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Author Topic:   Do We Live in an Infinite Universe?
GDR
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Posts: 4961
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.6


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.

www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=34&t=11&m=1 -->www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=34&t=11&m=1">http://www.evcforum.net/cgi-bin/dm.cgi?action=msg&f=34&t=11&m=1

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 yet responded
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 Message 4 by cavediver, posted 07-23-2006 1:11 PM GDR has not yet responded

    
RAZD
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Posts: 20120
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.8


Message 2 of 60 (334514)
07-23-2006 12:54 PM
Reply to: Message 1 by GDR
07-23-2006 11:56 AM


2cents
What does infinity actually mean in this context?

Is it just a mathematical solution to the question ...

um ... yes. sort of. mostly maybe ... ish ....

Consider a straight line and a circle. Both are mathematical concepts, and the mathematical concepts involve non-dimensional points anywhere along either -- each has an infinite number of points, but one is "bounded" and the other isn't (you can't even conceive where a "line" ends).

But in reality there are no circles or lines that have infinite points -- you can only go so far as the {discrete} subatomic particles -- nor are there any real "straight" lines.

Our concept of "infinite" is inevitably intertwined with our concept of math. Sometimes it is difficult to separate the concept from the math ...

Certainly our concept of cosmology (big bang to big crunch) is a mathematical concept that may or may not represent reality (whatever model you choose, it ends up with a {known universe} being a fraction of the {theoretical universe} ... a small fraction).

The universe is normally considered "infinite but bounded" - so it is conceptually closer to a circle than a line. An expanding circle if you will.

Of course by the mathematical concept the surface of the earth is an infinite surface (has infinite non-dimensional points on it), the "surface" of the sun could be considered an expanding and contracting envelope with an infinite number of non-dimensional points on it, but we have no trouble with considering their boundaries, nor to consider that the total number of sub-atomic particles that make up either (or the whole body in question), while being astronomical in number, are not infinite.

The mathematical concepts fail to depict the reality. They can assist our thinking and obstruct it.

If we live in an infinite universe would it be reasonable to think that what existed at T=0 was infinite energy?

Not necessarily - it could be zero {energy\matter}, and that everything we see is a temporary differentiation of {original null state} into {+/-energy and +/-matter ... (including gravity as -energy IIRC) where sum=0}

Or sum = ~0 ... and the original {cause} involved {part} of {something} and we cannot {see\touch\feel\smell\hear\conceive} the rest.

my 2cents worth.

It will be interesting to see Cavediver, Son Goku, et al with their responses.

Enjoy.


Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
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RebelAAmericanOZen[Deist
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This message is a reply to:
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nwr
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Posts: 5586
From: Geneva, Illinois
Joined: 08-08-2005


Message 3 of 60 (334515)
07-23-2006 12:55 PM
Reply to: Message 1 by GDR
07-23-2006 11:56 AM


It doesn't matter
If somebody had drawn a sphere, or radius 200 light years, around me at the time I was born, then pretty much everything that could affect me during my life depended only on what was inside that sphere.

We deal with finite data. We make mathematical models of the universe that are consistent with that data. If our model is of an infinite universe (or of a finite but very large universe), that is a matter of extrapolating from the evidence known to us.

It is generally known within mathematics that interpolation usually works pretty well, even if imperfect; extrapolation is a lot riskier.

We test our models by making predictions, and seeing whether they hold. But the predictions are all within that 200 light year sphere that I mentioned (our immediate space-time neighborhood). Since the model was designed to work well for our space-time neighborhood, this is expected. It doesn't really tell us whether our gross extrapolation is also correct. But since it make correct predictions in our own space-time neighborhood, that is surely enough for the theory to be a very useful explanation.

In summary, it really doesn't matter.


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cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 4 of 60 (334517)
07-23-2006 1:11 PM
Reply to: Message 1 by GDR
07-23-2006 11:56 AM


Gotta be brief, so just to start:

What is the definition of a universe?

I would go with EVERYTHING, i.e. the sum total of any multi-verse type idea. The Universe from the Big Bang could be all there is to it. Or the Big Bang could actually be a "nucleation" from a parent universe, and there may be an infinite number of such nucleations occuring in parallel. Or the universe could be cyclical in an oscillating universe type of thing. But it's only worth considering the largest "covering"-verse.

{Aside: Though there may be an infinite regress of "covering"-verses!!! Or even better, a cyclical set of "covering"-verses... there was an awesome cartoon in one of the old Humour threads with an astronaut who crash-lands on his own head :D }

Edited by cavediver, : No reason given.

Edited by cavediver, : No reason given.


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RAZD
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Posts: 20120
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.8


Message 5 of 60 (334520)
07-23-2006 1:22 PM
Reply to: Message 4 by cavediver
07-23-2006 1:11 PM


I would go with EVERYTHING, ...

A comedian (Bill Cosby?) once defined infinite as

"Everything ... plus a whole lot more ... "


Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
by our ability to understand

RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


This message is a reply to:
 Message 4 by cavediver, posted 07-23-2006 1:11 PM cavediver has not yet responded

  
cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 6 of 60 (334523)
07-23-2006 1:31 PM
Reply to: Message 3 by nwr
07-23-2006 12:55 PM


Re: It doesn't matter
But the predictions are all within that 200 light year sphere that I mentioned... Since the model was designed to work well for our space-time neighborhood, this is expected

Our model of the Universe is based upon observations of isotropy and homogeniety, both observed in the billions of lyr range... And the "stars" of greatest test of GR, the binary pulsar measurements, are substantially further away than 200 lyrs

In summary, it really doesn't matter.

