The observable Universe and its shape

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Discussion Overview

The discussion revolves around the shape of the observable universe, exploring analogies such as the surface of a balloon, the implications of cosmic expansion, and the nature of curvature in cosmological models. Participants delve into theoretical considerations, observational implications, and the limitations of current understanding regarding the universe's geometry.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that the universe can be likened to the surface of a balloon, expanding as the balloon inflates, suggesting that traveling in a straight line would eventually return one to the starting point.
  • Others argue that while this analogy is useful for understanding expansion, it is imperfect and does not accurately represent the universe's actual shape or structure.
  • There is a claim that the observable universe is a sphere, but this is contested as it may not reflect the true nature of the universe beyond what is observable.
  • Some participants note that the curvature of the observable universe appears consistent with flatness, while others highlight that evidence supports multiple geometries, including spherical and flat models.
  • Discussions include the implications of dark energy on curvature and the potential for measuring spatial curvature, with varying opinions on whether flatness should be considered the null hypothesis.
  • Participants discuss the nature of free parameters in cosmological models, debating whether curvature should be treated as a free parameter or a necessary aspect of the model derived from General Relativity.
  • There is a contention regarding the interpretation of the universe's expansion, with some asserting that it does not originate from a central point, challenging the notion of a spherical shape.
  • One participant emphasizes that the universe is conceptualized as "everywhere," lacking measurable shape, size, or center, which complicates the understanding of its geometry.

Areas of Agreement / Disagreement

Participants express a range of views on the shape and curvature of the universe, with no consensus reached. Disagreements persist regarding the validity of the balloon analogy, the implications of curvature, and the interpretation of expansion dynamics.

Contextual Notes

Limitations include the dependence on analogies that may not fully capture the complexities of cosmic geometry, as well as unresolved questions about the nature of curvature and its implications for cosmological models.

  • #31
wlminex said:
To me, a more germane question is: What energies, forces, mechanisms, processes etc, other than BB might be 'causing' space to expand
Why do you feel the need for other things? Basic expansion was a result of what was going on 14billion years ago and the acceleration of that expansion is caused by an as yet unknown thing we call dark energy (we understand what it does but not its fundamental nature, although there are candidates). What more do you feel is needed?
 
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  • #32
To me, a more germane enquiry might be: What energies, fields, forces, processes, mechanisms, etc. - other than remnant BB - might be 'causing' expansion of space/universe? Also, wha is the nature/source of the hypothesized cosmological constant?
 
  • #33
wlminex said:
To me, a more germane enquiry might be: What energies, fields, forces, processes, mechanisms, etc. - other than remnant BB - might be 'causing' expansion of space/universe?
I ask again, why do you feel there is any need for anything other than the remnant of the early universe for the basic expansion? What is it about that explanation that you think is insufficient? Quit avoiding the question.
 
  • #34
wlminex said:
To me, a more germane enquiry might be: What energies, fields, forces, processes, mechanisms, etc. - other than remnant BB - might be 'causing' expansion of space/universe? Also, wha is the nature/source of the hypothesized cosmological constant?
Lots, but the only evidence we have is the effects of dark energy. Dark energy could be the aggregate behavior of many forces, Occum's Razor tells us that it's probably one.

Like phinds said though: even without dark energy, the universe would still be expanding. The big bang introduced a lot of energy which pushed on everything, the only force that can bring everything back together is gravity. If the initial expansion had more energy than the escape velocity of the universe, it'll expand forever, if it's less, it'll still expand for a long time, then start falling back in.
 
  • #35
wlminex said:
To me, a more germane question is: What energies, forces, mechanisms, processes etc, other than BB might be 'causing' space to expand
Nothing "causes" space to expand (the present-day accelerated expansion notwithstanding). The fact that the universe is expanding is an initial condition set at the big bang -- it is not "fueled" by any force.
 
  • #36
revo74 said:
If the universe is expanding in all directions from one central point then how could the shape of the universe not be spherical?

The simple answer is the expansion outruns gravity.

If gravity is involved and it always is, expansion happens and then is pulled back by gravity so...sphere. Or balloon model. If expansion is too fast for gravity then straight as an arrow expansion...there is always room for both to happen. Spew a can of coke. Some coke will be on your hand and some will hit your mom across the room. Depends on the pressure applied to any given drop of coke. Ergo, some spherical curving bodies and some straight plain bodies of motion. Though eventually the straight bodies slow more and more, they never the less need never stop. They do not get pulled back as they our out of reach of a mass big enough to pull on them.
 
