The Cosmological Principle means infinite Observable Universes

[chasmanian]

TL;DR Summary

if the Cosmological Principle, isotropy and homogeneity are true, then there are an infinite number of Observable Universes (the vast majority of which are not observable by us).

I am posting to ask for any comments about a couple things.
I will post a link to a thread on another forum about this.
and would love to hear any and all thoughts about it.

the thread begins asking about 2 things.
the first one is about how fast we are moving.
I,402,00 mph relative to the CMB.
ok, I got that.
and don't need to know any more about it.

the second question asks: where is the center of the Universe?

the answer to that is found by way of the Cosmological Principle.

isotropy and homogeneity.

if these concepts are true, then if you logically think this through,
you will find that there are an infinite number of un-observable universes in every direction.
the closest ones, overlap with our observable universe.
all of the rest (an infinite number of them), do not overlap with ours.

 

[mfb]

Let's keep discussion to this thread, including external threads makes things messy.

Every observer has "their" observable universe and there is no center of the universe.

if these concepts are true, then if you logically think this through,
you will find that there are an infinite number of un-observable universes in every direction.
the closest ones, overlap with our observable universe.
all of the rest (an infinite number of them), do not overlap with ours.

Yes, that's the standard view in cosmology. We don't know if the universe is infinite but that's the easiest model consistent with observations.

 

[PeroK]

Summary:: if the Cosmological Principle, isotropy and homogeneity are true, then there are an infinite number of Observable Universes (the vast majority of which are not observable by us).

In the standard model of Cosmology there is only one universe. Our "observable" universe is the part of the universe that we can observe, as of today. Things outside of this observable universe are asumed to be just an extension of what we can see, with the same large-scale distribution of galaxies etc.

 

[supernova1054]

Think of a 2d universe, e.g., the surface of a balloon without the nozzle. If it is expanding uniformly, every point on this 2d surface appears to be the center of the expansion for a 2d being in that universe.
The same is true for our 3d (space) universe. If we are expanding into a 4d space, the center of our expansion is in that space not in our 3d universe.

 

[PeterDonis]

If we are expanding into a 4d space

We're not.

 

[chasmanian]

I am super grateful for all of you replies.
PeroK, no argument from me, about only 1 Universe.
please know that is true, as I do my best to describe how I think things are.

I will now copy and paste stuff from my thread on the other forum.
if anyone has thoughts and comments, I will be super glad to hear any and all.
"we are at the center of our 92 billion light year observable universe.
now go to any point in that sphere.
you will now be at the center of another 92 billion light year observable universe.
some of it overlaps with ours. some does not.
do this for as many points in our observable universe sphere as you wish.

now think of the limit of our observable universe. (the 46 billion light year sphere.)
imagine observers located there.
many many of them.
and imagine them looking in the opposite direction from us (they will see another 46 billion light years that we do not).
now do the same thing again.
those observers will have an observable universe that is completely out of our view.
now do that again and again, etc.
in every direction.

ok, if all of this is so, then
I visualize a soap bubble universe.
an infinite number of observable universes.
the close ones, we share part of.
but get far enough away, and we share none of them."

here is more:

"a further comment.
this is more on the soap bubble thing. fleshing it out a little.

nearby soap bubbles overlap and intersect.

there are an infinite number of observable universes. in all directions.

those that are within 92 bly of our observable universe, share some of their's with us.
there is some overlap, some intersecting.

observable universes who's center is exactly 92 bly away, share the edge only, with us.

those that are farther away, share nothing with us.

going away from here, the 92 bly observable universes repeat infinitely, in every direction.
there is an infinite number of them.
and it is only the nearest 2, that share stuff with us.

so, the vast majority (all the other infinite bunch), share nothing with us.

another cool thing, in my mind, about all of this:
go to any point in our observable universe.
all of the above is true for an observer at that point as well.

thus there are an infinite number of observable universes, in the universe."

and more:

"how does and how will the expansion of the Universe affect this?
won't the expansion of the Universe cause all of the observable universes to expand into each other?

my answer: the expansion of the Universe affects this, and will affect this, the same way that it has up till now.
the key is to understand that the expansion of the Universe means that there is more space.
more space gives more room for everything to expand and continue to expand, just as it is now.

so no, all of the observable universes will not expand into each other.
the ones that overlap and intersect with each other now, will continue to do so.
and the ones that do not overlap and intersect, will continue to stay separate from each other."

