Padmanabhan served as chairman (2006–09) of the Time Allocation Committee[6] of the Giant Meterwave Radio Telescope of NCRA. He was chairman (2008–11) of the Indian National Science Academy's National Committee[7] which interfaces with the activities of the International Astronomical Union. In addition to advising the Government on policy issues, this also required him to coordinate the International Year of Astronomy 2009 activities in the country.[5]
In addition to his scientific research, Padmanabhan worked actively to popularize science and gave over 300 popular science lectures and authored more than 100 popular science articles. He did a comic strip serialThe Story of Physics[9] aimed at school children. Published by Vigyan Prasar (New Delhi), it was translated into half a dozen regional Indian languages and made available at an affordable price at Indian schools. To commemorate the International Year of Astronomy (IYA) in 2009, he published (withJ. V. Narlikar and Samir Dhurde) the IYA Astronomical Diary 2009,[10] which comprises 53 illustrated pages of astronomical information. In 2019, he co-authored with Vasanthi PadmanabhanThe Dawn of Science (published by Springer[11]).
He was married to Vasanthi Padmanabhan, who has a Ph.D. in astrophysics from TIFR, Mumbai, and they had one daughter, Hamsa Padmanabhan, who herself has a Ph.D. in astrophysics from IUCAA, Pune.[12]
He died on 17 September 2021 at the age of 64 after a heart attack at his residence in Pune.[4][13] A tribute article written by his former graduate students and post-doctoral fellows and physics friends from college days has been posted on the Physics arXiv.[14]
His research work won prizes nine times (in 1984, 2002, 2003, 2006, 2008, 2012, 2014, 2018 and 2020) including the First Prize in 2008 from theGravity Research Foundation, USA.[28]
A Stanford study in 2020, listing top scientists in different fields, ranked Padmanabhan as 24th in the world in his research area.[29][30]
Padmanabhan's research was on the fields of gravitation and cosmology which includesquantum gravity and nature ofdark energy.[31][32] During 2002–2015, he provided a clear interpretation ofgravity as an emergent phenomenon (like elasticity or fluid dynamics) and showed that this paradigm extends to a wide class of theories of gravitation including, but not limited to, general relativity.[33][34] Padmanabhan could show that several peculiar aspects of classical gravitational theories find natural interpretations in this approach.[35] Such an interpretation also provides a novel solution to the cosmological constant problem.[36] He gave two lectures at the Oxford–Cambridge collaborative conference on "Cosmology and the Constants of Nature" about this.[37][38]
Popular (non-technical) descriptions of Padmanabhan's research have been published inScientific American (India),[39] and a more technical description is available in an article from theGravity Research Foundation in 2008, that describes his First Prize work. Another popular article about his work which appeared in a German science magazine[40] along with the English translation.[41] An interview of Padmanabhan by George Musser about his work can be foundhere.
In the earlier part of Padmanabhan's career (1980–2001), he made important contributions toquantum cosmology,structure formation in the universe and statistical mechanics of gravitating systems. In the 1980s, he came up with an interpretation of thePlanck length as the 'zero-point length' of thespacetime based on very general considerations.[42] This result, established by theoretical considerations and well-chosen thought experiments,[43] finds an echo in more recent results in several other candidate models forquantum gravity. He developed the complex path method (in 1998[44]) to studyblack hole thermodynamics which was a precursor to the 'tunneling paradigm' that became quite popular later on. He was a recognized authority in the subject of the statistical mechanics of gravitating systems[45] and was a pioneer in the systematic application of these concepts to study thegravitational clustering in anexpanding universe.[46] He was invited to lecture twice at the Les Houches Schools (in 2002 and 2008) to a broader community about this subject.
In November 2016, Padmanabhan published research studies advocating a newparadigm shift in understandinggravity.[47][48] A key question in quantum gravity lies in understanding the primordial, pre-geometric phase of the universe, from which the classical, geometric phase described by Einstein's equations emerges along with the notions of space and time themselves. Padmanabhan introduced the notion of Cosmic Information (called 'CosmIn'), which allows these two phases to be connected in a fascinating manner. CosmIn, which is aconserved quantity, measures the total information transferred from the quantum gravitational phase to the classical phase of the universe. Quantum gravitational considerations advocate an astonishingly simple value for CosmIn: 4π, the number of information 'bits' on the surface of a sphere of unit radius. Using these considerations, CosmIn was able to relate the numerical value of thecosmological constant – possibly the deepest unsolved problem intheoretical physics today – to the energy scale at which the universe made the quantum-to-classical transition.[49] This is the first time that a model with no adjustable parameters is able to provide a holistic explanation for both these observations, which has far-reaching implications for the quantum structure of spacetime. A non-technical account covering this latest development in Padmanabhan's research was published in the magazineNautilus.[50]
Do We really Understand the Cosmos?, Comptes Rendus Physique, 18 (3–4): 275–291, arXiv:1611.03505, Bibcode:2017CRPhy..18..275P. doi:10.1016/j.crhy.2017.02.001
The Story of Physics, a comic strip serialised in the magazine Science Age, from Sept. 1984 to Dec. 1986; published in book form byVigyan Prasar, New Delhi, (2002) and now translated into several Indian regional languages.
^Padmanabhan, Thanu (2002). "Statistical Mechanics of Gravitating Systems in Static and Cosmological Backgrounds".Dynamics and Thermodynamics of Systems with Long-Range Interactions. Lecture Notes in Physics. Vol. 602. pp. 165–207.arXiv:astro-ph/0206131.doi:10.1007/3-540-45835-2_7.ISBN978-3-540-44315-5.
Another set of lecturesArchived 10 January 2018 at theWayback Machine (15 hours) by Padmanabhan on Advanced Topics in general relativity at the 'troisieme cycle de la physique en suisse romande' course (Geneva, Switzerland).
