Alexander “Sasha” Markovich Polyakov, one of the world’s preeminent theoretical physicists and a leading authority on quantum field theory and string theory, transferred to emeritus on July 1, 2023, after thirty-four years on the faculty at Princeton University. His singular creativity and profound ideas have made a lasting mark on elementary particle physics, statistical mechanics, quantum gravity, and other cutting-edge research areas. Sasha is a prominent member of a group of scientists who were educated in the Soviet Union and gained a worldwide reputation while working there, but chose to leave for the West when such a move became possible.

Sasha was born in Moscow in 1945 into an academic family that was deeply affected by both World War II and the Stalinist purges. His special scientific talents were recognized very early, when he was a secondary school student, and brought him into contact with some of the leading Soviet theoretical physicists, including the great Lev Landau. While a student at the Moscow Institute of Physics and Technology (MIPT), Sasha collaborated with his friend Alexander Migdal on a paper that discovered the celebrated Higgs mechanism independently from researchers in the West. This mechanism later turned out to be of profound importance for the construction of the Standard Model of elementary particle physics.

Sasha graduated from MIPT in 1967 and two years later defended his Ph.D. dissertation at the Landau Institute for Theoretical Physics. In 1970, he wrote a seminal paper conjecturing that a statistical system at the point of second order phase transition is not only scale invariant but also has the so-called conformal symmetry. This key idea has continued to guide Sasha’s research for many years, and it has blossomed into a large research area called conformal field theory.

In 1974, Sasha proposed a set of consistency conditions for such theories that goes by the name “conformal bootstrap.” A dozen years ago, this approach was revived by Sasha’s former graduate student Slava Rychkov (a 2002 Princeton Ph.D.), and by now the conformal bootstrap has become an industry practiced by hundreds of researchers.

Sasha has also collaborated with Alexander Belavin and Alexander Zamolodchikov on a powerful application of the conformal bootstrap to two-dimensional systems. Their remarkable paper, which has been very influential for close to forty years, provided a classification and exact solution of an infinite class of conformally invariant models, which generalize the classic Ising model at its second-order phase transition. This paper was also of major importance for a new approach to string quantization, often called the Polyakov string theory. 

In the 1970s and 1980s, Sasha also made major contributions to the theory of quark confinement in quantum chromodynamics, the fundamental description of the strongly interacting particles such as the proton and neutron. He is also regarded for discovering the ’t Hooft-Polyakov monopole solution, which describes a magnetically charged heavy particle that may be present in some extensions of the Standard Model of particle physics. At the time of his emigration from Moscow in 1988, Sasha was the head of the Department of Quantum Field Theory at the Landau Institute and a corresponding member of the Academy of Sciences of the U.S.S.R.

After entering the U.S., Sasha was approached by several top universities with offers of full professorships. He accepted the offer from Princeton University and joined the physics department in September 1989. Also joining the department that year was Sasha’s friend and long-time colleague Migdal. Since 1999, Sasha has been the Joseph Henry Professor of Physics. An avid outdoorsman, Sasha came to appreciate the natural setting of Princeton and its surroundings. The proximity of the Jersey Shore enabled him to pursue another activity he really enjoyed — taking long swims in the ocean — and his talent for swimming is well-known among his colleagues. While on a trip to Corsica to lecture at a summer school, Sasha managed to swim to a small piece of land quite far from the shore. As a result, the students at the school named it the Polyakov Island. 

In the physics department, Sasha is appreciated for his special advanced graduate courses that are based in part on his beautiful monograph Gauge Fields and Strings (Routledge, 1987). Sasha developed his own signature style of lecturing from memory, without any notes, while emphasizing the conceptual foundations and the unity of theoretical physics. His special topics courses have helped educate and inspire several generations of theoretical physicists, including some of the current leaders of the field. Sasha also developed a popular course on fluid dynamics for advanced undergraduates, which had a broad conceptual appeal.

Sasha’s research in the 1990s was initially focused on two-dimensional quantum gravity, which helped provide a definition of certain low-dimensional models of string theory. Later on, he conjectured a modification of this approach to adapt it to his long-standing interest, the problem of quark confinement. This eventually led Sasha to a collaboration with his Princeton colleagues Steven Gubser and Igor Klebanov on a seminal paper connecting string theory with quantum gauge field theory. This 1998 paper, which is one of the three original works laying out the anti-de Sitter/conformal field theory correspondence, has accumulated close to 12,000 citations in Google Scholar, making it one of the most highly cited papers in high-energy physics. More recently, Sasha has been working on novel quantum approaches to cosmology, as well as on the theory of turbulence.

Sasha’s spectacular scientific accomplishments have earned him worldwide acclaim. He is a member of the U.S. National Academy of Sciences, the American Academy of Arts and Sciences, and a Foreign Member of the French Academy of Sciences. His honors include the American Physical Society’s Dannie Heineman Prize and the Lars Onsager Prize, the International Center for Theoretical Physics’ Dirac Medal, the Royal Netherlands Academy of Arts and Sciences’ Lorentz Medal, the Royal Swedish Academy’s Oscar Klein Medal, the Technion Israeli Institute of Technology’s Harvey Prize, and the German Physical Society’s Max Planck Medal.

In 2013, Sasha was awarded the Breakthrough Prize in Fundamental Physics “for his many discoveries in field theory and string theory, including the conformal bootstrap, magnetic monopoles, instantons, confinement/deconfinement, the quantization of strings in noncritical dimensions, gauge/string duality, and many others. His ideas have dominated the scene in these fields during the past decades.”

Sasha Polyakov has exhibited remarkable foresight throughout his scientific career, and we are confident that his work will remain influential and continue to be appreciated for many years to come. We offer Sasha our very best wishes for his retirement, and hope that he will keep in touch and continue sharing his great wisdom and ideas.

Written by members of the Department of Physics faculty.