Rethinking Cosmological Foundations: A First-Principles Mechanical Framework for Spacetime (The Elastic Spacetime Framework - ESUF)

Modern cosmology predominantly relies on the model, which requires unobserved entities such as Dark Matter and Dark Energy to account for galactic rotation curves and cosmic acceleration. This preprint proposes the Elastic Spacetime Framework (ESUF), a novel, first-principles mechanical alternative that re-evaluates spacetime not as a passive geometric manifold, but as a physical, visco-elastic continuum (the "Grid"). By introducing an inherent prestrain scale (a_0), scale-dependent quadratic stress responses, and treating entropic transition velocity as the fundamental driver of linear time, ESUF eliminates the need for ad-hoc entities like dark matter and dark energy. This framework restores rigorous continuum-mechanics and causal symmetry to theoretical physics, offering a unified, mechanical foundation for cosmic dynamics.