Black hole entropy reveals a twelfth dimension

The Bekenstein-Hawking black hole entropy in string theory and its generalizations, as expressed in terms of charges that correspond to central extensions of the supersymmetry algebra, has more symmetries;than U duality. It is invariant under transformations of the charges, involving a twelfth (or thirteenth) ''dimension.'' This is an indication that the secret theory behind string theory has a superalgebra involving Lorentz nonscalar extensions (that are not strictly central), as suggested in S theory, and which could be hidden in M or F theories. It is suggested that the idea of spacetime is broader than usual, and that a larger ''spacetime'' is partially present in black holes.