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The word we use to refer to what's inside the cosmic horizon is the 'universe', so what would you call the empty space outside of the horizon?

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    $\begingroup$ What makes you say that the space outside the cosmic horizon is empty? Standard cosmology assumes the universe is homogeneous on the very large scale, so we expect that the stuff beyond the horizon to be similar to what we can observe. Sure, it might be different on the other side, but a theory that predicts that is more complicated than one that predicts homogeneity, and you need to justify that added complexity, and to explain why we happen to live in a huge homogeneous region. $\endgroup$
    – PM 2Ring
    Aug 28, 2017 at 18:18

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The outside is also the universe, the inside is just the observable universe.

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  • $\begingroup$ I suppose we could call it the un-observable universe, but I like just plane "universe" better. $\endgroup$
    – userLTK
    Aug 31, 2017 at 7:06
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Since the universe is expanding, the things (galaxies, quasars, etc) that are currently in the observable region, on our side of the cosmic horizon, will someday be over the horizon. It stands to reason, then, that whatever is currently over the horizon is just the things that were once on our side, but long ago.

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The view of the philosopher physicist: The nature of science is empirical. Because "outside" the cosmic horizon is outside the realm of experience, we can make no well-founded claims about its "composition". We have the same with Black Holes - while we suppose they contain a lot of content, theory suggests strongly that the information content is encoded on the event horizon (as argued by Bekenstein and Hawking) as 2 dimensional information (volume loses cred!). Stuff falling into it becomes 2D as it meets this horizon. This is similar to the holographic universe investigated by 't Hooft and Susskind. This implies something deep about our human-centered way of engaging with the world, and it is somewhat odd that we insist that our perspective is uniquely the "correct" one. it would be as valid to take a string theoretical perspective with the information that makes the world an encoding on a cosmological "surface," which leaves the exterior of the cosmic horizon both physically and philosophically empty. Just because this is hard to think about as humans doesn't make it wrong.

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  • $\begingroup$ It's an interesting thought, but not really connected to the question at hand. The second sentence is, but the rest is at best tangential. Answers, especially to old questions, ought to be as focussed on the question as possible. $\endgroup$ Mar 24 at 22:23
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This relates to what I was saying about the universe was once the size of a grapefruit morphing into the observable universe was once the size of a grapefruit. Along with the universe is infinite. IMHO there is no evidence for the latter.

To be pedantic, I guess the answer to your question is "the non-observable universe". That’s because the word universe is derived from “uni” as in unicycle and “verse” as in vice versa. It means turned into one. It means everything. Hence the word "multiverse" doesn't float my boat.

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  • $\begingroup$ The first paragraph has nothing to do with the question and is arbitrary. You could say the observable universe was, at some point, the size of anything smaller than it is now. The second paragraph reads more as an opinion piece or etymology lesson. $\endgroup$ Sep 1, 2017 at 1:25
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    $\begingroup$ The first paragraph relates to BetaDecay's previous question. The second paragraph is factual. I didn't make up that etymology, the word universe means "everything". And by the way, you haven't answered a question here since July 19th. $\endgroup$ Sep 1, 2017 at 12:22

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