The 2026 Dirac Medal awarded to TIFR-ICTS (Bangalore) Prof. Deepak Dhar recognises his pioneering contributions to statistical mechanics and, more broadly, to our understanding of complex physical systems.
Deepak is the second Indian working in India to receive this highly prestigious international distinction. The International Centre for Theoretical Physics (ICTP), which confers the honour, ensures that it selects awardees who have not received other international science honours, such as the Nobel Prize, the Fields Medal, or the Wolf Prize.
Before discussing Deepak’s scientific contributions, I would like to share a personal reflection that I hope will help place his achievements in a broader context, one that goes beyond science alone.
The underrepresentation of people from certain regions of India in science is not necessarily because they lack interest or ability. Often, they simply lack exposure.
Small towns and big dreams
Growing up in Uttar Pradesh, the scientific atmosphere did not seem as vibrant as in some other parts of the country, at least in my experience. I knew of only two living Indian scientists: G. S. Agarwal and Jayant Narlikar. Both are alumni of Banaras Hindu University, where I was pursuing my Physics Honours degree.
My limited awareness of Indian scientists was certainly not the fault of Uttar Pradesh alone. It also reflected my own background. I grew up in a business-class Marwari family in a small town. My first major exposure to the broader world of scientific research came when I joined Physical Research Laboratory (PRL) for my PhD. Besides PRL, I had applied only to Inter-University Centre for Astronomy and Astrophysics (IUCAA), simply because these were the only research institutions I knew of that offered PhD programmes.
Over the course of my journey as a theoretical physicist, I have been fortunate to meet people from many towns of India and elsewhere in the world, and to learn about their cultures and ways of life. Yet, when I recently came across the name “Pratapgarh” while reading about Deepak, the Dirac Medal recipient, it resonated with me in a very different way.
I had heard of the town of Pratapgarh only during my childhood, when my aunt would talk about her sister who lived there and when it would occasionally come up in family conversations. Suddenly, I realised how rarely I had encountered the names of small towns in UP in the theoretical physics circles. Most people seemed to hail from bigger cities. That realisation also made me reflect on my own journey. Could this have been why it was more challenging for me to adjust to the unfamiliar environment of higher studies in theoretical physics than it was my peers? Perhaps I was simply longing to hear my own language, or to find people with whom I could share my culture and background.
In many small towns, children grow up knowing about careers in medicine, engineering, or the civil services, but the idea of pursuing an academic career in science may simply never enter their horizon.
There is a larger issue here. The underrepresentation of people from certain regions of India in science is not necessarily because they lack interest or ability. Often, they simply lack exposure. They grow up without knowing that such a world exists, without hearing about contemporary scientific developments, and without seeing visible role models who make a career in science appear possible and attainable.
And here comes along a boy from Pratapgarh. When his family suggested that he become an IAS officer, he reportedly replied, “Mujhe lagta tha IAS banna to itna mushkil nahi hai, mujhe Physics mein ruchi thi [I thought becoming an IAS officer is not that challenging, and I had my eyes set on Physics].” That boy from a small town in Uttar Pradesh went on to become one of India’s most distinguished theoretical physicists, making groundbreaking contributions to statistical physics, a major branch of the field.
Perhaps this is what makes Deepak’s journey particularly meaningful to me. His story is not only about extraordinary scientific achievement. It also highlights something less often discussed: the role of exposure in shaping career choices. In many small towns, children grow up knowing about careers in medicine, engineering, or the civil services, but the idea of pursuing an academic career in science may simply never enter their horizon. They may have the curiosity and aptitude for science, but without exposure to the world of research and academia, they may never discover that this too can be a path for them.
Grains of sand to complex systems
The idea of self-organised criticality was introduced by physicists Per Bak, Chao Tang and Kurt Wiesenfeld. Deepak’s Abelian sandpile model provided one of its most important exactly tractable mathematical realisations.
Physics is often broadly understood through three major domains. The first is classical mechanics, which describes much of what we experience in everyday life. For example, when you are rushing to a meeting, you may quickly calculate how long it will take to reach your office if you leave home at a certain time and drive at 50–60 km per hour. The same basic laws of motion also help us understand the movement of much larger objects, such as the Earth orbiting the Sun. The second, quantum mechanics, describes the behaviour of atoms, electrons and other particles at the smallest scales.
