Remembering Asoke Nath Mitra (1929-2022), theoretical physicist and role model

He wielded great influence on the nature of research work done in Delhi University.

Asoke Nath Mitra. | Photo Credit: By Special Arrangement

Professor Asoke Nath Mitra, emeritus professor at the University of Delhi and a well-known theoretical physicist, passed away on November 26 in Delhi. Mitra obtained his PhD from Delhi University in 1953 and went to Cornell University in Ithaca, US, to complete a second PhD in 1955. He worked with Hans Bethe and Freeman J. Dyson. Bethe is a Nobel laureate, while Dyson narrowly missed being one. Mitra worked in the area of renormalisation theory of quantum electrodynamics (QED) and elementary particles.

On his return to India in 1955, he joined Aligarh Muslim University as Reader. He moved to Delhi University in 1963 as a professor of physics at the relatively young age of 34. The appointment of Mitra, along with L.S. Kothari and a year later S.N. Biswas, was due to the efforts of R.C. Majumdar with the cooperation of D.S. Kothari. Majumdar also ensured that these eminent theorists were not burdened with practical classes and administrative work and could devote their time to setting up viable groups in their fields.

The office of the Department of Physics and Astrophysics (Main Block) of Delhi University ( a file picture). Delhi University is 100 years old now, and its physics department is 80 years old. Started by D.S. Kothari in 1942, it played a major role in the development of physics in the country in the second half of the 20th century.  | Photo Credit: Shanker Chakravarty

Delhi University is 100 years old now, and its physics department is 80 years old. Started by D.S. Kothari in 1942, it played a major role in the development of physics in the country in the second half of the 20th century. It has had its ups and downs but has managed to keep its head above water. The university was in bad shape when Mitra joined the faculty. From 1942, D.S. Kothari and Majumdar (who were friends and contemporaries of S. Chandrasekhar at Cambridge, UK) gave Delhi University a special status. Quantum mechanics was taught in MSc courses. The BSc (Hons) course, which was taught in the department and not in colleges, had modern and contemporary subjects. Maurice Gwyer was a far-sighted Vice Chancellor of the university then. Kitchlu, the well-known experimentalist, joined later. They attracted relatively bright young faculty members to the department. All this changed by the end of the 1950s.

Around 1948, revolutionary progress was made in QED, but it bypassed Delhi University and several other institutions in India. Both Kothari and Majumdar were aware of this. Bringing Mitra to Delhi was the first step that led to Delhi University recapturing some of its past glory in the 1960s and 1970s. The changes continued, and the department became a Centre for Advanced Study in 1964. A fair number of bright young people were appointed to the faculty.

‘Few body problems’

The trend in QED and particle physics was, and is, for a few leaders to come up with bright ideas and for the others to apply these ideas to calculate various processes between particles. Mitra tried to break away from this trend and build up an identity of his own. He was able to do this by entering the area of “few body problems”. In classical non-relativistic physics, the two-body problem can be solved by separating the relative motion of the two particles from the motion of the centre of mass.

The three-body problem is not solvable in classical physics. Quantum mechanics adds to the difficulties. Mitra succeeded in solving the problem, in the 1960s for the special case of a potential that is separable in momentum space. This gave special insight into the structure of the three-body wave function. This was the beginning of the area of “few nucleon studies”. One of the successful applications was to tritium, which is composed of one proton and two neutrons. This work with one of his students (V.K. Gupta) was published in Physical Review Letters in 1965. In the 1960s, while working on a model of the proton based on fermion quarks, Mitra found that a node occurred in the proton electromagnetic form factor. To avoid that, an extra degree of freedom was needed, which was the forerunner of what was later called “colour”.

