The speed of gravity and the LIGO constraint

Any alternative theory of gravity must explain how fast gravitational waves travel. In 2017, the neutron star merger GW170817 showed that gravitational waves and light from the same event arrive together. Gravity therefore travels at the speed of light.

The paper notes that standard hydrodynamic models of gravity fail this test. In an ordinary elastic medium, pressure waves and shear waves travel at different speeds, because each depends on a different stiffness.

RSI avoids this problem. The theory holds that the Eternal Consonance is a single continuous field with one baseline line tension of 0.73 N. Every wave is a different shape of disturbance in that same field. Light is a transverse, or side-to-side, oscillation. A gravitational wave is also transverse: it stretches and squeezes the medium across its direction of travel, as General Relativity predicts and LIGO and Virgo observations favor. An incompressible medium carries no pressure waves at all. Both are governed by the same vacuum tension and the same stiffness parameters, so the wave equation gives them the same speed. RSI is therefore consistent with the LIGO constraint without any fine-tuning.