Wait a minute - I thought that the prevailing theory (i.e. Relativity) was that gravity is a property of space-time, rather than matter, so where are you getting this idea that "gravity is an effect of mass" is the current model? It's not, it's the outdated Newtonian model, which is still plenty useful for the vast majority of applications.

Furthermore, to address some points in your later reply to @jacobtothe, light is not "supposedly" a particle, rather it was first proposed to be an electromagnetic wave back in 1865, and while that hypothesis has been challenged, it has never actually been debunked. Light has a dual nature, it behaves as both a particle and a wave, as any object at the quantum scale does. In other words, matter also has a dual nature, but matter behaves less and less like a wave as the corresponding particles get larger (look up "De Broglie wavelength" to see what I mean). The duality of matter is most easily observed with very small particles such as leptons (the class of particles that includes electrons). Also, c is definitely a constant. Experiments in which c is supposedly exceeded are always ones in which the group velocity of the wave has been accelerated, sometimes as high as 300c, but the phase velocity never changes. If c can be exceeded (by anything other than the expansion of the universe), kindly show us a single experiment in which the phase velocity exceeded 3x10^8 m/s.