When an em-wave red shifts due to leaving a gravitational field it loses energy, right? Where does that energy go, into gravitational potential energy of the photon? If so does this mean that the photon can "fall" back on the gravitating body to reclaim this energy? What happens to the energy if it escapes the gravitational field? I've also been told to think of red/ blue shift in terms of differing clock rates in the vicinity of a gravity field and that clock rates virtually stop at the event horizon of a black hole. Does this mean a photon that gets "sucked" into a black hole has an infinite frequency at the EH, since time has gone to zero?