Elastic Membrane Cosmology 5.3: Spacetime Evolution, Superfluid Bulk Dynamics, and the Deconstruction of Dark Mediators

We propose a fundamental paradigm shift in cosmology, transitioning from particle-based reductionism to an environmental-dynamic framework. We define the (3+1)-dimensional spacetime as a dynamic membrane possessing intrinsic viscosity and surface tension, em-bedded in a five-dimensional Superfluid Bulk characterized by a non-linear potential gradient. This framework unifies dark sector phenomena through the hydrodynamic interac-tion between the manifold and its environment. Core mechanisms in Version 5.3 include:(1) The Superfluid Vacuum Assumption, identifying the Bulk as a zero-viscosity, irrota-tional medium (analogous to Helium-II) that resolves the Horizon problem and low-ℓ CMB suppression; (2) Quantized Vortex Dynamics, reinterpreting black hole spins as stablevortex configurations; (3) Environmental Phase Transitions explaining the Milky Way’s evolution from turbulent infancy to disk stability; and (4) The Deconstruction of "Dark Mediators", identifying DM-neutrino interactions as hydrodynamic drag within the 5D ocean. We validate these mechanisms against 2026 data, including NASA’s Cloud 9, the gas sea of SPT2349-56, and persistent null results in sterile neutrino searches. Keywords: 5D Superfluid Bulk, Spacetime Viscosity, BH-First, Quantized Vortices, Vortex Reconnection, Hubble Tension, Cloud 9, Dark Mediator Critique.