Physical Time as an Emergent Vacuum–Metric Parameter in Cosmological Evolution

Preprint. This manuscript is a preprint and has not been peer-reviewed. It is currently under consideration for publication in a peer-reviewed journal. The status of physical time in cosmology remains conceptually ambiguous despite its centralrole in theoretical formulations and observational inference. While general relativity embeds timeinto spacetime geometry, standard cosmological models employ it primarily as an external orderingparameter rather than a quantity subject to physical evolution or stabilization. In this work, we develop a unified framework in which physical time is interpreted as an emergent, effective parameterdetermined by the dynamical state of the quantum vacuum and the associated spacetime metric. Wedemonstrate that the observed stability of physical time in the late Universe follows naturally fromvacuum relaxation processes rather than from the assumption of fundamental immutability. Theframework preserves all local tests of general relativity, remains consistent with laboratory, geophysical, and astrophysical constraints, and provides a coherent interpretation of temporal emergence,evolution, and stabilization across cosmological epochs. Observable consequences and potentialavenues for empirical verification are discussed.