We present a constitutive reformulation of weak-field gravity in which the observed gravi-tational field is treated as the nonlinear response of an effective vacuum medium, governedby a dimensionless response function κg that multiplies the gravitational field in a modifiedGauss law. The framework reduces to Newtonian gravity at high acceleration and repro-duces the deep-modified-Newtonian-dynamics (deep-MOND) scaling at low acceleration. Asin MOND, it reproduces the observed weak-field galactic phenomenology without invokingnon-baryonic dark matter, while incorporating the cosmological vacuum through a singleuniform term equal to the cosmological constant with a derived coefficient.We calibrate the global acceleration scale a0 and test the framework against the completeSpitzer Photometry and Accurate Rotation Curves (SPARC) sample using the standardquality cuts, yielding 132 galaxies (2652 rotation-curve measurements) after full nuisance-parameter marginalization over stellar mass-to-light ratio, distance, and inclination withliterature priors. Independent tests are performed using Sloan Digital Sky Survey (SDSS)Data Release 7 galaxy–galaxy weak-lensing measurements in three stellar-mass bins withfull covariance weighting.The constitutive framework achieves a median reduced chi-square of 2.0 per galaxyand reproduces the observed rotation curves with performance comparable to the standardMOND interpolating function evaluated through the identical fitting pipeline. A directgalaxy-by-galaxy comparison shows that the median difference in reduced chi-square is ap-proximately zero, while the mean exhibits only a modest overall preference for MOND.The weak-lensing fits are likewise comparable to MOND and remain competitive with aNavarro–Frenk–White dark-matter halo.The preferred acceleration scale is only weakly constrained once observational systematicsare marginalized, with a0 = (1.0–2.0) × 10−10 m s−2. These empirical results support inter-preting the constitutive framework as a physically motivated medium-response reformulationof MOND-like dynamics. The framework provides observational performance comparableto MOND on current galaxy and weak-lensing data while offering a unified interpretationin which galactic dynamics and the cosmological vacuum arise within the same constitutivefield equation.
Ralph C DeMartino (Mon,) studied this question.