The universe could be infinite in spatial volume and matter content. T or F?

[Klaynos]

If it isn't infinite what is it expanding into?

[YT2095]

empty, unoccupied by Anything, Space.

 

just Space, not Space/time, just Space.

[Klaynos]

Space implies a coordinate set, what is inside this space? without time how can something be expanding into it?

[YT2095]

Coord`s = Outside the Universe.

 

Contents = Zero

 

as for the rest, Time only happens when this Void becomes occupied (moved into).

[Klaynos]

for a concept of moved into something has to be changing with time... on the boundry...

[YT2095]

Void Space is neither Big nor small, it`s sum total = Nothing but it also surrounds Everything.

 

now I`m not saying it Doesn`t have Contents! but they are Not part of This universe.

Time exists When something moves into it, but only relative to itself!

and in this case that means our Universe.

[Martin]

In case anyone wants, I think a rather nice 49 page review or survey of modern cosmology just came out. I haven't read it all, just glanced at parts, but the guy is a top expert (Eric Linder), and an old hand with long experience, and the review article was invited by a reputable series of annual reports. they picked him to do it, and he put a fair amount of work into it.

 

so it might give useful perspective. I can't recommend really because I havent examined carefully.

 

http://arxiv.org/abs/0801.2968

Mapping the Cosmological Expansion

Eric V. Linder

49 pages, 29 figures; Review invited for Reports on Progress in Physics

(Submitted on 18 Jan 2008)

 

"The ability to map the cosmological expansion has developed enormously, spurred by the turning point one decade ago of the discovery of cosmic acceleration. The standard model of cosmology has shifted from a matter dominated, standard gravity, decelerating expansion to the present search for the origin of acceleration in the cosmic expansion. We present a wide ranging review of the tools, challenges, and physical interpretations. The tools include direct measures of cosmic scales through Type Ia supernova luminosity distances, and angular distance scales of baryon acoustic oscillation and cosmic microwave background density perturbations, as well as indirect probes such as the effect of cosmic expansion on the growth of matter density fluctuations. Accurate mapping of the expansion requires understanding of systematic uncertainties in both the measurements and the theoretical framework, but the result will give important clues to the nature of the physics behind accelerating expansion and to the fate of the universe."

[dichotomy]

If 3D space includes the universe and everything beyond it, I’d say true.

3D space is more likely to be infinite. It would be illogical if 3D space is a ‘box’ that is finite. I can believe an expanding ‘box’ that is expanding into something. I’d find it impossible to believe that there isn’t space outside of that ‘box’. If our Universe is one fixed finite box, then it is a box within a box, ad infinitum.

 

If space is matter, then yes, matter in its various forms is infinite too.

[Martin]

3D space is more likely to be infinite. It would be illogical if 3D space is a ‘box’ that is finite..

 

It is good you can imagine infinite 3D space. But don't get hung up on the idea of a BOX. A box image is seen as contained in larger surroundings. That is not how finite 3D space is normally modeled.

 

I can believe an expanding ‘box’ that is expanding into something. I’d find it impossible to believe that there isn’t space outside of that ‘box’.

 

You seem to almost get it, but not entirely. The word "expanding" may be confusing you. Think of your infinite 3D space and think of it expanding in the sense of internally---distances between points in the space are increasing.

 

There is no outside to infinite 3D space, so it is impossible to visualize it expanding looked at from the outside. There are no boundaries moving outwards. The expansion is all within.

 

The expansion looks the same at every point in the infinite 3D space. Picture it as uniform internal expansion throughout.

 

If 3D space includes the universe and everything beyond it, I’d say true.

 

here you sound confused again. the universe is everything that physically exists. the words "beyond it" are meaningless. the universe has no outer physical boundary. That is the ordinary concept of it.

 

When that idea is modeled mathematically (which is what we are talking about since cosmology studies mathematical models of the universe, not verbal models) then this boundaryless allinclusive space can be either finite or infinite volume.

matter is coextensive, roughly uniformly distributed throughout, in the usual picture. so if space is finite volume, the total amount of matter is finite, and if space is infinite volume, the total matter is infinite.

