M-theory
A multiverse of a
somewhat different kind has been envisaged within string theory and its
higher-dimensional extension, M-theory.[13]These
theories require the presence of 10 or 11 spacetime dimensions respectively.
The extra 6 or 7 dimensions may either be compactified on a very small scale,
or our universe may simply be localized on a dynamical (3+1)-dimensional
object, a D-brane. This opens
up the possibility that there are other branes which could support "other
universes".[14][15] This is unlike the
universes in the "quantum multiverse", but both concepts can
operate at the same time.[citation needed]