 

[phinds]

"we are at the center of our 92 billion light year observable universe.

yes

now go to any point in that sphere.
you will now be at the center of another 92 billion light year observable universe.

yes

some of it overlaps with ours. some does not.

Actually, an infinite number of them do and another infinite number of them don't

I visualize a soap bubble universe.

I see what you mean, but that's not a helpful analogy.

an infinite number of observable universes.

yes

the close ones, we share part of.
but get far enough away, and we share none of them."

yes

nearby soap bubbles overlap and intersect.

yes

there are an infinite number of observable universes. in all directions.

yes

those that are within 92 bly of our observable universe, share some of their's with us.
there is some overlap, some intersecting.

yes, but "intersecting" and "overlapping" mean exactly the same think in this instance.

observable universes who's center is exactly 92 bly away, share the edge only, with us.

yes

those that are farther away, share nothing with us.

yes

and it is only the nearest 2, that share stuff with us.

That doesn't even make sense. see above.

so, the vast majority (all the other infinite bunch), share nothing with us.

yes, as do the infinite number that DO share space with us.

another cool thing, in my mind, about all of this:
go to any point in our observable universe.
all of the above is true for an observer at that point as well.

yes

"how does and how will the expansion of the Universe affect this?

depends on what you are referring to by "this". Your question is very poorly stated.

the ones that overlap and intersect with each other now, will continue to do so.

no. Their centers are receding from each other way faster than their radii are increasing (*)

and the ones that do not overlap and intersect, will continue to stay separate from each other."

yes

*EDIT: my statement is not valid if the two observable universes are within a galactic cluster, since things the size of clusers and smaller do not recede from each other

 

[chasmanian]

thank you very much phinds! :)

 

[supernova1054]

We're not.

There are cosmologists and string theorists who would disagree. I know that either way is speculation. We really do not know.

 

[Vanadium 50]

There are cosmologists and string theorists who would disagree.

Who? Can you please give a reference?

 

[phinds]

Who? Can you please give a reference?

 

[supernova1054]

Look up brane cosmology on Wikipedia for some sources.

 

[phinds]

Look up brane cosmology on Wikipedia for some sources.

I see you are new to the forum, so you are perhaps not aware but that is not an acceptable response. On PF when you are asked for citations, that means what it says. Citations. Not a reference to to bunch of stuff that may or may not be what you are talking about.

 

[Vanadium 50]

And in this case, does NOT support what he was talking about. I feel like I was sent on a wild-goose chase.

 

[supernova1054]

I will follow your advice in the future and will avoid metaphysical ideas which are untestable.

 

[PeterDonis]

We really do not know.

Your original claim was that the universe could be "expanding into a 4d space". We do know that that is not correct.

The speculative brane models that you mentioned (a) are, as has been said, speculative, and discussion of them is off topic in this forum, it belongs in the BTSM forum; and (b) do not say the universe is expanding into a 4d space; they say that our 4d spacetime is embedded in a higher dimensional space.

Please do not clutter up threads with comments that are both inaccurate and off topic.

 

[chasmanian]

I am wondering about something.
any all comments welcome.

how many people know about this?
I am talking about how there are an infinite number of 96 billion light year diameter observable universes. stretching from here to infinity.
the original subject of my thread.

the Big Bang, everybody's heard of that.

but how many people do you think, know about the Cosmological Principle,
and homogeneity and isotropy?

and all that implies that we posted about here.

besides people like me and you guys and gals,
I'll bet hardly any.

this knowledge is out here to be found.
and yet I'm guessing that this knowledge is very rare.
rarer than how my brother likes his steak cooked.
which is just this side of raw.

 

[PeterDonis]

how many people do you think, know about the Cosmological Principle,
and homogeneity and isotropy?

I would say, everyone who has ever read a cosmology textbook, or pretty much any halfway decent discussion of cosmology.

However, that question is not a question of physics, so it's off topic here. It looks like your question of physics has been answered, so this thread is closed.