Is universe finite or infinite?

[goodoldrebel]

If the universe is finite then what is beyond? If infinite then how can humanity conceive the 'big picture'?

 

[cepheid]

We have an FAQ page for this: https://www.physicsforums.com/showthread.php?t=506986

 

[Farahday]

We have an FAQ page for this: https://www.physicsforums.com/showthread.php?t=506986

cite: "Standard cosmological models come in three flavors, open, flat, and closed,[Carroll] whose spatial curvatures are negative, zero, and positive. The open and flat types have infinite spatial volume. The closed one has finite spatial volume; spatially, it is the three-dimensional analog of the surface of a sphere. Since all three are solutions to the Einstein field equations, the finiteness or infiniteness of the universe is something that cannot be determined solely by logic but only by observation.

Current observations of the cosmic microwave background's anisotropy show that our universe is very nearly flat.[Komatsu] If it is exactly flat, then it is a special case lying on the boundary between the more general open and closed cases. However, the range of uncertainty in the curvature is wide enough to be consistent with either positive or negative curvature, so right now the finiteness or infiniteness of the universe is an open question.

Sometimes people use the word "universe" when they really mean "observable universe." The observable universe is finite in volume because light has only had a finite time to travel since the Big Bang."

May we presume the cosmological model is using the first definition and not the second?

 

[cepheid]

May we presume the cosmological model is using the first definition and not the second?

Yes, the theoretical models are for all of spacetime, not just the portion of it that we can see.

To elaborate on the OPs question about boundaries and what exists beyond them. The answer is that nothing exists beyond the boundaries, because there are no boundaries. In the standard models, if the universe is finite, then it is unbounded, meaning that it has no edges. This is made possible by spatial curvature. An analogy is a two-dimensional being living on the surface of a sphere. This surface has a finite area, and yet it has no edges for the being to reach. If the being travels far enough in any direction, it will end up back where it started.

 

[Farahday]

Yes, the theoretical models are for all of spacetime, not just the portion of it that we can see.

To elaborate on the OPs question about boundaries and what exists beyond them. The answer is that nothing exists beyond the boundaries, because there are no boundaries. In the standard models, if the universe is finite, then it is unbounded, meaning that it has no edges. This is made possible by spatial curvature. An analogy is a two-dimensional being living on the surface of a sphere. This surface has a finite area, and yet it has no edges for the being to reach. If the being travels far enough in any direction, it will end up back where it started.

I see. Then does there exist some point in the "whole of the universe" at which some object within a finite distance that was moving away from me is now moving toward me or does the rate of expansion preclude that from happening? And if that is the case, then wouldn't the rate of expansion have to exceed 'C' in order to preclude neutrinos from doubling back - thus invalidating Einstein (if neutrinos haven't already done that)?

 

[Mark M]

I see. Then does there exist some point in the "whole of the universe" at which some object within a finite distance that was moving away from me is now moving toward me or does the rate of expansion preclude that from happening? And if that is the case, then wouldn't the rate of expansion have to exceed 'C' in order to preclude neutrinos from doubling back - thus invalidating Einstein (if neutrinos haven't already done that)?

When talking about the expansion of the universe, you must specify two points, so a sufficiently far object will be receding much faster than light. But remember, general relativity puts no limit the expansion of the universe, just the observers within it. Also, neutrinos do NOT move faster than light. That is impossible, though they move very close.

 

[goodoldrebel]

Yes, the theoretical models are for all of spacetime, not just the portion of it that we can see.

To elaborate on the OPs question about boundaries and what exists beyond them. The answer is that nothing exists beyond the boundaries, because there are no boundaries. In the standard models, if the universe is finite, then it is unbounded, meaning that it has no edges. This is made possible by spatial curvature. An analogy is a two-dimensional being living on the surface of a sphere. This surface has a finite area, and yet it has no edges for the being to reach. If the being travels far enough in any direction, it will end up back where it started.

