Formal Notes on the c²-Model V: Accessibility Limits and Horizons

Subtitle: Information, Observation and the Boundaries of Accessible Reality This fifth formal note on the c²-Model examines accessibility limits and horizons as structural conditions of observability... This fifth formal note on the c²-Model examines accessibility limits and horizons as structural conditions of observability. Building on the relation S_obs = S_stable ∩ S_accessible, the note develops the distinction between stable structure, accessible information and observable reality. Cosmological horizons are interpreted not as boundaries of reality itself, but as boundaries of accessible information. The observable universe is therefore understood as an accessibility domain rather than necessarily the totality of reality. The note also introduces the hidden domain as stable but inaccessible structure: S_hidden = S_stable \ S_accessible. In addition to cosmological horizons, the work discusses experimental accessibility, reconstructable signatures, delayed and indirect observability, neutrino oscillations, quarks as examples of non-isolable but experimentally accessible constituents, and the role of information. It argues that observability depends not only on physical existence or stability, but also on coupling, detection, reconstruction and information transfer. This publication is intended as a formal supplement to Version 9.0 of the c²-Model of Realities.