Geometric Origin of Dark Components: A Causal-Asymmetry Hypothesis

We present a causal-boundary framework in which the apparent dark components of the cosmological energy budget — dark matter and dark energy — are emergent consequences of the bounded causal structure of the observable universe. Ordinary baryonic matter, together with the geometric scales R_H (Hubble radius), R_EH (event horizon), and R_PH (particle horizon), are the only fundamental inputs. The horizon shell, defined by R_EH < r < R_PH, is in one-way causal communication with the observer at the origin. The central geometric observation of this work is that, by the cosmological principle, every observer is at the center of their own particle horizon, and the particle horizons of distinct comoving observers do not coincide. As a consequence, the horizon shell defined relative to a reference observer O is, when viewed from any other point A ≠ O, asymmetric: portions of the shell lie outside A's particle horizon and cannot causally influence A. Newton's shell-theorem cancellation, which requires spherical symmetry of the source distribution about the test point, therefore does not apply to points A ≠ O within the shell. The cancellation is not assumed away — it is geometrically inapplicable. A direct calculation shows that this asymmetric configuration produces a net acceleration that is (i) outward and (ii) linear in the displacement r from the observer. Equating this acceleration with the second Friedmann equation as a functional identity in r yields the central relation: (Ω_b / 2) · (R_PH³ − R_EH³) / R_EH³ = Ω_Λ − Ω_m / 2 which agrees with Planck 2018 measurements to 0.30%. Combined with spatial flatness, this single relation determines Ω_m, Ω_Λ, and Ω_c at sub-percent accuracy: under flatness-consistent comparison, all three parameters match Planck 2018 to ~0.015–0.04%. The 95% of the cosmic energy budget conventionally attributed to unobserved components is, in this framework, jointly determined by the observed baryon density and the horizon geometry. To our knowledge, this is the most accurate quantitative determination of the cosmological dark-sector parameters available from a first-principles geometric construction. The framework additionally provides a natural geometric reading of the MOND acceleration scale a_0 ≈ cH_0/(2π): the factor 2π is the cosmic circumference scale, and a_0 is the gravitational acceleration whose Rindler horizon equals 2π·R_H. The deep-MOND functional form a = √(g_N · a_0) emerges naturally as the dimensional combination connecting galactic-scale Newtonian gravity to the cosmological horizon scale within the same Rindler causal structure.The framework establishes the qualitative form (outward, linear in r) of the horizon-shell effect directly from the geometry of particle-horizon cutting. The exact normalization — i.e., that the proportionality constant matches the Friedmann acceleration coefficient to 0.3% — follows from a self-consistency condition: the horizon shell is held together only by gravity (no other binding force is available between baryons), so the gravitational scale of the shell must match the expansion scale of the interior region for the observed cosmological configuration to persist. A first-principles general-relativistic derivation of this self-consistency, accounting for retarded propagation, cosmic expansion, and FRW curvature, is the subject of a planned follow-up paper.