Yet, a two-dimensional theory does not directly address the question. Pinning 'no beginning and no ending' on "Spatial curvature" does not solve the three dimensionality dilemma of the infinite universe

 

[Farahday]

When talking about the expansion of the universe, you must specify two points, so a sufficiently far object will be receding much faster than light. But remember, general relativity puts no limit the expansion of the universe, just the observers within it. Also, neutrinos do NOT move faster than light. That is impossible, though they move very close.

Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)? Certainly if the cosmos is only 13+billion light years in size, there must be some calclation as to the rate of expansion from t=1...or is it possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?

Also in some speculative models, Neutrinos have a tachyonic nature and travel faster than 'C'. Those Lorentz violating variants of quantum gravity are part of the Standard-Model Extension.

Also mass is just a condition - readily exchangeable with energy. Only those things with the property of mass are subject to the speed limit.

 

[cepheid]

Yet, a two-dimensional theory does not directly address the question. Pinning 'no beginning and no ending' on "Spatial curvature" does not solve the three dimensionality dilemma of the infinite universe

The theory itself is not two-dimensional. It is a full description of the four dimensions of spacetime that employs the idea of curvature and non-Euclidean geometry. In other words, saying that you live in a closed universe is saying that, in this universe, geometry doesn't behave like the way you learned in school. In a closed universe, parallel lines eventually meet. The sum of the three angles of a triangle is greater than 180 degrees. If you travel far enough in any given direction, you'll end up back where you started. So the geometry in this curved 3D space is analogous to the geometry on a curved 2D surface. I was using a direct lower-dimensional analogy to give you a way to visualize the implications of this curvature in the higher-dimensional case.

 

[goodoldrebel]

Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)? Certainly if the cosmos is only 13+billion light years in size, there must be some calclation as to the rate of expansion from t=1...or is it possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?

Also in some speculative models, Neutrinos have a tachyonic nature and travel faster than 'C'. Those Lorentz violating variants of quantum gravity are part of the Standard-Model Extension.

Also mass is just a condition - readily exchangeable with energy. Only those things with the property of mass are subject to the speed limit.

Two excellent points. I presume the calculated age reflects 'detectable' data.

 

[goodoldrebel]

The theory itself is not two-dimensional. It is a full description of the four dimensions of spacetime that employs the idea of curvature and non-Euclidean geometry. In other words, saying that you live in a closed universe is saying that, in this universe, geometry doesn't behave like the way you learned in school. In a closed universe, parallel lines eventually meet. The sum of the three angles of a triangle is greater than 180 degrees. If you travel far enough in any given direction, you'll end up back where you started. So the geometry in this curved 3D space is analogous to the geometry on a curved 2D surface. I was using a direct lower-dimensional analogy to give you a way to visualize the implications of this curvature in the higher-dimensional case.

Can you detail a bit more about three-dimensional universe curvature as it relates to infinitely? Many thanks.

 

[cepheid]

Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)?

It is unclear here what you mean by "no limit." If you mean that the expansion will continue forever, then that is the view that is currently supported by the best observational data.

In the simplified picture that was described in the FAQ page I linked to above, there is a direct relationship between the geometry of the universe (which is determined by its mass-energy content) and the ultimate fate of the universe. For the closed model, the universe is closed because there is enough mass to provide enough positive spatial curvature. It turns out that this critical amount of mass also determines whether the universe's expansion will continue forever, or if it will eventually slow down, and then reverse, leading to the universe recollapsing in a so-called "Big Crunch."

Since the condition for the universe being closed is that it has greater than the critical amount (or actually density) of matter, the conclusion is that closed universes will recollapse, whereas flat and open universe, which have (respectively) just equal to, and less than the critical density of matter, will continue to expand forever (albeit at an ever decreasing rate).

What muddles up this simplified picture is the presence of dark energy. In particular, dark energy breaks this simple relationship between the geometry of the universe, and its ultimate fate. It is possible for even a spatially-closed universe with dark energy to continue to expand forever, due to the repulsive effect that that dark energy tends to have.

In any case, the observational data currently support a universe with dark energy whose expansion rate is increasing and that will therefore continue to expand forever. Observations show that the geometry of the universe is very close to spatially flat (i.e. Euclidean).

