A flock of starlings turns simultaneously. A school of fish evades a predator in milliseconds. The standard explanation is alignment: each individual adjusts to match its neighbors' direction, and information propagates through the group as a wave of local adjustments. The models that formalize this — Vicsek, Cucker-Smale, and their descendants — treat alignment as the fundamental interaction. Collective turns happen because one region shifts direction and the rest follow, neighbor by neighbor.
Syga, Guha Ray, Nava-Sedeño, Peruani, and Deutsch (arXiv:2603.07254, March 2026) propose a different mechanism: collective turns are triggered not by gradual alignment but by abrupt reorientation in response to a single deviant neighbor.
The rule is simple. When an agent's local neighborhood is already highly aligned — nearly everyone is going the same direction — and one neighbor suddenly deviates, the agent copies the deviant rather than the majority. The condition is specific: the agent must be in a coordinated group, and the deviant must be strongly deviating, not drifting slightly. Under these conditions, the agent's own reorientation makes it the deviant for its other neighbors, triggering their reorientation, producing a cascade.
The cascades follow a heavy-tailed size distribution. Most are small — a few agents reorient and the disturbance dies. But occasionally a cascade sweeps the entire group. This happens without parameter tuning: the heavy-tailed distribution is robust across a broad range of noise levels and interaction strengths. The system spontaneously organizes near criticality, where cascades of all sizes occur.
The mechanism inverts the standard picture. Alignment models say that coordination produces stability — the more aligned the group, the harder it is to turn. The minority-triggered rule says the opposite: high alignment creates the condition for explosive response, because every agent in a coordinated region is primed to copy the next deviant it encounters. Order does not resist perturbation. Order amplifies it.
Syga, Guha Ray, Nava-Sedeño, Peruani, and Deutsch, "Minority-Triggered Reorientations Yield Macroscopic Cascades in Swarms," arXiv:2603.07254 (March 2026).