  • #37
tobyr65 said:
The simple answer is the expansion outruns gravity.

No, the simple answer is that the universe is not expanding in all directions from one central point. The Big Bang did not happen at one particular location in the universe. It happened everywhere in the universe.
 
  • #38
The Big Bang did not happen at one particular location in the universe. It happened everywhere in the universe.[/QUOTE]

Please list references. I can't reply to this theory as I haven't read it.
 
  • #39
tobyr65 said:
Please list references. I can't reply to this theory as I haven't read it.
This is the accepted mainstream theory and the only one that fits the evidence of the universe appearing to be expanding uniformly everywhere.
 
  • #40
tobyr65 said:
Please list references. I can't reply to this theory as I haven't read it.
Then you should do some reading in the absolute basics of cosmology since this is one of the first things you will learn.
 
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  • #41
newjerseyrunner said:
This is the accepted mainstream theory and the only one that fits the evidence of the universe appearing to be expanding uniformly everywhere.

Then it must have a name.
 
  • #42
phinds said:
Then you should do some reading in the absolute basics of cosmology since this is one of the first things you will learn.

I'm a reader so this must be a communication thing. '...? is one of the first things you will learn. Say the theory name. Just say it.
 
  • #43
tobyr65 said:
I'm a reader so this must be a communication thing. '...? is one of the first things you will learn. Say the theory name. Just say it.
The Big Bang Theory.
 
  • #44
tobyr65 said:
Then it must have a name.
It's called "The Big Bang Theory" and it's contrary to the other theory the "Steady State Theory." The Big Bang model replaced the steady state model in 1929 when Edwin Hubble concluded that the universe was expanding. The new theory predicted that the universe was slowly cooling and at some point in the past, there must have been a flash of light from the congealing of the first atoms. This was found in 1965 and is called the Cosmic Microwave Background.
 
  • #45
tobyr65 said:
The Big Bang did not happen at one particular location in the universe. It happened everywhere in the universe.

I thought you must have been talking about some theory other than TBBT.

The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it talks about the universe as we know it starting with a small singularity, then inflating over the next 13.8 billion years to the cosmos that we know today. - See more at: http://www.space.com/25126-big-bang-theory.html#sthash.kvDniLFH.dpuf
 
  • #46
tobyr65 said:
it starting with a small singularity
But keep in mind that singularity does not mean point, it may have even been infinite in size. Small is not the correct qualifier here, it was much denser. The OBSERVABLE universe was smaller.
 
  • #47
tobyr65 said:
I thought you must have been talking about some theory other than TBBT.

The Big Bang Theory is the leading explanation about how the universe began.
No, it most emphatically is NOT. It is the theory of how the universe evolved AFTER it began. The Big Bang Theory is silent on how things began and calls that a "singularity" meaning "the place where our model breaks down and we don't know what was really going on".

At its simplest, it talks about the universe as we know it starting with a small singularity, then inflating over the next 13.8 billion years to the cosmos that we know today. - See more at: http://www.space.com/25126-big-bang-theory.html#sthash.kvDniLFH.dpuf
Again, no. It does not specify the universe after the singularity as "small", just as "smaller than it is today". It might have been infinite then, in which case it is infinite now. "Small" doesn't enter into it.

Hard to see how your post #36 follows from any possibly interpretation of the Big Bang Theory.

EDIT: And to be totally correct, I really should not have said that The Big Bang Theory says that the universe was smaller in the past than it is today. That is a very common statement but not technically correct because if the universe was infinite then and now then it was not smaller then than now. What the BBT DOES say is that everything was closer together in the past than it is now.
 
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  • #48
phinds said:
EDIT: And to be totally correct, I really should not have said that The Big Bang Theory says that the universe was smaller in the past than it is today. That is a very common statement but not technically correct because if the universe was infinite then and now then it was not smaller then than now. What the BBT DOES say is that everything was closer together in the past than it is now.

Am I right in thinking that we can only measure the size of the universe and indeed the rate of expansion by observations made on physical objects we can detect. So aren't those measurements only telling us how that matter behaves? And therefore can we treat the space around that matter as a separate entity? If so can we have an infinite space but a finite area that the mater within that space spans?
 
