tidsuavhengige

Tidsuavhengige, literally 'time-independent', is a concept used across mathematics, physics, and engineering to describe quantities, systems, or processes that do not change as time progresses. In general, something tidsuavhengige is invariant under time translation; it contrasts with tidsavhengige phenomena, which vary over time. The term appears in Scandinavian language contexts and is often discussed alongside ideas such as stationarity and time invariance.

In physics, a time-independent Hamiltonian H has no explicit time dependence. For example, a particle in a static potential is described by a time-independent equation, and energy is conserved in isolated systems through Noether's theorem. Time independence also appears in quantum mechanics via the time-independent Schrödinger equation, Hψ = Eψ, where eigenvalues E are constants of motion.

In engineering and control theory, time-invariant systems have properties that do not change over time. Linear time-invariant (LTI) systems respond to inputs with fixed impulse responses, and their behavior is analyzed with convolution, Laplace transforms, and frequency-domain methods. Time invariance implies that shifting the input in time yields an equally shifted output.

In statistics and stochastic processes, a comparable idea is stationarity. A process is stationary if its statistical properties do not depend on the absolute time, typically meaning that distributions, moments, and autocovariance depend only on time lag. Strict stationarity requires all joint distributions to be invariant under time shifts, while weak stationarity requires only mean and autocovariance invariance.