Prof. Thanu Padmanabhan (10 March, 1957 – 17 September, 2021) (L0956)

Remembering Paddy

Professor Thanu Padmanabhan, known affectionately as Paddy, passed away on September 17, 2021, at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India. He had joined the Tata Institute of Fundamental Research, Mumbai, India, as a faculty member in 1980, before moving to IUCAA in 1992, where he stayed till his untimely demise.

In his illustrious career spanning more than four decades, Paddy contributed significantly to a broad spectrum of topics related to astrophysics, cosmology and classical and quantum aspects of gravitation. His research during the early days was aimed at exploring the implications of the quantization of the conformal degree of freedom of spacetime, which led to interesting results such as the avoidance of singularities and the nature of spacetime at short distances. Subsequently, he investigated the manner in which semiclassical gravity can be arrived at from a complete quantum theory and examined its domain of validity. Within semiclassical gravity, he examined the phenomena of vacuum polarization and particle production in different situations, including non-trivial effects that arise during the inflationary epoch in the early universe and around black holes. Simultaneously, he studied the formation of large scale structure in the universe utilizing semi-analytic methods as well extensive numerical simulations. Around the turn of the century, with the advent of precision cosmology, he worked on understanding the observational evidence for the cosmological constant as well as its possible nature and origin.

During the last decade-and-a-half, motivated by the thermodynamic nature of gravity, he was developing an approach to the emergent gravity paradigm and exploring its ramifications. Paddy was fascinated by the cosmological constant and, in fact, one of his recent aims was to understand the microscopic nature of the cosmological constant in the context of the emergent gravity paradigm.

An important and distinguishing feature of Paddy’s career has been his conscious effort towards writing textbooks aimed at students at different levels. He has also authored many popular science articles and books which have motivated students to pursue research in physics. We believe that his articles, books and lectures will continue to inspire generations of students and researchers to take up the challenge of understanding the laws of nature.

During his career, Paddy received numerous awards both at the national and the international levels, including the INSA Young Scientist Award (in 1984), the Shanti Swarup Bhatnagar Award (in 1996), the Millennium Medal (in 2000), the Al-Khwarizmi International Award (in 2002), the Miegunyah Award of the Melbourne University (in 2004), the Padma Shri (in 2007), the Inaugural Infosys Prize in Physical Sciences (in 2009) and the Third World Academy of Sciences Prize in Physics (in 2011). Very recently, he was conferred the Lifetime Achievement Award (Kerala Sasthra Puraskaram) of the Government of Kerala (in 2021). Notably, he also won the First Prize in the Gravity Essay Contest (in 2008) awarded by the Gravity Research Foundation, USA. He was a Fellow of all the three Science Academies in India as well as the Third World Academy of Sciences.

Paddy was a guiding light for all of his students and postdoctoral fellows who have interacted with him. The light having gone out has filled us with insurmountable grief and sorrow. Paddy was a father figure and a close friend to all of us. His sudden demise leaves a deep void behind. He will remain in our memories forever.

Paddy holds a singular place in our scientific journeys, and in his inimitable, irrepressible and intense manner, made our lives richer and engagement with science deeper in so many ways. He leaves behind an intellectual legacy of the highest calibre. We hope our memories of Paddy will give all of us the strength to carry ourselves through this difficult time, and his energy and enthusiasm will remain with all of us as a constant source of motivation and inspiration.

------------------------------------------------------------------------------------------------------------------------------
Jasjeet Bagla, Krishnakanta Bhattacharya, Sourav Bhattacharya, Sumanta Chakraborty, Tirthankar Roy Choudhury, Sunu Engineer, Valerio Faraoni, Jai-Chan Hwang, Harvinder K. Jassal, Nissim Kanekar, Sanved Kolekar, Dawood Kothawala, Kinjalk Lochan, Gaurang Mahajan, Bibhas Ranjan Majhi, Sujoy Modak, Ali Nayeri, Aseem Paranjape, Krishna Mohan Parattu, Karthik Rajeev, Sudipta Sarkar, Sandipan Sengupta, T. R. Seshadri, Shiv Sethi, S. Shankaranarayanan, Suprit Singh, Tejinder Singh, K. Srinivasan, L. Sriramkumar, Urjit A. Yajnik.
-------------------------------------------------------------------------------------------------------------------------------

Thanu Padmanabhan : An Ideal Student and Teacher

This is not a formal obituary but an appreciation of a scientist with many talents and achievements, with whom I had the privilege to interact. Like me, there will be many who will miss his wit and wisdom: indeed, his early demise has left a gap that will take a long time to bridge. For, Thanu Padmanabhan (commonly known as ‘Paddy’) was that academic rarity, a good student and a good teacher.
-----------------------
My interaction with Paddy started in 1979, at the Einstein Centenary Conference at the Physical Research Laboratory, Ahmedabad organized by Indian astronomers and relativists in 1979. The organizers had gone out of the way to attract postgraduate students to basic physics. Review talks were expected to make students aware of the current developments and challenges in physics in the hundred years since Einstein’s birth.

