The Mass Effect idea is about manipulating mass so an object has less or negative mass, thus lowering the amount of energy required to bust C to a practical level. I don't know that the mass effect is based on any valid science rather than fictional pseudoscience. I suspect it is not, but I don't know enough about physics to know if a negative mass would allow for FTL travel or not. Well, I suppose if we ever figure out how to manipulate the Higgs Field, we'll find out.