Time Curvature as the True Origin of Cosmic Acceleration

This work presents a geometric reinterpretation of cosmic acceleration by treating the cosmological constant as a manifestation of time curvature, not vacuum energy. Using the upstream admissibility framework, the analysis shows that the standard expansion equation splits into true physical evolution and an added projection-curvature term created when physical time is mapped into ordinary cosmological time. This curvature term is diffeomorphism-invariant and replaces Λ in Einstein’s equations, removing the cosmological constant problem and unifying early and late acceleration without invoking dark energy, scalar fields, or new matter components. The result preserves all observational predictions of ΛCDM while offering a new geometric mechanism for acceleration, coasting, slowing, or future cosmic transitions.