The third is closer to me: statistical physics. It addresses a very different kind of problem—one involving systems consisting of an enormous number of interacting components. Consider a crowd of thousands of people, a financial market involving thousands of individual stocks, or a traffic system containing a large number of vehicles. In such systems, it is neither practical nor always meaningful to follow every individual component. Instead, we seek to understand the collective, large-scale behaviour that emerges from their interactions. How does the temperature of a gas emerge from the motion of countless particles? How can collective fluctuations lead to a market crash? How can interacting particles suddenly change from one state to another in a phase transition? Statistical physics provides a framework for addressing such questions. It is in this fascinating field that Deepak has made some of his most profound contributions.
One of his landmark achievements was the development of the Abelian sandpile model, which became a foundational model in the study of self-organised criticality.
The Abelian sandpile model
The model starts with remarkably simple ingredients: grains distributed over a lattice and a simple local rule governing what happens when too many grains accumulate at one site. When a site becomes unstable, it ‘topples’, redistributing grains to its neighbouring sites. A single addition of a grain can therefore trigger a cascade of topplings, an avalanche, which may remain very small or propagate through a substantial part of the system. What makes the model particularly remarkable is that the system does not need to be externally tuned to reach a critical state. Through the repeated addition and redistribution of grains, it naturally evolves toward a state in which avalanches of many different sizes can occur.
The Abelian sandpile provides a beautiful illustration of one of the central ideas of modern complex systems science: simple local interactions can generate collective behaviour of enormous complexity.
This idea of self-organised criticality was introduced by physicists Per Bak, Chao Tang and Kurt Wiesenfeld. Deepak’s Abelian sandpile model provided one of its most important exactly tractable mathematical realisations. The word “Abelian” refers to a mathematical property.
He established the following: the final stable configuration does not depend on the order in which unstable sites are toppled. This seemingly simple property has deep consequences. It makes the model amenable to exact mathematical analysis and has allowed researchers to derive and understand many of its statistical properties in ways that are rarely possible for complex, interacting systems.
Local interactions, collective events
Complexity does not necessarily require complicated microscopic rules.
The significance of Deepak’s work, however, extends far beyond a mathematical model of sandpiles. The Abelian sandpile provides a beautiful illustration of one of the central ideas of modern complex systems science: simple local interactions can generate collective behaviour of enormous complexity. A grain interacts only with its immediate neighbours. Yet a single local perturbation can trigger an avalanche that spreads across the system. The resulting cascade can range from microscopic to system-wide.
This basic mechanism—local interactions giving rise to large-scale collective events—appears in many seemingly unrelated systems. For example, cascading failures in infrastructure networks, neuronal avalanches in the brain, earthquake dynamics, the spread of infectious diseases, and many other systems in which a local event can propagate through a network of interactions. This is precisely where Deepak’s work connects so naturally with the broader field of complex systems. Whether the interacting units are grains in a sandpile, oscillators in a synchronisation network, neurons in a brain network, or components of an infrastructure network, one encounters a recurring fundamental question: How do simple microscopic rules and local interactions give rise to collective behaviour, criticality and emergent large-scale phenomena?
Deepak’s work provides a particularly beautiful answer: complexity does not necessarily require complicated microscopic rules. Remarkably rich collective behaviour can emerge from the repeated interactions of simple components governed by simple local rules. This idea lies at the very heart of complex systems research today. The 2026 ICTP Dirac Medal recognises this broader intellectual contribution to statistical mechanics and our understanding of complex physical systems. Deepak Dhar shares the medal with Bernard Derrida, Marc Mézard and Haim Sompolinsky.
“The work of the 2026 Dirac Medallists has contributed to establishing theoretical physics, and particularly statistical mechanics, as a powerful framework to tackle a very broad range of questions that go far beyond its traditional domain of interest to encompass biology, computer science and artificial intelligence.” — ICTP Director Atish Dabholkar. Source: ICTP Official Announcement
Deepak’s story highlights something important about how scientific journeys begin. Often, the first barrier is not ability or even interest, but simply knowing that such a world exists. Knowing that research and academia can be a career, and having some sense of where that path might lead.
Once curiosity finds a direction, however, it is often the individual’s determination to seek that path that makes the journey possible. His journey is a remarkable example of this. His curiosity about physics led him far beyond the familiar career choices of his surroundings and eventually into one of the most fascinating areas of theoretical physics.
[Note: An earlier version of this article incorrectly stated that Deepak Dhar is the first Indian to receive the Dirac medal. In fact, Ashoke Sen received the medal in 2014 for his contributions to string theory.]
