The Cosmological Constant as the Infrared Constitutive Scale of Gravity

We revisit the cosmological constant Λ as a constitutive property of spacetime rather than as a parameter associated solely with cosmic expansion. Starting from Einstein’s field equations, we show that Λ implies a universal acceleration scale aQV ∼ cH0 independent of galactic phenomenology. Dimensional consistency then yields an associated gravitational surface density σQV ≡ aQVc2/G , which we interpret as the vacuum’s gravitational stiffness scale or stress threshold. We argue that this vacuum stiffness scale provides an organizing interpretive framework for understanding both cosmic acceleration and the characteristic acceleration threshold observed in galactic dynamics. In this perspective, dark matter and dark energy effects may arise as different regimes of a single vacuum response law, though whether this framework can quantitatively reproduce both cosmological and galactic observations remains an open question. This paper establishes a foundational link between the cosmological constant, vacuum stiffness, and emergent gravitational phenomenology, providing the conceptual basis for subsequent dynamical and field-theoretic developments presented in companion papers, and identifying potential observational discriminants—including redshift evolution of galactic scaling relations—that can test whether the infrared scale aQV tracks cosmological expansion or remains effectively constant.