Arbitrage Equilibrium, Invariance, and the Emergence of Spontaneous Order in the Dynamics of Birds Flocking

Abstract

The physics of active biological matter, such as bacterial colonies and bird flocks, exhibiting interesting self-organizing dynamical behavior has gained considerable importance in recent years. Recent theoretical advances use techniques from hydrodynamics, kinetic theory, and non-equilibrium statistical physics. However, for biological agents, these don't seem to recognize explicitly their critical feature, namely, the role of survival-driven purpose and the attendant pursuit of maximum utility. Here, we propose a novel game-theoretic framework and show a surprising result that the bird-like agents self-organize dynamically into flocks to approach a stable arbitrage equilibrium of equal effective utilities. While it has been well-known for three centuries that there are constants of motion for passive matter, it comes as a surprise to discover that the dynamics of active matter populations could also have an invariant. What we demonstrate is for ideal systems, similar to the ideal gas or Ising model in thermodynamics. The next steps would involve examining and learning how real swarms behave compared to their ideal versions. Our theory is not limited to just birds flocking but can be adapted for the self-organizing dynamics of other active matter systems.