Phenomenological Survey of M–theory ∗†

The Standard Model data suggests that the quantum gravity vacuum should accommodate two pivotal ingredients. The existence of three chiral generations and their embedding in chiral 16 SO(10) representations. The Z2 × Z2 orbifolds are examples of perturbative heterotic string vacua that yield these properties. The exploration of these models in the nonperturbative framework of M–theory is discussed. A common prediction of these constructions is the existence of super– heavy meta–stable states due to the Wilson–line breaking of the GUT symmetries. Cosmic ray experiments in the forthcoming years offer an exciting experimental window to the phenomenology of such states.