BCS theory - The theory put forth to elucidate both superconductivity and super fluidity. This suggests that in the superconducting (or super fluid) state electrons form Cooper pairs, where two electrons proceed as a single unit. This takes a non-zero quantity of energy to break these pairs, and the imperfections in the superconducting solid (that would usually lead to resistance) are incapable of breaking the pairs, therefore no dissipation takes place and there is no resistance.