We propose a constraint-first framework for late-time cosmology in which admissible expansionhistories are restricted by a small set of auditable physical “gates” rather than by flexibleparameterizations of the dark energy equation of state. Working within General Relativity(GR) on an FLRW background, we define a hierarchy of necessary constraints: (i) symboland units hygiene, (ii) covariant conservation, (iii) recovery of a baseline limit (e.g., ΛCDM),(iv) thermodynamic horizon constraints expressed via the apparent-horizon entropy, and (v) adistance-growth consistency condition in GR linking background expansion to linear structuregrowth. We show how these gates translate into inequalities and shape constraints on H(z)and derived quantities, formalizing their violation as operational null tests. We then specify areproducible reconstruction tool that infers H(z) and ρde(z) from distance data while enforcingthe gates as hard constraints or penalized priors, predicting f σ8(z) under GR to enable consistencytriangle checks against growth data. We include a worked synthetic-data demonstration and aminimal real-data application using public expansion measurements to illustrate gate diagnostics.The framework is designed to be falsifiable: if observations demand gate violation beyonduncertainties, at least one assumed pillar (GR, energy conditions, data systematics, or smoothdark energy) must fail.
SIKX HILTON (Thu,) studied this question.