Planck scale physics and testability in SU(5) supergravity GUT

Unification scale threshold corrections in minimal SU(5) supergravity grand unification are discussed. A probe of the underlying theory is outlined, where low energy measurements can in principle measure the effects of Planck scale (1/${\mathit{M}}_{\mathrm{Pl}}$) terms. A bound relating the strong coupling constant to the mass scales associated with proton decay and supersymmetry is derived including uncertainties associated with the high energy scale.