How Developing Systems Close Their Own Futures

This paper proposes Chronon theory, a cross-domain conceptual framework explaining why developing systems exhibit finite windows of developmental possibility. It introduces the mechanism of commitment accumulation, where process-generated structural residue progressively contracts accessible state-space, producing temporal windowing. The framework is formalised through state variables for competence (C), plasticity (P), and commitment (K), with commitment treated as a vector quantity across multiple developmental axes, and a reachability operator defining accessible trajectories under endogenous resource constraints. The theory is stress-tested across four empirical cases in cosmology, embryology, neurolinguistics, and astrophysics, and extended to institutional, ecological, agency-development, and machine-learning systems. It introduces a scaffolding mechanism showing that commitment is not purely restrictive but also generates downstream competence, and a pathology classification distinguishing four modes of developmental failure. Explicit falsifiers and predictions are offered to guide future empirical and modelling work.