Emergent Galactic Dynamics and Cosmic Acceleration from an Effective Viscoelastic Medium

We propose a unified framework in which spacetime behaves as an effective viscoelastic medium characterized by a finite relaxation timescale. In this approach, gravitational dynamics acquire a memory effect, leading to an additional emergent contribution beyond standard General Relativity. We show that this framework naturally explains the radial acceleration relation (RAR) observed in galaxies without invoking dark matter, and simultaneously accounts for late-time cosmic acceleration without introducing a cosmological constant. The characteristic acceleration scale emerges as a0 = κcH / (2π), linking galactic dynamics directly to the cosmological expansion rate. The model is tested against SPARC galaxy data and cosmic chronometer H(z) observations, showing consistency with empirical data. This work suggests that both dark matter and dark energy phenomena may arise from the same underlying viscoelastic relaxation dynamics of spacetime.=======================================================This work is part of a broader theoretical framework connecting spacetime, cosmology, and galactic dynamics through viscoelastic relaxation effects.