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 perfect fluid equation and the dissipative effects are considered negligible or completely canceled. However, the need for inclusion of viscosity and entropy merges 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 establishes from SN1 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 relativistic Navier-Stokes equations. The cosmological constant is identified as a dynamically evolving scalar providing a possible resolution to the 120-order-of-magnitude vacuum energy discrepancy by evolving from its maximum value at the Planck scale. The theoretical integrity is examined by deriving the divergence-free solution of the continuity equation according to the Bianchi identities. Finally, the equilibrium condition, g + h = 0, represents the curvature response of the background scaffold to the gravitating source. 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.