Brownian motion describes the random movement of particles in fluids, however, this revolutionary model only works when a fluid is static, or at equilibrium. In real-life environments, fluids often contain particles that move by themselves, such as tiny swimming microorganisms. These self-propelled swimmers can cause movement or stirring in the fluid, which drives it away from equilibrium.
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.
By explicitly solving the scattering dynamics between the passive particle and active swimmers in the fluid, the researchers were able to derive an effective model for particle motion in ‘active’ fluids, which accounts for all experimental observations.
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.
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.” (1)
Random movements.
In a random world.
Particles.
Observed by a human.
Under the Sun.
Shining bright.
Observed by the Galaxy.
Moving fast.
Under the void.
Look.
Particle moving.
Human watching.
The Sun setting.
Galaxy standing still.
Universe dying.
God looking…
Random movements…
