When Is a Configuration Physical? Admissibility, Chart Failure, and the Logic of Vacuum Selection

The problem of vacuum selection has resisted resolution across quantum gravity, string theory, cosmology, and effective field theory, often framed as choosing among vast landscapes using statistical or anthropic arguments. We argue that this difficulty reflects a mis-posed question: the implicit assumption that physics is defined everywhere in configuration space. Core physical structures—Hilbert spaces, probabilities, effective field theories, and renormalization group flows—are conditional constructions that presuppose stability, boundedness, and spectral separation. These conditions need not hold globally. Selection therefore cannot act pointwise on vacua, but only on admissible regions defined by dynamical and spectral inequalities. Such regions may be disconnected and inaccessible by continuous deformation, rendering standard landscape scans ineffective by construction. Recasting vacuum selection as an admissibility problem explains why existing approaches have struggled to converge and shifts emphasis from counting or weighting vacua to identifying where physics is well defined at all. The paper is intentionally theory-agnostic and aims to clarify the conceptual structure underlying selection rather than propose a new fundamental model.