I'm reasonably certain that this is not correct; this was a viewpoint held fairly briefly in the post-Einsteinian physics community, but abandoned because of a

I'm reasonably certain that this is not correct; this was a viewpoint held fairly briefly in the post-Einsteinian physics community, but abandoned because of a lack of evidence. For the purposes of general relativity, stress-energy is the mass/energy hybrid quantity, but the equivalence is not literal in the sense that in a given inertial reference frame momentum does not attach to energy, but only to mass.