The Quest for Unification

The quest for unification is a prevailing theme is physics, from Newton who unified
terrestrial and celestial mechanics, to modern day efforts to synthesize general relativity and
quantum mechanics. I will describe contemporary work on two fronts in this direction. The first
is the construction of phenomenological heterotic-string models and the study of a particular
class that produced solely the spectrum of the Minimal Supersymmetric Standard Model in
their low energy effective field theory. The second front is an attempt to identify a fundamental
principle underlying quantum gravity, in the context of the equivalence postulate
of quantum mechanics. The 750 GeV di-photon excess as a possible signature of a
string derived Z' model will be discussed.  The presentation will be non--technical 
and suitable for a general audience.