As a photon has no mass and must always have velocity c, if I were to shine a laser straight up (so Earth's gravity would be pulling straight back on it), what would the effect be on the photon? It wouldn't slow it down nor divert it, correct? My understanding is that it would reduce the frequency of the photon (as it's kinetic energy must be reduced, just as a classical object would lose kinetic energy). If it's the case that only gravitational redshift would occur given this trajectory (and please correct me if I am wrong there), I have two similar questions:
Would not light leaving a galaxy therefore be affected by a gravitational redshift? Is that included when physicists perform calculations regarding the expansion of galaxies away from us (and how accurate could these calculations be, given general estimates of mass distributions, etc., particularly given dark matter's gravitational effects)? If not, could it be that what we now think is a separation of these galaxies is somewhat, primarily, or even completely just light being affected by gravity?
Also, would not light then be able to escape a black hole provided it entered in precisely perpendicular to the event horizon and the black hole was not moving at all orthogonally to the photon's trajectory? (Or, perhaps more plausibly, if a photon is emitted from inside the black hole with a relative velocity of c towards the event horizon.) And then just come out the other side severely redshifted (to a frequency of almost 0 Hz)? I'm familar with the GR equations for gravitational redshift, but it also does not work inside the Schwarzschild radius (as the denominator becomes a square root of a negative number).
Apologies if this is just confused ramblings of someone who knows just enough to be dangerous.