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I guess this is still puzzling to me. From what I can gather, it sounds like our idea of cosmological homogeneity and isomorphism are roughly equivalent to my l
by Amezarak 2y ago
I guess this is still puzzling to me. From what I can gather, it sounds like our idea of cosmological homogeneity and isomorphism are roughly equivalent to my layman's conception of "things are evenly distributed and the universe, could it be viewed as a whole, is symmetrical."
But what I don't understand is why we would expect that to be true. Once we learned about galaxies, what would imply their even distribution on a galactic scale? The very existence of nonidentical galaxies / lack of obvious symmetry around us already suggests the existence of early perturbations that cause an uneven distribution and asymmetry, no?
- tzs 2y agoI don't think there was an obvious lack of symmetry. In any random direction you look with a powerful telescope you see about the same number of galaxies, the same mix of types of galaxies, the same kind of variation in brightness. It was only after decades of developing better and better ways to measure distances that we started getting good enough 3D galaxy position to recognize things like superclusters and filaments. It is only relatively recently that good enough 3D universe maps have been made to show the large voids that might might be distributed sufficiently non-uniformly that they must be taken into account. Throughout most of that time the models based on a reasonably homogeneous universe worked. It was only relatively recently that they ran into problems. For example in the last 10 or so years a couple different ways to measure the Hubble constant were refined enough to reduce their error bars to the point that the error bars no longer overlapped.