MTheory (The theory formerly known as Strings)Superunification underwent a major paradigm shift in 1984 when elevendimensional supergravity was knocked off its pedestal by tendimensional superstrings. This last year has witnessed a new shift of equal proportions: perturbative tendimensional superstrings have in their turn been superseded by a new nonperturbative theory called Mtheory, which describes supermembranes and superfivebranes, which subsumes all five consistent string theories and whose low energy limit is, ironically, elevendimensional supergravity. In particular, sixdimensional string/string duality follows from membrane/fivebrane duality by compactifying Mtheory on S1/Z2 ×K3 (heterotic/heterotic duality) or S1 ×K3 (Type IIA/heterotic duality) or S1/Z2 × T 4 (heterotic/Type IIA duality) or S1 × T 4 (Type IIA/Type IIA duality).


MultiMembrane Solutions of D = 11 SupergravityWe find exact solutions to the field equations of elevendimensional supergravity corresponding to stable multimembrane configurations. Their holonomy group is given by the SO (8) subgroup of an enlarged tangent space group SO ( l, 2 ) × SO (16), and hence one half of the spacetime supersymmetries are broken. The solutions saturate a Bogomol'nyi bound between the mass per unit area and the Page charge, which also guarantees their stability.


Superstrings in D=10 from Supermembranes in D=11The type IIA superstring in ten dimensions is derived from the supermembrane in eleven dimensions by a simultaneous dimensional reduction of the world volume and the spacetime.

