Proofs Confirming NeoGravity: The GW170817 Multi-Messenger Event as Evidence for Propagation Through the Ether Plenum

On 17 August 2017 the LIGO and Virgo detectors recorded a gravitational signal from the merger of two neutron stars in NGC 4993, and 1.74 seconds later the Fermi and INTEGRAL observatories recorded a short gamma-ray burst from the same location. The two signals had travelled approximately 130 million light years, roughly four times ten to the fifteenth seconds, and arrived within two seconds of one another. This constrains any difference between the propagation speed of gravitational influence and the speed of light to a fractional magnitude of order ten to the minus fifteen, an improvement of roughly fourteen orders of magnitude over previous bounds from binary pulsar timing. This paper examines what the event establishes for the Theory of NeoGravity, and states with precision both what it supports and what it does not. Under the standard reading, spacetime ripples and electromagnetic radiation travel at the same speed because each is separately postulated to do so. Under the reading this series requires, both are disturbances propagating through a single physical medium, and their equal speeds follow because the speed in question is a property of that medium rather than a coincidence between two independent postulates. The paper argues that this constitutes a genuine explanatory advantage while stating plainly that an explanatory advantage is not evidence, and that the measurement itself does not discriminate between the two readings. Because a companion paper in this series interprets the nanohertz pulsar timing background as pressure oscillations in the Plenum rather than as spin-two gravitational radiation, this paper also addresses directly the apparent tension between accepting the LIGO detection and reinterpreting the pulsar timing result. That tension is shown to be superficial: what the interferometers measure is a transient strain signal whose propagation speed is constrained, while what the pulsar timing arrays measure is the angular correlation pattern of a stochastic background, and only the second is polarization-discriminating. The paper concludes by identifying what would constitute genuine evidence for the Plenum reading, principally the polarization content of the nanohertz background examined in the companion paper, and by noting that the framework's own falsifiable prediction lies not in propagation speed but in the second-order light deflection coefficient.