I start by apologising if I have took sparse sentences to literally. If I didn't understand something that's is why I am asking.

In more or less divulgative literature, here, and also in the few cosmology books I went through so far, it appears as a wonder that universe is so homogeneous at a sufficiently large scale. This, together with the limit of the speed of light / information, prompts for questions such as "how can be that different and opposite sites of the observable universe have the same temperature" and the like. This, to me, would come to surprise if one assume a certain degree of pre-existing differentiation to be levelled out and smoothed.

I am puzzled because I would personally take the opposite view.

How it is that something that originates from the same event and from which everything tooks place differentiate in structures exceeding quantum fluctuation?

I am not asking for the answer to this question, but rather for why the observed homogeneity is presented as surprising and requiring a specific explanation.

Sentences such as "how could those parts of the universe knew of each others" are generally presented as obvious questions. But I don't see, perhaps naively, why things originated by the same big bang should be expected less homogeneous than what is observed.

I am otherwise fine with the current standard cosmology, I am missing the logic or the reason for which a specific explanation for the homogenous cosmic background radiation seems to be required. The history of each point in the universe should be the same, after all (except for fluctuations and the later formation of structures under gravitational influence).

  • $\begingroup$ Are you asking how structures form given that the universe is homogeneous, or are you asking why the universe is assumed to be homogeneous? $\endgroup$ – gabe May 31 '19 at 14:33
  • $\begingroup$ “How it is that something that was an unicum...” What is a unicum? $\endgroup$ – G. Smith May 31 '19 at 16:16
  • $\begingroup$ I feel like someone has overused a thesaurus on this post, or an overly aggressive translator. $\endgroup$ – Triatticus May 31 '19 at 17:35
  • $\begingroup$ @Triatticus that is my English. Consider that English isn't my mother tongue. For what shall I have used a thesaurus? Perhaps to see that unicum in not an English word or isn't understandable. I would change it to make the Q - possibly - clearer. $\endgroup$ – Alchimista Jun 1 '19 at 12:05
  • $\begingroup$ @Gabe. Rather for why the observed homogeneity is presented as surprising and not as a more obvious consequence, given that at beginning the universe must have been homogeneous, quantum fluctuations accounted for. $\endgroup$ – Alchimista Jun 1 '19 at 12:28

I think the question is fairly clear, regardless of language or translation used. The current understanding of our early cosmos makes assumptions about fields and forces, as well as particle types and numbers which are (ideally) consistent with present theory and observations. This is by far not settled. But one comes to the conclusion that at some point there are chaotic sound waves rushing through the early cosmos - before it becomes transparent. These turbulent waves would actually create pockets of higher density of matter or radiation. These pockets should only amplify over time. So even if it all started out as one kind of isotropic staff / uniformly, we do still have to explain why the universe today is so uniform. in any case don’t forget that the descriptions of what might have happened before the universe became transparent (cooled below T < 3000k) are highly speculative.

| cite | improve this answer | |
  • $\begingroup$ Thanks Jurgen. I see I must go through that early phase again. Glad that you got the point. I have written the Q not to get answers that I know but, surprisingly to me, it seems that I made it unclear. Though it is possible that sine people don't question their readings and/or need a thesaurus more often than me. $\endgroup$ – Alchimista Jun 2 '19 at 9:43

Not the answer you're looking for? Browse other questions tagged or ask your own question.