Testing Einstein’s Equivalence Principle and Its Cosmological Evolution from Quasar Gravitational Redshifts

We propose and apply a new test of Einstein's Equivalence Principle (EEP) based on the gravitational redshift induced by central super massive black hole quasars in surrounding accretion disk. Specifically, we compare observed Fe III$\lambda\lambda$2039-2113 emission line blend with predicted values wide, uncharted, cosmic territory ($0 \lesssim z_{cosm}\lesssim3$). For first time measure, statistical uncertainties comparable or better than those other classical methods outside Solar System, ratio between redshifts theoretical predictions 10 independent cosmological bins $1 z_{cosm}\lesssim3$ range. The average measured over this interval is $\langle z^m_g/z_g^p\rangle=1.05\pm 0.06$ scatter $0.13\pm 0.05$ showing no evolution EEP within these limits. This method can benefit from larger samples measurements S/N ratios, paving way for high precision tests (below 1\%) scales.