Spacetime Rigidity as a Unified Origin of Dark Matter and Dark Energy

Dark matter is reinterpreted as an *emergent phenomenon of spacetime rigidity*. Within the Quantum Ultrametric Rigidity (QUR) framework, the effective number of gravitational degrees of freedom is reduced by the formation of *coherent ultrametric blocks*. This reduction decreases the dynamical volume while preserving total mass-energy, leading to an apparent gravitational overdensity that reproduces galactic rotation curves and lensing effects without introducing new particles or parameters. The same constitutive law S · ρrig ∼ MP⁴ explains both dark energy and dark matter as complementary faces of spacetime rigidity.