Re: Riddle me this:
I was speaking to an astrophysicist recently and I was surprised to find out that red-shift is now calculated not only to take account of the recessive speed of the star/galaxy where the photon was emitted from (the further away the higher the speed because of the expansion appears faster), but also because the length of time the photon is in existence, it's wavelength actually DOES get significantly stretched by the universe's expansion. I didn't ask at the time but I suppose this happens to photons because they don't have any other weak or strong forces holding them together??? (I am not a professional physicist). I think this means that if the photon was for some reason not moving, but sitting around for billions of years (presumably listening to the director's cut of Wagner's Ring Cycle) it would be "red-shifted" (or at least just stretched) by the universe's expansion over that time.