Thanu Padmanabhan (10 March 1957 – 17 September 2021) was an Indian

theoretical physicist Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experime ...

and

cosmologist Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosopher ...

whose research spanned a wide variety of topics in

gravitation In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...

structure formation In physical cosmology, structure formation is the formation of galaxies, galaxy clusters and larger structures from small early density fluctuations. The universe, as is now known from observations of the cosmic microwave background radiation, beg ...

in the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...

and

quantum gravity Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics; it deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the vi ...

. He published nearly 300 papers and reviews in international journals and ten books in these areas. He made several contributions related to the analysis and modelling of

dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...

in the universe and the interpretation of gravity as an

emergent phenomenon In philosophy, systems theory, science, and art, emergence occurs when an entity is observed to have properties its parts do not have on their own, properties or behaviors that emerge only when the parts interact in a wider whole. Emergen ...

. He was a Distinguished Professor at the

Inter-University Centre for Astronomy and Astrophysics The Inter-University Centre for Astronomy and Astrophysics (IUCAA) is an autonomous institution set up by the University Grants Commission of India to promote nucleation and growth of active groups in astronomy and astrophysics in Indian univer ...

(IUCAA) at

Pune Pune (; ; also known as Poona, ( the official name from 1818 until 1978) is one of the most important industrial and educational hubs of India, with an estimated population of 7.4 million As of 2021, Pune Metropolitan Region is the largest i ...

, India.

Life and career

Born to Thanu Iyer and Lakshmi on 10 March 1957 in

Thiruvananthapuram Thiruvananthapuram (; ), also known by its former name Trivandrum (), is the capital of the Indian state of Kerala. It is the most populous city in Kerala with a population of 957,730 as of 2011. The encompassing urban agglomeration populati ...

(then Trivandrum), Padmanabhan attended school there. He earned his B.Sc. (1977) and M.Sc. (1979) in

Physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...

from the

University College Thiruvananthapuram University College, Thiruvananthapuram (UCT) is a constituent college of the University of Kerala, based primarily in Thiruvananthapuram, the capital of the Indian state of Kerala. The college was awarded 23rd rank by National Institutional Ran ...

, part of

Kerala University University of Kerala, formerly the University of Travancore, is a state-run public university located in Thiruvananthapuram, the state capital of Kerala, India. It was established in 1937 by a promulgation of the Maharajah of Travancore, Chit ...

. He published his first research paper (on

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...

) when he was still a B.Sc. student, at the age of 20. He joined the

Tata Institute of Fundamental Research Tata Institute of Fundamental Research (TIFR) is a public deemed research university located in Mumbai, India that is dedicated to basic research in mathematics and the sciences. It is a Deemed University and works under the umbrella of the ...

(TIFR) in

Mumbai Mumbai (, ; also known as Bombay — the official name until 1995) is the capital city of the Indian state of Maharashtra and the ''de facto'' financial centre of India. According to the United Nations, as of 2018, Mumbai is the secon ...

in 1979 for his Ph.D. and became a faculty member there in 1980. He held various faculty positions at TIFR from 1980 to 1992 and also spent a year (in 1986–87) at the

Institute of Astronomy, Cambridge The Institute of Astronomy (IoA) is the largest of the three astronomy departments in the University of Cambridge, and one of the largest astronomy sites in the United Kingdom. Around 180 academics, postdocs, visitors and assistant staff work ...

. He moved to Pune to work at the

in 1992 and served as its Dean, Core Academic Programmes, for 18 years (1997–2015). Padmanabhan served as adjunct faculty of TIFR, the

Harish-Chandra Research Institute The Harish-Chandra Research Institute (HRI) is an institution dedicated to research in mathematics and theoretical physics, located in Allahabad (officially Prayagraj), Uttar Pradesh in India. Established in 1975, HRI offers masters and doctora ...

(

Allahabad Allahabad (), officially known as Prayagraj, also known as Ilahabad, is a metropolis in the Indian state of Uttar Pradesh.The other five cities were: Agra, Kanpur (Cawnpore), Lucknow, Meerut, and Varanasi (Benares). It is the administra ...

