Equilibre

Equilibre (equilibrium) is a state in which opposing forces or processes balance, yielding stability and predictability. The word, from Latin aequilibrium, conveys the sense of being evenly balanced.

In physics, static equilibrium occurs when the resultant force and the resultant torque on a body vanish, so the body remains at rest or moves with constant velocity. Dynamic equilibrium describes a steady state where continuous processes occur but macroscopic properties stay constant, often through feedback.

In chemistry, chemical equilibrium is reached when there is no net change in the concentrations of reactants and products in a reversible reaction. The equilibrium position depends on temperature, pressure, and concentration, and is described by the equilibrium constant. Le Chatelier's principle explains how the system shifts in response to disturbances.

In economics and game theory, market equilibrium occurs where supply equals demand at a given price. In strategic contexts, equilibria such as the Nash equilibrium represent strategy profiles from which no participant has an incentive to deviate.

In biology and ecology, homeostasis describes the regulation that maintains internal stability, while ecological equilibrium refers to the balanced interactions of organisms within an environment, subject to disturbances and recovery via resilience.

Equilibre is often imperfect and context-dependent; shifts to new equilibria can occur after perturbations, leading to new stable states or regimes.