Does a finite universe make sense to you?

marcus

Sounds like you have made up your mind already on some of these issues
But the first scholarly book on the subject Beyond the Big Bang isn't due to be published until March 1 of 2009. It will have chapters written by leading experts about the various ideas and it will include some you just mentioned.

You might be jumping the gun. This thing is just beginning to get the focus of scientific attention it deserves and studying conditions around the big bang (by whatever means can be devised) is going to be high on the scientific agenda for the next 10 years or so for sure.
Might be good to withhold judgment for a while longer. Hear what the various ideas are, and what various other people say.

marcus

Doesn't make sense to me. Space is not a substance or material that needs to be produced. The words you use make it sound like a material.
I try to avoid using the words "expansion of space". Distances increase, that's all.

Nothing is created, nothing swells up, or stretches, or rises like yeasty bread-dough. Distances just increase.

There are no new distances that have to be made somehow---it's the same old distances as always---just that many of them, the longrange ones, increase by some percentage per year on average.
Like money in your savings account

BoomBoom

I must confess that this is an issue I have the most problems with comprehending.

As distances increase the result is more space in between the matter than was there before, yet at the same time it is said that the matter does not travel THROUGH space. It seems to me that the matter MUST be travelling through empty space for the amount of space to increase. Space is, after all, nothing....and the percentage of nothing is continually increasing.

marcus

Here is a thread with some quotes from Einstein.
http://www.physicsforums.com/showthread.php?p=1386960
Let's see if we can pinpoint the source of confusion with their help.

Here's post #24 by George Jones
http://www.physicsforums.com/showthr...55#post1386555
It has an interesting Einstein quote.

then I contributed #25 which has the following:
==quote==
“Dadurch verlieren Zeit & Raum den letzter Rest von physikalischer Realität. ..."

“Thereby time and space lose the last vestige of physical reality”.

(To try to paraphrase, I guess you could say space does not have physical existence, but is more like a bunch of relationships between events)

In case anyone wants an online source, see page 43 of this pdf at a University of Minnesota website
http://www.tc.umn.edu/~janss011/pdf%...Besso-memo.pdf

"...
...In the introduction of the paper on the perihelion motion presented on 18 November 1915, Einstein wrote about the assumption of general covariance “by which time and space are robbed of the last trace of objective reality” (“durch welche Zeit und Raum der letzten Spur objektiver Realität beraubt werden,” Einstein 1915b, 831). In a letter to Schlick, he again wrote about general covariance that
“thereby time and space lose the last vestige of physical reality” (“Dadurch verlieren Zeit & Raum den letzter Rest von physikalischer Realität.” Einstein to Moritz Schlick, 14 December 1915 [CPAE 8, Doc. 165]).
..."

Both quotes are from Nov-Dec 1915, one being from a paper on perihelion motion. and the other from a letter to Moritz Schlick a few weeks later.
==endquote==

One way to say the significance is you have to wean your mind away from thinking in the English language and focus on the distance function, the metric. And even more, focus on the web of distance relationships between events.

Events, like the collision between particles A and B, like the arrival of a flash of light at a telescope on Mount Palomar.
Maybe events are more real than points in space. Maybe, as Einstein suggested, points in space have no physical reality.
Only events and the relations (like distance) between events have objective reality.

In General Relativity, the gravitational field IS A METRIC, a distance function that allows you to compute distances between events.
It is nothing else besides the metric. And the metric set of distances determines the geometry (gravity is geometry, so the metric can serve as gravity, which is what he makes it do.)

It is a very economical theory. There is nothing extra, that one could do without. (Even more economical than I've said. Even the metric is boiled down. Two that are the same except for trivial differences are treated as one. All equivalent ones lumped together. All redundancy is gotten rid of.)

So he says, don't believe in the existence of space and time. Believe in the field---the relationships between events---for example, distances.

when someone says space expands, don't believe them, don't even listen to them. think: the DISTANCES are expanding.
the expansion is seen in the metric---the distance function---and nowhere else because space has not even a shred of phsical reality so there is nowhere else for the expansion to be make itself evident.

Learn to use your confusion. Discover what is the focus of it, what intensifies your confusion. Maybe these Einstein quotes can help distill the essence of it for you.

The spoken languages were invented by primitive tribesmen. There are some things if you insist on thinking purely in words you will always be misled.

BoomBoom

Nice post Marcus...that was helpful.

It does seem that a problem is the misleading words. But these words are continually used by many trying to describe an expanding universe. It is certainly no wonder why there is so much confusion with the subject.

sketchtrack

My intuition wants me to think that space isn't expanding, and things are just moving apart through space. Is the reason that that idea is false because our theory of gravity tells us that galaxies have no physical reason to be moving the way they would need to be?

MiltMeyers

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

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

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

"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)

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

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

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.


How might we possibly ascertain that the universe is or isn't bounded?


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.

Or, maybe it's the expanding front of the big wave that defines the border of our universe.

That, except for the evidence of apparent expansion, it's pretty much all speculative -- but interesting nonetheless.

eg180

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

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

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

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

I have no education in science since high school myself. All my knowledge is self-gained. It's never too late.