Research Area

My research focuses on active systems. These materials are driven out of equilibrium by a constant injection of energy at the scale of constituent particles that perform work in dissipating it. The microscopic energy input leads to the formation of novel phases and patterns whose scales can be hundreds to thousands of times the size of the individual driven or "active" unit. My research has generally attempted to answer fundamental questions regarding these out-of-equilibrium organised structures using phenomenological continuum-level descriptions. These "hydrodynamic" theories yield descriptions of the systems' large-scale and long-time properties that are insensitive to the microscopic details of an individual active unit (That is, to quote D. Forster, it buries our ignorance of microscopic details in a few phenomenological parameters). This is similar in spirit to the Navier-Stokes equation for fluid flows, which is insensitive to the details of the interactions of the constituent molecules of the fluid (for instance, hydrogen bonding of water molecules), but for microscopically driven particles. The microscopic driving fundamentally modifies the mechanics and statistical mechanics of active systems, leading to qualitatively distinct behaviours from matter at thermal and chemical equilibrium.

Biological systems ranging from cytoskeletal gels to bird flocks are natural realisations of active matter. Active hydrodynamic theories, applied to such systems, have succeeded in providing physical explanations for a variety of striking phenomena such as the rotation of the nucleus of a cell, swirls in dense collections of bacteria, and even starling murmuration. However, active hydrodynamics is not only limited to biological systems: platinum-gold rods immersed in a hydrogen peroxide solution or tapered particles that move on a vibrated base are also realisations of active systems. Furthermore, even the dynamics of some driven two-dimensional quantum systems can be usefully described by active matter theories. 

For links to all my publications, please see the publications list or my Google Scholar Page.