This is accomplished primarily by the comparison of mirror image opposites with each other. Let's begin with gravity. The author pictures gravity as a negative radiation pressure effect and antigravity as similar to ordinary radiation pressure. See the author's published gravity text for more information about these concepts. See this link also below for more information.
Photon holes are essentially negative radiation pressure, the absence of photons.
This is what the author pictures as matter as well as the space surrounding matter. The imbalance of photon holes is gravity, the curvature of space and time. Hence, matter automatically has gravity. In equation A below, it can be understood that photons can travel backwards in time. Recent experiments appear to verify that this is the case.