), the

Raman Research Institute The Raman Research Institute (RRI) is an institute for scientific research located in Bangalore, India. It was founded by Nobel laureate C. V. Raman in 1948. Although it began as an institute privately owned by Sir C. V. Raman, it is now fu ...

(

Bangalore Bangalore (), officially Bengaluru (), is the capital and largest city of the Indian state of Karnataka. It has a population of more than and a metropolitan population of around , making it the third most populous city and fifth most ...

) and the Indian Institute of Science, Education and Research (IISER, Pune) at different periods in his career. He was adjunct faculty of IISER,

Mohali Mohali, officially known as Sahibzada Ajit Singh Nagar, is a planned city in the Mohali district in Punjab, India, which is an administrative and a commercial hub lying south-west of Chandigarh. It is the headquarters of the Mohali district. ...

. Padmanabhan served as chairman (2006–09) of the Time Allocation Committee of the Giant Meterwave Radio Telescope of NCRA. He was chairman (2008–11) of the Indian National Science Academy's National Committee 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. He was elected president of the Cosmology Commission (2009–2012) of the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

(IAU) and provided advice to IAU activities in this field. He was elected in 2011 as chairman of the Astrophysics Commission (2011–2014) of the

International Union of Pure and Applied Physics The International Union of Pure and Applied Physics (IUPAP ) is an international non-governmental organization whose mission is to assist in the worldwide development of physics, to foster international cooperation in physics, and to help in the ...

(IUPAP) and co-ordinated the activities of IUPAP in this area. He was also a visiting faculty at many institutes including the

California Institute of Technology The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

Princeton University Princeton University is a private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the ...

, and a Sackler Distinguished Astronomer of the

. He was an elected fellow of

The World Academy of Sciences The World Academy of Sciences (TWAS) is a merit-based science academy established for developing countries, uniting 1,000 scientists in some 70 countries. Its principal aim is to promote scientific capacity and excellence for sustainable deve ...

and of all three National Academies of Science in India (the

Indian National Science Academy The Indian National Science Academy (INSA) is a national academy in New Delhi for Indian scientists in all branches of science and technology. In August 2019, Dr. Chandrima Shaha was appointed as the president of Indian National Science Acade ...

Indian Academy of Sciences The Indian Academy of Sciences, Bangalore was founded by Indian Physicist and Nobel Laureate C. V. Raman, and was registered as a society on 24 April 1934. Inaugurated on 31 July 1934, it began with 65 founding fellows. The first general meet ...

, and the National Academy of Sciences, India). 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 serial ''The Story of Physics'' 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 (with J. V. Narlikar and Samir Dhurde) the IYA Astronomical Diary 2009, which comprises 53 illustrated pages of astronomical information. In 2019, he co-authored with Vasanthi Padmanabhan ''The Dawn of Science'' (published by Springer). 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. He died on 17 September 2021 at the age of 64 after a heart attack at his residence in Pune. 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.

Key awards and distinctions

Padmanabhan received several national and international awards including: * Kerala Shastra Puraskaram, 2021 * M. P. Birla Memorial Award, 2019 * Homi Bhabha Lecturer at UK (IoP-IPA award), 2014 *

TWAS Prize This is a list of recipients of the TWAS Prize, awarded annually by The World Academy of Sciences (TWAS). Summary Agricultural Sciences Biology Chemistry Earth Sciences Engineering Sciences Mathematics Medical Sc ...

in Physics (2011) * Infosys Science Foundation Prize for Physical Sciences (2009) * J. C. Bose National Fellowship ( Science and Engineering Research Board, DST) (2008) *

INSA The Intelligence and National Security Alliance (INSA) is a non-profit, nonpartisan 501(c)(6) professional organization based in Arlington Virginia for public and private sector members of the United States Intelligence Community. History ...

