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M-theory is a theory conjectured by [[Edward Witten]] of the Institute for Advanced Study, that would unify the five different superstring theories ([[Type IIA string theory]], [[Type IIB string theory]], [[Heterotic string theory]], [[SO(32) string theory]], and [[heterotic ''E''<sub>8</sub>×''E''<sub>8</sub> string theory]]). [[Edward Witten]] has used M-theory to explain a number of observed dualities, such as the T-duality, U-duality and S-duality.
