effects lead to surprising results.
In the early 1980s, Adrian turned to the fundamental question of whether quantum behavior can be understood from something more fundamental. He noted that the assumed equipartition of energy, which in the late 19th century led to the failed attempts to understand blackbody radiation within the classical framework and which led Planck to introduce his quantum hypothesis, was not as well founded as many researchers had believed. Inspired by the seminal study of Enrico Fermi, John Pasta, and Stanislaw Ulam, who were arguably the first to document the failure of equipartition in a nonlinear classical system, Adrian studied a variety of nonlinear systems with potentially infinitely many degrees of freedom and found nonergodic behavior (resulting in violation of equipartition), which, in some cases, led to a Planck-like spectrum. Whether his observation actually could lead to a “classical” foundation for quantum behavior remains an intriguing open question.
Adrian’s earlier work with Rouet on the problematic aspects of the semiclassical approximation led directly to the main research theme of Adrian’s later years, during which he questioned the validity of perturbation theory in asymptotically free field theories (four-dimensional Yang–Mills theory and two-dimensional classical ferromagnets with non-abelian symmetry) and hence of asymptotic freedom itself. He began this enterprise in 1984 and was joined in 1987 by one of us (Seiler). They argued that, despite its widespread acceptance, the presence of asymptotic freedom in models with non-abelian symmetry was an unresolved mathematical question. Because the question was central to particle physics (in particular, quantum chromodynamics) and condensed matter physics (low-dimensional ferromagnets), Adrian considered a mathematically rigorous resolution to be of great importance.
Adrian and Seiler used a multipronged attack, analytical as well as numerical, to back their dissident view that the perturbation theory approach, on which asymptotic freedom rests, is mathematically unjustified in those non-abelian models. In the course of their work, they produced a number of new ideas; one of the more interesting was the reduction of the question in the ferromagnetic case to a percolation problem. The percolation approach has proven quite fruitful and has led to some novel rigorous results. The central problem of asymptotic freedom, however, remains mathematically unsolved, although Adrian and Seiler accumulated a large body of evidence supporting their perspective. At the time of his death, Adrian was actively engaged in a number of new projects related to that research theme.
Although Adrian’s devotion to his research was passionate, he pursued other interests with almost equal fervor. He brought to those pursuits many of the same traits that marked his physics research. For example, his love of music was intense but idiosyncratic. He prided himself on finding lesser-known gems, such as Bizet’s “other” opera, The Pearlfishers. This work has since seen renewed public interest, but Adrian was convinced of its merits long before the popular revival. Adrian’s passion for sports was equally intense: He was an avid skier, tennis player, and weightlifter. At the same time, he was a warm and generous person, enriched by an impish, ironic, and often self-deprecating humor. He was a devoted family man, and was especially proud of his daughter and son.
Adrian’s life and career revolved around his tenacious search for the ultimate physical laws. His uncompromising personal honesty never allowed him to be satisfied with a theory that he did not find compelling, even if the weight of the entire physics community was behind it. His friends and colleagues will warmly remember Adrian as a physicist of the highest scientific integrity.