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Does a finite universe make sense to you?

by epkid08
Tags: finite, sense, universe
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MiltMeyers
#109
Jul4-08, 03:19 PM
P: 32
Marcus I disagree and believe that space time is something. It is a quantum foam were virtual particle pop in and out of existence. It is what "Blew up" in the beginning and is still expanding with each passing day. ST consists of at least 4 dimensions and more I'm almost sure. The matter we see around us in in the far past was carried to were it is by ST in the beginning and now as it exspanses. ST has zero point energy and can create matter even now. As it in the beginning created matter and anti matter which may have repealed each other by gravity. This created neutrinoes which condensed into Hydrogen and some helium. The creation of matter from ST is still going on. In the beginning ST exspanded faster than light and that is how the temparature of ST is the same all over the viewable universe. Before ST there was nothing and that means time before the initial impulse function of space time was nothing. Zip nada nothing. Now that said, I stand in respect of what you have to say Marcus so don't rain down fire and brim stone on me. Also forgive my spelling as I only passed English 101 with a C and alway drew the red undrerlined comment SPELLING. Ahhhhh memories.
marcus
#110
Jul4-08, 07:28 PM
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Milt did you see the recent Scientific American article about spacetime foam and the emergence of classical deSitter spacetime at large scale (from the micro-scale foam)?

The people who are farthest along with computer models of spacetime foam are Renate Loll's group at Utrecht and their collaborators (Athens, Tokyo, Reykjavik, Warsaw, Copenhagen etc.)

it's a strong group. You should know about their work if you are interested in the quest to find out what space time and matter are made of----what the fundamental degrees of freedom are. Maybe things can be made out of pure geometry (includng topology)---pure relationship and interconnection. I wouldn't exclude the possibility.

anyway they do computer modeling of quantum spacetime-----and big averages like Feynman path integrals, where they average up many random quantum spacetimes. Even the dimensionality of the spacetime is up for grabs and not always the same.

the article is available free, if you follow a link at Renate Loll's website.
http://www.phys.uu.nl/~loll/Web/title/title.html
Or you can read it in the July 2008 Scientific American.

========
BTW I don't think you contradicted what the Einstein quotes said. All the things you mentioned can take place in the context of the gravitational field. they don't require a new kind of material called space in which to occur, they don't require space to have object-like reality so that it expands and more is created etc.---all the things people say about it here when they think of it as a substance.

the things you mentioned, events, occur without question, I am saying that points of space don't have to have an independent existence so that these events can occur at those points. there can simply be a web of distance relation and other geometric relations----mere information. Isn't that enough for the things you mentioned to take place in that context? Or do you insist on more? Be careful or Occam will get you
=============

About brimstone. that is the Mentor's job. Guru is an unofficial democratically elected annual party-hat. It rotates. Be listening to what other rankandfile non-Mentor members are saying and get an idea of who you want to elect to wear the hat next year!
In any case you wouldn't get any brimstone even if I had it to hand out.
sketchtrack
#111
Jul4-08, 07:43 PM
P: 62
There are a few things that have me confused now.

1) Is space expanding equally everywhere, or is it only expanding in between galaxies. If it is only happening between galaxies, then why?

2) When space expands, molecules occupying that space would have to either break apart as distances between the bonds increase, or it would have to expand itself, or it would have to move inwards to compensate for the distance increasing. Which of these options is thought to be correct?
marcus
#112
Jul4-08, 08:21 PM
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Quote Quote by sketchtrack View Post
There are a few things that have me confused now.

1) Is space expanding equally everywhere, or is it only expanding in between galaxies. If it is only happening between galaxies, then why?
"Space expanding" is kind of a bad phrase to use. Distances increase in the normal natural course of things according to the best model of gravity we have.

Distances within our solar system and within our galaxy are distances between gravitationally bound objects. They don't increase as part of this pattern. The pattern is only largescale distances between objects that are not bound in orbits around each other.
Even some nearby galaxies can be bound together.

so the answer is NO. not all distances expand. the Hubble law relationship is only true ON AVERAGE FOR VERY LARGE distances.

the thing is, it is amazingly regular if you look on large scale. nearly everything is receding by the same percentage amount each year.
====================

the Einstein equation of Gen Rel governs the distance function. the distance function changes constantly and dynamically and is affected by the distribution of matter.
so its behavior is not totally regular------it is the solution to a differential equation. like the surface of the ocean or the winds in the atmosphere which have their differential equations governing them.
but the expansive pattern is very close to regular (matter, which affects the distance function, is distributed roughly uniform, so the expansion at large scale is roughly uniform too.)

