reversibly

Reversibly is the adverbial form of reversible. It describes something that can be reversed or undone, returning to its original state without permanent change. In science and engineering, reversibly often refers to processes that can be run forward or backward under ideal conditions.

In thermodynamics, a reversible process is a theoretical, quasi-static change that takes place in infinitesimally small steps, keeping the system in near-equilibrium with its surroundings. If such a process could be completed and then reversed, both the system and the environment would be restored to their initial states and, for a complete cycle, the total entropy change would be zero. Real processes are irreversible due to friction, rapid changes, and finite temperature differences.

In chemistry, a reversible reaction can proceed in both directions, depending on conditions. At chemical equilibrium the forward and reverse rates are equal, so macroscopic properties remain constant even though molecular reactions continue. Le Chatelier's principle describes how changes in temperature, pressure, or concentration can shift the balance toward products or reactants.

In computing and information theory, reversible (and thus reversibly executable) processes conserve information and can, in principle, be executed without energy dissipation. Reversible computing uses bijective logic gates, such as Toffoli or Fredkin gates, to reduce energy loss in computation, in line with foundational limits like Landauer's principle.

In everyday use, reversibly simply means capable of being undone or restored to the original condition, though real-world systems often exhibit irreversibility due to practical constraints.