# Grigory Isaakovich Barenblatt

## Professor of Mathematics, Emeritus

Grigory Isaakovich Barenblatt was a Russian mathematician and physicist who arrived in Berkeley as a visiting professor in 1996, with a joint appointment as a senior scientist at the Lawrence Berkeley Laboratory. He died in Moscow on June 22, 2018. Barenblatt (Grisha to his friends) was born on July 10, 1927. He was the son of the virologist Nadezhda Veniaminovna Kagan, who developed a vaccine against encephalitis and who became infected and died in a laboratory accident, and the endocrinologist Isaak Grigorievich Barenblatt. His grandfather was the mathematician Veniamin Kagan. He was the son-in-law of Pelagueya Yakovlevna Polubarinova-Kochina, illustrious pioneer of Soviet applied mathematics, who reached her centenary without stopping her work.

Barenblatt graduated in 1950 from Lomonosov Moscow State University, in the famous Department of Mechanics and Mathematics, where he studied under Boris Moiseevich Levitan and Andrei Nikolaevich Kolmogorov. He obtained his first doctorate degree (*Kandidat Nauk*) in 1953 under the supervision of Kolmogorov, who had a deep influence on him, especially in the areas of turbulence, dimensional analysis, and scaling. Barenblatt maintained a life-long passionate interest in these topics, which have acquired an enormous role in contemporary mathematical physics. He was also greatly influenced by a long collaboration with Yakov Borisovich Zeldovich, which later led to a seminal generalization of the approach that Kolmogorov had used, uncovering the relationship between similarity and asymptotics. This work would be the cornerstone of his many contributions to continuum mechanics, including fluid flow in porous media, elasto-plastic porous media, turbulence, and fracture.

Barenblatt received the title of *Doktor Nauk *(second doctorate, a post-doctoral degree equivalent to the British D.Sc.) in 1957. In 1962 he became a Professor at Moscow State University. He held the following positions in the USSR: Research Scientist, Senior Research Scientist, Institute of Petroleum, USSR Academy of Sciences (1953-56); Head, Department of Plasticity, Institute of Mechanics, Moscow University (1961-75); Head, Theoretical Department, Institute of Oceanology, USSR Academy of Sciences (1975-92).

With the onset of glasnost the doors were opened in the USSR and Barenblatt arrived in the West in 1990, when he visited the Université de Paris VI. In 1991, he spent the spring at the IMA Institute of the University of Minnesota, where two of the authors of this memorial resolution (MB, JLV) first met him. It was a moment in which Barenblatt presented his ideas and posed multiple mathematical problems that would occupy researchers for years. He came from “the World on the Other Side” with his physically motivated equations, a permanent smile, and an endless store of stories. He sought to unite in science the best of both worlds and his life is an example that shows that it is possible. A number of the attendees reoriented their research to incorporate his ideas and mathematical problems, and have been solving some of those problems and raising new ones ever since. Since that spring in Minnesota in 1991 they never lost scientific and human contact with Grigory Isaakovich.

Barenblatt became G. I. Taylor Professor of Fluid Mechanics at the University of Cambridge from 1992 to 1994 and has been G.I. Taylor Professor Emeritus of Fluid Mechanics since then. He cherished this as his highest honor, and the stay in Cambridge affected him deeply. Nobody understood better than he the importance of the longstanding British tradition in fluid mechanics, and he had a deep scientific and personal relationship with several of its representatives, such as Batchelor, Crighton and Lighthill. As an active Professorial Fellow of the Gonville & Caius College in Cambridge, he enjoyed British academic traditions in general. Just before his arrival in Cambridge he was a visiting professor at the University of Rome Tor Vergata (1992). In 1993 he visited the Department of Mathematics of the Universidad Autónoma of Madrid as BBVA Visiting Professor. In 1994, he was a visiting professor at the University of Minnesota. He returned to Spain in 1996 as Iberdrola Visiting Professor at the Universidad Autónoma de Madrid.

Grigory Isaakovich arrived in Berkeley in February 1996 as a visiting professor, after a stay at the University of Illinois. This was when another of the present authors (AJC) met him; it was the beginning of a long collaboration and friendship.