Vainu Bappu Gold Medal (2007) *

Padma Shri Padma Shri ( IAST: ''padma śrī''), also spelled Padma Shree, is the fourth-highest civilian award of the Republic of India, after the Bharat Ratna, the Padma Vibhushan and the Padma Bhushan. Instituted on 2 January 1954, the award is conf ...

(from the

President of India The president of India ( IAST: ) is the head of state of the Republic of India. The president is the nominal head of the executive, the first citizen of the country, as well as the commander-in-chief of the Indian Armed Forces. Droupadi Murm ...

, 2007) * Miegunah Fellowship Award (

University of Melbourne The University of Melbourne is a public research university located in Melbourne, Australia. Founded in 1853, it is Australia's second oldest university and the oldest in Victoria. Its main campus is located in Parkville, an inner suburb ...

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

, 2004) * Homi Bhabha Fellowship (2003) * G. D. Birla Award for Scientific Research (2003) * Al-Khwarizmi International Award (2002) * The Millennium Medal ( CSIR, 2000) *

Shanti Swarup Bhatnagar Award The Shanti Swarup Bhatnagar Prize for Science and Technology (SSB) is a science award in India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-la ...

(1996) * The Birla Science Prize (1991) * Young Scientist Award, (

) (1984) 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 the

Gravity Research Foundation The Gravity Research Foundation is an organization established in 1948 by businessman Roger Babson (founder of Babson College) to find ways to implement gravitational shielding. Over time, the foundation turned away from trying to block gravity an ...

, USA. A Stanford study in 2020, listing top scientists in different fields, ranked Padmanabhan as 24th in the world in his research area.

Research

Padmanabhan's research was on the fields of gravitation and cosmology which includes

and nature of

. During 2002–2015, he provided a clear interpretation of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

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. Padmanabhan could show that several peculiar aspects of classical gravitational theories find natural interpretations in this approach. Such an interpretation also provides a novel solution to the cosmological constant problem. He gave two lectures at the Oxford–Cambridge collaborative conference on "Cosmology and the Constants of Nature" about this. Popular (non-technical) descriptions of Padmanabhan's research have been published in

Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...

(India), and a more technical description is available in an article from the

in 2008, that describes his First Prize work
Another popular article
about his work which appeared in a German science magazine along with th
English translation
is available on his home page. An interview of Padmanabhan by George Musser about his work can be foun
here
In the earlier part of Padmanabhan's career (1980–2001), he made important contributions to

quantum cosmology Quantum cosmology is the attempt in theoretical physics to develop a quantum theory of the universe. This approach attempts to answer open questions of classical physical cosmology, particularly those related to the first phases of the univer ...

in the universe and statistical mechanics of gravitating systems. In the 1980s, he came up with an interpretation of the Planck length as the 'zero-point length' of the

spacetime In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differ ...

based on very general considerations. This result, established by theoretical considerations and well-chosen thought experiments, finds an echo in more recent results in several other candidate models for

. He developed the complex path method (in 1998) to study

black hole thermodynamics In physics, black hole thermodynamics is the area of study that seeks to reconcile the laws of thermodynamics with the existence of black hole event horizons. As the study of the statistical mechanics of black-body radiation led to the developm ...

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 and was a pioneer in the systematic application of these concepts to study the gravitational clustering in an

expanding universe The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not exp ...

. 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 new

paradigm shift A paradigm shift, a concept brought into the common lexicon by the American physicist and philosopher Thomas Kuhn, is a fundamental change in the basic concepts and experimental practices of a scientific discipline. Even though Kuhn restricted ...

in understanding

. 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 a

conserved quantity In mathematics, a conserved quantity of a dynamical system is a function of the dependent variables, the value of which remains constant along each trajectory of the system. Not all systems have conserved quantities, and conserved quantities are ...

, 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 the

cosmological constant In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant, is the constant coefficient of a term that Albert Einstein temporarily added to his field eq ...

– possibly the deepest unsolved problem in

theoretical physics Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experim ...

today – to the energy scale at which the universe made the quantum-to-classical transition. 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 magazine ''Nautilus''.

