An internationally renowned mathematician in probability theory, Freidlin was once a Russian “refusenik.”

After more than 30 years at the University of Maryland, Distinguished University Professor Emeritus of Mathematics Mark Freidlin retired on July 1, 2021. After being barred from leaving his home country 40 years ago and shut out of academic life for nearly a decade, Freidlin moved to Maryland and traveled the world as an invited speaker at prestigious mathematical conferences and research institutions. 

Freidlin was born in Moscow and began his career in mathematics during the Cold War between the United States and the former Soviet Union. As a professor of mathematics at Moscow State University in the 1960s and ’70s, Freidlin earned both privilege and status in a country that valued higher education and revered rigorous intellectual pursuits. 

But as a person of Jewish descent, Freidlin was also subjected to government harassment, discrimination and policies that limited his professional and economic opportunities. He applied for an exit visa in 1979 with hopes of leaving the Soviet Union with his wife, Lera, who was also a mathematician, and their two children. They were denied an exit visa without an explanation, and they were promptly fired from their jobs and barred from publishing papers in the Soviet Union or attending scientific conferences. 

During those years, the Soviet Union ran a brutal political campaign to separate its citizens and citizens from other East bloc countries from the Western world behind what Winston Churchill called the Iron Curtain. Scientists and mathematicians were often denied permission to leave the country. After Freidlin and his wife requested permission to emigrate, they were labeled “refuseniks”—Soviet citizens denied the freedom to leave their country by the Soviet government. Freidlin was 41 years old.

For eight years, Freidlin and his wife made a living as tutors. Lera also got work translating documents, and Freidlin continued working on mathematics on his own. But he had already earned an international reputation, in part because of a book he and his colleague Alexander Wentzell published right before he was shut out of academia.

“I waited until after the book was published to apply for an exit visa, because I knew if I applied before, the book would never be published,” Freidlin recalled.

The book was first published in Russian in 1979 and was translated into English in 1984. Several editions followed, with the latest published in 2012. The book introduced a theory, now known as the Freidlin-Wentzell theory, which explains how small, seemingly insignificant, perturbations in complicated systems can create critical changes in the system over long time periods. The theory is widely used in mathematical modeling in fields as diverse as physics, biology, economics, and the social sciences.

The Freidlin-Wentzell theory laid the groundwork for much of his later research that seeks to describe the effects of small random fluctuations on dynamical systems. 

“In many mathematical models, if you don’t take into account random perturbations in the system, that may work fine over certain time intervals,” Freidlin explained. “But over longer time intervals, these perturbations can become critical enough to cause a transition from one stable behavior to another stable behavior, and our goal is to describe these transitions.” 

Freidlin would eventually work with Wentzell again, years after the Soviet Union fell and they were both in the U.S., but in the eight years between publication of his first book and his arrival in Maryland, Freidlin was forced to work largely on his own. During that time, his western colleagues helped Freidlin communicate with the outside world. 

Visiting colleagues smuggled Freidlin’s letters and academic papers out of the country, and he remained an important figure in the world of mathematics, publishing several papers in academic journals outside of the Soviet Union during his time as a refusenik.

But those papers represented just a fraction of Freidlin’s work during those years, so he compiled his unpublished works into a second book that his wife translated into English. They had it smuggled out of the country, and his former Ph.D. advisor Eugene Dynkin arranged for it to be published through Princeton University Press. Dynkin left the Soviet Union in 1977 and was teaching mathematics at Cornell University. 

“A colleague carried it out of the country,” Freidlin recalled. “We changed the cover page to make it look as if he was the author of the book so that if he was caught it would not appear to be mine.”

Freidlin’s second book “Functional Integration and Partial Differential Equations” was published in 1985. Two years later, under pressure from the international community, the Soviet government granted Freidlin and his family permission to leave. He and Lera packed up their two children and moved to Maryland in 1987.

“I had some other offers from different countries,” Freidlin recalled, “but various colleagues including Dynkin convinced me to go to Maryland.” 

Lera took a job as a statistician at the National Institutes of Health. And after waiting so many years to leave his homeland, Freidlin embarked on a few years of travel to share his mathematical ideas as an invited speaker in France, Israel, Germany, Italy, England, Canada, and all over the U.S. He was even an invited speaker at the International Congress of Mathematicians in 1998.   

“After eight years, we were happy to come to the United States,” he said. “I had liked to teach students, and I enjoyed teaching again and being able to travel and talk with colleagues openly. I was very happy.” 

During his tenure at UMD, Freidlin mentored more than a dozen Ph.D. students and several postdoctoral associates. He has given more than 170 invited talks around the world and published nearly 100 refereed papers (making a combined total exceeding 150 papers over the course of his career). 

Through these works, Freidlin made prolific contributions to the field of stochastics, which is the study of complex processes that can be analyzed and predicted statistically but defy prediction of precise outcomes. 

“I was very lucky to be a mathematician,” Freidlin said. “It is very interesting work, and it’s a world where you can live outside these other problems you know. There is always something interesting in mathematics that you can be challenged to think about and to solve.” 

Freidlin will continue to work on mathematical theories in his retirement and spend more time with his grandchildren. He also looks forward to resuming travel once the threat of COVID-19 is in the rearview mirror. Hopefully, he should not have to wait eight years.

Written by Kimbra Cutlip