Hello and a question about our universe....

Lensman

Hello. I'm new to this forum, and I've been reading lots of interesting stuff in this forum, especially under this Cosmology Heading, which is where my main interest lies.
On another thread Janus said, "The observable universe is just that part of the universe for which light has had time to reach us since the Big Bang, it does not represent what we would consider the entire universe." This is just one sentence out of a paragraph, and I want to make sure nobody thinks I am taking what he said out of context. That sentence has helped me understand the following: Our observable universe lies within the unobservable universe? Is this a safe conclusion?

DaveC426913

Certainly.

Lensman

Thank you Dave! This understanding I now have in regards to our, may I say, Known Universe and it being somewhere within the Unknown Universe gives me all kinds of questions to ask further. It may take me some time to ask these other questions. This is so exciting, this new awareness I have! I hope Known Universe and Unknown Universe are suitable descriptive phrases to use on this thread from now on?

minio

Really? I was under impression that it is most likely, but that the theory, that observable universe is the same size or larger than actual universe was not ruled out.

DaveC426913

How could the actual universe be larger than the observable universe? That would mean we can see parts of the universe that don't exist.

Radrook

Since we presently have no reason to believe that the observable suddenly undergoes some mysterious transformations somewhere beyond our perceptual reach, we can extrapolate from what we know as long as we recognize the basic nature of such extrapolations.


Here is an interesting article on the subject based on what we know via the observable.
It bases its conclusions on the current view of the rate of accelleration of universal expansion after the BB.

marcus

As a side comment, the observable portion keeps on growing.
It keeps on including more and more material. Because it is not a FIXED region, it is just the matter whose light (or other radiation) has reached us so far.

there is other stuff whose light has not reached us YET (so is not part of our observable yet) but which WILL reach us next year or in 1000 years from now. then that stuff will also be in our observable region.

And if we lived in Andromeda galaxy instead of here in Milky, then our observable region would be slightly different. It would extend a bit farther in some directions and less far in others. It's not a big deal. One should not attribute "cosmic importance" to the idea of an observable region, the region that is observable from this place at this time.

For practical purposes it hardly changes because percentagewise it changes so slowly. What difference can a few light years this way or that make? We assume the simplest, namely rough uniformity, because we have no evidence of non-uniformity. It's a common time-honored practice to take, as a working assumption, the simplest model that fits the data---and to keep alert for anything that might not fit! Assume the simplest but keep testing it

minio

I mean that it is possible, that we see some distant objects from both sides, but we consider each side as separate objects, if you understand me.

DaveC426913

Ah, you mean that the very distant parts of our observable universe might actually wrap around, and we are looking back at ourselves?

Yes, good point. You are right. That would indeed be a situation where our observable universe is actually larger than the universe.

People have been looking for this, but have yet to find any evidence of it.

Lensman

Wouldn't that be an illusion, so-to-speak?

Lensman

Another question, please. If the unobservable universe is actually infinite, and our observable universe is within an infinite universe we canna perceive, yet, then is it possible that other universes similar or perhaps not similar to our own observable universe could lie within but distant to our own observable universe, so distant that the light hasn't arrived here yet so that we could become aware of these other, as-yet-unseen universes? This is assuming these other universes are filled with light from stars such as our own observable universe is. Also, I'm aware that there may be parts of our observable universe that are not yet observable due to the limitations of the speed of light.

DaveC426913

Define 'illusion'.

In a universe 14 billion light years wide (for example), looking 16 billion light years west would be the same as looking 12 billion years East. Neither is less illusional than the other.

phinds

If so, these regions would not be "other" universes, they would be part of the universe, which by definition, contains all there is. If you are asking are there possibly regions of the universe that have different laws of physics than our region, I don't know that such a concept can be conclusively ruled out, but it seems unlikely and there is NO reason to think it to be so.

Lensman

Thanks. You answered my question.

Lensman

I see I made an error asking my question. Sorry for the confusion. If our observable universe lies within an unobservable universe, and the unobservable universe is truly infinite, then is it possible other universes which began with Big Bangs as it is thought ours did also exist somewhere in the unobservable universe?

I see I am having problems with using the correct terms. Let's see...if the unobservable universe could be called the Grand Universe, and our own observable universe could be called a Pocket Universe which lies within the Grand Universe, could there be other Pocket Universes within the Grand Universe?

cepheid

I think you're confused. By definition, the universe is everything that exists. The observable universe is just the portion of it that we can see, and therefore that we can be certain exists. However, we think based on our theories and models that there is more of the universe outside of this observable region.

So don't think of the "observable universe" as a separate universe within some other "grand universe." Just think of it as a portion, or area of THE universe.

(Of course this discussion excludes multiverse theories, which posit that the universe is NOT all that exists (making the term a misnomer), and that there are, in fact, many universes. But let's not get into that so far completely untestable set of theories. )

EDIT: I see that I put a parenthetical remark inside of a parenthetical remark. I think this is evidence that I overuse parenthetical remarks.

Lensman

I am confused, I see. I'm trying to understand. I see that I am just curious about the possibility that there could be other parts/portions of THE universe that might have universes each which may have began with a Big Bang as our observable universe began with a Big Bang. Universes each filled with huge numbers of galaxies as ours is. As many universes or more scattered within THE universe as ther are galaxies scattered within and across our own home observable universe.