Horizons Without Geometry

Arc I — Accessibility Paper 4 Title Horizons Without Geometry Zenodo DOI 10.5281/zenodo.18180797 Description This paper demonstrates that horizons arise as limits of operational accessibility rather than as geometric or causal boundaries in spacetime. By treating horizons as regions where coordination of records becomes impossible due to vanishing null accessibility, the work reframes event horizons, Rindler horizons, and observational cutoffs under a single non-geometric principle. The analysis shows that horizons emerge whenever the rate of accessible correlation between events collapses below the threshold required for frame construction. This collapse produces horizon-like behavior—loss of predictability, redshift divergence, and causal decoupling—without invoking spacetime curvature, singular metrics, or global geometric structure. By removing geometry from the definition of horizons, the paper resolves ambiguities surrounding observer dependence, horizon complementarity, and coordinate artifacts. Horizons are shown to be operationally real but ontologically secondary, reflecting limits of inference rather than features of spacetime itself. This result provides a foundation for later treatments of black hole horizons, acceleration horizons, and quantum measurement boundaries within a unified accessibility framework. Keywords horizons; accessibility limits; operational causality; observer dependence; non-geometric horizons; null coordination Notes Arc I — Accessibility (core conceptual result) Horizons derived without spacetime geometry Unifies event, Rindler, and observational horizons Reframes causal boundaries as inference limits Foundational for later gravity and quantum arcs