  The Standard Model data suggests the realization of grand unification
structures in nature, in particular that of SO(10). A class of string vacua
that preserve the SO(10) embedding, are the three generation free fermion
heterotic-string models, that are related to Z2xZ2 orbifold compactification.
Attempts to use the M-theory framework to explore further this class of models
are discussed. Wilson line breaking of the SO(10) GUT symmetry results in
super-heavy meta-stable states, which produce several exotic dark matter and
UHECR candidates, with differing phenomenological characteristics. Attempts to
develop the tools to study the properties of these states in forthcoming UHECR
experiments are discussed. It is proposed that quantum mechanics arises from an
equivalence postulate, that may lay the foundations for the rigorous
formulation of quantum gravity.
