Mimicking magnets with lattices of bacterial vortices

Speaker : Dr Francis Woodhouse – Cambridge University

Venue    : Thu 7 Apr 2016 @ 4pm, Murdoch University, room ECL1.031 (below ECL2.031)

When alone in an unbounded fluid, a rod-shaped motile bacterium like E. coli will swim in straight lines punctuated by random turns. Pack many of them together in the same fluid, however, and they adopt collective swirling patterns akin to macroscopic turbulence. Confining the bacteria within a small circular cavity tames this turbulence and leads instead to a steadily spinning bacterial vortex. If many such vortices are then linked together in a square lattice of cavities, the rotation sense of a vortex becomes dependent on those of its neighbours. By declaring the senses to be ‘up’ and ‘down’ spins, the result is a bacterial analogue of an Ising ferromagnet. After explaining the background to these so-called ‘active matter’ systems, I will explore the challenges involved in mapping classical statistical physics models to this decidedly non-classical system – but only after revealing an entirely unexpected twist in the experiments.