Vacuum Relaxation as a Unifying Mechanism for Cosmological Stability

Preprint. This manuscript is a preprint and has not been peer-reviewed. It is currently under consideration for publication in a peer-reviewed journal. Modern cosmology is characterized by an apparent paradox: while the Universe exhibits dramaticdynamical evolution on large scales, many fundamental and effective physical parameters displayextraordinary stability in the late cosmological epoch. Standard cosmological models typically treatthis stability as an implicit assumption rather than as a phenomenon requiring explanation. In thiswork, we develop a unified framework in which late–time cosmological stability emerges naturallyfrom vacuum relaxation processes. We argue that the observed robustness of expansion dynamics,temporal scales, and effective physical parameters reflects the approach of the quantum vacuumtoward a quasi–stationary state. The framework preserves all local tests of general relativity, remainsobservationally degenerate with ΛCDM at late times, and provides a coherent explanation for thehierarchy of cosmological constraints across epochs. Observable consequences and routes towardempirical discrimination are discussed. key words: Vacuum relaxation, late-time cosmological stability, quantum vacuum dynamics, effective physical parameters, cosmological evolution, ΛCDM degeneracy, temporal stability, expansion dynamics, general relativity consistency, observational constraints