It soon became clear that the Mathematics Department at Berkeley would be delighted to have Grigory Isaakovich for a much longer stay as Professor in Residence, a highly honored position that does not require a heavy teaching load, with a concurrent appointment as a senior scientist at the Lawrence Berkeley National Laboratory. Many of the applied mathematicians at Berkeley were oriented towards computing, and were enthusiastic to collaborate with a great master who had a different perspective. When he came to Berkeley, Grigory Isaakovich was already committed to a semester-long visit to Stanford, so he went there for a few months and then returned to Berkeley.

The mathematics group at the Lawrence Berkeley Lab had a suite of offices where the doors were open and it was easy for faculty, postdocs, and students to talk and collaborate. Barenblatt fit wonderfully into this environment. He provided advice, information, perspective, and leadership. He used to invite the young mathematicians to afternoon tea in his office where he talked to them about great scientific problems, about his career and life, and about science in the Soviet Union. They loved it, stayed for hours and asked questions; he gave them a perspective on the joys and possibilities of a great scientific career and a model to emulate. He taught some extraordinary courses, on topics such as fluid mechanics, fracture, turbulence and porous media. A large part of his audience was made up of faculty, from a variety of departments. He became an essential part of the applied mathematics seminar; some adaptation was needed because traditionally scientific seminars in Russia tend to be more confrontational that the ones in the United States, and Grigory Isaakovich could be quite critical of under-par presentations. Under his impact, the seminars became more lively, more interesting and more instructive.

Grigory Isaakovich excelled at linking different worlds, such as Russian and western science. His major impact at Berkeley was to link computing approaches to asymptotics and scaling methods. This produces better scientists and its impact continues to grow.

Grigory Isaakovich returned to live full time with his family in Moscow in his last years. At 90, he still went to work in his Oceanology laboratory every day that he could.

Barenblatt held foreign memberships in the US National Academy of Sciences, the US National Academy of Engineering, the American Academy of Arts and Sciences and the Royal Society of London, as well as in a long list of scientific societies in several countries. The impressive list of his honors and awards includes the G.I. Taylor Medal of the U.S. Society of Engineering Science, the J.C. Maxwell Medal and Prize of the International Congress for Industrial and Applied Mathematics, and the Timoshenko Medal of the American Society of Mechanical Engineers.

Much of Barenblatt’s work over the years has been the development and application of scaling ideas to a variety of problems. Much of this grew out of his seminal work with Ya.B. Zeldovich on self-similarity as intermediate asymptotics. This was summarized in a remarkable Annual Reviews of Fluid Mechanics article (G.I. Barenblatt and Ya.B. Zeldovich, *Self-similar solutions as intermediate asymptotics*, Annual Review of Fluid Mechanics, 4 (1) (1972), pp. 285-312). His book, *Similarity, Self-similarity and Intermediate Asymptotics*, proved to be highly influential. His ideas are currently having a large impact on the development of the theory and application of nonlinear partial differential equations.

The writers of these lines believe that Barenblatt’s life adventure will endure as a brilliant tale of the fruitful encounter of two worlds, a rare event that we were fortunate enough to witness, and that was in a large part due to his immense curiosity. Grisha held clear ideas about the need for a strong engineering-physics-mathematics interaction that includes pure mathematics, and also about the need for a strong connection between science and culture, and for a better understanding between cultures. He will always remain in our memory as an example and a scientific hero.

Barenblatt is survived by his daughters Nadezhda Kochina and Vera Kochina, sons-in-law Sergey Isayuk and Vadim Kantor, and half-brother Yakov Sinai.

*[An extended version of this obituary appeared in the European Mathematical Society Newsletter 2018-9(109):33-38, DOI: 10.4171/NEWS/109/8.]*

Michiel Bertsch

University of Rome Tor Vergata

Alexandre Chorin

University of California at Berkeley

Lawrence Berkeley National Laboratory

Nigel Goldenfeld

University of Illinois at Urbana-Champaign

Juan Luis Vázquez

Real Academia Española de Ciencias

Univ. Autónoma de Madrid

Univ. Complutense de Madrid

2021