Virialisation-induced curvature as a physical explanation for dark energy

The geometry of the dark energy and cold dark matter dominated cosmological model (ΛCDM) is commonly assumed to be given by a Friedmann-Lemaître-Robertson-Walker (FLRW) metric, i.e. it assumes homogeneity in the comoving spatial section. The homogeneity assumption fails most strongly at (i) small distance scales and (ii) recent epochs, implying that the FLRW approximation is most likely to fail at these scales. We use the virialisation fraction to quantify (i) and (ii), which approximately coincide with each other on the observational past light cone. For increasing time, the virialisation fraction increases above 10% at about the same redshift ( ~ 1-3) at which Ω_Λ grows above 10% ( ≈ 1.8). Thus, instead of non-zero Ω_Λ, we propose an approximate, general-relativistic correction to the matter-dominated (Ω_m = 1,Ω_Λ = 0), homogeneous metric (Einstein-de Sitter, EdS). A low-redshift effective matter-density parameter of Ω_m^eff(0) = 0.26±0.05 is inferred. Over redshifts 0 < z < 3, the distance modulus of the virialisation-corrected EdS model approximately matches the ΛCDM distance modulus. This rough approximation assumes ``old physics'' (general relativity), not ``new physics''. Thus, pending more detailed calculations, we strengthen the claim that ``dark energy'' should be considered as an artefact of emerging average curvature in the void-dominated Universe, via a novel approach that quantifies the relation between virialisation and average curvature evolution.