The Universe - infinite or not ?

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  • #1
drag
Science Advisor
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Greetings !

Well, I'm just a poor amatuer.
This is the thread for you - the experts, to argue
about it (at lenght, I hope :wink:) and for us to read your
words of wisdom.

Live long and prosper.
 

Answers and Replies

  • #2
bogdan
191
0
Yes...
 
  • #3
Mentat
3,918
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As everyone from the original PFs knows, I do not think the universe is infinite. This is on account of the abundant proof of the BB theory (which rather clearly states that space itself is expanding, which leads me to believe that it cannot already be infinite (since something that is infinite cannot get any bigger)).
 
  • #4
I can't agree with you more, Mentat. I would say, maybe, that the universe is on the verge of infinity?[?]
 
  • #5
Eh
746
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Logically, there is no problem with an expanding infinite universe. If there was, physicists and mathematicians would love to know why. Intuition is not logic.
 
  • #6
CJames
369
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I often agree with you Mentat but not here. I have long suspected the universe is finite but I'm having second guesses. Anyway, I never believed it to be an absolute fact. I believe in the big bang as well. However, cosmology allows for the big bang to work even with an infinite universe. The universe simply needs to have infinite size at its creation. A singularity of infinite size AND infinite density. It's weird I know.
 
  • #7
bogdan
191
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universe = ?
 
  • #8
cragwolf
169
0
Is the universe infinite? Well, according to the evidence, the answer is ... we don't know. And unfortunately, this may be the best answer we'll ever get. While the curvature of the universe is something that we might get a precise fix on (the data suggest a flat universe, i.e. no spatial curvature), the global topology might never be known because of the smallness of our Hubble volume. And the global topology is just as important as the curvature is in determining the size of our universe.
 
  • #9
russ_watters
Mentor
21,937
8,973
Yes...
No... ;)

Is the universe infinite? Well, according to the evidence, the answer is ... we don't know. And unfortunately, this may be the best answer we'll ever get. While the curvature of the universe is something that we might get a precise fix on (the data suggest a flat universe, i.e. no spatial curvature), the global topology might never be known because of the smallness of our Hubble volume. And the global topology is just as important as the curvature is in determining the size of our universe.
We can detect measure the velocity of galexies quite a long distance away. The evidence we have now certainly suggests a BB like event and a finite but boundless universe.
 
  • #10
bogdan
191
0
universe = space ?
or
universe = space-time-and-so-on ?
And...how could we find out that the universe is infinite or not ?
Give a method...even if it's impossible to be realized...
 
  • #11
Eh
746
1
Originally posted by russ_watters
No... ;)

We can detect measure the velocity of galexies quite a long distance away. The evidence we have now certainly suggests a BB like event and a finite but boundless universe.

The big bang does not say the universe is finite or infinite.
 
  • #12
Mentat
3,918
3
Originally posted by CJames
I often agree with you Mentat but not here. I have long suspected the universe is finite but I'm having second guesses. Anyway, I never believed it to be an absolute fact. I believe in the big bang as well. However, cosmology allows for the big bang to work even with an infinite universe. The universe simply needs to have infinite size at its creation. A singularity of infinite size AND infinite density. It's weird I know.

Well, you are entitled to your opinion. However, to say that there can be a singularity of infinite spatial extent is contradictory, and makes no sense to me.
 
  • #13
Mentat
3,918
3
Originally posted by Eh
The big bang does not say the universe is finite or infinite.

You know what, you bring this up a lot, but I still disagree. Sure, BB theory may not say which it is - but isn't the idea behind the BB, that the spatial dimensions themselves are expanding? If so, then the universe cannot already be infinite, because the spatial dimensions couldn't possibly get any bigger.
 
  • #14
Mentat
3,918
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Originally posted by MajinVegeta
I can't agree with you more, Mentat. I would say, maybe, that the universe is on the verge of infinity?[?]

Well, for all practical purposes, it may have the potential to continue expanding infinitely. However, it will never reach infinity (if it is finite now), and so cannot really be "on the verge of infinity".
 
  • #15
Eh
746
1
Originally posted by Mentat
You know what, you bring this up a lot, but I still disagree. Sure, BB theory may not say which it is - but isn't the idea behind the BB, that the spatial dimensions themselves are expanding? If so, then the universe cannot already be infinite, because the spatial dimensions couldn't possibly get any bigger.

The important thing seems to be that expansion does not necessarily make the universe larger. This is one of the weird things you get from infinity, but it does not seem to have an inherent problem. As you noted before, each region in an infinite universe is infinitesimal compared to space as a whole. That is, each point is pretty much zero compared to the universe.

