A unified-field theory for all the known fundamental interactions that involves supersymmetry. Supergravity is most naturally formulated as a Kaluza–Klein theory in eleven dimensions. The theory contains particles of spin 2, spin 3/2, spin 1, spin 1/2, and spin 0. Although supersymmetry means that the infinities in the calculations are less severe than in other attempts to construct a quantum theory of gravity, it is not clear whether perturbation theory in supergravity gives finite answers due to the great complexity of the calculations. It is thought by many physicists that to obtain a consistent quantum theory of gravity one has to abandon quantum field theories, since they deal with point objects, and move to theories based on extended objects, such as superstring theory and supermembrane theory, and therefore that supergravity is not a complete theory of the fundamental interactions. However, it may well be a key ingredient in such a theory since it is related to superstring theory by duality.