Robert Guyer

Robert Guyer was born on 30 July 1936 and died from leukemia on 3 May 2025. Guyer earned his PhD in physics in 1966, embarking on a career that would bridge academia and applied science. His early work in condensed-matter physics laid the groundwork for his later interdisciplinary research, which spanned condensed-matter physics and geophysics.

At 18, Guyer enrolled at New Mexico State University (NMSU). His enrollment at NMSU and participation in the co-op program—which included work at White Sands Missile Range calibrating cameras—afforded him a means to finance his education and provided valuable hands-on experience. Following his undergraduate work, Guyer pursued his PhD at Cornell under James Krumhansl . They developed the foundational Guyer–Krumhansl equation , which provided a more accurate description of heat flow in certain regimes than did classical models.

In 1963, Guyer began his academic career at Duke University as part of the low-temperature physics group led by Henry Fairbank . During his time at Duke, Guyer provided the theoretical underpinnings necessary to design experiments that successfully confirmed the existence of “second sound,” contributing to major advancements in the understanding of quantum fluid dynamics. After his time at Duke, he held a fellowship at Harvard University before joining the physics faculty at the University of Massachusetts Amherst in 1969.

Guyer served as a professor at the UMass Amherst from 1969 to 2006. Here he made fundamental contributions across a range of physics and materials-science domains. His research at UMass was characterized by a shift toward the study of complex materials and nonlinear phenomena. One of Guyer’s most impactful and enduring contributions during his time at UMass was in the development of the field of nonlinear mesoscopic elasticity. In this pioneering work, conducted in collaboration with researchers at Los Alamos National Laboratory (LANL), Guyer spearheaded the theoretical investigation into the unusual elastic behavior exhibited by a wide range of disordered materials. Those materials, including rocks, granular media in general, and some biological tissues, display strong nonlinear responses when subjected to stress. The responses manifest in several key phenomena, including stress–strain hysteresis, discrete memory, the ability of the material to “remember” past stress states, and slow dynamics, characterized by the gradual change in elastic properties following a stress perturbation.

To elucidate those complex behaviors, Guyer, with Katherine McCall, developed a theoretical framework, centered on the concept of mesoscopic defects such as grain boundaries and microcracks and their reaction to applied stress, known as the Preisach–Mayergoyz theory of elasticity . The theory provided a crucial basis for characterizing and understanding the mechanical behavior of those materials. An overview of the topic authored by Guyer and Paul Johnson appeared in 1999 as a cover article in Physics Today, introducing a broad audience to the topic. Guyer’s coauthored book, Nonlinear Mesoscopic Elasticity: The Complex Behaviour of Rocks, Soil, Concrete, stands as a testament to this substantial body of work undertaken during his time at the university.

Building upon his seminal work in nonlinear elasticity, Guyer extended his investigations to the phenomena of hysteresis and slow dynamics across a diverse range of materials beyond Earth materials. Those included polymers, where he studied their viscoelastic and hysteretic properties, seeking to unravel the time-dependent aspects of their mechanical response. Later in his career at UMass, Guyer began to examine the complex mechanical behavior of wood, including the significant influence of moisture content on its properties, a pursuit that involved collaborations with individuals at ETH Zurich. Across those varied material classes, the overarching aim of his research was to identify unifying principles that govern the time-dependent and history-dependent behaviors, seeking a deeper understanding of the fundamental mechanisms at play.

After retiring from UMass in 2006, Guyer moved to Reno, Nevada, where he continued teaching and research in the areas of nonlinear acoustics, geophysics, and materials science, with individuals at LANL and ETH Zurich. His contributions here included efforts to unravel the complexities of earthquake dynamics, to characterize the behavior of rocks under the immense pressures found within Earth, and to improve downhole measurement techniques for fracture characterization, demonstrating the practical relevance of his theoretical insights.

Guyer is survived by family, colleagues, former students, and a large scientific community that continues to benefit from his work. We will remember him for the generous spirit with which he shared his scientific insight—never seeking recognition for himself—and for his unwavering dedication to mentoring and uplifting young scientists.

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