Within any region, local expansion occurs where distances between points increases. But even though local expansion is occurring within the region, the size of that region is infinitely small compared to the whole universe - and always will be. There is nothing preventing local expansion from occurring, and the size of the universe never changes. Again, this is because of the nature of infinity.
 
  • #16
AN IDEA!

The universe(universe=everything) is infinite, but the spatial dimensions are the ones expanding into the actual universe. It's like, what is the universe expanding into? Well, let's substitute "universe" as "subuniverse". So it's what is the subuniverse expanding into? the actual universe. I hope you understand what I mean(as I am having a hard time describing this).
 
  • #17
CJames
369
0
I agree with Eh, although not necessarily in the way he explained it. To me it is much simpler. An infinite number is not "the biggest number possible." An infinite number, actually, has an infinite amount of room to grow. You can add, divide, multiply infinities together and you get back another infinite number. If you didn't, you'd get all sorts of paradoxes in mathematics.

Mentat, by saying an infinite universe can't get any bigger, you are saying an infinite universe has no more room to grow. You are implying that the universe has to have space to grow into. You know that is not the case.
 
  • #18
Olivers bells thesis 201 says that a universe can not expand without stretching and bursting causing a catastrophic wave of death and destruction of neutrinos and protons, the force of the rip will be 1.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001*10Exp
 
  • #19
Eh
746
1
Are you sure that's not just an accelerating universe?
 
  • #20
Originally posted by JamesBell
Olivers bells thesis 201 says that a universe can not expand without stretching and bursting causing a catastrophic wave of death and destruction of neutrinos and protons, the force of the rip will be 1.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001*10Exp


How about the big crunch?
 
  • #21
Mentat
3,918
3
Originally posted by CJames
I agree with Eh, although not necessarily in the way he explained it. To me it is much simpler. An infinite number is not "the biggest number possible." An infinite number, actually, has an infinite amount of room to grow. You can add, divide, multiply infinities together and you get back another infinite number. If you didn't, you'd get all sorts of paradoxes in mathematics.

Mentat, by saying an infinite universe can't get any bigger, you are saying an infinite universe has no more room to grow. You are implying that the universe has to have space to grow into. You know that is not the case.

No, I never said that it was because it didn't have room to grow into. I said that it was because it was as big as it could possibly get.
 
  • #22
Mentat
3,918
3


Originally posted by MajinVegeta
The universe(universe=everything) is infinite, but the spatial dimensions are the ones expanding into the actual universe. It's like, what is the universe expanding into? Well, let's substitute "universe" as "subuniverse". So it's what is the subuniverse expanding into? the actual universe. I hope you understand what I mean(as I am having a hard time describing this).

This is very near (if not identical) to one of the BB theories, that people bring up quite a bit, especially in threads about the incompatibility of infinite universe with BB theory.
 
  • #23
Mentat
3,918
3
Originally posted by Eh
The important thing seems to be that expansion does not necessarily make the universe larger. This is one of the weird things you get from infinity, but it does not seem to have an inherent problem. As you noted before, each region in an infinite universe is infinitesimal compared to space as a whole. That is, each point is pretty much zero compared to the universe.

Within any region, local expansion occurs where distances between points increases. But even though local expansion is occurring within the region, the size of that region is infinitely small compared to the whole universe - and always will be. There is nothing preventing local expansion from occurring, and the size of the universe never changes. Again, this is because of the nature of infinity.

I understand all of this, I was talking about the idea that the spacial dimensions themselves are expanding. I had thought that this is what BB theory was all about. If this were the case, then the universe could not be infinite.
 
  • #24
Mentat
3,918
3
CJames, infinity is not the biggest that you can get mathematically. But is the biggest that you can get physically.
 
  • #25
Zakkur
1
0
you got to think outside the box man. like the universe can grow and grow. but like, what is it growing in? yknoe, what outside this box man, is the universe square? and outside of each wall is there an equal and opposite universe, or if its a circle, it wouldn't matter if you left te universe and looked at it because it wouldn't be there, you would be in a place where time and space didnt exist until you got there, and you would float forever thinking until you turned into your own universe, and you were the creator man. i swear i don't knoe what I am talking about man. lmao.
 
  • #26
Hesh
2
0
The universe is not infinite nothing is naturally infinite we only see the universe as infinite because we are so small compared to it and we really don't know where it ends but it does have an end and won't expand forever because like all things it will eventually run out of energy. Space may be infinite but the universe is not.Now whether it will just stop or collapse in on itself is another thing maybe it will collapse and just create another big bang or just stop and for what's outside the universe it could be nothing or it could be another universe how do we know that there wasnt a universe when the big bang happened and that the force from the big bang didnt push that universe out of the way or push or destroy part of that universe so our universe could form but our universe could just be a galaxy or a planet in an even bigger universe if you get what i mean but yes the universe does have an end and it is not infinite.
 
