Emergence of collective oscillations in massive human crowds

François Gu, Benjamin Guiselin, Nicolas Bain, Iker Zuriguel and Denis Bartolo ()
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François Gu: ENS de Lyon, CNRS, LPENSL, UMR5672
Benjamin Guiselin: ENS de Lyon, CNRS, LPENSL, UMR5672
Nicolas Bain: Universite Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, UMR5306
Iker Zuriguel: Unversidad de Navarra
Denis Bartolo: ENS de Lyon, CNRS, LPENSL, UMR5672

Nature, 2025, vol. 638, issue 8049, 112-119

Abstract: Abstract Dense crowds form some of the most dangerous environments in modern society1. Dangers arise from uncontrolled collective motions, leading to compression against walls, suffocation and fatalities2–4. Our current understanding of crowd dynamics primarily relies on heuristic collision models, which effectively capture the behaviour observed in small groups of people5,6. However, the emergent dynamics of dense crowds, composed of thousands of individuals, remains a formidable many-body problem lacking quantitative experimental characterization and explanations rooted in first principles. Here we analyse the dynamics of thousands of densely packed individuals at the San Fermín festival (Spain) and infer a physical theory of dense crowds in confinement. Our measurements reveal that dense crowds can self-organize into macroscopic chiral oscillators, coordinating the orbital motion of hundreds of individuals without external guidance. Guided by these measurements and symmetry principles, we construct a mechanical model of dense-crowd motion. Our model demonstrates that emergent odd frictional forces drive a non-reciprocal phase transition7 towards collective chiral oscillations, capturing all our experimental observations. To test the robustness of our findings, we show that similar chiral dynamics emerged at the onset of the 2010 Love Parade disaster and propose a protocol that could help anticipate these previously unpredictable dynamics.

Date: 2025
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DOI: 10.1038/s41586-024-08514-6

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