B How can the Universe grow if it is infinite?

[russ_watters]

Just to clarify: are you thinking of the two analogies in this way...
Balloon = curved/finite
Rubber Sheet = flat/infinite

Yes.

 

[russ_watters]

Sorry, I missed that you had read it. Yes, I meant the Insights article. If that doesn't explain to you how really simple the balloon analogy is, really, then I can't add anything.

Really? You can't even answer a yes or no question? Or respond to what looks to me like contradictions in the descriptions?

You seem to want to be taking the analogy to places it wasn't designed to go.

Can you respond to what marcus says in his sticky thread about one of the things the analogy helps us visualize?:

3. to understand that something can be finite (finite area if 2D or finite volume if it's 3D) without having any boundary.

To make it easy, can you answer yes or no that you agree or disagree?

or with this one:

It might be infinite, an infinite radius of curvature is equivalent to zero curvature, complete flatness.

 

[Comeback City]

Yes.

Maybe this is the problem then. For example, the balloon model is still used to describe expansion of an flat/infinite universe.

There is definitely more to these analogies than just that galaxies are getting further apart.

In your opinion, what more is there to it?

 

[phinds]

Really? You can't even answer a yes or no question? Or respond to what looks to me like contradictions in the descriptions?

I'm sorry, Russ, I'm not trying to avoid any question, I've just lost track of what's what in this thread. To me the balloon analogy is nothing more than a simple description of how galaxies move apart metrically with no center and no edge. It is, as I say in the article, agnostic about infinite/finite, flat/curved, and so forth.

 

[russ_watters]

Maybe this is the problem then. For example, the balloon model is still used to describe expansion of an flat/infinite universe.

How?

In your opinion, what more is there to it?

See here:

1. to picture how distances can increase between stationary objects

2. to picture distances increasing at a percentagewise rate. Like one percent per minute.
So the longer the distance the faster (inches per minute) it increases. This is Hubble Law.

3. to understand that something can be finite (finite area if 2D or finite volume if it's 3D) without having any boundary

4. to understand that something can be curved without there being an extra dimension---part of the mental exercise is to picture the balloon surface as all there is, there is no inside the balloon and there is no outside---only the balloon surface exists.
I haven't talked about this part yet.

5. to picture light traveling between stationary points, as wrigglers traveling across the balloon surface at a fixed speed of one inch per minute----and to understand how the distance from a wriggler's starting point can increase faster than one inch per minute even tho the wriggler is always only traveling at one inch per minute.

https://www.physicsforums.com/threads/effort-to-get-us-all-on-the-same-page-balloon-analogy.261161/

 

[russ_watters]

I'm sorry, Russ, I'm not trying to avoid any question, I've just lost track of what's what in this thread.

? Are you ok, phinds? We're only talking about one post! (#44)

To me the balloon analogy is nothing more than a simple description of how galaxies move apart metrically with no center and no edge.

Others, including well-respected physicists, have said it has more to offer than just that.

 

[phinds]

? Are you ok, phinds? We're only talking about one post! (#44)

I took the heart of that post to be asking how the analogy explains the cause of the expansion and I responded that it does not. It describes how the expansion looks, not what causes it.

Your questions

1. How can we see it as finite if we aren't supposed to visualize the whole balloon?
2. How is the curved shape not a part of it/differentiate it from the rubber sheet? If we're only supposed to think of the expanding balloon as a flat rubber sheet, why bother with it at all?

I thought were addressed in the article and I still think that.

Others, including well-respected physicists, have said it has more to offer than just that.

OK, then I'm taking an overly simplistic view of the analogy. I would add, however, that the article was contributed to and proofed by several of the senior staff in the cosmology section and no one mentioned that I was missing anything significant regarding the analogy.

 

[russ_watters]

I would add, however, that the article was contributed to and proofed by several of the senior staff in the cosmology section and no one mentioned that I was missing anything significant regarding the analogy.

Ok, well I guess I'll wait and see if any are willing to assist.

