  We introduce a notion of topological M-theory and argue that it provides a
unification of form theories of gravity in various dimensions. Its classical
solutions involve G_2 holonomy metrics on 7-manifolds, obtained from a
topological action for a 3-form gauge field introduced by Hitchin. We show that
by reductions of this 7-dimensional theory one can classically obtain
6-dimensional topological A and B models, the self-dual sector of loop quantum
gravity in 4 dimensions, and Chern-Simons gravity in 3 dimensions. We also find
that the 7-dimensional M-theory perspective sheds some light on the fact that
the topological string partition function is a wavefunction, as well as on
S-duality between the A and B models. The degrees of freedom of the A and B
models appear as conjugate variables in the 7-dimensional theory. Finally, from
the topological M-theory perspective we find hints of an intriguing holographic
link between non-supersymmetric Yang-Mills in 4 dimensions and A model
topological strings on twistor space.
