A Unified Dissipative Model for the Dark Sector

The possible role of viscosity in cosmology is an actively investigated area in parallel with the evolution of the theory of General Relativity and the observation of its consequences. At the same time, the most accepted and accurate CDM model deals with the perfect fluid equation, and the dissipative effects are considered negligible or completely canceled. However, the need to include viscosity and entropy emerges in many cases in cosmological descriptions, e. g. the description of black hole properties, and they provide a promising alternative to mitigate potential cosmological tensions, as the differing Hubble-parameter values established from SN Ia supernovae and CMB measurements or the nature of dark energy. We present a unified model of the dark sector, which interprets its components not as exotic substances but as manifestations of the internal geometric viscosity of spacetime expressing an elastic, fluid-like resistance of spacetime to deformation, which manifests as negative pressure during expansion. Dark matter and dark energy are postulated as two distinct phase states described dynamically by the relativistic Navier-Stokes equations. The cosmological constant is identified as a dynamically evolving scalar. We subjected the framework to a broad set of phenomenological consistency tests, including existing physical benchmarks and limiting regimes. These comparisons are not presented as independent derivations, but as nontrivial compatibility checks. The theoretical integrity is examined by deriving the divergence-free solution of the continuity equation according to the Bianchi identities and the equilibrium condition, h ₒ₂ + h ₒₑ₂ = 0. The present work should be regarded as an initial conceptual framework intended to motivate further investigation and refinement. The author welcomes constructive feedback and professional discussion regarding the findings of this paper.