Certainly if the cosmos is only 13+billion light years in size,

The universe is not merely 13 billion ly in size, not even the observable portion of it. See here: https://www.physicsforums.com/showthread.php?t=506987 for an explanation why.

Also in some speculative models, Neutrinos have a tachyonic nature and travel faster than 'C'. Those Lorentz violating variants of quantum gravity are part of the Standard-Model Extension.

Highly speculative models. I had thought that tachyons were the name for a new theorized particle that was capable of traveling faster than light. (As as opposed to an adjective used to described faster than light neutrinos). I had also thought that the theory that proposed the existence of tachyons had mostly been ruled out. Furthermore, there is no ONE single extension to the Standard Model of particle physics. This is an area of active research, and many different theories are attempting to achieve such an extension.

Also mass is just a condition - readily exchangeable with energy. Only those things with the property of mass are subject to the speed limit.

I don't know if I'd call it a "condition", but rather a property of matter. I do agree that it is interchangeable with energy. I also agree that only massive particles are restricted to speed less than c by Special Relativity. I'm just not sure what your point is.

 

[cepheid]

possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?

The age of the universe is NOT estimated based on the size of the observable portion of it. It is determined independently through other observational means.

 

[Farahday]

Two excellent points. I presume the calculated age reflects 'detectable' data.

Thank you.

I must; however, admit I am somewhat skeptical about the validity of expansion related red shift. Would it not seem reasonable to assume if a body is moving away at high velocity that its signature - width of its apparent diameter and strength of signal or luminocity - should also evidence a correspoding dimunition? I know of no such corroborating data or evidence.

Any links you might provide would be appreciated.

 

[cepheid]

years in size, there must be some calclation as to the rate of expansion from t=1.

Yes, there is. See here:

http://en.wikipedia.org/wiki/Friedmann_equations

 

[cepheid]

Can you detail a bit more about three-dimensional universe curvature as it relates to infinitely? Many thanks.

It's unclear what you're asking. But as described in the first FAQ page that I linked to, only the models with a closed spherical geometry are spatially finite. These are the models with positive curvature. The 2D analogy for them is the surface of a sphere.

Models with a flat geometry would be spatially infinite. The 2D analogy for them would be a flat infinite plane.

Models with open geometry (also called hyperbolic geometry) would also be spatially infinite. The 2D analogy for them would be an infinite 2D surface shaped somewhat like a "saddle."

See the first figure in this article:

http://en.wikipedia.org/wiki/Shape_of_the_Universe

 

[cepheid]

Thank you.

I must; however, admit I am somewhat skeptical about the validity of expansion related red shift. Would it not seem reasonable to assume if a body is moving away at high velocity that its signature - width of its apparent diameter and strength of signal or luminocity - should also evidence a correspoding dimunition? I know of no such corroborating data or evidence.

Any links you might provide would be appreciated.

*Sigh*

I have no idea what you mean by the part in bold, so I cannot address your specific objection. However, we have an FAQ page for this as well. This is the third cosmology FAQ article that I have linked to this thread:

https://www.physicsforums.com/showthread.php?t=506994

Maybe you just check out all of them first, and then come back with questions:

https://www.physicsforums.com/forumdisplay.php?f=206

 

[Farahday]

The age of the universe is NOT estimated based on the size of the observable portion of it. It is determined independently through other observational means.

Yes CMB not light. 13+B light years of it may be calculable, but that is the limit of our ability to detect, not necessarily the limit of the phenomenon. Any observations we might make are limited by our technology, not the nature of the cosmos.

 

[Mark M]

Hmmmmm. So there is no limit to the expansion. Could it therefore be or have been infinite (no limit)? Certainly if the cosmos is only 13+billion light years in size, there must be some calclation as to the rate of expansion from t=1...or is it possible we can only detect 13+B light years of data...which would render the age approximation of the cosmos moot?

