pöördumatud

Pöördumatud is the Estonian plural form of the adjective pöördumatu, meaning irreversible or irrevocable. It describes things that cannot be reversed to their original state by purely internal actions. The term is used across disciplines, including science, philosophy, and everyday language, typically in phrases such as pöördumatud protsessid (irreversible processes) or pöördumatud muutused (irreversible changes).

Etymology and usage: The word derives from pöörduma, "to turn back," combined with the negative suffix -matu ("without"), with the usual plural ending -ud. In standard Estonian, pöördumatu is the singular form, and pöördumatud is the plural nominative.

In science, pöördumatud protsessid are processes in which energy dissipation, friction, heat transfer with finite temperature gaps, mixing, or chemical reactions prevent a complete return to the initial state without external intervention. The concept is closely related to the second law of thermodynamics and entropy. In ordinary language, pöördumatud can refer to decisions or events with lasting consequences that cannot be undone by mere repetition.

See also: pöördumatu; pöördumatud protsessid; entropy; irreversible processes in physics. The term is mostly used in Estonian-language texts but appears in multilingual discussions of thermodynamics and philosophy when describing irreversibility.