Scale Corrections to the ΛCDM Model to Explain a Time-Dependent Dark Energy Density, and the Hubble and S₈ Tensions

A number of approaches to a theory of quantum gravity assume the fabric of spacetime is distinct from the spacetime of the material world of matter and energy. On a short time scale, one cannot distinguish between the fabric of spacetime expanding, nominally due to dark energy, or the scale of the material world contracting with respect to the fabric of spacetime. Contraction of the scale of the material world (length, time, mass, and charge contracting equally) maintains observable physical laws and results in a decreasing derived dark energy density matching that reported by the DESI Collaboration in March 2025. The DESI fits to the dark energy density over time show a distinct difference between those using scale-dependent supernovae data and those using mostly scale-independent angular measurements, such as from CMB and BAO measurements. That difference is resolved by applying a scale contraction rate of -3%/Gyr to the supernovae data. Scale contraction of the material world eliminates the need for dark energy to explain the apparent expansion of space, resolving the ~10¹²² discrepancy between the dark energy density required to match observation and that calculated for the vacuum energy as the mechanism for dark energy. The large force of the vacuum energy is a potential mechanism for compression of the material world, and would explain why the observed expansion only occurs outside of gravitationally bound systems. A scale-contraction model for cosmological kinematics explains why the dark energy density appears to be decreasing without requiring the underlying vacuum energy to be changing with time. Scale contraction of the material world predicts the observed directions and order of magnitude of the Hubble tension and the S₈ tension, which has been a challenge to other proposed modifications of ΛCDM since those two tensions have opposite trends over time, the Hubble constant being about 10% larger in the late universe compared to the early universe, and the structure constant, S₈, about 10% smaller. Scale contraction of the material world can be tested by modifying the LCDM cosmological model to include scale contraction over time, and assessing if the Hubble and S₈ tensions are quantitatively reduced or resolved.