irréversible

Irréversible is the French adjective meaning not reversible; something that cannot be returned to its previous state or undone. The English cognate is irreversible. The term is used across diverse contexts, from physical processes to moral or historical consequences, where reversal is not possible or meaningful.

In physics and thermodynamics, an irreversible process is one that leaves a net change in the surroundings and cannot be reversed without additional changes elsewhere. Entropy tends to increase in irreversible processes; most real-world processes, such as friction, inelastic deformation, mixing of fluids, and heat transfer across finite temperature differences, are irreversible. By contrast, reversible processes are theoretical idealizations representing infinitesimally slow changes with zero entropy production.

Etymology and usage: the word derives from Latin irreversibilis, from in- “not” + reversibilis “that can be turned back.” In French, the form irr é versible is standard, with the acute accent reflecting French spelling. In scientific and academic writing, the term appears in both French and English with corresponding spellings and conventions.

In culture: Irréversible is also the title of a 2002 French film directed by Gaspar Noé, released internationally as Irreversible. The film stars Monica Bellucci and Vincent Cassel and is noted for its graphic violence and its nonlinear, reverse-chronology narrative, which unfolds the story backward in time to probe causality and consequence.

---