Abstract
Many animal species organise into disordered swarms, polarised flocks or swirls to protect from predators or optimise foraging. Previous studies suggest that such collective states are related to a critical point, which could explain their balance between robustness to noise and high responsiveness regarding external perturbations. Here we provide experimental evidence for this idea by investigating the stability of swirls formed by light-responsive active colloids which adjust their individual motion to positions and orientations of neighbours. Because their behaviour can be precisely tuned, controlled changes between different collective states can be achieved. During the transition between stable swirls and swarms we observe a maximum of the group’s susceptibility indicating the vicinity of a critical point. Our results support the idea of system-independent organisation principles of collective states and provide useful strategies for the realisation of responsive yet stable ensembles in microrobotic systems.
Highlights
Many animal species organise into disordered swarms, polarised flocks or swirls to protect from predators or optimise foraging
In order to cope with noise and external perturbations, collective states should keep a balance between robustness and flexibility regarding changing environmental conditions
When a laser spot is directed to an active particles (APs), it self-propels with velocity ^v 1⁄4 vu^ with the cap at the back, where u^ is a unit vector along the particle orientation[37,38] (“Methods”)
Summary
Many animal species organise into disordered swarms, polarised flocks or swirls to protect from predators or optimise foraging. 1234567890():,; Living organisms frequently arrange into spatio-temporal patterns being classified as disordered swarms, polarised flocks or rotating groups ( termed swirls or vortices)[1,2,3,4,5] Because such states are observed in many animal species, including fish[6,7], birds[8], insects[9] and down to bacteria[10], this suggests the presence of stable and size-independent overarching organisation principles. Further evidence of a close relation between collective and critical states is obtained from theoretical studies of interacting particles that adjust their motion to their neighbours via local interaction rules[16,17,18,19,20] Such simulations demonstrate a maximum of the responsiveness to perturbations in groups of fish at the transition from milling to schooling, which strongly resembles the behaviour at a critical phase transition[16]. We observe a continuous transition between swirls and swarms, which is accompanied by large fluctuations resembling critical behaviour
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call