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Author Topic:   Do We Live in an Infinite Universe?
GDR
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Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 1 of 60 (334504)
07-23-2006 11:56 AM


Cavediver says that we may very well be living in an infinite universe. What does that mean. First off I think that we need to define our terms.
http://EvC Forum: Kalam Cosmological argument -->EvC Forum: Kalam Cosmological argument
What is the definition of a universe?
I have always thought of it as simply is everything that constitutes all of the mass and energy in our inter-galactic system. However when we start to talk about multi-universes I'm not so sure.
What does infinity actually mean in this context?
Is it just a mathematical solution to the question and if not then what does inifinity look like in terms of the Big Bang? Is there going to be a Big Crunch? Does it allow for a T=0? I would imagine that an infinite universe has no boundaries in either time or distance, but then again it seems that many physicists divide time up into planck length chunks of time. If time is a series of nows is that compatible with a universe that is infinite in distance?
If time in an infinite universe is depicted as a circle would it be correct to say that the period between the BB and the BC, (or however else time as we know it ends), could be depicted as a tear drop attached to the circle so that time flows out of the large circle travels around the tear drop and then flows back into the large (infinite) circle again?
I'm just looking for some description that a lay person can get their head around.
If we live in an infinite universe would it be reasonable to think that what existed at T=0 was infinite energy?
It seems to me that if we live in an infinite universe then I can't see how the singularity could have been finite.

Replies to this message:
 Message 2 by RAZD, posted 07-23-2006 12:54 PM GDR has not replied
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GDR
Member
Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 12 of 60 (334561)
07-23-2006 5:36 PM


I really like RAZD's explanation of infinity as it applies to math vs. reality. It does leave me still wondering though what infinity means in terms of what we are talking about. Is it mathematical, (like as in there being an infinite number of points along a straight line), or is it reality, (as there actually are a number of points limited by the number of partiles, presumably planck length, along that line).
From cavediver I understand it when he says that everything that there is constitutes the universe. However, that says to me then that when scientists talk about parallel universes, or when they talk about every now being an eternal universe they mean something different by the term universe.
I still have trouble conceiving of a universe where there was point when T=0 being a universe of infinite time unless there is something to my example in the OP of a teardrop within a circle, but even that leaves me uncertain.

Everybody is entitled to my opinion.

Replies to this message:
 Message 13 by cavediver, posted 07-24-2006 4:39 AM GDR has replied

  
GDR
Member
Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 14 of 60 (334804)
07-24-2006 10:45 AM
Reply to: Message 13 by cavediver
07-24-2006 4:39 AM


cavediver writes:
I'm not sure what you mean here. Do you mean a universe where there is no T<0? In that case, the universe can only be semi-infinite in time, i.e. has an infinite future. This is how our universe appears at the moment. If our universe was closed and there was no cosmological constant, then the universe would also have an end: the Big Crunch, and then the universe would be truly finite in extent both spatially and temporally.
I'm not sure what I mean either. From some of the things that I've read, I thought that some were suggesting that T=0 at the BB, but that possibly time was just being restarted at that point. I thought it might be like travelling south from the north pole until we passed the south pole and arrived back at the north pole and then starting all over again.
That idea would represent a universe where time is continually starting, then ending and starting again. The suggestion that I made in the OP that time was like a teardrop within a circle. The tear drop would represent time as we know it starting and ending just once but flowing back into infinite time as represented by the circle.
The problem as I see it with that scenario is that appears to me to require the Big Crunch. I thought however that as the expansion is accelerating the theory of the BC has been pretty much discounted with or without a cosmological constant.
In regards to the expansion of the universe, I have another question. As I understand it the gravitational field of each galaxy affects every other galaxy. However as the universe expands gradually all of the other galaxies will expand beyond the event horizon for our galaxy. As gravity moves at light speed we will no longer be in the gravitational effect of any other galaxy. Does that matter to us? (That's assuming that we were planning on being here in a few billion years from now. )
I'm wondering if there is a point where the gravitational forces would have changed so much that everything would just fly apart.
By the way, it is like the tree in the forest. If a galaxy is beyond the event horizon and we can no longer perceive it, does it still exist?