 

[Comeback City]

See here:
https://www.physicsforums.com/threads/effort-to-get-us-all-on-the-same-page-balloon-analogy.261161/

I am going to start here if it is alright with you...
1) (already covered)
2) also covered; expansion, but with different units
3) This is just referring to a curved/finite universe (which refers to positive or negative curvature just for mental note) and how it needs no boundary
4) This is a little bit tricky, but this seems to be referring to the fact that the universe isn't expanding into anything (ie there is no outside to the universe that the universe is moving into)
5) I may be wrong on this one, but it seems to be describing the acceleration of the expansion of the universe

 

[russ_watters]

I am going to start here if it is alright with you...
1) (already covered)
2) also covered; expansion, but with different units
3) This is just referring to a curved/finite universe (which refers to positive or negative curvature just for mental note) and how it needs no boundary
4) This is a little bit tricky, but this seems to be referring to the fact that the universe isn't expanding into anything (ie there is no outside to the universe that the universe is moving into)
5) I may be wrong on this one, but it seems to be describing the acceleration of the expansion of the universe

Right, so I am of course referring to #3...

 

[Comeback City]

Right, so I am of course referring to #3...

Are you referring to how the balloon analogy relates to curved/finite universe?

 

[russ_watters]

Are you referring to how the balloon analogy relates to curved/finite universe?

Yes.

 

[Comeback City]

Yes.

Well, the main points (if there are even any more at all) are that there is no center to the universe and galaxies are moving away from each other. Let's just go through them one at a time...

1) With the balloon analogy (and I personally think this may be what puts it slightly ahead of the rubber sheet analogy) it is impossible to choose a center point on the balloon's surface. Indeed, you cannot use the inside of the balloon, as it is irrelevant in this 2-D example (the problem with the rubber sheet that is just becoming more clear to me is that you could choose a center point on the rubber sheet (unless it is infinite, of course), and this goes against everything we know about the universe, as the Big Bang theory says there was no center point for the universe when the Big Bang occurred).

2) Galaxies are moving farther and farther away from each other. I think that has been covered in this thread so far.

Now, expand the 2-D balloon sheet into the 4-D spacetime, and you have the universe: no center point and universal expansion.

 

[russ_watters]

1). .2). .

That's all fine, but how about 3? I'm really struggling to understand why people are simply ignoring my questions/concerns!

How about this (from the Insight article):

The universe not only has no center, it has no edge, but that does not imply that it is necessarily infinite, it could be finite but unbounded (like the surface of the Earth, for example).

"like the surface of the Earth" sounds like an analogy to me. Since there is already a spherical analogy on the table, why not just use it here instead of introducing a new analogy?

 

[Comeback City]

That's all fine, but how about 3? I'm really struggling to understand why people are simply ignoring my questions/concerns!

How about this (from the Insight article):

"like the surface of the Earth" sounds like an analogy to me. Since there is already a spherical analogy on the table, why not just use it here instead of introducing a new analogy?

I mentioned 2 main points of the balloon analogy but did not mention a 3rd point... where are you getting this from?

As for the analogy thing, I honestly don't know. Maybe it just comes down to opinion of the author. No need to really stress over that.

 

[russ_watters]

I mentioned 2 main points of the balloon analogy but did not mention a 3rd point... where are you getting this from?

I quoted it in my previous posts twice now and you even quoted it once without addressing it!

As for the analogy thing, I honestly don't know. Maybe it just comes down to opinion of the author. No need to really stress over that.

I'm not stressing, I'm just asking a simple yes or no question: is that use of the analogy valid?

 

[Comeback City]

I quoted it in my previous posts twice now and you even quoted it once without addressing it!

We've gone into a state of misunderstandings of one another. I will try to clear things up once and for all...
Balloon analogy and Rubber Sheet analogy can be treated as the same. The fact that one is curved and one is flat is not relevant. They both represent the same concept; universe has no center and the distance between galaxies in the universe is increasing. They also both represent taking the 4-D spacetime and placing it onto a 2-D surface, since it is much too complex (for laymen like us at least ) to comprehend it on the 4-D level.

That being said, the Balloon analogy really does not depend on the shape of the universe, which I believe is where all the confusion is coming from. The Balloon analogy works for curved/finite. The Balloon analogy works for flat/infinite. And now to the big question you have been waiting for all along::::: How?

