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.