Working with Marc Ross, Mitra also discovered the quark recoil effect to explain the enhanced heavy meson modes of decay. Over the years, Mitra “developed a comprehensive dynamical framework leading to an integrated view of the dynamics of 2- and 3-body systems at successively deeper levels of compositeness, from nuclear to sub-hadronic. This attempts to bridge the traditional gap between theoretical sophistication and empirical fits to data.” Mitra had one of his finest moments in December 1975 when he successfully hosted an international conference on few body problems at Delhi University. In the 1980s, Mitra lectured on these ideas at Caltech, US, and got the appreciative attention of Richard Feynman. Mitra often claimed that whatever he learnt in mathematics he owed to his father, Jatindra Nath Mitra. In 1969, Mitra received the Shanti Swarup Bhatnagar award. He was probably the first theoretical physicist to get it. In 1975, he received the Meghnad Saha Award and in 1986 the S.N. Bose Medal of the Indian National Science Academy.

Head of department

Mitra became head of the physics department in 1973, when D.S. Kothari, Majumdar, and F.C. Auluck had retired. He started by consulting teachers, both senior and junior, and tried to bring about the much needed change in the courses offered and in administration. He succeeded to some extent but soon found it difficult to persuade others to go along. Midway through his term of three years, he gave up the headship. Two of his contemporaries, L.S. Kothari and S.N. Biswas, also resigned halfway through their terms. Some scientists committed to their research probably do not like to be administrators or departmental politics takes a big toll on them. During his headship, one particular issue on which Mitra had a long correspondence with the higher authorities was the freedom of the department and the university to invite experts from abroad to visit, lecture, and spend time at the university and interact with students and teachers.

In the 1950s and 1960s, the physics department at Delhi University hosted a large number of foreign and resident and non-resident Indian scientists who inspired students and teachers. This was partially because scientists visiting India for the Science Congress and other conferences around New Year usually passed through New Delhi. Around 1972, a well-known particle physicist from the US was invited to spend a few weeks at the university and give lectures in the department. Unfortunately, the invitee was also a member of a committee advising the US government on science relating to warfare. Some leftist groups in the university became aware of this and organised a protest to stop his lectures. They succeeded after some scuffles and disturbances at the lecture hall. Besides media coverage, there was also a political fallout. Mitra, the head at that time or a little later, had to answer a large number of queries and give clarifications to higher bodies such as the University Grants Commission, the Ministry of Education, and Parliament.

Academic autonomy

I had an occasion to see the bulky file later. Mitra’s pleading for academic autonomy was evident in every letter that he wrote, but unfortunately, many constraints such as getting permissions and clearances from higher bodies were imposed. Academic freedom was and is curtailed in many ways, subtle and blatant, even now. What amazed me was the fact that Mitra never mentioned or took credit for all his efforts in minimising the constraints. Probably, it was the most natural thing for an academic do and that was that as far as he was concerned.

Mitra had a way of underplaying himself and trying not to take centre stage, which sometimes led to amusing situations as the following anecdote shows. N. Mukunda was once giving a lecture at Delhi, when Mitra came in a little late and tried to sneak in quietly at the back. Mukunda paused and asked him to come forward. Mitra said apologetically: “I am only an observer, please ignore me.” Mukunda said: “When the observer comes, the wave function collapses. We cannot ignore you.” (In quantum mechanics, the wave function describing a state can be a superposition of two mutually exclusive states, like a dead cat and a cat that is alive. When a measurement is performed by the observer, the wave function changes [usually called collapse] to a definite physical state, either a dead cat or a live cat.)

Mitra rarely spent any time without teaching students. Most of it was at Delhi University. He was an excellent teacher, with a distinctive style, though in the early years he faced some problems. Soon after he joined the university, some students found his detailed arguments and derivations difficult to follow in class and complained to Majumdar, who spoke to Mitra about it. Mitra promptly submitted his resignation, and Majumdar had to make more than one trip to Mitra’s house to persuade him to withdraw it.