The reason it works for both is what I just said (the "how" it works). Forget about the balloon real quick: There is no center of universe for either a finite or an infinite universe. There is no center of universe for either a curved or a flat universe. Distances between galaxies are increases regardless of whether the universe is flat, curved, infinite, finite, male, female, short, tall, fat, thin, black, white, or whatever! It really is that simple. Is the universe as a whole that simple? Absolutely not! But the balloon analogy is.

I'm not stressing, I'm just asking a simple yes or no question: is that use of the analogy valid?

Depends on what you are trying to accomplish with the analogy: if you want to demonstrate expansion, probably not (unless you know how to inflate the Earth ). If you are simply showing a finite but unbounded object, then yes, it will work.

If this doesn't satisfy what you are asking, then we will need a true expert to settle this out. Anyways, I will get back to you in the morning. Good conversation so far though!

 

[Daisyroots]

It's all so counter intuitive: a 'big bang' that yet didn't happen at any given place or hence any 'where'; an expansion (by every indication outward and with a measure of regularity) without, yet, a spacetime start point; a regular outward 'expansion' to infinity of something that was, yet, always in-and-of-itself infinite.

Doesn't it all look as if we might be coming at it from the wrong direction? I.e. mightn't it be better to be perhaps more up-front with ourselves with regard to our actual findings about 'matter' itself?

 

[weirdoguy]

Doesn't it all look as if we might be coming at it from the wrong direction?

No it does not. And to see that you really need to delve into the maths of the model. Heuristics won't do the job.

 

[Comeback City]

It's all so counter intuitive: a 'big bang' that yet didn't happen at any given place or hence any 'where'; an expansion (by every indication outward and with a measure of regularity) without, yet, a spacetime start point; a regular outward 'expansion' to infinity of something that was, yet, always in-and-of-itself infinite.

Doesn't it all look as if we might be coming at it from the wrong direction? I.e. mightn't it be better to be perhaps more up-front with ourselves with regard to our actual findings about 'matter' itself?

Being a new member, you will soon notice that what @weirdoguy said is a common recurring theme here on PF: "one can only go so far in layman terms until you have to start learning the math."

 

[Daisyroots]

Heuristics won't do the job.

But does anything even look like 'doing the job'? I mean, for example, if we'd have dreamed 30 years ago that we'd have had anywhere near the computing capacity to examine the issues, using modeling etc., that we have today, wouldn't we have actually thought that we'd have got somewhere (other, that is, than effectively deeper in the mire)? What do we actually know reference the thread question? We can apparently observe some sort of expansion, but of what, quite, into what, quite? I can't see that the thread question has been touched yet.

 

[Daisyroots]

Being a new member, you will soon notice that what @weirdoguy said is a common recurring theme here on PF: "one can only go so far in layman terms until you have to start learning the math."

Thanks you Comeback (and weirdoguy). I'll bow out. It seems to me we all want to know how the thing (the world) works, but regardless the language employed (maths, 'the word' or whatever) we incline towards delving deeper and ever deeper into a correspondingly ever more confined space, and in so doing lose sight of the question. We end up vanishing up our own backsides whilst patting ourselves heartily on the back for our cleverness. Philosophy, whilst it makes progress, has come up with no answers. Physics, whilst it makes progress, has come up with no answers. Religion makes no progress but purports to have all the answers whilst patently failing to demonstrate anything. And art, given that it evidences a modicum of creativity, is something of an enigma which seems happy to produce bad copies of the an unfailingly perfect original. Hey ho!

 

[russ_watters]

Depends on what you are trying to accomplish with the analogy: if you want to demonstrate expansion, probably not (unless you know how to inflate the Earth ). If you are simply showing a finite but unbounded object, then yes, it will work.

That's most of what I wanted: a simple yes or no answer to whether it works the way I use it (apparently yes) even if others like to limit it more.

That said, I still don't see an answer (or at least an explanation) as to the balloon and rubber sheet being mutually exclusive, so I will continue treating them as such until someone says I shouldn't. Indeed, given that it seems scientists think the universe is flat and infinite, not curved and finite, that would seem to be the better analogy to focus on.

 

[Comeback City]

Physics, whilst it makes progress, has come up with no answers.

Physics has definitely come up with answers. Sure, not to everything, but more than philosophy and religion. Out of the 3, physics is the only one that come up with evidence and proof for what it explains.