Everybody is entitled to my opinion.

This message is a reply to:
 Message 13 by cavediver, posted 07-24-2006 4:39 AM cavediver has replied

Replies to this message:
 Message 15 by cavediver, posted 07-24-2006 11:12 AM GDR has replied

  
GDR
Member
Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 16 of 60 (334822)
07-24-2006 12:01 PM
Reply to: Message 15 by cavediver
07-24-2006 11:12 AM


cavediver writes:
The acceleration is driven by the CC. With no CC, there is no acceleration, and we are back to the good old days of the three BB scenarios: closed, flat, and open, of which the latter two have semi-infinite time, just as with the accelerating universe.
I thought that it is pretty much conceded that the expansion of the universe is accelerating. However, I gathered that there could still be a CC that is limiting the acceleration.
Are you meaning then that the expansion could still at some point stop accelerating and start to collapse. If that were to happen wouldn't that have a profound impact on the flow of time. What would happen when the rate of collapse exceeds light speed in the way that expansion does now?
Although I can't begin to understand it your suggestion that time and space is just a function of what is perceived by consciousness makes a lot of sense. Actually that is why I asked if galaxies that have expanded past the event horizon still exist.
cavediver writes:
Any new perturbations to the local gravitational field will propegate out at c and never reach the other galaxies. But the original curvature is still there. You could say that the gravitational potential is always felt, but changes to the potential can be hidden.
Isn't it also possible though that the gravitaional field could collapse in that scenario, resulting in Big Disintegration?

This message is a reply to:
 Message 15 by cavediver, posted 07-24-2006 11:12 AM cavediver has replied

Replies to this message:
 Message 17 by cavediver, posted 07-24-2006 12:24 PM GDR has replied
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GDR
Member
Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 19 of 60 (334893)
07-24-2006 2:17 PM
Reply to: Message 17 by cavediver
07-24-2006 12:24 PM


cavediver writes:
Ok, we've got to be more precise here then. The acceleration is driven by a field, we'll call A. If A is positive, the universe gets pulled in on itself; if it is negative it accelerates the universe apart, as observed.
Now A could be made up of several things, but we'll just consider the important two: the Cosmological Constant,L (should be lambda but I'm too lazy to put in Greek) and some dark energy field, D.
So A = L + D. Now L can be positive, zero or negative. D can be positive, zero or negative. But we can't tell them apart at the moment. So L could be doing the accelerating, or D or both. So there's often little point separating the two concepts. When I say CC, I mean sun of the two, which is an abuse of terminology on my part.
OK. I think I have that. However, (there is always a but isn't there? ) it seems to me then if L is a constant the only way that an expanding universe can contract is if D becomes more positive. Wouldn't any change in D likely be caused by the fact that with the acceleration wouldn't any change in D be caused by the fact that the dark energy field is becoming more diffuse, thus reducing its gravitational pull?
If this is the case then wouldn't we expect that instead of starting to contract that we would arrive at a point where A is neutral and there would be a state of equilibrium which might leave us in a state of infinite time.
GDR writes:
If that were to happen wouldn't that have a profound impact on the flow of time.
cavediver writes:
It was once thought that it would, but entropy again seems to rule that out.
If entropy is always increasing in an expanding universe then what happens at the point of max entropy. If the universe is contracting then doesn't that mean that entropy is decreasing. We have only known a universe with increasing entropy, what does the opposite look like if it is even possible? (By the way, my understanding of entropy is extremely limited, so if I'm talking nonsense don't be surprised and I won't have my feelings hurt if it is pointed out to me. )
cavediver writes:
That's not really what I was saying... although it is a discussion for another day. What I was saying was that the "flow of time" is a construct of conciousness.
If I can try rephrasing that are you saying that time is just the way that we perceive change as Barbour would say? (I think) If space and time are both illusions it sure becomes difficult to sort out reality from from perception.
cavediver writes:
No. There is no gravitational field in that sense. There is curvature. It is the Universe, as a whole, and doesn't have much respect for horizons and c which are local concepts.
This I don't understand. Isn't the gravitational field largely what holds things together so to speak. With an expanding universe it would seem to me that the field would be weakened.
When we look at the Earth the gravitational pull is constant because of the curvature of the earth. Are you saying that this would hold true for the universe in the same way when the dimension of time is included?
It seems to me though that if the mass of the universe was increasing then the gravitational field would still be as strong. Wouldn't it be true that if the circumference of the Earth were to increase without any increase in its mass we on the surface would experience reduced gravity. (Beats dieting ) Why wouldn't this hold true for the universe as well?
Thanks for the time you are spending with the layman's layman.