If we were only worried about things that "mattered", cosmology would have died long ago!


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 Message 7 by nwr, posted 07-23-2006 1:36 PM cavediver has responded

  
nwr
Member
Posts: 5586
From: Geneva, Illinois
Joined: 08-08-2005


Message 7 of 60 (334525)
07-23-2006 1:36 PM
Reply to: Message 6 by cavediver
07-23-2006 1:31 PM


Re: It doesn't matter
Our model of the Universe is based upon observations of isotropy and homogeniety, both observed in the billions of lyr range... And the "stars" of greatest test of GR, the binary pulsar measurements, are substantially further away than 200 lyrs

The photons, by virtue of which we are able to make such observations, were already within that 200ly radius at the time I was born.

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 Message 8 by cavediver, posted 07-23-2006 1:43 PM nwr has responded

  
cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 8 of 60 (334527)
07-23-2006 1:43 PM
Reply to: Message 7 by nwr
07-23-2006 1:36 PM


Re: It doesn't matter
The photons, by virtue of which we are able to make such observations, were already within that 200ly radius at the time I was born.

I thought that must be what you meant... I would say that believing what those photons show is one of our safer extrapolations, unless you really think God invented them all 6000 yrs ago ;)


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Replies to this message:
 Message 9 by lfen, posted 07-23-2006 2:46 PM cavediver has not yet responded
 Message 10 by nwr, posted 07-23-2006 4:24 PM cavediver has responded

  
lfen
Member (Idle past 2937 days)
Posts: 2189
From: Oregon
Joined: 06-24-2004


Message 9 of 60 (334535)
07-23-2006 2:46 PM
Reply to: Message 8 by cavediver
07-23-2006 1:43 PM


Re: It doesn't matter
unless you really think God invented them all 6000 yrs ago

He has an odd sense of humor doesn't he? He wants followers who will pick out one religion and one interpretation from all the rest and then be willing not to be taken in by the elaborate hoax put in place by God for just this purpose so that by believing an ancient myth and figuring out the true age of the universe they will not be dissuaded by the apparent age which is heavily evidenced. Quite a selection process. Why not just use his omniscience to pick the blind believers from all the rest?

My conclusion is either God went insane in the lonely eternity before he came up with the idea of creating humans or that Paul and his cronies were a little funny in the head.

I guess fragmenting into multiple personalities didn't provide God with sufficient companionship and so he wants worshippers who will believe whatever he tells them and so this test separates the sheep from the goats, that is those who think vs. those who blindly obey. But why he would create people who can think and then consign the lot of them to hell because of a design failure revealed in the Garden of Eden, saving only those who are willing to stop thinking and do as they are told? Sounds like God is a collosal egotist only loving those who will fawn all over him and punishing in a rage those who don't suck up to him.

As religion amply demonstrates we live in our imaginations. Are they infinite? Could we patiently keep doing science and see what we discover? At this point except in mathematics haven't we found we are always dealing with finite quantites no matter how large? Maybe this is all we can say at present?

lfen


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nwr
Member
Posts: 5586
From: Geneva, Illinois
Joined: 08-08-2005


Message 10 of 60 (334550)
07-23-2006 4:24 PM
Reply to: Message 8 by cavediver
07-23-2006 1:43 PM


Re: It doesn't matter
I would say that believing what those photons show is one of our safer extrapolations, ..

I don't have a problem with that. But expecting to deduce that there must have been a creator, or that there must not have been a creator, takes the extrapolation further than the evidence can stretch.

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cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 11 of 60 (334552)
07-23-2006 4:45 PM
Reply to: Message 10 by nwr
07-23-2006 4:24 PM


Re: It doesn't matter
But expecting to deduce that there must have been a creator

We're not though, are we? As far as I am aware, this thread is purely for discussing the possibility and implications of an infinite universe. I think I've stated my belief before: that physics can only push out the bounds of any potential creator, never prove (or even provide evidence for) such a creator.


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GDR
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Posts: 4961
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.6


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. :)

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cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 13 of 60 (334734)
07-24-2006 4:39 AM
Reply to: Message 12 by GDR
07-23-2006 5:36 PM


I still have trouble conceiving of a universe where there was point when T=0 being a universe of infinite time

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.

However, that says to me then that when scientists talk about parallel universes

This is still the same universe as I would define it.

or when they talk about every now being an eternal universe

This is going a bit far for this discussion. This is talking about the nature of time way beyond GR. I would leave this alone for now, as we are getting to conjecture upon conjecture. Let's just stick with conjecture :)


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GDR
Member
Posts: 4961
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.6


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. :frazzled: 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. :)

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cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 15 of 60 (334812)
07-24-2006 11:12 AM
Reply to: Message 14 by GDR
07-24-2006 10:45 AM


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.

Ok, I got you. The way I would look at it is that time flow is just something we experience. If anything, it is almost the definition of conciousness. From the Universe's POV there is no flow. There is just all of time, just as there is all of space. You can look at that as a circle if you like, but nothing is going around the circle; it is simply fixed. The problem comes in joining the ends, becasue although it would be nice to think of the end of time simply flowing back into the beginning of time, there is the problem of entropy. The universe is in a very different state at the BC than at the BB.

The problem as I see it with that scenario is that appears to me to require the Big Crunch.

True.

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.

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.

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?

Awesome question :D I've never herad that one before! The answer is yes and no. 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.


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