Emergent Gravity and Galactic Dynamics in a Viscous Cosmic Medium.

We propose a novel hydrodynamic framework for the vacuum, characterizing it as a physical medium with a finite kinematic viscosity \bm{\eta \approx 10^{26} \text{ m}^2/\text{s}}. We demonstrate that the phenomena currently attributed to Cold Dark Matter (CDM) can be interpreted as emergent effects of viscous drag within this medium. By applying the Navier-Stokes limit to galactic scales, we derive a rotation velocity equation that matches the observed flat rotation curves of M31 (Andromeda) without requiring dark matter halos or empirical modifications to Newtonian gravity. Furthermore, we address the persistent Hubble Tension by modeling gravitational wave (GW) propagation through this viscous vacuum. Our analysis predicts a frequency-dependent energy dissipation of approximately \bm{0.34\%} over cosmological distances (\bm{d \approx 400 \text{ Mpc}}). This attenuation provides a physical mechanism for the discrepancy between electromagnetic and gravitational-wave-derived luminosity distances. We provide specific damping coefficients that are falsifiable with forthcoming LIGO/Virgo O5 data and the future LISA mission. This model offers a unified, material-based resolution to the "Dark Sector" problems by treating the Hubble Constant (\bm{H_0}) as the global shear rate of a universal fluid. How to fill out the Zenodo "Description" field: 1. Paste the Abstract above. 2. Add a "Key Prediction" bullet point: * Key Finding: Derives the MOND acceleration constant (\bm{a_0}) from first principles (\bm{c H_0 / 2\pi}). • Key Finding: Resolves the 5-\bm{\sigma} Hubble Tension via viscous attenuation of Standard Sirens.