The estimate of the age of the universe at 13.7 billion years is correct, we know this. But, it is non-relativistic. If an observer was around at the time of the big bang he would most certainly measure the universe as having a different age on his watch. This is why in eternal inflation, there can be many infinitely large bubble universes.

When an observer falls into a black hole, (we'll call him 'A') another observer in flat space ('B') sees him slowing down due to gravitational time dilation, until he reaches the event horizon, when B will say A is moving infinitely slow. So while A says a finite amount of time passed during his fall, B would say it is infinite. Similarly an observer inside an inflating region of spacetime will say that time is flowing infinitely slow - allowing his region to become infinite in spatial extent.

Alan Guth actually did the calculation, and showed it is possible.(though I can't find his paper!)

But in regard to your original question, 13 billion years is the completely objective age of the universe, and is correct.

 

[cepheid]

Yes CMB not light. 13+B light years of it may be calculable, but that is the limit of our ability to detect, not necessarily the limit of the phenomenon. Any observations we might make are limited by our technology, not the nature of the cosmos.

No. If you think that the determination of the age of the universe using the CMB is based on the measurement of the redshift/distance out to the CMB (which is the farthest out we can see), then you are mistaken.

How it's actually done is that the distribution (i.e. power spectrum) of the angular sizes of the statistical temperature fluctuations of the CMB is used to measure the values of the cosmological model parameters including H₀, Ω₀, Ω_Λ. The age of the universe is a parameter that can be derived from these fundamental ones.

Just to be clear: the different models all stem from the same underlying theory. How they differ is in the values of the model parameters, which lead to different spatial geometry and expansion history. What the observations enable us to do is to measure the values of these quantities in nature, thereby determining which of the specific models best describes the universe.

 

[Farahday]

*Sigh*

I have no idea what you mean by the part in bold, so I cannot address your specific objection. However, we have an FAQ page for this as well. This is the third cosmology FAQ article that I have linked to this thread:

https://www.physicsforums.com/showthread.php?t=506994

Maybe you just check out all of them first, and then come back with questions:

https://www.physicsforums.com/forumdisplay.php?f=206

Thanx for the link, but I saw no references that might tell me where to find observational data that receding galaxies are dimming at a rate appropriate to their predicted velocities relative to us. I would consider such observations to be crucial in support of expansion redshift theory. Do you have a specific link you might suggest that covers this?

 

[goodoldrebel]

Thank you.

I must; however, admit I am somewhat skeptical about the validity of expansion related red shift. Would it not seem reasonable to assume if a body is moving away at high velocity that its signature - width of its apparent diameter and strength of signal or luminocity - should also evidence a correspoding dimunition? I know of no such corroborating data or evidence.

Any links you might provide would be appreciated.

Are you referring to more than just time dilation?

 

[cepheid]

Thanx for the link, but I saw no references that might tell me where to find observational data that receding galaxies are dimming at a rate appropriate to their predicted velocities relative to us. I would consider such observations to be crucial in support of expansion redshift theory. Do you have a specific link you might suggest that covers this?

I can supply such a link, but first I need to explain some background. Luminiosity is the term in astronomy for the rate at which an object outputs energy (in the form of light or EM radiation). So luminosity is measured in watts (or, more typically, in units of "sun luminosities"). Luminosity distance is a distance measure in cosmology that is made by assuming that the inverse square law for the dimming of light is true. In other words, if you compare the apparent brightness of an object (how much light you receive from it per unit area and per unit time) to the intrinsic brightness of that object (its luminosity), and you assume the inverse square law is true, then you can infer a distance to that object. The distance you infer is called the "luminosity distance." The luminosity distance is a distance measure that is based on how bright an object appears.

Now, any given cosmological model predicts a definite relationship between the luminosity distance to an object and the redshift of that object. This relationship is basically the one that you are asking about above. Different models (i.e. with different parameters) predict different curves for this relationship. If you have something that is of a known intrinsic luminosity (a so called "standard candle"), then you can figure out its luminosity distance. You can also figure out its redshift through spectroscopy. This gives a way of determining the actual measured relationship between luminosity distance and redshift. You can then go and fit a theoretical curve to the data (i.e. you can see which model best matches the observations).