  • #49
rede96 said:
aren't those measurements only telling us how that matter behaves?

Directly, yes. Indirectly, no, because spacetime and matter are not independent, at least not according to our best current theory, GR. In GR, matter and spacetime are linked by the Einstein Field Equation, so if you know the matter is behaving a certain way, you also know the geometry of spacetime.

rede96 said:
can we have an infinite space but a finite area that the mater within that space spans?

Not for the entire universe, no. More precisely, there is no solution of the Einstein Field Equation that has this property but also describes our observation of the universe as a whole. Solutions with this property (a finite extent of matter surrounded by an infinite empty space) work well at describing isolated objects like stars, planets, etc., but don't work well at describing the whole universe.
 
  • #50
rede96 said:
Am I right in thinking that we can only measure the size of the universe and indeed the rate of expansion by observations made on physical objects we can detect.
No, we cannot measure the size of the universe at all. It might be infinite.

And therefore can we treat the space around that matter as a separate entity? If so can we have an infinite space but a finite area that the mater within that space spans?
No, that would violate the Cosmological Principle and the tenet that the big bang expansion happened everywhere at once. "Everywhere" MEANS everywhere, not in some localized area.
 
  • #51
rede96 said:
Am I right in thinking that we can only measure the size of the universe and indeed the rate of expansion by observations made on physical objects we can detect. So aren't those measurements only telling us how that matter behaves? And therefore can we treat the space around that matter as a separate entity? If so can we have an infinite space but a finite area that the mater within that space spans?
No, the expansion is happening "faster" than the force of gravity can "grab" it and pull it back, as is the case with local groups being gravity bound and having no expansion.

To imply a finite expansion within an infinite space requires gravity being the dominant force to limit how "far" it can expand, that isn't the case, with no gravity to resist the expansion then, in theory, the expansion will continue to expand until the finite limit is reached (if the universe is finite) or continue to expand into infinity(if the universe is infinite). I've seen it discussed that expansion is "slowing" but I don't think that means it will ever stop because there is no verifiable opposing force to "stop" it. Expansion happens in the spaces that are void of "normal" matter(not counting the theorized dark matter which may or may not be the force causing the expansion, that is also debated), not within the boundaries of spaces occupied by accumulated matter, such as galaxies or groups of galaxies that are relatively close enough for gravity to be a factor in their associations.

If you are implying that space itself may be infinite but the "space" occupied by matter in the universe is a finite amount inside of a boundary within that infinite space, then, no would be the theorized/debated answer.

I'm not exactly clear on that because of a lot of things that are said, my understanding is that matter has always occupied the entirety of space from the beginning, only the expansion of that space has changed.
 
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  • #52
Phinds re: No. 47
OMG Okay, the singularity caused time space and matter and something from nothing….

Then a force pushed this something outward. Something we call a universe.

Most likely NOT an explosion, due to lack of spherical evidence. ( message 36)

I don’t want to discuss curvature vs. flat because curvature infers the universe runs into force obstacles to make it curve whereas the original ‘pushing’ gravity is snap back and did not stop the galaxies from separating much less causing the universe to sphere. It’s all guess work there for now anyway.

Still the outrunning gravity was my point for commenting on 36.

But tomorrow … and apparently yesterday, I thought partial spherical sounded right. I know I’ve seen something in the past inferring round and it may have been the microwave picture, you know the one it looks like the world globe laid out flat, but today I’m all for flat universe.

The ring of Saturn has a relatively minor thickness as it circles Saturn. Hell our universe is probably part of a ring around a giant we can’t see for all we know. Flat and moving at such a distance we can’t see the curve until its behind us a few billion years and appears as a ‘big bang’ instead of the density of objects in the distance.

Thank you for the reading you and the others made me do. I enjoy the reading. Yours and the professional findings out there to date.
 
  • #53
tobyr65 said:
Phinds re: No. 47
OMG Okay, the singularity caused time space and matter and something from nothing….
No, we don't know that. Again, "singularity" means we don't KNOW what was going on.

Then a force pushed this something outward. Something we call a universe.

Most likely NOT an explosion, due to lack of spherical evidence. ( message 36)
No, it was not "most likely not" an explosion, it was NOT an explosion. The evidence is clear on that.

