Ion Santra

I work on Nonequilibrium Statistical Physics. Before I preach you about the topic, here are links to Past Affiliations + List of Publications ; and my hobbies Photography and Theatre.

Equilibrium is a state of balance — no net flows of energy, matter, or momentum, and of course “nothing changing with time” (though very importantly, it’s not just that). Imagine a bucket of boiling water left untouched: it slowly cools until it reaches room temperature, after which everything becomes still. The water is uniform and calm; if you were to film it and play the movie backward, it would look essentially the same. Disturb it slightly, and it quietly returns to rest — this is the hallmark of equilibrium.

Nonequilibrium, by contrast, describes systems that are driven or fueled, continuously exchanging energy or matter with their surroundings. Even if they appear steady — nothing visibly changing with time — they harbor persistent currents and fluxes beneath the surface. Think again of the bucket of water, but now you keep stirring it, or heat it from below, or pump water in and out at the same rate, or drop in a few energetic fish. The fluid keeps swirling; energy keeps flowing. It may look stationary from afar, yet it never truly settles. This sustained motion — this breaking of time-reversal symmetry — is the signature of nonequilibrium.

My goal is to understand such nonequilibrium states, by studying model systems and comparing their behavior with equilibrium counterparts. Equilibrium is relatively well charted territory, thanks to the giants of statistical mechanics — Maxwell, Boltzmann, Gibbs, Einstein, Onsager, and others — who established a unified framework linking microscopic dynamics to macroscopic observables. Nonequilibrium, in contrast, remains the restless frontier with no unified descriptions.

In the past few years I have been working on the following topics:

• Active particle dynamics

• Reduced descriptions of nonequilibrium

• Activity driven transport

• Classical dynamical density functional theory

• Stochastic resetting

• Quantum Brownian motion

The models I use are most often far from the super complexities as seen in the real world, but like Pablo Picasso's minimalist painting I believe in 'getting rid of the irrelevant details from a real complex situations and looking at minimal mathematical models taking into account only the irreducibly essential elements needed to expose the phenomenon of interest.'