For reasons I won't get into here, Type Ia supernovae are thought to be such a standard candle. In other words, they are all thought to have the same luminosity. (It is actually slightly more complicated than this, but that is the basic idea). There is a paper by Perlmutter et al. 1999

http://iopscience.iop.org/0004-637X/517/2/565/pdf/39148.web.pdf

that shows (figure 2) essentially apparent brightness (which equivalent to luminosity distance) vs. redishift for a large number of supernovae from a couple of different supernova surveys. The data strongly favour a particular cosmological model in which the density of "dark energy" is non-zero. This is some of the first observational evidence for accelerated expansion. This, of course, is just one (very notable) example of a measurement of apparent brightness vs. redshift and comparison to theory.

EDIT: Figures 7 and 9 from that paper are really neat too. They make great summaries of how where you are (in parameter space) affects various things (like curvature, expansion history/future, and acceleration).

 

[Farahday]

I can supply such a link, but first I need to explain some background. Luminiosity is the term in astronomy for the rate at which an object outputs energy (in the form of light or EM radiation). So luminosity is measured in watts (or, more typically, in units of "sun luminosities"). Luminosity distance is a distance measure in cosmology that is made by assuming that the inverse square law for the dimming of light is true. In other words, if you compare the apparent brightness of an object (how much light you receive from it per unit area and per unit time) to the intrinsic brightness of that object (its luminosity), and you assume the inverse square law is true, then you can infer a distance to that object. The distance you infer is called the "luminosity distance." The luminosity distance is a distance measure that is based on how bright an object appears.

Now, any given cosmological model predicts a definite relationship between the luminosity distance to an object and the redshift of that object. This relationship is basically the one that you are asking about above. Different models (i.e. with different parameters) predict different curves for this relationship. If you have something that is of a known intrinsic luminosity (a so called "standard candle"), then you can figure out its luminosity distance. You can also figure out its redshift through spectroscopy. This gives a way of determining the actual measured relationship between luminosity distance and redshift. You can then go and fit a theoretical curve to the data (i.e. you can see which model best matches the observations).

For reasons I won't get into here, Type Ia supernovae are thought to be such a standard candle. In other words, they are all thought to have the same luminosity. (It is actually slightly more complicated than this, but that is the basic idea). There is a paper by Perlmutter et al. 1999

http://iopscience.iop.org/0004-637X/517/2/565/pdf/39148.web.pdf

that shows (figure 2) essentially apparent brightness (which equivalent to luminosity distance) vs. redishift for a large number of supernovae from a couple of different supernova surveys. The data strongly favour a particular cosmological model in which the density of "dark energy" is non-zero. This is some of the first observational evidence for accelerated expansion. This, of course, is just one (very notable) example of a measurement of apparent brightness vs. redshift and comparison to theory.

EDIT: Figures 7 and 9 from that paper are really neat too. They make great summaries of how where you are (in parameter space) affects various things (like curvature, expansion history/future, and acceleration).

Cepheid -

APPLAUSE!

I thank you for the link. It certainly identifies all the problems involved in trying to calculate the effect of vast distances of ambient matter on fragile light waves - and the vagarities of dealing with somewhat unknown quantities - high and low redshift supernovas which, themselves, redden over time. As an observer of ardent perspective (infinite and eternal cosoms) it has reminded me modern cosmology deals with statistical probability rather than iron-clad fact and the multiple interpretations therefrom are not so much dogma as they are data based. They link those probabilities to a large number of variables - known variables. I would suggest the number of unknown variables is vastly larger.

Cite: "the data are strongly inconsistent with the flat universe model that has been the theoretically favored cosmology. If the simplest inflationary theories are correct and the universe is spatially flat, then the supernova data imply that there is a significant, positive cosmological constant. Thus the universe may be flat or there may be little or no cosmological constant, but the data are not consistent with both possibilities simultaneously. This is the most unambiguous result of the current data set."

While I remain unconvinced, at least I can see where the interpretation comes from.

