Playing with Active Matter

TL;DR

This paper demonstrates how commercially available toy robots can be used to perform macroscopic active matter experiments, revealing behaviors like motion, interaction, sorting, and Casimir-like forces, thus bridging fundamental physics and accessible experimentation.

Contribution

It introduces a simple, accessible experimental setup using toy robots to study active matter phenomena at a macroscopic scale, expanding research possibilities beyond microscopic systems.

Findings

Toy robots can perform active Brownian and chiral motion.

Robots can interact with and move passive objects.

Active particles induce Casimir-like attraction between objects.

Abstract

In the last 20 years, active matter has been a very successful research field, bridging the fundamental physics of nonequilibrium thermodynamics with applications in robotics, biology, and medicine. This field deals with active particles, which, differently from passive Brownian particles, can harness energy to generate complex motions and emerging behaviors. Most active-matter experiments are performed with microscopic particles and require advanced microfabrication and microscopy techniques. Here, we propose some macroscopic experiments with active matter employing commercially available toy robots, i.e., the Hexbugs. We demonstrate how they can be easily modified to perform regular and chiral active Brownian motion. We also show that Hexbugs can interact with passive objects present in their environment and, depending on their shape, set them in motion and rotation. Furthermore, we show that, by introducing obstacles in the environment, we can sort the robots based on their motility and chirality. Finally, we demonstrate the emergence of Casimir-like activity-induced attraction between planar objects in the presence of active particles in the environment.