Long-lived Giant Number Fluctuations in a Swarming Granular Nematic

TL;DR

This study demonstrates that a granular nematic system exhibits giant, long-lived number fluctuations with standard deviation growing linearly with mean, contrasting equilibrium systems and highlighting flocking behavior without communication.

Contribution

It provides experimental evidence of giant, long-lived number fluctuations in a granular nematic, revealing non-equilibrium behavior distinct from thermal liquid crystals.

Findings

Number fluctuations grow linearly with mean

Fluctuations decay logarithmically over time

Flocking occurs without particle communication

Abstract

Coherently moving flocks of birds, beasts or bacteria are examples of living matter with spontaneous orientational order. How do these systems differ from thermal equilibrium systems with such liquid-crystalline order? Working with a fluidized monolayer of macroscopic rods in the nematic liquid crystalline phase, we find giant number fluctuations consistent with a standard deviation growing linearly with the mean, in contrast to any situation where the Central Limit Theorem applies. These fluctuations are long-lived, decaying only as a logarithmic function of time. This shows that flocking, coherent motion and large-scale inhomogeneity can appear in a system in which particles do not communicate except by contact.