  • #27
dad3
4
0
the universe is not infinite because it is currently thought that the universe is expanding but we could have an infinite number of parallel universes.......................but also the Earth was flat at one time and every planet was manipulated by Earth's gravitational force???
 
  • #28
jposs
20
0


The universe(universe=everything) is infinite, but the spatial dimensions are the ones expanding into the actual universe. It's like, what is the universe expanding into? Well, let's substitute "universe" as "subuniverse". So it's what is the subuniverse expanding into? the actual universe. I hope you understand what I mean(as I am having a hard time describing this).

I think i do. So there is a "wall" at the edge of the universe.... say the expansion of matter is the only definition of this wall. It has more room but no stuff. The expanding universe continues on its path, I would guess dispersing at its edges more and more. But even on the outer limits of what could physically hold together we could not tell there is nothing there because there is nothing to mark its presence, other than nothing.

So say one day we could count the physical universe on any level I think we would have to call that infinite (even being quantifiable) because we have no words in any language to describe it.... Just like a Dodo first seeing things that could eat them, how could they tell there birdbrained friends that didn't see the other colony that got slaughtered anything about what happened when so many words are missing.

Well kind of went off on a different direction... sorry, it happens.
 
  • #29
jposs
20
0
.......but also the Earth was flat at one time and every planet was manipulated by Earth's gravitational force???

We think too much of ourselves. That was destruction and undeniable forces that brought us back there. And our way too "I'm better than you" mentality that keeps us there. IMnotsoHO if we weren't so good at those traits our species would be either way more primitive or as my optimism likes to think way more developed than it is today. Maybe not the same, but more.

When did a people invent the printing press? Columbus proved it was round right? Hell we didn't even know an apple falling from above you would hit you on the head until after the guy who once again proved the basics of what is was told to shut up or die. We are a bit full of ourselves, maybe not a bunch of you all, but I would be tempted to say a majority of all of us peoples.
 
  • #30
IsometricPion
187
3
the universe is not infinite because it is currently thought that the universe is expanding but we could have an infinite number of parallel universes.......................but also the Earth was flat at one time and every planet was manipulated by Earth's gravitational force???
The best http://en.wikipedia.org/wiki/Friedmann_equations" [Broken] near the edge).

Off topic (and irrelevant): This may be the first time I've seen a thread from 2003 necroposted (though I guess it was also posted to in 2009, but that was also a necropost, and it lead to no discussion so I don't think it counts).
 
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  • #31
dad3
4
0
We think too much of ourselves.

Exactly
 
  • #32
binbots
170
3
I do not see how the universe or the multiverse can be finite. It is a all or nothing situation. Nothing can't co exist with something. If you say the universe started with the big bang then how long was this tiny super dense singularity sitting there for before the bb? If you say the universe if spacialy finite then what would happen if you reached the end? The fact that we exist means time and space are both infinite.
 
  • #33
Chronos
Science Advisor
Gold Member
11,435
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I would argue that proposal, binbots. Nothing exists amongst something all around us - like empty space between stars. It is difficult to prove the universe is either finite or infinite. Einstein surely thought it was infinite and I'm not inclined to argue with him. But, his logic was newtonian and he waffled a lot. WMAP suggests the universe is almost exactly flat - which implies it is infinite, or at least too close to call. What does that mean? A universe comprised of a finite amount of matter expanding into an endless void? An infinite amount of matter expanding into an even more endless void? The only relevant part, IMO, is the observable universe. Beyond that is the playground of mathematicians and philosophers - who remind us why our ancestors found theology appealing.
 
  • #34
mdmaaz
42
0
I believe the universe is finite. Richard Feynman's law of "alternative histories" states that each incidents happens in a different way in a different universe. If our universe was infinite, how could there be many universes. I believe that the size of a universe is finite, but the number of universes is infinite. Besides, ever since the big bang, the space between celestial objects has been increasing. Only finite things can increase in size.
 
  • #35
yenchin
545
3
I believe the universe is finite. Richard Feynman's law of "alternative histories" states that each incidents happens in a different way in a different universe. If our universe was infinite, how could there be many universes. I believe that the size of a universe is finite, but the number of universes is infinite. Besides, ever since the big bang, the space between celestial objects has been increasing. Only finite things can increase in size.

The last part wasn't exactly true. If you start with the set of integer which is infinite, you map each element to twice their size i.e. n maps to 2n, then the two sets have the same cardinality, although distance between each integer is now twice as before. So when we say the universe is expanding, all we are saying is the the scale factor of the metric changes, in much the same way as "expanding" the set of integers. Thus an infinite space can expand in such a way. That said, I personally prefer a finite universe ;-)
 

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