Crowd Control

Many of life’s molecules flock together – water for example is polarised, its differently charged ‘ends’ pull droplets together in clusters, a form of condensation. Yet researchers studying these polarised Janus particles see something else at play – when meeting at particular angles, repulsive forces between particles cause them to turn. Fast-moving particles spin others towards the crowd, like bewildered tourists finding themselves at a street party. Clusters forming in this way are dynamic, with participants constantly leaving and re-entering – for living examples of ‘active matter’ this may be a way to mingle, then exchange chemicals or information. As bacteria and human cells use polarised movement, how they condense may be important to the spread of bacterial colonies, or the metastasis of migrating cancer cells.

Written by John Ankers

John Ankers

Writer

A former researcher in systems biology, John is now an online biology tutor and professional coach supporting the wellbeing of scientists and NHS professionals. He's writing, too, of course.

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• Video from work by Jie Zhang, Ricard Alert, Jing Yan, Ned S. Wingreen & Steve Granick
• Center for Soft and Living Matter, Institute for Basic Science (IBS), Ulsan, South Korea; Lewis-Sigler Institute for Integrative Genomics, Princeton University, NJ, and Department of Physics, University of California at Santa Barbara, CA, USA
• Video copyright held by the original authors
• Research published in Nature Physics, May 2021