How can the Universe grow if it is infinite?

  • #101
Why the discussion at all if expansion of the universe is infinite? What is that containing space?
 
  • #102
jbriggs444
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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.
 
  • #103
Not visualizing this somehow? Explain... Please.
 
  • #104
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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.
 
  • #105
phinds
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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.
 
  • #106
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.
 
  • #107
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.
 
  • #108
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?
 
  • #109
phinds
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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.
 
  • #110
phinds
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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.
 
  • #111
PAllen
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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.
 
  • #112
phinds
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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.
 
  • #113
PAllen
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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.
 
  • #114
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
 
  • #115
PAllen
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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.
 

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