 

[Comeback City]

That said, I still don't see an answer (or at least an explanation) as to the balloon and rubber sheet being mutually exclusive, so I will continue treating them as such until someone says I shouldn't. Indeed, given that it seems scientists think the universe is flat and infinite, not curved and finite, that would seem to be the better analogy to focus on.

If this is the only issue, then it has been addressed several times. The balloon analogy and the rubber sheet analogy can both be used, AS LONG AS you do not begin to think that the there is a center in the rubber sheet (as, once again, there is no center to the universe regardless of its shape)

 

[Daisyroots]

Physics has definitely come up with answers. Sure, not to everything, but more than philosophy and religion. Out of the 3, physics is the only one that come up with evidence and proof for what it explains.

I'm not so sure, Comeback, though I can see why you might suppose it. It has many successes under its belt in the form of partial proofs of theories. For example many fabulous scientific developments are directly attributable to quantum theory and to the extent that each one of them works they of course prove the theory. In common with most things human, for most that is good enough. Those who use quantum theory as a work-a-day experience could not care less what causes the wave function to collapse. But since we do not know what causes it to collapse we have no idea of the nature of what it brings brings about, ie. the 'reality', phenomena, objectivity per se, 'MATTER'. We can ignore the question and pretend we do til the cows come home but the fact is that physics is no nearer an explanation of 'the world' than is even religion.

 

[Comeback City]

I'm not so sure, Comeback, though I can see why you might suppose it. It has many successes under its belt in the form of partial proofs of theories. For example many fabulous scientific developments are directly attributable to quantum theory and to the extent that each one of them works they of course prove the theory. In common with most things human, for most that is good enough. Those who use quantum theory as a work-a-day experience could not care less what causes the wave function to collapse. But since we do not know what causes it to collapse we have no idea of the nature of what it brings brings about, ie. the 'reality', phenomena, objectivity per se, 'MATTER'. We can ignore the question and pretend we do til the cows come home but the fact is that physics is no nearer an explanation of 'the world' than is even religion.

To be honest, I don't feel the need to argue over personal beliefs, as it really isn't accepted here on PF. Maybe someone else can chime in on how physics provides evidence to what it explains while philosophy is merely thought experiments and religion is simply "beliefs."

 

[russ_watters]

If this is the only issue, then it has been addressed several times. The balloon analogy and the rubber sheet analogy can both be used...

Fair enough, but since no one actually addressed the concerns I raised about using the balloon analogy for an infinite/flat universe, I'll make a different choice. If it speaks well to other people, great, but I suspect I'm not the only one who has trouble visualizing an infinite/flat sphere.

 

[weirdoguy]

I can't see that the thread question has been touched yet.

Just because you are not satisfied with the answers doesn't mean it hasn't been touched and that we don't know. We know what expands, we know what that means and we know that it does not have to expand into something. And to fully understand it you need to know the maths.

 

[Comeback City]

but I suspect I'm not the only one who has trouble visualizing an infinite/flat sphere.

Here is the issue! The universe is not a sphere (or at least it isn't known to be). Maybe overusing the balloon analogy has gotten you to think that since the balloon is a sphere, then the universe is a sphere. If the universe is infinite, then it will continue in all directions infinitely. The idea of the universe being a sphere implies that it would have boundaries, which is not compatible with an infinite universe.

 

[Daisyroots]

We know what expands,...

Is this to say that we know what matter is?

...to fully understand it you need to know the maths.

But aren't all the mathematical symbols effectively abbreviations? Can't each one of them be literated (or perhaps the expression should be literalised)? If not, then how did you yourself come to comprehend them? I'm not being facetious, weirdoguy, I'm genuinely interested.

 

[russ_watters]

Here is the issue! The universe is not a sphere (or at least it isn't known to be).

I'm aware.

Maybe overusing the balloon analogy has gotten you to think that since the balloon is a sphere, then the universe is a sphere.

No, I'm aware it isn't a sphere.

The idea of the universe being a sphere implies that it would have boundaries, which is not compatible with an infinite universe.

Agreed, but that isn't what the analogy says: the analogy considers only the 2d surface. However:

If the universe is infinite, then it will continue in all directions infinitely.

