Correct me if I'm wrong but as of yet, we do not even know for sure if Electrons (and other sub-atomics) even have a "volume" per se. As far as I know (from internet sources), they are singular points, possibly infinitely small, emitting a repulsive radiation (negative electromagnetic for electrons.) In this sense, the force of gravity at or near a singularity, could simply compress the energy waves emitted by the electrons (effectively compressing the electron itself.) If applicable at all to other subatomic particles, a singularity could in theory, compress matter at a quantum level to arbitrarily small spaces. First post on the forum by the way, hi all!