Active matter is a new field in soft matter physics. It studies the properties of assemblages of self-propelled particles

Self-propelled particles

Self-propelled particles , also referred to as self-driven particles or as the Couzin–Vicsek algorithm, is a concept used to model swarm behaviour. The concept was introduced in 1995 by Vicsek and Couzin et al. as a special case of the Boids model introduced in 1986 by Reynolds...

, which is to say objects which can convert energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 to movement. Active matter can include objects such as schools of fish and flocks of birds as well as cytoskeletal filament

Cytoskeleton

The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...

s like microtubule

Microtubule

Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...

s and actin

Actin

Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...

, which move under the influence of molecular motors.