 

if for some reason you are unable to imagine a boundaryless allinclusive space which is finite volume, then you should only imaging space as your infinite 3D space that you CAN imagine (of course with an infinite amount of matter uniformly distributed throughout).

 

If you can't imagine the finite case, then concentrate on the infinite case and at least get that right.

 

(the finite case is a 3D sphere analog, which some people find hard to imagine living in---it may be better to do what you can do than try to do what you can't and keep getting confused)

[losfomot]

(the finite case is a 3D sphere analog, which some people find hard to imagine living in---it may be better to do what you can do than try to do what you can't and keep getting confused)

 

When you say 'some people find hard to imagine living in' you do not mean that some people can actually picture this do you? Or do you just mean that some people can accept the 3-sphere analog concept.

[Martin]

When you say 'some people find hard to imagine living in' you do not mean that some people can actually picture this do you? Or do you just mean that some people can accept the 3-sphere analog concept.

 

that is a fine point Losfomot. I appreciate what you are saying.

I think it is possible to imagine what it's like to live inside S³ and explore it with your friends.

 

I mean a small 3-D space that is not expanding. So you would notice.

 

I think it is very possible that we live in a large S³ with of course some random bumps and dimples caused by local gravity. But it is hardly distinguishable from R³, essentially indistinguishable.

It is too big and expanding to ever make the circuit.

 

What I agree I can't do is imagine an entire S³ from the outside. I would have to have the imagination of a 4D being to do that. there is no outside.

 

but I can imagine a motion picture of a SLICE moving thru S³

and I can imagine living in a small nonexpanding version, say like a mile circumference, so one could do the circuit just by taking a little jaunt.

the optics would boggle me. I might have to shut my eyes or turn off the lights outside my room, to keep from getting sick or going bonkers

[losfomot]

but I can imagine a motion picture of a SLICE moving thru S³

and I can imagine living in a small nonexpanding version, say like a mile circumference, so one could do the circuit just by taking a little jaunt.

the optics would boggle me. I might have to shut my eyes or turn off the lights outside my room, to keep from getting sick or going bonkers

 

By 'circumference' and 'circuit' do you just mean going in a straight line until you come back to your starting point, or would going in a straight line feel like going around a bend?

 

Also, with a pair of binoculars, would you be able to see the back of yourself?.. if so, would it matter what direction you looked in?

 

(These questions are pertaining to the 'mile circumference' S³)

[thedarkshade]

If there was infinite matter, there would be no space. You cannot have infinite matter taking up infinite space, there is either more of one or the other and obviously there is more space.

Universe is infinite (at least we all seem to think that way)! And because it is infinite, it can stand infinite expansions, and thus in can stand infinity. Infinite matter fits in infinity too! Simply because it is located in something that is infinite!

 

There is a lot of room in infinity you know!

[Martin]

By 'circumference' and 'circuit' do you just mean going in a straight line until you come back to your starting point, or would going in a straight line feel like going around a bend?

 

Also, with a pair of binoculars, would you be able to see the back of yourself?.. if so, would it matter what direction you looked in?

 

(These questions are pertaining to the 'mile circumference' S³)

 

for me it's simpler to imagine in dim light so the optics don't bewilder me so much. going along geodesics feels like inertial motion---like drifting in zero gravity.

two people who push off from each other in opposite directions will meet at an antipodal point

if they dodge each other there and contine each sailing along they will meet back at the starting point having each done a circuit.

they each feel like they have traveled in a straight line

 

with light, and binoculars, I believe you could see yourself in focus at the antipodal point (about half a mile away if it was mile circumference) and that would be true in any direction. this boggles my imagination

 

maybe you Lofsomat have a clearer picture, or someone else can help.

