The phenomenon of vortex formation in fluids such as tea or coffee is explained by treating the fluid as a continuum and using basic fluid mechanics laws to understand large-scale flows. However, in dense crowds, where individuals interact in confined spaces, mathematical models predict spontaneous oscillations that lead to collective chiral motion without external cues. Researchers studied crowds at the San Fermín festival to observe the emergence of underdamped oscillations in dense crowds, which are periodic and not chaotic. This collective behavior is characterized by orbital trajectories and orientational oscillations, offering insights into crowd dynamics and crowd safety measures.
https://www.nature.com/articles/s41586-024-08514-6