[psc]

I've had the same question and I don't have the answer, but what you're asking about might be referred to as the cosmological principle

https://en.wikipedia.org/wiki/Cosmological_principle

Seems like so far our observations are that the universe is pretty homogeneous. Cosmological principle being the default position, my best understanding is that it's just a lack of evidence otherwise:

> The End of Greatness is an observational scale discovered at roughly 100 Mpc (roughly 300 million light-years) where the lumpiness seen in the large-scale structure of the universe is homogenized and isotropized in accordance with the Cosmological Principle. At this scale, no pseudo-random fractalness is apparent.

https://en.wikipedia.org/wiki/Observable_universe#End_of_Gre...