The Physical Origin of the Cosmological Constant from Spacetime Rigidity

Editorial Note — December 2025 (Historical Edition) This short note records the original derivation of the cosmological constant Λ from spacetime rigidity in its simplest late–time, homogeneous form, based on the scaling ρrig(L) = (MPl² / 4π) · (1/L²) with L = ζ / H and a constant geometric coefficient ζ. The mapping ΩΛ = Ωrig = 1 / (12πζ²) and Λ = H₀² / (4πζ²c²) remains valid as a background–level relation within the rigidity framework. A complete and updated treatment of spacetime rigidity and its role in late–time cosmology is now provided in Spacetime Rigidity and the Emergence of Dark Energy (v3) (Zenodo DOI: 10.5281/zenodo.17330437). The unified description of dark matter and dark energy, together with the cosmological implications, is developed in Spacetime Rigidity as a Unified Origin of Dark Matter and Dark Energy (v2) (Zenodo DOI: 10.5281/zenodo.17704249). For this reason, the present text is kept as a compact historical reference to the original Λ–from–rigidity argument, without further updates to its content.