Achromatic Geometric Polarization Drag at M87* and Sgr A* A Falsifiable Observational Test for the Geometric Fluid Spacetime Universe

Recent polarimetric observations by the Event Horizon Telescope (EHT) have mapped twisted polarization patterns around the supermassive black holes M87* and Sgr A*. In the standard interpretation these patterns are attributed primarily to Faraday rotation in magnetized plasma, a process that scales strictly as λ². Within the Geometric Fluid Spacetime Universe (GFSU) framework the universe is described as a finite-norm multivector fluid U(X, σ) valued in the flat infinite-dimensional geometric algebra Cl∞,0. Extreme rotor gradients near a black-hole region produce a pure-geometric vector drag on the polarization bivector of photons that skim the photon sphere. This drag is achromatic. Starting from the GFSU master expression for the cumulative geometric phase and reducing it under the photon-orbit impact-parameter scaling, we obtain a mass-independent formula that depends only on the dimensionless spin a* and the inclination i. Insertion of current EHT parameters yields a predicted achromatic twist of 5.7° ± 1.0° for M87* and a range 3.6°–6.6° for Sgr A* (depending on the adopted spin). The forthcoming multi-frequency EHT data set that combines 230 GHz and 345 GHz observations supplies a direct, binary test: a residual rotation angle that remains constant across the two bands after Faraday subtraction would support the geometric-drag mechanism; a clear λ² decline would favor the conventional plasma interpretation.