Mitra was interested, to some extent, in questions that go beyond science. Persuaded by E.C.G. Sudarshan, in the 1970s, he attended a few conferences on consciousness, and spirituality and science. Later, Mitra collaborated with his daughter Gargi Delmotte in studying the origin of consciousness and life.

During the 2005-10 period, Mitra undertook the mammoth task of editing a book, India in the World of Physics: Then and Now, for the Centre for Studies in Civilizations, in Delhi. The time taken indicates the difficulties associated with the task. 

During the period 2005-10, Mitra was editing a book, India in the World of Physics: Then and Now, for the Centre for Studies in Civilizations, in Delhi. It was a mammoth task and took Mitra all of five years. The time taken indicates the difficulties associated with such a task. Unfortunately, the price of such books makes them inaccessible to most scholars. Mitra’s descriptive English writing was always a source of admiration. He brings out the nuances and subtleties in the themes, and the intellectual level of his articles is very high.

Mitra kept himself up to date with events and trends in India and the world in politics and in science, but his first love was research in science. In his Nehru Memorial Lecture in the 1970s, George Sudarshan said that scientists were the modern rishis (sages). This is easy to believe when one thinks of some of the eminent teachers at Delhi University and elsewhere. Their simplicity and lack of worldliness were striking. Their commitment and devotion to the study and teaching of science were so intense that they forwent many other interests and economic advantages in life.

Mitra was a role model and had a great influence on the nature of research work done in Delhi University. This is because a large number of his students who occupied and still occupy teaching positions in the physics department and the university’s constituent colleges. Mitra constantly tried to identify, propose, and support possible candidates for election as Fellows to the three science academies in India. He succeeded in some cases but was unsuccessful in others.

In one particular case of a bright scientist, he failed because of disunity among the teachers of the department and their supporters in the academy. Senior professors often disagree. Sometimes, they discuss among themselves and agree on a common approach. This is what happened when D.S. Kothari and Majumdar were senior professors. With professors who came later, this process did not quite work out. This caused difficulties in running the department from time to time.

Mitra married Anjali Ghosh in 1956 and had two daughters. The elder, Bani, lived in Sweden and died a few years ago. The younger, Gargi lives in France. Anjali Mitra died in January this year. Mitra followed within 11 months.

Natarajan Panchapakesan is a retired professor of the University of Delhi.

The article is adapted and abbreviated from an article the author wrote for Current Science for the series Living Legends of Indian Science in the January 10, 2014, issue.

The Crux

• Asoke Nath Mitra, emeritus professor at the University of Delhi and a well-known theoretical physicist, passed away on November 26 in Delhi.
• He obtained his PhD from Delhi University in 1953 and went to Cornell University in Ithaca, US, to complete a second PhD in 1955. He worked with Hans Bethe, a Nobel laureate, and Freeman J. Dyson.
• Mitra worked in the area of renormalisation theory of quantum electrodynamics (QED) and elementary particles.
• In 1955, he joined Aligarh Muslim University as Reader.
• In 1963, he joined Delhi University as a professor of physics.
• He entered the area of “few body problems” and succeeded in solving the three-body problem, in the 1960s for the special case of a potential that is separable in momentum space.
• This gave special insight into the structure of the three-body wave function ands was the beginning of the area of “few nucleon studies”.
• Working with Marc Ross, Mitra discovered the quark recoil effect to explain the enhanced heavy meson modes of decay.
• IN 1973, Mitra became head of the physics department at Delhi University.
• He had one of his finest moments in December 1975 when he successfully hosted an international conference on few body problems at the university.
• In the 1980s, Mitra lectured on these ideas at Caltech, US, and got the appreciative attention of Richard Feynman.
• In 1969, Mitra received the Shanti Swarup Bhatnagar award, probably the first theoretical physicist to get it. In 1975, he received the Meghnad Saha Award, and in 1986 the S.N. Bose Medal of the Indian National Science Academy.
• A large number of his students occupied and still occupy teaching positions in the physics department of DU and the university’s constituent colleges.