A cow trying to learn calculus
Jack (BS - of course)

 

[Farahday]

Are you referring to more than just time dilation?

Things change slower in the presence of mass (gravity). Kind of gives a mystical property to time, but then all kinds of things effect rates of change.

When two masses approach each other, the space between them shrinks...ever thought about the possibility it might be just that simple. Not the masses acting on each other, but on space itself - lessening the density/volume? Things can only directly alter the condition of other things with which they are in contact...further change is called propagation.

 

[goodoldrebel]

Things change slower in the presence of mass (gravity). Kind of gives a mystical property to time, but then all kinds of things effect rates of change.

When two masses approach each other, the space between them shrinks...ever thought about the possibility it might be just that simple. Not the masses acting on each other, but on space itself - lessening the density/volume? Things can only directly alter the condition of other things with which they are in contact...further change is called propagation.

Technically, we reject Newtonian mechanics as they relate to time, length and mass at speeds < the speed of light even though differences are infinitesimal.

 

[cepheid]

I thank you for the link. It certainly identifies all the problems involved in trying to calculate the effect of vast distances of ambient matter on fragile light waves - and the vagarities of dealing with somewhat unknown quantities - high and low redshift supernovas which, themselves, redden over time.

Look no offence, but it is unclear to me again what exactly you are trying to say here, nor does it seem as though you have said anything coherent at all. I'm not sure what you mean when you say that supernovae themselves redden over time. Keep in mind that a supernova is visible for something like a few days at the most, and its light curve (brightness vs. time) has a pretty well-defined shape. It would be accurate to say that, over that period, it first brightens, reaches a peak, and then dims. But I don't know what you mean about it reddening.

Yes, some supernovae are observed at high redshift, and others at low redshift. What of it? The fact that they are visible out to cosmological distances is what makes them useful as standard candles for testing cosmological models in the first place.

As an observer of ardent perspective (infinite and eternal cosoms) it has reminded me modern cosmology deals with statistical probability rather than iron-clad

Actually, most cosmologists would say that in the last decade we finally entered the era of "precision cosmology" in which we were able to test models and measure parameters of the universe with unprecedented precision (beyond our wildest dreams, before this time, really). Cosmology has long since left the realm of mere speculation. In many areas, we have exquisite agreement between theory and observational data sets, including big bang nucleosynthesis, structure formation, and the thermal history of the early universe, to name a few.

fact and the multiple interpretations therefrom are not so much dogma as they are data based.

Again, I don't understand what you are getting at here. ALL science is data-based. It should never be dogmatic. We don't cling to theories that don't agree with experiment, no matter how elegant or mathematically-beautiful or philosophically-satisfying they are.

Maybe you're trying to say that cosmology is only "phenomenological." In other words, in analogy with Kepler's laws before Newton, we understand that this is how things work, because we have observed it empirically, but we have no underlying theory that can explain why those laws are true. If that is what you are trying to say, then I would refute that point. The underlying theoretical framework is General Relativity (which in turn has been confirmed ridiculously well by experiment, time and time again), and all of our observations are able to be explained by a cosmological model that comes directly from that theoretical framework (general relativity). The model is not an ad hoc model that we just "guessed" or "fudged" to be in agreement with observations. The model is based on that deep underlying physics of Einstein.

They link those probabilities to a large number of variables - known variables. I would suggest the number of unknown variables is vastly larger.

Again, you are guilty of making a statement that is just too vague to really be meaningful.

Cite: "the data are strongly inconsistent with the flat universe model that has been the theoretically favored cosmology. If the simplest inflationary theories are correct and the universe is spatially flat, then the supernova data imply that there is a significant, positive cosmological constant. Thus the universe may be flat or there may be little or no cosmological constant, but the data are not consistent with both possibilities simultaneously. This is the most unambiguous result of the current data set."

While I remain unconvinced, at least I can see where the interpretation comes from.

