Emergent Quantum Dynamics from Interacting Semiclassical Universes with Variable Gravitational Coupling

We propose a covariant multiverse framework in which quantum phenomena arise effectively for observers restricted to a single semiclassical universe. Each universe is endowed with a classical Lorentzian metric and a scalar--tensor sector that realizes a spacetime- and age-dependent gravitational coupling \(G(x,\tau)\), where \(\tau\) is a cosmic-age scalar defined with respect to a preferred cosmological congruence. Inter-universe interactions are modeled by proximity-weighted couplings that permit coherent amplitude exchange between nearby universes and by stochastic sector events that induce transitions and decoherence. For an observer in a given universe, tracing over the remaining sectors yields a reduced, open-system description that is linear and completely positive in the weak-coupling/Markovian regime, providing an explicit route to Lindblad-type generators. Metric superpositions are excluded within each universe by construction; apparent ``superpositions of geometries'' are instead identified with coherence over universe labels, with a definite classical geometry in every sector. We relate this construction to Many-Interacting-Worlds models, semiclassical and stochastic gravity, and standard open-quantum-systems techniques, and we outline phenomenological constraints from bounds on \(\dot G/G\) and proposed gravitationally mediated entanglement tests. We outline concrete next steps, including toy-model demonstrations of interference and tunneling, parameterization of scalar–tensor functions consistent with Solar-System bounds, and quantitative predictions for gravitationally mediated entanglement experiments. We supplement the conceptual framework with quantitative toy-model demonstrations (qutrit and oscillator), including plots of coherence $C_{01}(t)$, purity $\mathcal{P}(t)$, and interferometric visibility $\mathcal{V}(t)$, and we illustrate departures from Markovian LGKS dynamics via time-dependent rates in a non-Markovian variant.