Cosmic Acceleration Without Dark Energy: A MIDH-Based Toy Model of Scale-Factor-Dependent Inertia

TThis paper develops a minimal cosmological toy model grounded in the Mutual Information Density Hypothesis (MIDH) and the informational-inertia conjecture introduced in earlier work, exploring late-time acceleration as a structural effect of correlation dilution rather than vacuum energy. If inertial resistance reflects the cost of reconfiguring correlations under acceleration, and if that cost declines as large-scale mutual information thins with expansion, then the Friedmann acceleration equation naturally acquires a positive term that mimics Λ without new fields or fluids. Embedding a scale-factor-dependent interface capacity μ(a) into the acceleration equation and adopting the volumetric ansatz μ(a) = 1/(f · a³) reproduces ΛCDM’s expansion history and the transition redshift z ≈ 0.6. We outline three routes toward a microphysical basis for this scaling – discrete vacuum networks, a covariant scalar–matter coupling for informational inertia, and area/volume capacity competition – and list observational signatures that could distinguish these realizations from a strict cosmological constant. The model remains a sketch; its value is to show how an informational interpretation of inertia can recover ΛCDM phenomenology and suggest concrete tests.