That, again, is my problem: picking a clearly and exclusively finite object and calling it infinite is.

 

[rootone]

can you have a viable idea of infinity that possesses, yet, a start point?

The set of natural numbers, (positive integers), You can start with 0 or with 1, either way the set has an initial value and extends to infinity.

 

[Daisyroots]

To be honest, I don't feel the need to argue over personal beliefs, as it really isn't accepted here on PF. Maybe someone else can chime in on how physics provides evidence to what it explains while philosophy is merely thought experiments and religion is simply "beliefs."

The set of natural numbers, (positive integers), You can start with 0 or with 1, either way the set has an initial value and extends to infinity.

Hi rootone. Yes I can see how that works. It's just that I wonder about the validity (and/or utility) of a unidirectional infinity, if you see what I mean.

 

[jbriggs444]

Hi rootone. Yes I can see how that works. It's just that I wonder about the validity (and/or utility) of a unidirectional infinity, if you see what I mean.

As for utility, there are a lot of students who have been taken through an approach to Real Analysis which begins with the Peano Axioms which characterize a unidirectional infinity and using this as the basis for a set theoretical construction of the real numbers.

Peano Axioms => unsigned integers with addition
Equivalence classes of ordered pairs of unsigned integers => signed integers with addition, subtraction and multiplication
Equivalence classes of ordered pairs of signed integers => rational numbers with addition, subtraction, multiplication and division
Equivalence classes of Cauchy Sequences [or Dedekind cuts] of rationals => real numbers with addition, subtraction, multiplication and division which satisfy the least upper bound property.

 

[Daisyroots]

As for utility, there are a lot of students who have been taken through an approach to Real Analysis which begins with the Peano Axioms which characterize a unidirectional infinity and using this as the basis for a set theoretical construction of the real numbers.

Peano Axioms => unsigned integers with addition
Equivalence classes of ordered pairs of unsigned integers => signed integers with addition, subtraction and multiplication
Equivalence classes of ordered pairs of signed integers => rational numbers with addition, subtraction, multiplication and division
Equivalence classes of Cauchy Sequences [or Dedekind cuts] of rationals => real numbers with addition, subtraction, multiplication and division which satisfy the least upper bound property.

I can imagine. Thanks rootone.

 

[Comeback City]

Hi rootone. Yes I can see how that works. It's just that I wonder about the validity (and/or utility) of a unidirectional infinity, if you see what I mean.

Did you want me to respond to that or did you quote me by accident?

 

[weirdoguy]

But aren't all the mathematical symbols effectively abbreviations?

No, it's the other way around. They can be 'literated' but to keep their full meaning it can't be done in laymans terms. That is the whole point of using mathematics to construct physical models. It's not ambiguous, everything has concrete meaning which you can't fully translate to ordinary language. Especially in advanced theories such as cosmology or quantum field theory.

If not, then how did you yourself come to comprehend them?

Well, I studied physics for 6 years at university, learned from textbooks, PhysicsForums and not from pop-sci stuff. Comprehension just 'happend'

Is this to say that we know what matter is?

For me matter=particles=certain states of quantum fields. If that doesn't satisfy you, well... The only thing that matters for physicists is to answer the questions "how it works?" not "what it really is and why it is so?" because at some point trying to answer the latter turns into philosophy.

 

[Daisyroots]

No, it's the other way around. They can be 'literated' but to keep their full meaning it can't be done in laymans terms. That is the whole point of using mathematics to construct physical models. It's not ambiguous, everything has concrete meaning which you can't fully translate to ordinary language. Especially in advanced theories such as cosmology or quantum field theory.
Well, I studied physics for 6 years at university, learned from textbooks, PhysicsForums and not from pop-sci stuff. Comprehension just 'happend'
For me matter=particles=certain states of quantum fields. If that doesn't satisfy you, well... The only thing that matters for physicists is to answer the questions "how it works?" not "what it really is and why it is so?" because at some point trying to answer the latter turns into philosophy.

Thank you very much for your patience and trouble, weirdoguy.

 

[Comeback City]

For me matter=particles=certain states of quantum fields. If that doesn't satisfy you, well... The only thing that matters for physicists

Ahh I see that low key pun you threw out there

 

[Daisyroots]

For me matter=particles=certain states of quantum fields. If that doesn't satisfy you, well...

