I am not an expert, just a enthusiast, so if possible please keep explanation simple. That said I have start reading about universe expansion and the idea seems to me revolutionary (the image of an infinite bigger universe that inflate). So I am questioning how researcher validate that specific theory excluding other causes that IMHO would be more intuitive?

For example how they exclude that the expansion is not only a local effect (that's happening on ours patch of observable universe)?

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    $\begingroup$ Well, we can't exclude that, apart from using Occam's Razor: a theory that has uniform expansion in the observable universe but different expansion beyond the observable universe would be more complicated. The evidence of the expansion from the CMB radiation is very uniform, to better than 1 part in 100,000 over the entire surface of a sphere which is now ~46 billion light years in radius. $\endgroup$
    – PM 2Ring
    Apr 10, 2021 at 18:31
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    $\begingroup$ Intuitiveness is not a requirement for a theory to be accepted or we would not be using e.g. quantum theory or general relativity, which profoundly challenge our intuitions. You kind of have to learn new intuitions to be comfortable with these theories. $\endgroup$ Apr 12, 2021 at 14:56
  • $\begingroup$ The immense size of the Universe will always be challenging intuition and especially might render every theory about it unfalsifiable. I am afraid cosmology will always suffer of that. Unless something totally new or about closed universe emerges. $\endgroup$
    – Alchimista
    Apr 14, 2021 at 12:53


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