OK, if the universe started with the big bang, then all stuff would have been very close together. So it seems to me if the universe is expanding at the speed of light, then everything should still be visible to us no matter what direction it went. What am I missing.
The fact that, according to Einstein the speed of light is the same from any frame of reference. Where one goes from there is sort of up to you, I guess but the old “man at the station vs. the man on the train” ain’t helpful.
That WE may not be at the center.
Here is the problem. If the Big Bang is true, matter began moving outward at some velocity less than speed of light. Any light generated in the time frame close to the event would begin accelerating in all directions at the speed of light into regions of the universe devoid of observers. Hence , there are no observable, “original” photons”. In fact, when you think about it, there was no matter for these photons to interact with and create 2nd generation photons either. So the “background” 5 Hz radiation has to be at least 3rd or 4th generation photons.