Active matter: An introduction and some recent advances

In this talk, I will introduce the new, fast-growing, interdisciplinary field of active matter and present some recent important advances.

Active matter is the term now used by physicists to designate out-of-equilibrium systems in which energy is spent in the bulk, locally, to produce persistent motion/displacement. Examples abound, not just within living systems (bird flocks, fish schools, collective motion of cells, etc.) but also, increasingly, in man-made, well- controlled, non-living systems such as micro- and nano- swimmers, active colloids, in vitro mixtures of biofilaments and motor proteins, etc.

I will show some striking experimental/observational examples and then proceed to give an account of our current understanding of some of the simplest models, which consist of self-propelled particles locally aligning their velocities. In this context, the fluid in which the particles move is neglected, and one speaks of ”dry active matter”. I will argue that these models do have experimental relevance, in addition to being important per se, much as the Ising model is important in statistical mechanics. I will show that a wealth of new physics arises, which calls for further theoretical studies.