>>1
Good question, i have been taking three courses of quantum related subjects now, yet it has never come up. We even neglect the gravitational part in the hamiltonian frequently, let alone using time independent schrödinger equation. The mysteries behind gravitation hasn't been resolved quite yet( see CERN page for updates about Higgs boson) so it is early to give a definite answer. However i might speculate. Photons that are electromagnetic radiation interact with ordinary matter such as electrons if certain conditions are met. Now physics prohibit interbosonic interactions but gravity is not independent of matter. The gravitation field is affected by mass of a matter and matter can indirectly affect photons. May be there is a roundabout relation but i think bosons can interact, what is matter anyway? How a quark is different from a boson except for having fractional spin quantum number? The fundamental differences become ambiguous when you think thoroughly.