This paper continues the previously released preprint Theory of Spacetime Energy Conservation: A Complete Model for Photon Energy Variation in Gravitational Fields. The earlier work only described the four-dimensional energy flow of photons but failed to elaborate the physical carrier of spacetime strain energy and the origin of mass. To fill this theoretical gap, we propose a fundamental ontological postulate: spacetime itself is a continuous medium with zero effective viscosity and autonomous deformability, named the spacetime fluid. The prior work established a global four-part energy conservation law: spatial kinetic energy ES, intrinsic temporal energy of particles ET, and spacetime geometric strain energy EG, distinguishing two modes of photon energy exchange: microscopic curvature of the medium and global gravitational curvature of celestial bodies. In the present paper, we lay an ontological foundation for this conservation system and develop an original NT dimensional rotation-tiling mathematical model. The framework unifies the descriptions of light, mass, gravitation, gravitational waves, black holes, four fundamental interactions, quantum entanglement and spin. We strictly differentiate the spacetime fluid proposed herein from the 19th-century mechanical luminiferous ether. The framework is consistent with the Michelson–Morley experiment, general relativity and quantum mechanics, without refuting existing established theories; instead, it provides a deeper underlying unified ontology. A consistent symbolic system is established across the two papers, connecting the photon dimensional partition formula quantitatively with the temporal allocation ratio. Predictive observable correction terms and dedicated follow-up research directions are presented.
Q Chen (2026) studied this question.