What if we are looking at it backwards? That mass is an effect of gravity, rather than gravity a property of mass.

Consider that gravity is a centripetal effect and when waves synchronize, the effect is centripetal. For example, lasers are synchronized lightwaves.

So if there is a synchronizing effect going on across the entire radiological spectrum, from the very faintest curvature of light, to the vortices at the center of galaxies, with what we think of as mass as a middle ground between these poles, then lots of invisible mass is unnecessary.

Also, isn't a rest frame still implicit in Special Relativity? Given that in a frame traveling at the speed of light, the ruler is reduced to zero and the clock is stopped, then wouldn't the frame with the longest ruler and fastest clock be closest to the equilibrium of the vacuum? The unmoving void of absolute zero.

So space would be like the number line, from zero to infinity.

Galaxies are energy radiating out, toward infinity, as structure coalesces in, toward equilibrium.

Black holes to black body radiation.