naturally operate out of thermodynamic equilibrium and hence provide a testing ground for
theories of non-equilibrium statistical physics. They also have potential as micro-machines,
creating mechanical work from chemical energy. In this talk I shall discuss two cases where
the activity drives flow.
We first consider microswimmers, such as bacteria, which, because of their size, swim at
low Reynolds number. The flow fields created by microswimmers move nearby particles in a
way relevant to their feeding strategies. We discuss how passive tracers are advected by the
swimmers, and hence how microswimmers can stir as they swim.
We then turn to denser active matter, such as suspensions of microtubules and molecular
motors. These materials behave as ‘active nematics’ and we show how turbulent-like flow (at
first sight surprising at low Re) is driven by topological defects.