The story so far: Theoretical physicist Deepak Dhar has been awarded the Dirac Medal for his contributions to statistical physics — an honour he is sharing with three other physicists, Bernard Derrida, Marc Mézard, and Haim Sompolinsky. The Dirac Medal is awarded by the International Centre for Theoretical Physics (ICTP) in Trieste, Italy, on the birthday of the late British physicist Paul A.M. Dirac, for significant contributions to theoretical physics.
Dhar has spent most of his career in India. He is also the second Indian winner of the Dirac Medal; the first was string theorist Ashoke Sen in 2012.
In physics circles, Dhar is known for his work on a concept called Abelian sandpiles.
What is an Abelian sandpile?
Imagine dropping grains of sand, one at a time, on a flat surface. The pile slowly grows until it gets steep enough. Then, sometimes new grains on the pile will shift it, maybe cause a modest slide, sometimes even trigger an avalanche. And it is hard to predict in advance which grain will trigger which size of event.
In the late 1980s, physicists Per Bak, Chao Tang, and Kurt Wiesenfeld proposed that this behaviour could be a general principle underlying many phenomena in nature, from earthquakes to forest fires to the extinction of species. They called it self-organised criticality. The term refers to a system that sometimes organises itself into a delicately balanced critical state where even small nudges can produce effects of any size, from trivial to significant.
Dhar and his collaborators then developed the so-called Abelian sandpile model as a mathematical version of the sandpile idea. ‘Abelian’ means no matter in which sequence grains topple and cascade, the pile always settles into the same final shape. This was Dhar’s important insight — a property that lets physicists calculate exact answers and thus predict the final shape.
The Abelian sandpile model has numerous applications fundamentally because it captures a very general kind of behaviour: of systems that build up some kind of instability until they can release it in unpredictable ways. Scientists have used it to model earthquakes, the spread of forest fires, bursts of activity in neural networks in the brain, and fluctuations in financial markets.
Biographical sketch
Dhar was born in 1951 in Pratapgarh, Uttar Pradesh. He studied at Allahabad University, got his master’s degree from IIT-Kanpur, and then went to the California Institute of Technology (Caltech) for his PhD, which he completed in 1978. While at Caltech, he was a teaching assistant to Richard Feynman.
After finishing his doctorate, Dhar returned to India rather than stay in the U.S., and spent most of his career at the Tata Institute of Fundamental Research, Mumbai, before moving to the Indian Institute of Science Education and Research (IISER), Pune, in 2016.
Since 2024, he has been the INSA Distinguished Professor at the International Centre for Theoretical Sciences, Bengaluru.
The Abelian sandpile is Dhar’s most well-known work but not his only one. Across nearly five decades, Dhar has made important contributions to statistical mechanics — the branch of physics concerned with how the collective behaviour of vast numbers of particles, like grains or neurons, gives rise to large-scale patterns.
He won the Shanti Swarup Bhatnagar Prize in 1991, the TWAS Prize from the World Academy of Sciences in 2002, the Padma Bhushan in 2023, and the Boltzmann Medal in 2022, together with John Hopfield, who shared the physics Nobel Prize 2014 for laying the foundations of neural networks. In fact, the Boltzmann Medal, awarded once every three years, is often considered the single most prestigious prize in statistical physics.
What is the Dirac Medal?
The ICTP Dirac Medal was established in 1985 to honor Paul Dirac, the British physicist whose equations helped lay the foundations of quantum mechanics. It is announced each year on Dirac’s birthday and awarded to physicists who have made outstanding contributions to theoretical physics but who have not already received the very top honours.
In fact, the medal is explicitly not given to Nobel laureates, Fields Medallists, or Wolf Prize laureates. Past recipients include Edward Witten, Stephen Hawking, and Leonard Susskind. Notably, several past Dirac Medallists have gone on to win a Nobel Prize.
All four of this year’s winners have been feted for pioneering work that applied the tools of statistical mechanics in distinct fields like non-equilibrium systems, optimisation problems, theoretical neuroscience, and artificial intelligence. He is only the second scientist based in India, after string theorist Ashoke Sen, to receive the Dirac Medal.
The ICTP itself was founded in 1964 by the Pakistani physicist and Nobel laureate Abdus Salam, together with the Italian government and the International Atomic Energy Agency. Salam had envisioned it as a place where physicists from the Global South could work together and exchange ideas with colleagues from around the world.
Published – August 11, 2026 08:45 am IST
