Single Universal Layer Theory

This preprint presents the Single Universal Layer (SUL) theory, a unified framework in which gravitational dynamics, relativistic geometry, and dark-sector phenomena emerge from momentum exchange with a homogeneous background substrate. The approach modifies Einstein field equations through momentum–substrate coupling, naturally generating effects attributed to dark matter and dark energy without introducing additional particles or exotic fields. Weak-field and cosmological limits are analyzed, leading to observationally consistent predictions for galaxy rotation curves, weak lensing, and Hubble-scale tension. Connections to Einstein–Æther, Proca-type, and teleparallel theories are discussed, along with stability and energy-condition considerations. This incomplete preprint offers a structured foundation for future theoretical and observational investigations.