Very targeted question on multiple universes hypotheses

[phinds]

Rather than hijack an on-going thread that is similar, I'm starting a new one to ask very specific question.

Regarding the question of multiple universes, there seem to be two (maybe more, I'm new to this) types that are frequently discussed. The first are the types that are separated from our OU by space, as opposed to the second type which seem to be usually discussed as "branes". I guess a third is multiple time-lines, but I don't want to go there as that has no relvance to my question.

I have a question about the first type.

Let's consider first the existence (hypothetical, I understand) of a place some, say, 500 billion light years from earth. It also has an OU of about 14 billion LY, as do we. As we now understand physics, it is absolutely impossible for there to be any interaction of any kind whatsoever between what is in that space and what is in our OU, and it seems reasonable to hypothesize that there will likely NEVER be any possibility of interaction.

SO ... I find it completely reasonable that such areas can be thought of and spoken of as separate universes since for all practical purposes, they truly are.

My question then is this: is what I have just described the scenario being talked about as that type of multiverse or is there some other type of "other universe" that is separated from us only by space?

The distinction I'm trying to understand is perhaps illustrated if I further describe more about the scenario I have hypothesized. Take an OU that has as its center a point that is about 100 billion LY from earth. It still fits the same discussion as the one 500BLY away, but it seems to me that one can reasonably hypothesize yet another "universe" that has an OU of about 15BLY and that has its center 50BLY from Earth and this one can see portions of both the one farther out and ours. Under the picture I'm painting here, you can perhaps see why I can't get past the feeling that all of these "separate Universes" are really just different parts of space in the same universe we are in. Yes, they are separate for all practical purposes, but they do not constitute a multiverse, just a manifestation of the currently perceived total inability for us to interact beyond our OU.

I realize that I can HYPOTHESIZE any damn thing I want, so the scenario I have hypothesized is reasonable in that regard. What I DON'T understand is whether the scenario I have hypothesized is what folks are talking about when they talk about multiverses separated from us by space alone, or is there some other kind of separation I'm not understanding.

Sorry to be so long-winded but I wanted to attempt clarity in what I'm asking. I am NOT asking for comments on the reasonableness of my hypothesized scenario (although I WOULD like to hear if it is considered absurd), I'm just asking it if fits the "multiverses separated by space" discussion that I see from time to time or if there is some other distinction being made in those discussions

Thanks

 

[Calimero]

My question then is this: is what I have just described the scenario being talked about as that type of multiverse or is there some other type of "other universe" that is separated from us only by space?

Yes. There is one guy, Max Tegmark, MIT professor, I think, who tried to classify different multiverse possibilities, and according to his classification, you are talking about level I multiverse. These are regions of space sufficiently far away, so they never been in casual contact.
Would you like to call different parts of the same universe multiverses or not, would be a matter of taste, if there is not one simple and straight-forward fact:
If you have finite number of particles in finite volume of space, there is finite number of possible arrangements of that particles, or there is a limit of how many particles, at given temperature can be packed in given volume, so in sufficiently large universe, pattern must repeat. What does that mean? There must be exact replica of our OU, together with copies of me and you in it, sufficiently far away, something like 10^(10^110) meters. In my mind that constitutes parallel universe.

 

[phinds]

Thanks. Good info.

Yes, I'm very aware of the semantic difficulties in getting agreement on the terminology. I'm content in this case to understand that there is this "Type I" multiverse concept which is to my mind the same universe even though it is quite reasonable to also think of it as a multiverse or parallel universes for all practical purposes.

I have read numbers as big as 10^500LY but had not seen 10^(10^110)LY. I wonder if there is even remotely any justification for pulling that particular number out of whatever it was pullled out of.

I'll see if I can find more about Tegmark and get a better handle on the "Types" of multiverses. Thanks again.