Why do alternative explanations of redshift imply centricity
Dear Robert, in a recent live session you mentioned how alternative explanations for redshift also placed the Earth at the center of the universe. However, it was not ellaborated why. One explanation was that it is gravitational redshift. However, it seems to me that if redshift comes from the gravity of the emissor, light emmited in all directions by it will be red-shifted, so no matter where you are at the universe (that is, not necessarily at the center of the universe) we would see all galaxies with redshift. Another explanation was that of tired light and similar, that because of the space environment, light is affected in a way that makes it become red-shifted. However, this would make it so that no matter where we are, we would see everything with redshift. So if these were the cause, why would someone not in the center see something different?
Answer
Yes, gravity will produce redshift. Hence if we see redshifted galaxies all around, that is another explanation for Hubble's experience other than the galaxies spreading outward. That is the whole point. The only difference would occur in Hubble's explanation if the Earth was not in the center. If the Earth was not in the center than Hubble had nothing to worry about, which would have been the case if he had seen blueshifts.