Mostly what the distance function is doing these days is that all the largescale distances increase about 1/140 of a percent every million years.
=====================

the Einstein equation is our theory of gravity. until we get a better theory of gravity we have to accept that the gravitational field is the distance function and it is dynamic and changing---geometry is changing (or another way: spacetime is curved)

2) When space expands, molecules occupying that space would have to either break apart as distances between the bonds increase, or it would have to expand itself, or it would have to move inwards to compensate for the distance increasing. Which of these options is thought to be correct?
If that's the choice, I'd have to say move inward.
"space expands" is an unclear phrase that often confuses people, you could try thinking in terms of distances increasing
distances between bound-together things don't increase in General Relativity. like the two ends of a stick or the two sides of a crystal. or two things in circular orbit. those distances between bound-together things do not increase

But in a borderline case I would have to say that they move inward and in
some extreme cases stuff that was gravitationally bound can come unbound. It isn't typical. Some theorical models allow for even chemical bonds to be broken like in those Big Rip scenarios. they have little to do with everyday astronomy. I tend to filter that stuff out.
The ordinary expansion of distances is very gentle and doesn't interfere with sytems held together by atomic and molecular forces. (That is why we aren't used to seeing distances between stationary things change. The distance between New York and San Francisco is more or less constant, almost.)

Wallace and Cristo are the experts about this. I trust they will correct me if I'm seriously wrong about anything.
robheus
#113
Jul5-08, 04:27 PM
P: 143
Quote Quote by marcus View Post
If that's the choice, I'd have to say move inward.
"space expands" is an unclear phrase that often confuses people, you could try thinking in terms of distances increasing
distances between bound-together things don't increase in General Relativity. like the two ends of a stick or the two sides of a crystal. or two things in circular orbit. those distances between bound-together things do not increase

But in a borderline case I would have to say that they move inward and in
some extreme cases stuff that was gravitationally bound can come unbound. It isn't typical. Some theorical models allow for even chemical bonds to be broken like in those Big Rip scenarios. they have little to do with everyday astronomy. I tend to filter that stuff out.
The ordinary expansion of distances is very gentle and doesn't interfere with sytems held together by atomic and molecular forces. (That is why we aren't used to seeing distances between stationary things change. The distance between New York and San Francisco is more or less constant, almost.)

Wallace and Cristo are the experts about this. I trust they will correct me if I'm seriously wrong about anything.
I have also always struggled with this (esp. if you are used to the ontological definition of space as merely distance relations between objects) and in most (popular) descriptions, the issues related to that (why only space expansion at large scales and not at small scales) are often not mentioned, side-stepped as not important, or only briefly mentioned and which we then have to take at faith value.

What is important of course first is that it is well-established (in the context of GR) what "space" is.
In the Newtonian sense, space is not "something". So, expansion of space or two bodies moving from each other can not be distringuished.
In GR it is taken that those are different notions of reality (which would lead to "space" being something, i.e. "some form of aether"). Yet, on the other hand, there is no "absolute frame of reference" acc. to GR.

All of this together however is not very obvious and seemingly contradictionary.
Would GR somehow say that - energetically - distantiating two bodies from each other (two far away galaxies) is somehow different in case of:
1. Two bodies moving "in" space and receding from each other
2. Two bodies stationary in (local) space, but with the space between them expading

Further, if normal stuff (molecules) etc. have to somehow compensate for the (local) expansion of space, wouldn't that mean that this produces energy? (at least that is the case for gravitational bound objects).

WRT terminology, in cosmology the expanding of space (in distinction with movement in space) is often termed as expansion of the spacetime metric and/or references as the increase of the scale factor
ThomasT
#114
Jul7-08, 02:50 PM
P: 1,414
Quote Quote by epkid08 View Post
Starting from any point in the universe, shine light in all directions; given infinite time has passed, will it have reached the edge of the universe?
Infinite time isn't a physically meaningful term. Would light emitted in any direction ever reach the boundary of a bounded universe that is expanding at the speed of light? Is that a meaningful question? I don't know.


