We present a unified field theory, termed Quantum-Elastic Geometry (QEG), wherein spacetime is modeled as a fundamental, physical substrate with quantum, elastic, and dissipative properties. The state of this medium is described by a single, symmetric rank-2 tensor field, whose dynamics are governed by a generally covariant action. Known physical interactions are shown to emerge as distinct, irreducible deformation modes of this unified field: gravity, electromagnetism, and a new field --denominated "thermo-entropic field"-- that gives rise to irreversible thermodynamics. Furthermore, fundamental constants of nature are shown to be uniquely determined and interrelated by the substrate's properties through a principle of self-consistency, and predicts a scale-dependent gravitational coupling that resolves key cosmological tensions, including the Hubble crisis. In summary, the developed framework offers a coherent origin for fields and constants, unifying them as emergent properties of a single, dynamic spacetime substrate.