Why do astrophysical and cosmological theories accept the merely mathematically thinkable ISOTROPY (the principle that all directions in the cosmos are alike, and hence no direction is preferred in any manner than any other) in large regions of the cosmos as the general empirical case and as the absolute case in the cosmos? I think the most important reason is the dogmatic faith of physicists and mathematicians in the statistical "counts" / "measurements" of particular regions of the universe.
In fact, the reason why statistical measurements are being used is that there are differences between every two regions, subregions, etc. everywhere and in every direction in the universe. This fact is forgotten in the dogmatic faith in the power of mathematics!
If there are local differences here, and local differences there, and the same everywhere, then we cannot generalize the same local differences into supra-regional overall isotropy! But, for mathematical purposes, some theories generalize these details statistically, but this is never the absolute case anywhere, in any direction!
Even in the pages of RG, I have had discussions where some have continued to insist on the power of mathematics over physics and that those who cannot take the statistical average as the general case (and hence as the absolute case) are being stupid, because mathematics does wonders!
Let me now take the simple example of a balloon in order to discuss the cosmological aspect of identity of parts, ISOTROPY (of course, this is not identity), simultaneity of processes, cyclic cosmic evolution, etc.
I consider them all as very simplistic and silly, ad hoc, meant only for ideal mathematical consumption, and not meant for physics and cosmology. For example, how can anything absolutely cyclic, spherical etc. be the real case, if there are ANISOTROPIES everywhere in the universe?
A balloon may be inflated with air at a measurably very stable and constant rate. But between any two points of it there must be some difference of rate of expansion. This is the natural case. Nothing else can come and stop this process in the cosmic case. If not, all the points in it would naturally have to be made of the SAME thing, which is impossible.
Similarly, all our measurements and the predictions of isotropy and related equalities of potentially measurable and comparable spacetimes, may be good in theory. But these cannot be as equal as we may conclude from the theories that result.
Merely because of the minute but naturally true difference between their existence in terms of the different potentially measurable spacetimes, it should naturally be concludable that there is no absolute identity of physical existence, structure, evolution, etc. between any two parts in the cosmos.
NATURALLY, THE MINUTE DIFFERENCES IN PARTS OF THE COSMOS, IN THE COURSE OF TIME, SHOULD EXPRESS THEMSELVES AS GREAT DIFFERENCES AND RESULT IN THE MANY COSMIC ANISOTROPIES THAT WE SHOULD FIND AND THEORETICALLY PRESUPPOSE, NOT ONLY IN SOME OBJECTS OF THE COSMOS BUT ALSO IN VAST REGIONS OF THE COSMOS. NATURALLY, THIS MUST BE THE CASE EVEN IN THE VARIOUS UNIVERSES WITHIN THE COSMOS, IF THE COSMOS IS AN INFINITE-CONTENT CONGLOMERATION OF AN INFINITE NUMBER OF FINITE-CONTENT UNIVERSES.
This then becomes a pre-physically self-evident fact. This shows something interesting: Concluding CONSTANCY OR EQUALITY OF RATE OF EVOLUTION from the values concluded “at present”, “a few times”, that seem to be “constant" CAN AUTOMATICALLY BECOME A SELF-GOAL IN PHYSICS, ASTROPHYSICS, AND COSMOLOGY.
Hence, in my opinion, any sufficiently big portion of the cosmos, under expansion or contraction, should at some time experience some sort of contraction or expansion as the opposite evolutionary case. This evolutionary case is not a recurrence of everything as such, but a forward process!
This must be the case also in the infinite number of parts of the cosmos, if the cosmos is of infinite matter-energy content.
Penrose and some of his colleagues seem to have held a sort of CONFORMALLY CYCLIC COSMOS theory. On the other hand, we have the miracle-feeder theories of CONSTANT INFLATION WITH RESPECT TO OUR LOCAL UNIVERSE. I consider these theories, too, as fads INVENTED TO EXPLAIN SOME COSMIC DISCOVERIES.
In the case of Penrose, it was the recent discovery of circles (spheres) of the CMB which they claim are "around the big bang universe of ours".
In the case of Alan Guth and others, the inflation theory has been a contrivance to keep astrophysics and cosmology away from some speculations, which Guth recently admitted to be not a very realistic solution!
The extent of inapplicability involved in the concept of isotropy may be extended also to theories of the overall shape of the outermost realms of each expanding universe. Some speak of empirical evidence for the outermost layer of such a universe to be spherical. From this conclusion, they even proceed to emphasize that it is absolutely spherical, citing again the same “empirical” evidence! They do not forget to claim that all cosmic shapes are such! But the question to be put at them is whether the so-called spherically exact expansion of our universe would mean also that the clusters of galaxies, galaxies themselves, stars, planets, etc. should also expand as do the universe in a spherical manner as they claim!