  A canonical formalism for quantum electrodynamics in curved spacetime is
developed. This formalism enables a systematic investigation of photons in the
Schwarzschild gravitational field, yielding novel results as well as refining
previous results that were predicted by heuristic methods. The claim that "the
gravitational redshift is a shift in the sharp frequencies of the photons for
all frequencies of the spectrum" is proved. It is shown the gravitational
decoherence is due to photon-gravity coupling and observer-dependent quantum
electrodynamics in curved spacetime phenomena. The proper value of the photon
gravitational interferometric relative phase shift is calculated and its full
quantum-general relativistic nature is demonstrated. It is shown its
observation will falsify the validity of Newtonian gravity and the extension of
the Einstein equivalence principle beyond a single point (even in the weak
uniform gravitational field.)
