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Assume the emitting object is receding (relative to Earth) at 1.5c.
"dark night sky paradox." The paradox states that at any angle from the Earth the sight line will end at the surface of a star, so the night sky should be completely white.
A fish is swimming at a constant speed of 1 m/s. If the fish starts 100 km away from you, it will take 100,000 seconds to reach you. Now suppose you have a water faucet every meter pouring .001 m³/s into the canal. 100,000 faucets pour in enough water to produce a current of 1 m/s. So, if the fish starts 100 km away, it will never get any closer to you.
The speed of light is constant relative to comoving space.
True, but relativity does not require that you perceive the fish approaching you at 1 m/s, in spite of the current. Would I not be right in thinking that you must see light as approaching you at c, in spite of the expansion of the Universe?
This comoving system you are discussing, it's relative the Hubble expansion right?
So the observer in such a coordinate system should then be at rest with this Hubble constant? And so observe a isotropic universe without a 'expansion' and redshift, as I understands it?
But I don't see how to apply it to the reality of a (possibly) expanding universe, as it does it in all directions possible, as measured from any observer? To be 'at rest' in such a system you too would need to 'expand' constantly, and in all directions simultaneously?