Collective motion. We can find it everywhere in all kinds of natural phenomena — from a flock of birds all the way to self-propelled microorganisms. In these groups, we seem to observe choreographed displays — they appear to be working as one organism instead of multiple individuals. Despite the physical and environmental differences of each system, there are similarities such as polarity, density dependence, and large density fluctuations that suggest the existence of universal principles underlying the coherent formations.
Physicists from Technische Universität München and Ludwig-Maximilians-Universität München are developing and implementing a novel technique to study these phenomena utilizing highly concentrated actin filaments and immobilized molecular motors on microscope coverslips. Their experiments show that at low densities the filaments move at random, but once a critical density is reached, patterns emerge consistent with other mass systems. Clusters, swirls and interconnected bands — movement characteristics of large, dense groups — can be observed, even in the actin filaments.
The early news is encouraging and raises the hope that this and similar experiments could result in a scientific explanation for this sort of phenomena. But the vastness of the subject makes understanding difficult. All of the theoretical models have a broad parameter space with a wide variety of possible patterns, a large proportion of them not experimentally verified. Constrained to such a small platform, more complex patterns are difficult to observe, especially when you think of the space a free-roaming flock of birds has.
Still, these inherent principles of mass movement exist from one side of the biological spectrum to the other. These patterns are observed in the organization of biological processes such as the formation of the cellular cytoskeleton and protein transport, which is controlled by motor proteins. The patterns are also observed in human activities like crowd movements and, of course, traffic jams. Clearly, we need this information.