Publications

Books authored

Padmanabhan authored several advanced level textbooks. In addition, he authored several popular-level science books.
''The Dawn of Science: Glimpses from History for the Curious Mind''
Springer, Heidelberg (2019)
''Quantum Field Theory: The Why, What and How''
Springer, Heidelberg (2016)
''Sleeping Beauties in Theoretical Physics: 26 Surprising Insights''
Springer, Heidelberg (2015)
''Gravitation: Foundations and Frontiers''
Cambridge University Press, Cambridge, (2010)
''An Invitation to Astrophysics''
World Scientific, Singapore, (2006)
Theoretical Astrophysics - Volume III : ''Galaxies and Cosmology''
Cambridge University Press, Cambridge, (2002)
Theoretical Astrophysics - Volume II : ''Stars and Stellar Systems''
Cambridge University Press, Cambridge, (2001)
Theoretical Astrophysics - Volume I : ''Astrophysical Processes''
Cambridge University Press, Cambridge, (2000)
Review

''Cosmology and Astrophysics through Problems''
Cambridge University Press, Cambridge, (1996
Review

''Structure Formation in the Universe''
Cambridge University Press, Cambridge, (1993)

''Gravity, Gauge Theories and Quantum Cosmology''
(co-authored with J.V. Narlikar), Reidel (1986)
''Quantum Themes: The Charms of the Microworld''
World Scientific, Singapore, (2009)
''After the First Three Minutes - The Story of Our Universe''
Cambridge University Press, Cambridge, (1998)

Selected technical review articles

''Gravity and Quantum Theory: Domains of Conflict and Contact''
Invited Review, IJMPD (2020) 2030001
''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
''Emergent Gravity Paradigm: Recent Progress''
Mod. Phys. Letters A, 30, 1540007 (2015)
''Statistical Mechanics of Gravitating Systems''
Physics Reports, Vol.188, pp. 285–362 (1990)
''Cosmological Constant - the Weight of the Vacuum''
Physics Reports, Vol. 380, pp. 235–320 (2003)
''Thermodynamical Aspects of Gravity: New insights''
Reports in Progress of Physics, 73, 046901 (2010)
''Lessons from Classical Gravity about the Quantum Structure of Spacetime''
J. Phys. Conf. Ser., 306:012001 (2011)
''Physical significance of Planck length''
Annals of Physics, Vol. 165, pp. 38, (1985)

Selected popular science articles

''The Universe Began With a Big Melt, Not a Big Bang''
Nautilus, Issue 53, 5 October 2017
''Grappling with Gravity''
Scientific American India, January 2011, 30-35

53 illustrated pages of astronomical information, celebrating the

International Year of Astronomy The International Year of Astronomy (IYA2009) was a year-long celebration of astronomy that took place in 2009 to coincide with the 400th anniversary of the first recorded astronomical observations with a telescope by Galileo Galilei and the pu ...

(2009) (with J.V.Narlikar and Samir Dhurde).
''The Story of Physics''
a comic strip serialised in the magazine Science Age, from Sept. 1984 to Dec. 1986; published in book form by Vigyan Prasar, New Delhi, (2002) and now translated into several Indian regional languages.

References

External links

Thanu Padmanabhan's Home page

A 50-hour course by Padmanabhan on Quantum Field Theory
(available on YouTube)

on general relativity by Padmanabhan

(15 hours) by Padmanabhan on Advanced Topics in general relativity at the 'troisieme cycle de la physique en suisse romande' course (Geneva, Switzerland). {{DEFAULTSORT:Padmanabhan, Thanu 1957 births 2021 deaths 20th-century Indian astronomers 20th-century Indian physicists 21st-century Indian astronomers 21st-century Indian physicists Indian cosmologists Indian theoretical physicists Recipients of the Padma Shri in science & engineering Scientists from Thiruvananthapuram Tata Institute of Fundamental Research alumni TWAS laureates University College Thiruvananthapuram alumni University of Kerala alumni