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"exec" writes:

Arthur T Knackerbracket has found the following story:

Einstein’s theory of Brownian motion, which describes the random movement of particles in fluids, is widely used to model randomness throughout science. However, this revolutionary model only works when a fluid is static, or at equilibrium.

[...]Experiments have shown that non-moving 'passive' particles can exhibit strange, loopy motions when interacting with 'active' fluids containing swimmers. Such movements do not fit with the conventional particle behaviours described by Brownian motion and so far, scientists have struggled to explain how such large-scale chaotic movements result from microscopic interactions between individual particles.

Now researchers from Queen Mary University of London, Tsukuba University, École Polytechnique Fédérale de Lausanne and Imperial College London, have presented a novel theory to explain observed particle movements in these dynamic environments.

They suggest the new model could also help make predictions about real-life behaviours in biological systems, such as the foraging patterns of swimming algae or bacteria.

Dr Adrian Baule, Senior Lecturer in Applied Mathematics at Queen Mary University of London, who managed the project, said: "Brownian motion is widely used to describe diffusion throughout physical, chemical and biological sciences; however it can't be used to describe the diffusion of particles in more active systems that we often observe in real life."

[...] Their extensive calculation reveals that the effective particle dynamics follow a so-called 'Lévy flight', which is widely used to describe 'extreme' movements in complex systems that are very far from typical behaviour, such as in ecological systems or earthquake dynamics.

Dr Kiyoshi Kanazawa from the University of Tsukuba, and first author of the study, said: "So far there has been no explanation how Lévy flights can actually occur based on microscopic interactions that obey physical laws. Our results show that Lévy flights can arise as a consequence of the hydrodynamic interactions between the active swimmers and the passive particle, which is very surprising."

Journal reference:
K Kanazawa, T Sano, A Cairoli, and A Baule. Loopy Lévy flights enhance tracer diffusion in active suspensions, Nature (DOI: doi:10.1038/s41586-020-2086-2) (arXiv link )

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