Swimming microbes steer themselves into mathematical order

For News Media FOR IMMEDIATE RELEASE - × - A sheet of tiny swimming organisms that "push" themselves through fluid with, say, flagella, create forces in the liquid that bend the sheet in asymmetric, shrinking folds. Image courtesy of Saverio Spagnolie Freeing thousands of microorganisms to swim in random directions in an infinite pool of liquid may not sound like a recipe for order, but eventually the swarm will go with its own flow. Theoretical modeling led by University of Wisconsin-Madison applied mathematician Saverio Spagnolie shows that the forces generated by different kinds of tiny swimmers will sweep them all up in predictable ways. "When each individual particle experiences the flows created by all the other particles, it's known that really surprising effects can naturally emerge," says Spagnolie. "The flows and orientations of the swimmers become coherent on a length scale much longer than any individual particle, resulting in huge flocks of organisms swimming in the same direction and, perhaps unintentionally, working together." When a computer simulation of a sheet of swimming particles (yellow marks their highest concentration, blue empty liquid) is nudged into action, the forces and flows bend, disperse and gather the organisms in what looks like coherent flocks. Video courtesy of  Saverio Spagnolie The movement of crowds of things too small to easily see - like single-celled organisms and filaments inside individual cells responsible for cell-division - is critically important to research in materials science, engineering and biochemistry.