Active matter thermodynamics: Powering an E. coli engine with help from field theory*

Active matter particles convert energy from their environment into mechanical work, such as self-propulsion. A well-studied example of self-propulsion is ‘run-and-tumble’ motion performed by E. coli. When many run-and-tumble particles are brought together they exhibit behaviour like a gas. This run-and-tumble gas differs from everyday gases in many ways. Most significantly, it is a non-equilibrium system, a property that could allow us to devise machines, such as an autonomous E. coli engine, that are impossible to construct from everyday gases.

To construct an E. coli engine, we need to better understand the thermodynamic properties of run-and-tumble gases. For instance, the engines in our everyday lives are the culmination of over 150 years of classical thermodynamics. So how can we reinvent these thermodynamic laws for run-and-tumble gases?

This problem is not as straightforward as classical thermodynamics, as the non-equilibrium nature of these gases makes the equations governing them difficult to solve. However, field theory provides an intuitive framework that makes these equations easier to attack. My work focuses on deriving a field-theoretic model of heat conduction for run-and-tumble particles, thereby giving an insight into active matter thermodynamics.