Active matter
Active matter is matter made of units that consume energy locally and turn it into motion, force, shape change, or organized collective behavior.
What active matter is
Active matter is a class of physical systems made of many units that consume energy and convert it into motion, force, or internal change. The units might be living cells, bacteria, molecular motors, animals, synthetic colloids, vibrating grains, or small robots.
Why it is active
In ordinary passive matter, particles may move because of temperature, external fields, or imposed flows. In active matter, each unit has its own energy source or drive. A bacterium uses metabolism to swim, a motor protein consumes chemical energy, and a robot uses stored power to move.
Far from equilibrium
Active matter constantly dissipates energy. That makes it different from systems that simply relax toward equilibrium. Because energy is injected locally at many small units, active systems can form patterns, flows, and fluctuations that would be surprising in passive materials.
Collective motion
One of the signature behaviors of active matter is collective motion. Many simple moving units can align, cluster, swirl, jam, separate into dense and dilute regions, or move as a flock. These patterns can emerge even when each unit follows only local rules.
Biological examples
Biology supplies many active systems: bacterial suspensions, cell layers, tissues, cytoskeletal filaments, sperm cells, fish schools, insect swarms, and bird flocks. Studying them as active matter can reveal how physical forces and energy use shape living organization.
Synthetic active matter
Researchers also build nonliving active systems such as self-propelled colloids, chemically powered microswimmers, light-activated particles, vibrated grains, and swarming robots. These systems help test theory because their interactions and driving forces can sometimes be controlled more cleanly than in living organisms.
Models and measurements
Active-matter research uses experiments, simulations, hydrodynamic models, kinetic theory, and statistical mechanics. Models often ask how local rules for motion, alignment, noise, density, and interaction produce large-scale order, turbulence-like flows, or phase separation.
Why it matters
Active matter connects physics, biology, materials science, robotics, and nanotechnology. It helps explain how living systems move and organize, and it may guide new materials that self-heal, transport cargo, mix fluids, adapt to surroundings, or assemble themselves.