irreversibelt

Irreversibelt is a term used in Norwegian to describe systems, processes, or events that cannot be returned to their original state by any natural or internal means alone. In everyday language and in scientific contexts, it is opposed to reversible phenomena, where the progression of steps can be undone to restore the starting conditions without lasting changes to the surroundings.

In thermodynamics and physics, irreversibility is closely linked to the second law of thermodynamics. Real processes tend to increase the overall entropy of a system and its environment, making spontaneous return to the initial state highly improbable. Common examples include mixing two fluids, diffusion of substances, frictional heating, and chemical reactions. Although energy may be conserved, the exact microscopic arrangement of particles cannot be reinstated without external intervention, such as cooling or external work.

In information theory and computation, irreversibility has a related but distinct meaning. A process is logically irreversible if it loses information about its prior state, so the original input cannot be uniquely reconstructed from the output. Erasing data is a canonical example and, according to Landauer’s principle, has a fundamental energy cost.

Beyond physics and computation, irreversibelt appears in discussions of time, philosophy, and economics. It describes events or decisions that cannot be undone or reversed in practice, such as taxonomic changes, historical accidents, or irreversible investments where hindsight cannot recreate the original conditions.

See also: entropy, arrow of time, Landauer’s principle, irreversible investment.