I noticed that although different students would respond differently (if at all!), there was one who stood out distinctly ‘ahead in the pack’. Almost after each talk when the session Chairman called for questions, this student had something to say. On my enquiry I was told that he was T. Padmanabhan from Kerala, an M.Sc. student in physics. That his intervention was nontrivial could be seen from the nature of reply by the speaker.

After the conference I returned to TIFR (Tata Institute of Fundamental Research) and in my daily routine lost touch with that student. Every year in July, TIFR Physics Faculty recruited students for the graduate school after a series of rigorous interviews. As a rule I took part in the deliberations of the Final Selection Committee which decided which students were good enough for the offer of TIFR studentship.

However, that year I was abroad in July and so missed the selection process. But the Director (Professor B.V. Sreekantan) informed me that one student was found to be exceptionally good and answered all questions correctly. The reason for informing me was that when the Final Selection Committee made the offer of admission to this student, he had his own condition! He would join only if he were permitted to work with me.

Normally, a graduate school student would work to clear all the required lectures and tests in the first year and the Faculty would then assign him/her to what it considered the most suitable guide. Thus a student asking for a specific guide right at the beginning was most unusual. But the Director felt that the student’s performance at the interview was so good that he had agreed to it.
That was how Paddy came to be my student.

--------------------------------

His interests were more in formal aspects of fundamental physics, than in astronomy although he was well read in both. I set him to work on quantum cosmology. I had been working on this since my visit to John Wheeler in 1977. As I discovered, Paddy was quick to pick up the basic idea. In fact his thesis was completed in less than four years.

Later in his post doctoral work he was never short of ideas and had a growing number of students of his own. In fact slowly but surely his reputation as an excellent teacher began to grow. Thus he was in great demand as a speaker both for technical and nontechnical meetings.

His books mainly from Cambridge University Press are excellent examples of pedagogical writings.

----------------------
His major mission in research was to link gravity with thermodynamics. This may look like (but is much deeper than) Stephan Hawking’s linkage between the laws of black hole physics and the laws of thermodynamics. Paddy himself talked of gravity as an emergent phenomenon. This work was part of his presentation for the Infosys Award.
Paddy was honored on several occasions with awards like the S.S. Bhatnagar Award, Fellowships of academies, including the international Al-Khwarizmi award from Iran. His brief biodata gives a glimpse of these.

For me though, his joining IUCAA was a great help. As expected, he brought impeccable standards in teaching and research. An example of plain living and high thinking, he expected others to be equally disciplined. His ‘hard judge’ image sometimes made him unpopular! But this helped in maintaining good standards.
Paddy is survived by his wife Vasanti who had been his research colleague and a valuable assistant in his writings. Their daughter Hamsavahini (Hamsa) is herself an excellent research scientist.

-------------------
Thanu Padmanabhan
Date of Birth: 10 March, 1957
M.Sc. in University College, University of Kerala in 1979
Ph.D. Mumbai University at Tata Institute of Fundamental Research, 1983
Broad area of research : Fundamental physics – gravity, quantum theory
Publications: Several advance level text books, review articles and popular science articles
Positions: Senior Faculty positions at TIFR and later at the Inter-University Centre for Astronomy and Astrophysics (IUCAA)
2006-2009 President of Cosmology Commission of the International Astronomical Union (IAU)
Fellowship of Indian Academy of Sciences, Indian National Science Academy, Third World Academy of Sciences (TWAS)
Member and sometime President of the Indian Association of General Relativity and Gravitation, Astronomical Society of India
S.S. Bhatnagar Award in Physics, TWAS Award in Physics, INFOSYS Award, Khwarizmi International Award (KIA)
Padmashri Award 2007
Paddy’s biodata is very extensive… here I mention only a few highlights.

-----------------------------------------------------------------------
Jayant Narlikar
-----------------------------------------------------------------------