Quote Quote by epkid08 View Post
It doesn't make sense to me to define the universe as finite, as there is no edge of the universe to cross.
How might we possibly ascertain that the universe is or isn't bounded?


Quote Quote by epkid08 View Post
You could imagine the universe shaped like a sphere, and traveling a constant distance in a straight path would eventually get you back to your original position, but still you would never reach the edge of the universe.
I do imagine it as an isotropically expanding 3D sphere, with us and everything else that constitutes the contents of the universe inside the boundary surface of the sphere. So, if you travel any distance in a straight line, then you will end up somewhere other than where you began.

Quote Quote by epkid08 View Post
At the border of our universe lies a dimensionless quantity.
Or, maybe it's the expanding front of the big wave that defines the border of our universe.

Quote Quote by epkid08 View Post
What are your thoughts?
That, except for the evidence of apparent expansion, it's pretty much all speculative -- but interesting nonetheless.
eg180
#115
Jul7-08, 03:28 PM
P: 2
Quote Quote by BoomBoom View Post

I think that is why many ideas proposed by string theorists (multi-verses, parallel dimensions, etc.) seem so far off in "left-field" because they seem to ONLY see the math without any observation or logic to back it up.


Thank "God" many of the scientist that came before us didn't let what would appear to be "logical" hinder progressive ideas and fledgling theories that eventually were given more credence. When you think about it, we are the oddballs of the universe - things don't often go past light speed and our temperatures, densities, and velocities are quite mild in comparison with the universe's quite volatile, and violent nature. It is not surprising that our common sense fails to grasp the true universe...our common sense does NOT represent reality.
DaveC426913
#116
Jul7-08, 03:38 PM
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Quote Quote by eg180 View Post
...our temperatures, densities, and velocities are quite mild in comparison with the universe's quite volatile, and violent nature. It is not surprising that our common sense fails to grasp the true universe...our common sense does NOT represent reality.
Well said. This is something I find myself repeating over and over to people who think that our physical universe has to make common sense.
eg180
#117
Jul7-08, 04:03 PM
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Quote Quote by DaveC426913 View Post
Well said. This is something I find myself repeating over and over to people who think that our physical universe has to make common sense.
Hey, Dave. I'm new here and I am by no means a scholar or well versed in physics or cosmology - I've just recently found a fascination with quantum physics/cosmology, etc at 28 years old, when I wish I would have been exposed to this in my early teens. (I was raised in a fundamentalist Christian household, so these topics rarely came up, unless they were in the form of a bible verse. ("In the beginning God created the heavens and the Earth..etc.)

