MPI-DS Colloquium: Motility regulation as a self-organization principle

Equilibrium statistical mechanics tells us how to control the self-assembly of passive materials by tuning the competition between energy and entropy to achieve desired states of organization. Out of equilibrium, no such principles apply and self-organization principles are scarce. In this talk I will review the progress which has been made over the past ten years to control the organization of self-propelled agents using motility control, either externally or through interactions. I will show that generic principles apply and illustrate the theoretical developments presented in the talk using recent experiments on run-and-tumble bacteria. I will show how the mediated interactions between the bacteria, that are non-reciprocal by nature, have a subtle fate upon coarse-graining: At large scales, non-reciprocity can indeed fade out, leading to bona fide equilibrium physics, or survive, leading to a wealth of dynamical effects ranging from steady traveling bands to chaotic ones.