Editing M-theory (section)

===Supersymmetry===

{{main article|Supersymmetry}}

Another important theoretical idea that plays a role in M-theory is [[supersymmetry]]. This is a mathematical relation that exists in certain physical theories between a class of particles called [[bosons]] and a class of particles called [[fermions]]. Roughly speaking, fermions are the constituents of matter, while bosons mediate interactions between particles. In theories with supersymmetry, each boson has a counterpart which is a fermion, and vice versa. When supersymmetry is imposed as a local symmetry, one automatically obtains a quantum mechanical theory that includes gravity. Such a theory is called a [[supergravity theory]].<ref name="Duff 1998, p. 64">Duff 1998, p. 64</ref>

A theory of strings that incorporates the idea of supersymmetry is called a [[superstring theory]]. There are several different versions of superstring theory which are all subsumed within the M-theory framework. At low [[energy|energies]], superstring theories are approximated by one of the three supergravities in ten dimensions, known as [[type I supergravity|type I]], [[type IIA supergravity|type IIA]], and [[type IIB supergravity|type IIB]] supergravity. Similarly, M-theory is approximated at low energies by supergravity in eleven dimensions.<ref name="Becker, Becker, and Schwarz 2007, p. 12"/>