All the statement that you have quoted is saying is that either the data support a flat universe with non-zero cosmological constant, or a highly-curved universe with no cosmological constant. So I'm unsure of what it is that you are "not convinced" about. Bear in mind that this paper marks some of the first observational evidence for dark energy. As I alluded to before, we've come a long way since 1999. These results have been subsequently confirmed by a) more supernovae measurements b) CMB observations , and c) observations of baryon acoustic oscillations. These three independent observational data sets completely confirm (and much more precisely measure) the non-zero value of the cosmological constant that was hinted at in this early paper. Data from (b) are particularly worthy of mention. After nine years of WMAP data, there is very little question remaining about the values of the cosmological parameters. We've reached what is known as a "concordance" model (one with values for parameters that are in concordance with multiple data sets). All we're really doing now with our wealth of data is steadily reducing the size of the error bars on those parameter estimations. I'm not trying to say that there are no unanswered questions in cosmology. There are many unanswered questions. I'm just saying that questions such as the value of the cosmological constant, (and the values of other parameters and things you can derive from them like the age, expansion history, and geometry of the universe) are not among them.

 

[granpa]

the map is not the territory.

it may seem in your head that time and space should go on forever but that's just the map in your head.

the territory itself is entirely finite in both time and space

 

[Drakkith]

Things change slower in the presence of mass (gravity). Kind of gives a mystical property to time, but then all kinds of things effect rates of change.

The only things I'm aware of that change time are relative velocity and mass.

When two masses approach each other, the space between them shrinks...ever thought about the possibility it might be just that simple.

Spacetime does not shrink. It is altered in a way that is commonly called curvature.

Not the masses acting on each other, but on space itself - lessening the density/volume?

What?

Things can only directly alter the condition of other things with which they are in contact...further change is called propagation.

There is no such thing as "direct contact" the way you are imagining it. When I press my finger into a key on the keyboard, there is space between the key and the atoms in my finger due to repulsive electromagnetic force between electrons.

 

[GeorgeDishman]

Thanx for the link, but I saw no references that might tell me where to find observational data that receding galaxies are dimming at a rate appropriate to their predicted velocities relative to us. I would consider such observations to be crucial in support of expansion redshift theory. Do you have a specific link you might suggest that covers this?

In addition to the links you have been given already, I think the Tolman Test is relevant to your question. This brief article gives an overview and the reference at the bottom lists several papers on actual tests:

http://en.wikipedia.org/wiki/Tolman_surface_brightness_test

 

[granpa]

http://supernova.lbl.gov/

https://forums.craigslist.org/?ID=201719435

 

[lostprophets]

if infinite means growing quicker than you can measure then yes infinite is possible.
if it is growing then i see (without fact) that its a spiral growth
if its finite that would mean an overlap which kinda makes it infinite..
or an finite inward spiral..
i kinda feel that there's at least 3.or 3 parts to 1
all guess work and my thoughts on the question.

 

[DWEdmondson]

if infinite means growing quicker than you can measure then yes infinite is possible.
if it is growing then i see (without fact) that its a spiral growth
if its finite that would mean an overlap which kinda makes it infinite..
or an finite inward spiral..
i kinda feel that there's at least 3.or 3 parts to 1
all guess work and my thoughts on the question.

My thoughts are more along the line of infinite 3D spirals of infinite size in either direction...if you can get your head around that!
Can someone show me how to express that mathematically??

p.s. by "3D SPIRAL" I mean a spherical spiral with the diminishing point at the centre and all other infinite spirals having the same common diminishing point

 

[GeorgeDishman]

It is useful to qualify the term to avoid ambiguity, will the universe last for an infinite time or is space of infinite size at any particular time. I'll assume you are asking about the latter.

if infinite means growing quicker than you can measure then yes infinite is possible.

It does not mean that, it means that that no matter how far you travel, you will not find yourself in a region you have already traversed.

if it is growing then i see (without fact) that its a spiral growth

The expansion of the universe is a linear scaling, it grows in all directions at the same rate (currently roughly 1% per 200 million years).

if its finite that would mean an overlap which kinda makes it infinite..

It would wrap round so you start passing through regions you have already seen.