Consistency with the PPN formalism

The Parameterized Post-Newtonian (PPN) formalism is a standard way to test gravity theories against Solar System measurements. It describes a theory with a set of parameters. General Relativity requires two of them, γ and β, to equal 1. Here γ measures how much space curves, which shows up in the bending of light. β measures the nonlinearity of gravity, which shows up in the slow turning of planetary orbits, called perihelion precession.

RSI addresses both. Its refractive index derivation from Chapter IV gives a light deflection of 1.75 arcseconds at the Sun, which corresponds exactly to γ = 1. For β, the nonlinear term in RSI's Lagrangian, which the theory calls the Twist, reproduces the self-interaction energy of the gravitational field. In the weak-field limit this mimics the Schwarzschild metric and gives β ≈ 1.

The theory holds that it matches these values without adopting curved geometry. It reproduces the same energy density gradients through fluid mechanics.