A unified theory of the fundamental interactions involving supersymmetry, in which the basic entities are two-dimensional extended objects (supermembranes). They are thought to have about the same length scale as superstrings (see superstring theory), i.e. 10−35 m. At the present time there is no experimental evidence for supermembranes. Supermembranes and other higher-dimensional objects have been found as solutions in superstring theory.