Everybody is entitled to my opinion.

This message is a reply to:
 Message 17 by cavediver, posted 07-24-2006 12:24 PM cavediver has replied

Replies to this message:
 Message 20 by cavediver, posted 07-24-2006 6:47 PM GDR has replied

  
GDR
Member
Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 21 of 60 (335034)
07-24-2006 10:28 PM
Reply to: Message 20 by cavediver
07-24-2006 6:47 PM


I keep running this through my mind trying to put the pieces together. One thing that seems strange to me is this:
cavediver writes:
Now A could be made up of several things, but we'll just consider the important two: the Cosmological Constant,L (should be lambda but I'm too lazy to put in Greek) and some dark energy field, D.
So A = L + D. Now L can be positive, zero or negative. D can be positive, zero or negative. But we can't tell them apart at the moment. So L could be doing the accelerating, or D or both. So there's often little point separating the two concepts. When I say CC, I mean sun of the two, which is an abuse of terminology on my part.
As you point out, A can function quite nicely with L being zero. Why did scientists reconsider the idea of L at all. Wouldn't it be more reasonable to think that A=D and that L is zero or non-existent?
I realize that you consider this a possible solution but I don't see why it wouldn't be considered the most likely solution.
cavediver writes:
It's not exerting a gravitational pull exactly, but it may certainly reduce. Then again, it could get stronger as time goes on, which would give you the Big Rip scenario. It all depends on the particular dynamics of the field, and we are a very long way from determining that. This kind of field, outside of current Standard Model physics, is the sort of thing you expect from String Theory and similar. But don't think of it like a dust which thins out as such. It is more akin to an electromagnetic field through space-time, just with different properties.
If the universe is expanding I don't understand how any field, either gravitational or electromagnetic could be growing stronger. As I said wouldn't a more diffuse field be weaker?
If it is an open universe I don't think that necessarily means an infinite one. It seems to me that the universe would meet some critical mass and self-destruct.
I don't understand how the gravitational pull would grow stronger with expansion and I also don't understand why a stronger gravitational pull would cause the Big Rip. I would have thought that a stronger gravitational pull would help hold that whole shebang together.
I read this and would like your opinion. It is short.
Page not found | American Institute of Physics
Thanks
Greg

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GDR
Member
Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 33 of 60 (336881)
07-31-2006 10:06 AM
Reply to: Message 31 by 2ice_baked_taters
07-31-2006 9:43 AM


taters writes:
Considering that our existence as a species on this planet will likely come to pass this will also place a finite limit to our understanding of what exists. Our experience has shown us though, that the harder we look, the more there is to see.
I asked earlier in the thread if infinity was something that was strictly mathematical or if it represented reality.
It strikes me that if I understand what Penrose and cavediver are suggesting, (very good chance I don't), then everything that exists depends on consciousness. If there is no consciousness to perceive something does it exist?
If a huge comet hit the earth and all conscious life was destroyed would the universe cease to exist even though mathematically we might come to the conclusion that the universe is infinite?

Everybody is entitled to my opinion.

This message is a reply to:
 Message 31 by 2ice_baked_taters, posted 07-31-2006 9:43 AM 2ice_baked_taters has not replied

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