Unified Gravity Model Based on Equivalent Density under the Spacetime Stacking Hypothesis(Version 2)

To address the macro-micro dichotomy between general relativity and quantum field theory, this paper constructs a unified gravity model based on the spacetime monistic ontology: the rest mass of matter is not an independent entity but a steady-state condensation product of continuous local spacetime stacking. The model uses equivalent spacetime density and spacetime pressure as core physical quantities, decomposing the total equivalent density into five linearly superposed components: vacuum background density, gravitational equivalent density, relativistic kinematic equivalent density, quantum fluctuation density, and spacetime stacking rate additional density, without requiring a separate term for rest mass density. Through rigorous relativistic dynamics, dimensional analysis, and logical self-consistency optimization, the force expression is corrected to a volume-dependent form, the dimension of the pressure constant K is fixed as L2T−2, and the correct relativistic kinetic energy formula is used to recover the classical limit. It should be noted that the linear pressure-density relation P=KρΣ is currently phenomenological; its microscopic dynamical origin remains to be derived from the statistics of spacetime stacking. This paper provides the calibrated values of all phenomenological parameters: c0=299792458.0166 m·s−1, ρc=1.8×1030 kg·m−3, ρvac=9.9×10−27 kg·m−3, K=1.47×104 m2s−2, determined solely from two independent experimental data sets (GPS gravitational time delay and the Casimir force experiment; the latter is used to calibrate K and is not an independent verification). Multi-scale quantitative verification shows that on macroscopic scales, the model’s predictions for the gravitational redshift of Sirius B, the relativistic muon lifetime, and the orbital precession of the Hulse-Taylor binary pulsar differ from general relativity and observations by less than 5×10−4; on microscopic scales, the model, by introducing a single fitting constant η≈2.3×10−3, simultaneously describes the α-decay half-lives of U-238, Pu-239, and Ra-226 to within 0.045% accuracy, and naturally yields the Heisenberg uncertainty principle. The model provides a unified explanation of the vacuum speed of light, the four fundamental interactions, relativistic spacetime effects, black hole holography, and the superluminal expansion of the universe, and proposes eight falsifiable quantitative experimental predictions. Version 2 Updates (2026-06-07)Added detailed derivations for key equations , including boundary conditions and dimensional consistency checks.Updated comparison with existing theories with quantitative parameter matching.Corrected minor typos in symbols and references.Improved clarity in the discussion of multi-scale verification.