I don’t want to discuss curvature vs. flat because curvature infers the universe runs into force obstacles to make it curve whereas the original ‘pushing’ gravity is snap back and did not stop the galaxies from separating much less causing the universe to sphere. It’s all guess work there for now anyway.
I have no idea what that means.

Still the outrunning gravity was my point for commenting on 36.
I think I get what you mean and although it's an awkward way to phrase it, it's correct. The accelerated expansion will not be reined in by gravity.

But tomorrow … and apparently yesterday, I thought partial spherical sounded right. I know I’ve seen something in the past inferring round and it may have been the microwave picture, you know the one it looks like the world globe laid out flat, but today I’m all for flat universe.
That picture, and no other picture, ever implied that the universe is spherical. That is a mis-interpretation on your part. The OBSERVABLE universe is spherical for sure and that may be where your confusion comes from.

The ring of Saturn has a relatively minor thickness as it circles Saturn. Hell our universe is probably part of a ring around a giant we can’t see for all we know.
This is nonsense and you need to be careful about that. It sounds like an unsubstantiated personal theory and the mods don't like those.

Flat and moving at such a distance we can’t see the curve until its behind us a few billion years and appears as a ‘big bang’ instead of the density of objects in the distance.
Once again, I have no idea what you are saying.
 
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  • #54
That picture, and no other picture, even implied that the universe is spherical. That is a mis-interpretation on your part. The OBSERVABLE universe is spherical for sure and that may be where your confusion comes from..[/QUOTE]

Are you saying spherical as in flat circle or as in ball shape?
 
  • #55
tobyr65 said:
Are you saying spherical as in flat circle or as in ball shape?
A flat circle and a sphere are two different things, a circle is 2D and a sphere is 3D.

And please learn to use the reply buttons correctly or learn how to properly quote if you are doing it manually. The way you are doing it forces anyone that is quoting what you post to have to edit our posts to correct how you quoted whoever you're responding to.
 
  • #56
This is nonsense and you need to be careful about that. It sounds like an unsubstantiated personal theory and the mods don't like those..[/QUOTE]

It isn't nonsense nor is it my theory. I am not educated enough to have theories. We are in the middle of discussing universal shape. The universe does not appear ball shaped by the pix I looked up. Here is a cut and paste of the only three theories I've found:
th?id=OIP.M66f56d949cdcfc9af2423b8da8ebd1abo0&pid=15.1&P=0&w=300&h=300.jpg

Whichever one wins, right now, it appears that we are on a 'flat' area of the model.

I read something. If the reading makes sense to me I tend to believe it until I read something that contradicts it that makes more sense. Then I read something else. My thoughts change with new information that may or may not be correct. If my statements are unsubstantiated I can still point to who said/published it first.

Do I think the universe is a blip on a immeasurably large ring around an immeasurably large body? I have no opinion but, in the Journal of Cosmology, 2011, Vol 13, In press Journal of Cosmology.com February-March 2011, Joseph Rhawn, Ph.D. (Cosmology.com) makes a case for it (not his intention) when he writes on patterns. Infinity, Patterned Symmetry, Pythagoras, and the Black Hole at the Edge of the Universe ( 1. REPEATING PATTERNS ARE THE LAW OF NATURE & THE COSMOS).

But if you want to refer me to your proof, I'll read it.

I would use bold and underlines and italics in the last paragraph but I never learned to properly site references.

I am not being argumentative so much as explaining my remark... which you appear to have understood to have maybe been my personal theory ...and nonsense. I am not the best common correspondent much less the best scientific correspondent so I am truly not offended by our mutual confusion.
 
  • #57
Re: number 55... ugh, I thought I had it!
 
  • #58
Chill everybody.
We don't know if the Universe is infinite or not.
We do know that our observable universe is spherical and the centre of it is somewhere between your eyeballs.
 
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  • #59
tobyr65 said:
Re: number 55... ugh, I thought I had it!

Lol, you did it again, look at your post.

I think you're improperly editing the posts you are quoting, make sure the QUOTE tabs are correct before and after the post you are quoting before you send.
 
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  • #60
rootone said:
the centre of it is somewhere between your eyeballs.

From whatever vantage point you are in at the time.
 

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