B How can the Universe grow if it is infinite?

[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.

 

[infinitebubble]

Why the discussion at all if expansion of the universe is infinite? What is that containing space?

 

[jbriggs444]

Why the discussion at all if expansion of the universe is infinite? What is that containing space?

Expansion has nothing to do with any containing space -- if any.

 

[infinitebubble]

Not visualizing this somehow? Explain... Please.

 

[stoomart]

Not relevant in a science forum.

How good can a discussion about infinity be between science fans and a philosopher without a theologian? : )

A scientist, a philosopher, and a theologian walk into a bar, it hurt.

 

[phinds]

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?

Absolutely not. (1) As jbriggs said, there is no need for anything to expand "into", and (2) IF there is a multiverse (which I personally do not believe) there is no theory or evidence that different universes could be in casual contact with each other.

 

[fencewalker]

the way i see it, the space between the galaxies is expanding within the universe. they are moving in relationship to each other. space itself doesn't change, just the distances between the objects within space.

 

[infinitebubble]

Absolutely not. (1) As jbriggs said, there is no need for anything to expand "into", and (2) IF there is a multiverse (which I personally do not believe) there is no theory or evidence that different universes could be in casual contact with each other.

If galaxies are moving away from each other which is proven and they are expanding into 'something' the furthest galaxies should be feeling this ultimate wall at some point? Well many theorists might disagree on the single universe idea but that is not the idea of this discussion.

 

[infinitebubble]

the way i see it, the space between the galaxies is expanding within the universe. they are moving in relationship to each other. space itself doesn't change, just the distances between the objects within space.

So this this realm the universe is infinite? How can this be proven?

 

[phinds]

If galaxies are moving away from each other which is proven and they are expanding into 'something' the furthest galaxies should be feeling this ultimate wall at some point? Well many theorists might disagree on the single universe idea but that is not the idea of this discussion.

No they are not. You need to read some basic cosmology. I recommend Googling "metric expansion" as a start.

 

[phinds]

So this this realm the universe is infinite? How can this be proven?

It is NOT known that the universe is infinite. The consensus these days seems to be that it is but there is no proof. Regardless of whether it is infinite or finite but unbounded, it is not moving "into" anything.

 

[PAllen]

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

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

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

I completely agree with this. The balloon analogy is aimed showing the possibility of isotopic recession with no center. It happens to use a finite surface. You cannot meaningfully pretend it is infinite.

 

[phinds]

I completely agree with this. The balloon analogy is aimed showing the possibility of isotopic recession with no center. It happens to use a finite surface. You cannot meaningfully pretend it is infinite.

I agree completely. As I state in the referenced Insights article, the analogy is not intended to comment on the size of the universe.

 

[PAllen]

Maybe something like this has been presented earlier -apologies for not reading the whole thread. I was trying to 'reverse engineer' how I came to grips with infinite expansion long ago. I came up with the following:

Imagine a flat infinite plain. Imagine cutting it up into a countably infinite set of 1 inch squares. Now expand each 1 inch square into a two inch square. Reassemble the squares into an infinite plain. It is still just an infinite plain, but clearly, every piece of it has expanded. Repeat ad naeseum.

 

[infinitebubble]

Properties of the Expanding Universe
The equations of the expanding universe have three possible solutions, each of which predicts a different eventual fate for the universe as a whole. Which fate will ultimately befall the universe can be determined by measuring how fast the universe expands relative to how much matter the universe contains.
The three possible types of expanding universes are called open, flat, and closed universes. If the universe were open, it would expand forever. If the universe were flat, it would also expand forever, but the expansion rate would slow to zero after an infinite amount of time. If the universe were closed, it would eventually stop expanding and recollapse on itself, possibly leading to another big bang. In all three cases, the expansion slows, and the force that causes the slowing is gravity.
A simple analogy to understand these three types of universes is to consider a spaceship launched from the surface of the Earth. If the spaceship does not have enough speed to escape the Earth's gravity, it will eventually fall back to Earth. This is analogous with a closed universe that recollapses. If the spaceship is given enough speed so that it has just enough energy to escape, then at an infinite distance away from the Earth, it will come to a stop (this is the flat universe). And lastly, if the ship is launched with more than enough energy to escape, it will always have some speed, even when it is an infinite distance away (the open universe).

Quote: http://skyserver.sdss.org/dr1/en/astro/universe/universe.asp

 

[PAllen]

why cut up space itself, that is not what is moving. drop some marbles on ur infinite plane and watch them expand away from each other. the marbles are galaxies in ur infinite plane. as i c it...

The goal is that many people have trouble picturing expansion everywhere in something already infinite. Marbles don't help this intuition problem - they just ask how all the marbles can make room for each other over an infinite surface. You can include marbles in my model. Cut the infinite grid of marbles into sections. In each one, move the marbles further apart. Now reassemble. I think breaking it into these steps make visualization easier for some people.