Just some conceptual ideas that I don't understand A spaceship starts falling under gravity with an acceleration g as measured by an observer Barry at rest on Earth. At the instant that the ship starts to fall, an astronaut Harry at the base of the rocket ship sends a light signal of frequency w vertically upward to another astronaut Sally a distance h above. Barry argues that the light signal reaching Sally ought to be Doppler shifted toward the blue. This Doppler shift Δw is given by (Δw/w)_Doppler = (Δu/c) where Δu is the velocity of the rocket ship after a time Δt = (h/c) But Sally does not see this shifted frequency. So why is this? What compensates for the Doppler shift in frequency? And if another observer (let's call her Kelly) was to see the red-shifted light, what is required for her?