Spontaneous emergence of counterclockwise vortex motion in assemblies of pedestrians roaming within an enclosure

Abstract

The emergence of coherent vortices has been observed in a wide variety of many-body systems such as animal flocks, bacteria, colloids, vibrated granular materials or human crowds. Here, we experimentally demonstrate that pedestrians roaming within an enclosure also form vortex-like patterns which, intriguingly, only rotate counterclockwise. By implementing simple numerical simulations, we evidence that the development of swirls in many-particle systems can be described as a phase transition in which both the density of agents and their dissipative interactions with the boundaries play a determinant role. Also, for the specific case of pedestrians, we show that the preference of right-handed people (the majority in our experiments) to turn leftwards when facing a wall is the symmetry breaking mechanism needed to trigger the global counterclockwise rotation observed.

Steering self-organisation through confinement

“…Hard vs. soft. Hard confinement is not affected by the dynamics of the self-organising system (as in the case of a solid wall for soft and active matter 4,[31][32][33] ), while soft confinement can deform, reshape, adapt and evolve in response to the dynamics of the self-organisation process (as in the case of flexible membranes 34,35 or fluid interfaces 36 ). Hence, in the latter case, there is a feedback mechanism between the units and the confining boundary, as exemplified by, e.g., stem cells that can change their fate depending on the softness of their confining environment.…”

“…From molecular aggregates 1 to groups of animals 2 and human crowds, 3,4 from microswimmers 5 to granular materials 6 and robotic swarms, 7 examples of systems that self-organise can be found across a wide diversity of length and time scales. 8,9 The concept of self-organisation in soft matter and related fields came to the fore in the 20th century 10 and defines the spontaneous emergence of large-scale collective structures and patterns in space and/or time from the interaction of many individual units, 8,9 such as molecules, colloidal particles, cells, animals, robots, pedestrians or even astronomical objects.…”

Steering self-organisation through confinement

“…From molecular aggregates [1] to groups of animals [2] and human crowds [3,4], from microswimmers [5] to granular materials [6] and robotic swarms [7], examples of systems that self-organise can be found across a wide diversity of length and time scales [8,9]. The concept of self-organisation, as a modern field of study, came to the fore in the 20 th century [10] and defines the spontaneous emergence of large-scale collective structures and patterns in space and/or time from the interaction of many individual units [8,9], such as molecules, colloidal particles, cells, animals, robots, pedestrians or even astronomical objects.…”

“…Physical confinement is imposed by the presence of a physical obstacle that confines the phase space available to a system (e.g. a flexible membrane for cells [27] or a rigid wall for microswimmers [28], robots [29] or pedestrians [4]); in contrast, effective confinement stems from an apparent or virtual boundary that is mediated by an intrinsic capability of the units to sense or perceive it (e.g. the extent of a chemical trail for bacteria [30] or ants [31], a force field for colloidal particles [32], a timedependent distribution of resources consumed by microswimmers [28], the communication range for animals and robots [33], the gravitational field confining Earth's atmosphere for turbulent flows [15] or the gravitational field of black holes that keeps a galaxy together [16]).…”

Diffusive regimes in a two-dimensional chiral fluid

“…C hiral fluids display a rather complex dynamics, featuring a variety of peculiar properties that cannot be found in traditional fluids. Albeit these properties actually play a major role in biological processes 1 , where flow chirality is ubiquitous 2 , research work on this line is currently in progress [3][4][5][6][7][8] . In fact, the hydrodynamics of chiral fluids is characterized by an antisymmetric component in the stress tensor, and by a whole new set of transport coefficients.…”