Open Universe Model (OUM-2/200526): Intermediate Model between the Classical Closed Universe and the Infinite-Dimensional Multiverse Model

This paper introduces the Open Universe Model (OUM) — an intermediate methodological step between the classical closed Universe (ΛCDM) and the Infinite-Dimensional Multiverse Model (IDM). The classical model, based on closure, unitarity, and determinism, faces unresolved problems: lack of quantum gravity, the cosmological constant problem, the black hole information paradox, the complementarity problem, absence of dS/CFT, and the fine‑tuning of constants. The OUM relaxes the closure assumption, postulating that our Universe interacts with external objects — half‑spaces A and B (from the interference vacuum model) and a finite number of neighbouring universes. This reframes several problems: information is not lost but leaks into the external environment; the cosmological constant may be dynamic; constants may be evolutionary attractors. The total system (Universe + environment) remains closed and unitary. However, the OUM does not address questions requiring infinity (the nature of decaying interaction, the limit of conditionality, the possibility of recovering full unitarity). These are passed to the next level — the IDM, where dimensionality and nestedness are infinite. The paper establishes three modelling levels: Level 0 (ΛCDM), Level 1 (OUM), Level 2 (IDM). The OUM can be tested through observational signatures of interaction with neighbouring universes (CMB anomalies, constant variations, dynamic Λ).