Teacher Notes: Curved space
There are many different explanations for the Pound Rebka result. The one I favour at the moment is the loss of energy approach. So as photons rise up the tower they lose energy and therefore have reduced frequency. An alternative is the clocks tick slower closer to the earth approach.The derivation of the Schwartzchild radius is a little mystifying since it uses Newtons model of gravity but gives the correct result.