Deepak Dhar. Credit score: IISER Pune
Deepak Dhar is a professor on the Worldwide Centre for Theoretical Sciences, Tata Institute of Elementary Analysis. He’s the recipient of the 2026 Dirac Medal, instituted by the Worldwide Centre for Theoretical Physics in Trieste, Italy, for his work in statistical mechanics.
Q. I’m interested in your work on the sand pile mannequin, the statistical physics idea that helps perceive such various issues as earthquakes and inventory market crashes.
A. The sand pile mannequin, or the self-organized criticality mannequin, was proposed by Per Bak, Chao Tang, and Kurt Wiesenfeld in 1987. They steered that there are various pure techniques, comparable to earthquakes, forest fires or inventory markets, that exhibit quite a lot of ‘burst-like leisure occasions’.
Contemplate this – for those who take dry sand and make a pile, after which maintain including small grains one by one, generally they simply stick there, however generally they’ll trigger an avalanche. There’s a regular state through which the avalanches happen with some irregularity. Greater avalanches are fewer and smaller ones are extra. They confirmed that many pure techniques agree with this normal situation. This mannequin was studied by pc simulations in two dimensions; individuals nonetheless have not been capable of finding the precise distribution of sizes of such occasions.
There have been substantial developments to the thought since then. We outlined a directed model of the mannequin through which the impact of gravity, which may truly be solved in all dimensions, is included. So, some issues of the sand pile mannequin stay unsolved, another issues have been developed and solved.
Q. How did you get within the sand pile mannequin?
A. Round 1979, Per Bak got here to India and he gave a lecture at our institute, TIFR Mumbai. He was a really provocative speaker. He mentioned the sand pile idea may clarify the fluctuations of River Nile, earthquakes and organic extinctions. We weren’t very satisfied. I studied their mannequin and realised that there was an Abelian group construction to it. What it means is that if we add sand particles at totally different occasions, the order through which they’re added doesn’t matter, the consequence stays the identical. This will then be used to resolve some properties of this mannequin precisely. It was very helpful then since there have been no different precisely solved fashions of self-organized criticality. Then we confirmed that this mannequin could be associated to quite a lot of different beforehand studied fashions.
Bak et al famous for the primary time that long-ranged correlations happen with none fine-tuning of parameters. They referred to as it ‘self-organized criticality’ – you could possibly attain some extent of criticality with out fine-tuning one thing to a essential level.
I feel it’s unfair to name it ‘the idea of all the pieces’, as some individuals do. It offers a fundamental framework for describing techniques. However for those who actually need to perceive inventory markets, the idea of inventory markets shouldn’t be an identical to the idea of earthquakes. They may all be barely totally different, however some fundamental ideas are the identical in all of them.
Q. The utility or want for this mannequin in theoretical physics is well-known, however how does it apply to actual life? Are you able to give us some examples?
A. It offers a conceptual foundation for understanding actual world issues. It does not at all times result in predictable penalties. You possibly can take the philosophy of this mannequin and apply it to earthquakes. However to let you know when the subsequent earthquake will happen, it might want extra native commentary from seismographs and geographical inputs. These variables will not be a part of the idea, they’re gildings of it. But it surely helps perceive the final precept of those large and small occasions. The overall precept right here is that in a gradual state, large occasions occur. It’s legitimate for earthquakes and inventory market and forest fires, however its detailed software shouldn’t be an identical. You need to add particular options of the precise downside to foretell them higher.
Individuals have used the idea in inventory markets to foretell crashes. Others estimated the area most affected by lava movement from a volcanic eruption of Mount Etna in Italy a few years again. There are claims of great progress within the prediction of Southern Californian earthquakes over a 30-day window.
Q. How do you see the expansion of such elementary analysis in India?
A. At the moment, there may be extra emphasis on purposes and results-oriented analysis with financial outcomes inside three to 4 years. I’m not towards utilized analysis, it is essential with actual purposes out there. However I feel, there ought to be a part of not-so-immediate purposes in how the nation funds analysis. There ought to be a considered mixture of pure analysis and utilized analysis.
Some kinds of pure analysis are like cultural inputs. Similar to we help individuals who write novels, despite the fact that it does not result in fast financial beneficial properties for the nation. It is, nonetheless, a helpful exercise. Equally, some sorts of sciences are additionally helpful as they increase the mental degree of the nation and never simply of the individual doing it.
Scientists increase this subject now and again, however they’re handled as a vested curiosity group. There ought to be some extent of accountability for blue skies analysis, as there ought to be provision for it.
Q. What are you involved about in India’s science ecosystem proper now?
A. There may be quite a lot of anti-science within the nation and we don’t adequately counter it. That’s deeply worrying for me. If some senior minister says one thing very unusual like, there have been quite a lot of flying machines in India 2000 years in the past, then it’s worrying. We do not need our ministers to be like that.
It is also very exhausting to separate misinformation from appropriate data. Within the previous days, we used to learn newspapers, and we took them to be true. However now it seems that half the information in newspapers could also be unfaithful. I do not know which to belief.
Q. What’s the subsequent frontier in theoretical physics that excites you probably the most?
A. Non-equilibrium techniques and the way they differ from equilibrium techniques. And the way they’re necessary in our understanding of the world. The overall framework to explain these, on the degree of generality of equilibrium phenomena, doesn’t exist even now.
To elucidate equilibrium in easier phrases – for those who have a look at a system now and also you have a look at it after a short while, and it appears roughly the identical, it’s in equilibrium. For instance, the properties of a field stuffed with fuel remaining unchanged over a time period means it’s in a system of equilibrium. But when techniques will not be in equilibrium – say, the properties of the fuel within the field are altering – there’s a turbulence. It might be fascinating to review such turbulent techniques. And if the techniques are quantum mechanical, like superconductors, which have some macroscopic quantum behaviours, we attempt to perceive them with the ideas of ‘quantum entanglement’.
Probably the most fast software of quantum entaglement is in quantum computation. Whereas giant scale quantum computation remains to be not reachable within the foreseeable future, individuals could make computer systems to do calculations to the tune of hundred qubits. Maybe small, however nonetheless helpful issues, comparable to quantum cryptography for safe transmission might be doable in close to future.
