That "something" would be a violation of the conservation laws; specifically the conservation of momentum and the conservation of energy. EM fields can't do that because they're rank-1 tensor fields. Only gravity can produce reactionless propulsion effects because it's a deformation of the spacetime matrix itself, a rank-2 tensor field effect. I looked at every academic and cockamamee internet theory on the planet before I properly understood that EM physics couldn't get the job done. Only GR can yield the kind of field propulsion we see with AAVs. EM fields can be useful as a "handle," but the key is at the nuclear scale - manipulating the nucleons to magnify GR phenomena for practical applications, as Robert Forward suggested way back in 1963. If there's any truth to the anomalous and high-precision isotopic distribution found in the Argentinian case sample investigated by Jacques Vallee, this would confirm that the crucial factor is nuclear in nature because nuclear matter is basically neutronium; the link between matter and spacetime.