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Does a finite universe make sense to you? 
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#109
Jul408, 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 As it in the beginning created matter and anti matter which may have repealed each other by gravity.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.



#110
Jul408, 07:28 PM

Astronomy
Sci Advisor
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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 microscale 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 ofwhat 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 spacetimeand 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 objectlike 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 relationsmere 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 partyhat. It rotates. Be listening to what other rankandfile nonMentor 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. 


#111
Jul408, 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? 


#112
Jul408, 08:21 PM

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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 regularit 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 changinggeometry is changing (or another way: spacetime is curved) "space expands" is an unclear phrase that often confuses people, you could try thinking in terms of distances increasing distances between boundtogether 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 boundtogether 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. 


#113
Jul508, 04:27 PM

P: 143

What is important of course first is that it is wellestablished (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 


#114
Jul708, 02:50 PM

P: 1,414




#115
Jul708, 03:28 PM

P: 2

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. 


#116
Jul708, 03:38 PM

P: 15,319




#117
Jul708, 04:03 PM

P: 2

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.) :) 


#118
Jul708, 04:12 PM

P: 293

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?". 


#119
Jul708, 10:10 PM

P: 15,319




#120
Jul808, 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.



#121
Jul808, 08:27 AM

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#122
Jul808, 10:05 AM

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P: 522

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. 


#123
Jul808, 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. 


#124
Jul808, 12:25 PM

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P: 522

How does a finite 4D sphere explain there being no centre of gravitation? 


#125
Jul808, 12:52 PM

P: 15,319

A finite bounded universe will have a bias in gravity, a finit but unbounded universe will not. 


#126
Jul808, 01:13 PM

PF Gold
P: 522

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 smartarse response. Thanks



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