I hope to learn a lot from everyone on this board. It's great to find an outlet on the net for these things that I've only recently become fascinated with. I'm only a pupil but it's never too late to learn. (I guess it would help if I were good at math though.) :)
BoomBoom
#118
Jul7-08, 04:12 PM
P: 293
Quote Quote by eg180 View Post
Thank "God" many of the scientist that came before us didn't let what would appear to be "logical" hinder progressive ideas and fledgling theories that eventually were given more credence.
I agree with this statement. Logic builds on knowledge and what may seem logical in one era may seem a foolish notion to a subsequent era. The old logic is replaced with new logic as knowledge is acquired.
But, generally speaking, things that do not make logical sense often turn out to be untrue. I have no doubt that future generations will look back on some of the cosmology theories of the turn of the 21st century (especially pertaining to string theory) and say, "now that's just silly...what were they thinking?".
DaveC426913
#119
Jul7-08, 10:10 PM
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Quote Quote by eg180 View Post
Hey, Dave. I'm new here and I am by no means a scholar or well versed in physics or cosmology - I've just recently found a fascination with quantum physics/cosmology, etc at 28 years old, when I wish I would have been exposed to this in my early teens.
I have no education in science since high school myself. All my knowledge is self-gained. It's never too late.
MiltMeyers
#120
Jul8-08, 12:08 AM
P: 32
Glad to hear we are all about equal in knowledge. Now let me restate. that as we look out to a time and distance of the cosmic background that it fills the sky in every direction that we look. The universe is much smaller then and all directions we travel will take us back to that time. Now go beyound that event back to the singularity and it also would be in every direction we can go. So now I ask you what direction would you go to get to the edge of space time? To escape we need a new dimension a 5D but our universe is only 4D. I've always thought that space time was exspanding at C but of course the matter was at a slower rate. The real noodle problem is that we are in the oldest state of the universe and so is every man women or child. Any direction we go from us is back in time to a smaller universe. IE the Sun is in a universe 8 minutes smaller from were we are. This can only be if we are in a 4D sphere or bottle as I like to call it. Nothing is ever lost from it and since nothing can travel faster than light nothing is lost. Some have said that the greater the distance that the faster an object can go till it is going faster thanC, like maybe 2C. I say that that C is the limit and all you do when you add space time is lower the frequency. The faster an object goes fromus the lower the frequency and that is why the back ground is in the microwave range. That is why the red shift. That is the way I see things so feel free to jump in and straighten me out.
DaveC426913
#121
Jul8-08, 08:27 AM
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Quote Quote by MiltMeyers View Post
Glad to hear we are all about equal in knowledge. Now let me restate. that as we look out to a time and distance of the cosmic background that it fills the sky in every direction that we look. The universe is much smaller then and all directions we travel will take us back to that time.
You are confusing travelling with looking. When we look outward we see back in time, but we can't travel there.
mysearch
#122
Jul8-08, 10:05 AM
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I have only quickly read through all the contributions, so apologises if my point has been raised before and I missed it. However, I was wondering whether a finite universe would have a gravitational centre of mass?

When Newton first came up with his theory of gravitation, he was unsure whether gravity acted with respect to the surface or centre of mass. Subsequently, he formulated what has become known as the Newton’s Shells:
http://en.wikipedia.org/wiki/Shell_theorem

However, the flip side of this theorem shows that a particle within the cavity, surrounded by a uniform shell, would feel no net force of gravity, or possible spacetime curvature is more exact according to GR. However, the question being raised is whether an infinite universe would act as an infinite thick shell to any point in the visible universe and thus have no centre of gravity? While, in contrast, a finite universe must have some form of centre of gravity? Just a thought.
MiltMeyers
#123
Jul8-08, 11:14 AM
P: 32
Dave Yes I agree and what I should have said if we could travel instantaneously which we can't but it is a way to describe what we see as that is the shape of the universe. It was late and I'm really not a bright bulb.

Mysearch, the only thing like a center is the spot were the singularity was and it is now spread all over the universe so my answer, if you care is there is no center. You have to visualize a 4d sphere and that is very hard, to see what I mean. So the universe has no center and no outside and nothing before the initial singularity.
mysearch
#124
Jul8-08, 12:25 PM
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the only thing like a center is the spot were the singularity was and it is now spread all over the universe so my answer, if you care is there is no center. You have to visualize a 4d sphere and that is very hard, to see what I mean. So the universe has no center and no outside and nothing before the initial singularity.
I am not pretending that I know the actual answer, but would be genuinely interested in how a 4D-sphere changes the basic physics of gravitation. Newton’s shell theorem provides some tangible mechanism by which gravity might cancel out in an infinite universe, but not a finite universe. While Newton's laws of gravity are superseded by GR, I believe Newton’s basic laws still applied in this case. The terms centre of gravitational mass may be misleading as it is really only referring to a point corresponding to the net resultant of all gravitational forces/curvature in a finite universe. So my response is really just another question:

How does a finite 4D sphere explain there being no centre of gravitation?
DaveC426913
#125
Jul8-08, 12:52 PM
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Quote Quote by mysearch View Post
Newton’s shell theorem provides some tangible mechanism by which gravity might cancel out in an infinite universe, but not a finite universe.
You need to specify one more qualifier: boundary.

A finite bounded universe will have a bias in gravity, a finit but unbounded universe will not.
mysearch
#126
Jul8-08, 01:13 PM
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Hi, accept the implication of the correction, but do not understand why. Can you qualify your statement about a "finite but unbounded universe" with any reference that explains the physics? Again, this is intended as a genuine inquiry and not as a smart-arse response. Thanks


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