A mob is a fearful thing, daring to act in ways each individual within the crowd might not. If “the whole is greater than the sum of its parts,” how is it possible to understand collective behavior?

In a new study, a team of English, French and Turkish scientists used particles in a solution as a way to explore human behavior and group dynamics. The researchers observed that particles dispersed as their environment became increasingly chaotic. The team believes the same may be true in all other instances where active beings congregate, whether crowds of people or groups of live molecules.

We are always seeking to know ourselves, to better understand our often confusing human natures. Because of this, we like to draw comparisons, sometimes far-fetched, sometimes not, to shed some much-needed light on who we are: “Birds of a feather flock together,” we say. “Monkey see, monkey do.” While these metaphors may help explain individual motivation, the dynamics underlying crowd behavior remain elusive and in some situations — whether at rock concerts, such as Altamont in 1969, or within flash mobs, such as the 2013 Brooklyn mall incident — lead to panic and violence.

Wouldn’t it be worthwhile to create a proxy for humans, which could then be placed in a controlled environment so that behavior could be observed responding to change? Such thoughts inspired the experiment led by Dr Giorgio Volpe, University College London Chemistry.

Medicines and Crowd Control

A colloid is a chemical solution with tiny particles that remain intact and evenly distributed instead of settling at the bottom of the container. A colloid could represent a crowd, Volpe and his colleagues believed, and so they created one formed by silica microspheres suspended in a solution. This would serve as the controllable environment into which they could introduce external factors and observe any resulting action through the lens of a microscope. Here, they might learn the rules of human motion.

They began by shining a smooth beam (or “active potential”) onto the colloid; this created an area of illumination where, like moths to a flame, the microscopic particles gathered. Next, they introduced E. coli to the bath and observed the particles as they began to randomly collide with the bacteria, which also strove to feed off the energy of the light. Finally, using a speckle beam pattern, the scientists further disordered the bath. Here, they observed the colloids begin to disperse; timing the process, they discovered the dispersal rate to be 0.6 particles per minute over 30 minutes.

Based on this experiment, the researchers believe that individual particles switch between gathering and dispersing depending on the level of disorder in their environment. This result, they say, suggests any active matter might be controlled by influencing some external factors.

“Similar dynamics can determine the growth, health, and survival of living matter systems such as bacterial colonies and biofilms,” wrote the researchers in their published study. Application of these principles in a more practical situation might include controlling of delivery of medicines to target sites within an ailing body or improving crowd security in a panic situation.

Source: Pince E, Velu SKP, Callegari A, et al. Disorder-mediated crowd control in an active matter system. Nature Communications. 2016.