All humans who have ever lived were once each an individual cell, which then divided countless times to produce a body made up of around 10 trillion cells. These cells have busy lives, executing all kinds of dynamic movement: contracting every time we flex a muscle, migrating toward the site of an injury, and rhythmically beating for decades on end. Cells are an example of active matter. As inanimate matter must burn fuel to move, like airplanes and cars, active matter is similarly animated by