Spacetime Location as a Mediated Proxy for Planetary Habitability: An Information-Theoretic Framework with an Explicit Falsifiability Ladder

The spatial distribution of habitable environments across the Milky Way is commonly summarized by the Galactic Habitable Zone (GHZ). A stronger and more provocative claim—that a planet's spacetime location is itself a hidden variable governing its habitability—appears to conflict with the cosmological principle and with the general covariance of physical law, under which bare coordinates carry no intrinsic causal power. We reconcile the two by formalizing location as a strictly non-causal proxy: a variable X whose mutual information with habitability H is fully mediated by a vector of latent local physical factors L, so that I(X;H) > 0 while I(X;H|L) = 0. Within this information-theoretic framework we (i) recover the three canonical habitability baselines—circumstellar-only, chemical GHZ, and spatiotemporal GHZ—as nested special cases; (ii) rank four candidate latent mechanisms—radiative/dynamical history, fine-structure-constant variation, dark-sector coupling, and quantum-vacuum variation—on an explicit falsifiability ladder; and (iii) implement a fully reproducible Bayesian analysis, anchored to measured Galactic gradients, that identifies which mechanisms current data actually constrain. Using the observed radial metallicity gradient, the gamma-ray-burst lethality profile, the local dark-matter density, and quasar-based bounds on Δα/α, we find that the proxy model reduces to the spatiotemporal GHZ to within a Kullback–Leibler divergence of ∼9×10⁻¹⁵ bits: with present data the exotic factors add no measurable predictive information (∼6×10⁻⁸ bits). The Bayesian posteriors sharpen this into a diagnostic: the metallicity (+) and radiation (−) couplings are well constrained, the dark-matter and α couplings are bounded within ∼10⁻³ of zero, and the quantum-vacuum coupling is formally non-identifiable (its posterior equals its prior; R̂ ≈ 1.00 only because the sampler explores the prior). We prove the corresponding conditional-independence, information-bound, and non-identifiability theorems, quantify the observational precision that would raise each exotic mechanism above the detection threshold, and release the complete analysis code with unit tests. The contribution is not a new habitability effect but a falsifiable scaffolding that states precisely what would have to be observed for spacetime location to matter beyond the known astrophysical factors.