 

If I try to picture bright illumination, every point of my body is scattering light in every direction, and all that light is coming back from the opposite direction having made a circuit. So I am surrounded by incoming light that is the color of the clothes I'm wearing but completely scrambled and out of focus. Maybe I am looking at thousands of tiny overlapping images of myself so that it looks like a mottled mosaic of blue denim and checkered flannel shirt fabric. For some reason it makes me feel sick. The only way I can get a focused image is to use a good pair of binoculars and look for an image of myself half a mile away (in any direction) at the antipodal point.

 

If you can correct this description of the optics please do. Moving around on geodesics seem relatively simple but the visual experience would be very strange.

 

It makes me grateful that our own universe is expanding so fast that light can never make it all the way around. So we don't have to experience this.

There are real advantages to expanding space!

[dichotomy]

It is good you can imagine infinite 3D space. But don't get hung up on the idea of a BOX. A box image is seen as contained in larger surroundings. That is not how finite 3D space is normally modeled.

 

I was just using a ‘BOX’ as a simple example. It could be any amorphous 3D shape. A spherical object did cross my mind.

 

You seem to almost get it, but not entirely. The word "expanding" may be confusing you. Think of your infinite 3D space and think of it expanding in the sense of internally---distances between points in the space are increasing.

 

There is no outside to infinite 3D space, so it is impossible to visualize it expanding looked at from the outside. There are no boundaries moving outwards. The expansion is all within.

 

The expansion looks the same at every point in the infinite 3D space. Picture it as uniform internal expansion throughout.

 

Besides on a C.A.D program on my PC V.D.U, I can’t image space expanding from within, unless it has a without. If I look at simulated digital expanding space on my VDU, I’d look around the room that my VDU is located within and this would prove that the within space needs a without space to even exist.

 

 

here you sound confused again. the universe is everything that physically exists. the words "beyond it" are meaningless. the universe has no outer physical boundary. That is the ordinary concept of it.

 

I say ‘beyond’ for the people who think the universe is a finite concept. Like there are walls at the end of it, or it’s a closed loop, or something mystical like that. If you are saying the universe is all there is, an infinite all, boundless, then I can understand and agree with this concept. Some people (backyard scientists ) seem to say that the universe is one type of 'blanket of matter' (with planets and stars, and known matter/energy, etc) and the stuff it expands into is another, as yet unknown, matter. And this I can also accept as a possibility.

 

If you can't imagine the finite case, then concentrate on the infinite case and at least get that right.

 

I can easily imagine the ‘star field simulation’ screen saver that most of us know, demonstrating infinite expanding space within a finite video monitor. But again, outside of the digital world of the monitor there is more space in the real world.

[Martin]

I was just using a ‘BOX’ as a simple example. It could be any amorphous 3D shape. A spherical object did cross my mind.

...

 

Doesnt matter if it is cubical box or a triangular pyramid box or a box round like a ball. If you are thinking box then you are not getting the idea. A box has a boundary---some kind of wall. and it has an outside.

 

the thing you have in mind is something a 3D being can look at it from the outside.

 

That cannot happen with space as modeled mathematically in normal mainstream cosmology. Space in cosmology has no outside. It has no walls, no boundary. If you can't get this, don't bother yourself about it. Just move on and think about something else besides cosmology. People differ as to what they find easy to imagine. It doesnt mean one person is better. there are just different kinds of intelligence.

[gcol]

Martin:

 

Your last couple of posts have been (unless I have misunderstood, again...) extremely illuminating. I can now visualise how space could be both infinite and finite at the same time. I am bathed in an unfocussed corpuscular glow of self-satisfaction. Ta very much.

[dichotomy]

Space in cosmology has no outside. It has no walls, no boundary.

 

Oh, I think this is absolutely true.

 

You seem to be misunderstanding me. I just don’t agree with the below statement you made. That is except if it is purely a mathematical concept that has no claims to be able to be physically reconstructed, which I think is what you are claiming –

 

"There is no outside to infinite 3D space, so it is impossible to visualize it expanding looked at from the outside. There are no boundaries moving outwards. The expansion is all within."