Yeah, for me the thinking side of things tends to be a little bit more involved than that, though it it doesn't leave it out. For me objective existence (such as, I think, you describe) is only a part of the equation. I can't leave out the sentient beings doing the work of observation/correlation. They are, after all, just as much a part of the 'certain states of quantum fields' as any and everything else. The fact that they (we), as it were turn our eyes back in on themselves and analyse the situation, makes them, for me, warrant more inclusion rather than less.

 

[stoomart]

Fair enough, but since no one actually addressed the concerns I raised about using the balloon analogy for an infinite/flat universe, I'll make a different choice. If it speaks well to other people, great, but I suspect I'm not the only one who has trouble visualizing an infinite/flat sphere.

I'm not familiar with the "balloon analogy", but it seems to me the two analogies are indeed mutually exclusive. My understanding of a "flat universe" means two parallel lines will never intersect, three connected 90^o angles will never create a triangle, and traveling in one direction will never bring you to the same point; all of these would occur in a "curved universe".

 

[Comeback City]

I'm not familiar with the "balloon analogy", but it seems to me the two analogies are indeed mutually exclusive. My understanding of a "flat universe" means two parallel lines will never intersect, three connected 90^o angles will never create a triangle, and traveling in one direction will never bring you to the same point; all of these would occur in a "curved universe".

The whole point of the balloon analogy is to show how galaxies move farther away from each other without they themselves moving at all. It is the expansion of the universe, caused by dark energy, that is moving them. Just because the balloon has a curved surface, DOES NOT imply that the analogy only works for a curved universe. It works equally well for a flat/infinite universe. And I guess I will do the honors... read the article in the link of @phinds signature on the balloon analogy!

 

[stoomart]

The whole point of the balloon analogy is to show how galaxies move farther away from each other without they themselves moving at all. It is the expansion of the universe, caused by dark energy, that is moving them. Just because the balloon has a curved surface, DOES NOT imply that the analogy only works for a curved universe. It works equally well for a flat/infinite universe. And I guess I will do the honors... read the article in the link of @phinds signature on the balloon analogy!

It seems silly to use an analogy with a layman (like myself) that requires so much fine-print so it won't be misunderstood by the target audience. I would just say unbound galaxies are like a bunch of brownies whose space increases between them like they are magically shrinking.

Edit: I was already reading it before your post to see what all the fuss was about. : )

 

[stoomart]

Just because the balloon has a curved surface, DOES NOT imply that the analogy only works for a curved universe. It works equally well for a flat/infinite universe.

I think this thread has gone far too off-topic, so I will conclude with this thought: using curved balloon and flat rubber sheet analogies that can each describe a flat and curved universe is terribly confusing.

My personal belief is God created the infinite universe as a picture of his infinite power and greatness (see my profile for reference), but I do enjoy learning the theories we humans come up with to explain our observations.

 

[PeroK]

My personal belief is God created the infinite universe as a picture of his infinite power and greatness (see my profile for reference), but I do enjoy learning the theories we humans come up with to explain our observations.

When you meet him, you can ask him and that'll resolve the issue. I doubt I'll get the chance!

 

[Comeback City]

using curved balloon and flat rubber sheet analogies that can each describe a flat and curved universe is terribly confusing.

It's because you are overthinking the main purpose of them

 

[phinds]

My personal belief is God created the infinite universe as a picture of his infinite power and greatness ...

Not relevant in a science forum.

 

[infinitebubble]

Excellent topic... new to the conversation... Question just as in a pile of soap bubbles... if the multiverse model is true should the expanding universe model be expanding into other universes and those other universes are expanding into 'our' universe? Would we not see these other universes... so I do not think we have an infinite universe and our expansion of the universe will hit some unseen wall?

 

[jbriggs444]

Excellent topic... new to the conversation... Question just as in a pile of soap bubbles... if the multiverse model is true should the expanding universe model be expanding into other universes and those other universes are expanding into 'our' universe? Would we not see these other universes... so I do not think we have an infinite universe and our expansion of the universe will hit some unseen wall?

There is no need for an expanding universe to be embedded in any containing space within which it is expanding.