M-theory ($R_{11}=g_s\sqrt{{\alpha }^{\prime }}$)

An eleven-dimensional nonperturbative framework suggested by superstring dualities, with eleven-dimensional supergravity as its low-energy limit. Type IIA at coupling $g_s$ has an interpretation on a circle of radius $R_{11}=g_s\sqrt{{\alpha }^{\prime }}$, so an additional dimension becomes visible at strong coupling. Perturbative string descriptions represent particular limits of this framework.