 

IMO, expansion just doesn’t happen without available space to expand into, no matter how impossibly fast it is occurring. Therefore, infinite space is both still and infinite. Or, if expansion is physically occurring, it is the matter and energy that we know of, but not the stuff that matter/energy is immersed in ,dark matter, or whatever it turns out to be might be what known matter is expanding into. I think I'll stick with 3D space as being infinite and still, with lots of galaxies sprinkled about for colour... for now.

 

If you can't get this, don't bother yourself about it. Just move on and think about something else besides cosmology. People differ as to what they find easy to imagine. It doesnt mean one person is better. there are just different kinds of intelligence.

 

Thanks mom!

[Martin]

...

 

IMO, expansion just doesn’t happen without available space to expand into, no matter how impossibly fast it is occurring.

 

Be a little more explicit about this.

In standard cosmology, since like 1923, expansion DOES happen without available space to expand into. So you are opposing your view to that of several generations of cosmologists.

 

It's your opinion (even though I know of no evidence to support you view) so why not?

 

What I'm curious about is this. Is this your opinion because:

 

A. you can't imagine expansion without some surrounding empty space, or

 

B. you can imagine it as a possibility but it is your opinion that it just is not happening?

[YT2095]

or C: there is a Void Space unoccupied, that we are expanding into.

 

Void Space, for our Physics friends would be that space that was there Before the Big Bang happened, but we just haven`t expanded into.

yet.

[losfomot]

two people who push off from each other in opposite directions will meet at an antipodal point

if they dodge each other there and contine each sailing along they will meet back at the starting point having each done a circuit.

 

I believe you could see yourself in focus at the antipodal point (about half a mile away if it was mile circumference) and that would be true in any direction.

 

I don't think both these statements can be true regarding the 'antipodal point'. If the first statement is correct (which I suspect), then the second statement should be changed to something like:

 

'I believe you could see yourself in focus about a mile away (if it is a mile circumference) and that would be true in any direction.'

 

And as far as the optics... I would describe it as being like you were surrounded by one solid fun-house mirror that was all wavy... some parts stretched, some parts compressed... except in a mirror your image is facing you, in an s^3 you would be facing away from yourself.

 

By the way, thank you Martin. I appreciate you taking your time to explain some of this stuff. And the links are great too.

[dichotomy]

 

A. you can't imagine expansion without some surrounding empty space

 

No I can't, because I have never observed this happening, have you?

 

I can imagine this if I am standing inside an expanding an invisible rubber balloon, observing the walls moving away from me with special glasses. But logic and experience tell my mind that outside of that balloon there must be space for the expansion to move into, even though I cannot see this whilst I'm inside of the balloon.

 

So are you saying because we can't see outside of that balloon that there is no possibility of an outside existing?

 

or C: there is a Void Space unoccupied, that we are expanding into.

 

Void Space, for our Physics friends would be that space that was there Before the Big Bang happened, but we just haven`t expanded into.

yet.

 

I can totally understand and visualise this. If there is expansion there must be a void space, or some other medium to either,

a. expand into.

b. push further away.

c. consume

 

If there is no expansion involved it is just still infinite space, with bits within it that expand and move, like solar systems and things getting sucked into blackholes.

[Martin]

...

I can imagine this if I am standing inside an expanding an invisible rubber balloon, observing the walls moving away from me with special glasses. But logic and experience tell my mind that outside of that balloon there must be space for the expansion to move into, even though I cannot see this whilst I'm inside of the balloon.

...

 

You brought up the balloon analogy. People often use it in this kind of discussion. But I'm not sure you are picturing it in the way folks normally do.

 

the usual balloon analogy would have you be a 2D being confined to the skin of the balloon.

 

except for the fact that a real balloon is embedded in our usual 3D space (as lower dimensional illustrations have to be, for us 3D creatures) ----except for that fact there does not need to be anything inside the balloon or outside it.

 

there is no center of expansion in the 2D space experienced and explored by the 2D creature living in it.

 

so the 2D creature experiences expansion internally, simply because stationary points are getting farther away from each other

 

Notice there is no receding wall or boundary to the creature's space.

