hysteresia

Hysteresia, also spelled hysteresis in many languages, is a phenomenon in which a system's output depends not only on its current input but also on its past states. The term derives from the Greek hysterēs, meaning "late" or "behind," reflecting the memory effect that characterizes these systems.

In physics and materials science, magnetic hysteresis occurs when magnetization lags behind the applied magnetic field, tracing a loop in a magnetization versus field diagram and dissipating energy as heat. The loop arises from domain dynamics, defects, and energy barriers within the material. Mechanical hysteresis appears in viscoelastic and elastoplastic materials, producing a loop in stress–strain curves as loading and unloading paths differ. Shape-memory alloys show pronounced hysteresis between different crystallographic phases, with transitions driven by temperature or stress and dependent on the material's thermal and mechanical history.

In electronics and control theory, hysteresis is used to create robust switching behavior, as seen in Schmitt triggers. Here, the output changes state only when the input crosses two distinct thresholds for rising and falling signals, providing noise immunity by incorporating history into the decision rule.

In biology and medicine, biological systems can exhibit hysteresis in gene regulation, enzyme activity, and neural adaptation, where past states influence present responses. Pharmacodynamics may also display hysteresis when drug effects persist after concentrations fall, due to receptor regulation or downstream signaling.

In economics and social sciences, hysteresis describes path dependence, where shocks produce persistent effects on variables such as unemployment or capital stock, delaying recovery even after favorable conditions return. In climate and ecology, history-dependent transitions between states reflect hysteresis in responses to forcing, influencing resilience and the potential for abrupt shifts.