 

that is how people normally use the balloon as an illustration---maybe you know this and are consciously using it in a different way.

[Anu-Ki Ptah]

If space is a boundless finite volume then the amount of matter is finite as well.

 

In neither the finite or infinite case is there any edge or boundary to space, and since the region occupied by matter coincides with the whole of space there is no edge or boundary to the occupied volume either.

 

the question of space infinite or finite has not been resolved yet.

 

What is your opinion? Do you think space volume could be infinite?

 

Well It is my OPINION on the matter of Boundless Time/Space Continuum that is in fact Not at all Boundless.

Here is why.

 

I think we have to first clear the mind of the idea of infinite 3d Space.

let's look at in in a different fashion for only a moment.

First I would like to begin with the Concept that It is space that is in fact the one sold and only solid thing in existence and all else is variable forms of energy. Simplified statement but bare with me.

So given that all forms of matter are localized particles/Waves yet still remain

on a sub-atomic level (for lack of a better Terminology) Separated by Space ..no matter how small we go things must differentiate between themselves otherwise there is no difference between an electron or a neutron and whatever else. due to electromagnetic fields repelling and pushing and difference in frequencies/Rates of vibratory Variation one form of matter (even sub-atomic matter/energy) is separated from another. So we find energy in various cluster formations.

 

In that we move outward (if we can say that accurately...) to a point ton the universe where we would begin to see that a given edge would take place..and a very peculiar spherical Shape would become apparent. but like our position on earth is relative to perspective.. so as we walk along a highway in a given direction. So wrap A hypothetical highway around the globe like an equator. then to us walking on that highway we would perceive ourselves as walking infinitely in one direction were it not for points of familiar perspective (such as landmarks) which give us a sense of location. In space however we haven't that luxury so to realize we are within a spherical construct is next to impossible in a visual sense..we have but to calculate that result based on observation of known laws and reflective value ..(Via Cluster formation) or spherical behavioral patterns of almost all things..more often than not or a given average.

 

Thats my hypothesis

[Martin]

Well It is my OPINION on the matter ... peculiar spherical Shape would become apparent. but like our position on earth is relative to perspective.. so as we walk along a highway in a given direction. So wrap A hypothetical highway around the globe like an equator. then to us walking on that highway we would perceive ourselves as walking infinitely in one direction were it not for points of familiar perspective (such as landmarks) which give us a sense of location. In space however we haven't that luxury so to realize we are within a spherical construct ...

 

Welcome Ptah,

at the level of opinion I am in agreement with you. And I think several others would agree----favoring the finite volume sphere-analog case.

 

It IS possible to do some measurment. There is a number called Omega for which the 68 percent errorbar is currently [1.010, 1.041]. If that number is exactly one then we are NOT in the spherical case like what you are talking.

 

If that number turns out to be, like, 1.01, then we are in the finitevolume case. It isnt determined yet. 68 percent is not enough certainty to say which it is.

 

So we DO have the luxury after all. We just have to send up some better instruments and measure Omega more accurately. That will be done. the WMAP mission will be follwed by the Planck mission. Eventually we will know.

 

In the finite volume case, space has no wall, no boundary, no surrounding space. Space is analogous to the surface of a sphere, but is 3D. Geometrically the name for it is written S³

and pronounced ess-three. I think what you are talking about in your post is S³ but you just aren't using the technical name for it.

 

So yeah, I think space could very well turn out to be that. But I also think that the infinite case cannot be ruled out on the basis of the data yet. the issue is not which version you prefer but which does the data point at. It isnt clear yet. 68 percent points at what you say and what I like too. But 68 percent is not enough.

 

The poll was about what it COULD be. I said it COULD be infinite, although 68 percent confidence points at the finite boundaryless case.

 

=======================

BTW just because we favor the same finite space alternative doesn't mean we come at it from the same direction. For all I know your approach may be purely mystical, or highly individualistic. But wherever you are coming from you can still end up agreeing on a few things which people who come to it by way of everyday quantitative empiricism.