Questions regarding "infinite" universe

[derekmcd]

lol, now I of course have to ask a question. I am aware that through popular theories, red shift, etc... the universe & space-time expands in volume with a given area as any volume measurement would.

First thing we need to do here is define the difference between "space" and "spacetime" in accordance with General Relativity. Space is a metric based on distance. Spacetime is a metric defined by events within space. Spacetime does not expand.

but like all volume measurements, there is something it expands into (ie. a flask, a box, etc...) whatever the case may be. Volume is measured by how full something is, which leads me to believe there is an actual border somewhere to the universe. Whether another form of space-time, a void, or the sandbox of a giant baby alien exists containing the universe or housing it's enormous bubble from the beyond. Wouldn't the conception of volume require a containment area to be measured within? or is it merely the estimated distance to which we believe the Big bang occurred the only method we use for measuring the area in which the volume is measured? (make sense?) Also, if the universe is expanding by volume in a given area, and a planet existed close to the edge of this area, could they theoretically see beyond the edge of the universe with powerful telescopes as we can see +13.7 Billion ly's from our current location?

When cosmologists speak of a volume, it is defined by the finite speed of light. It can be described with basic geometry, but the volume that cosmologist ascribe it to does not have a physical, tangible boundary. It's a visible boundary only. Rather similar to the horizons on Earth depending on where you choose to map it. Instead of the finite speed of light defining your volume, you must define your volume based on the curvature of the earth and what you are capable of visually defining.

 

[michaelmozina]

No Michael, as usual you are skewing things toward the lunatic fringe. It is not hotly debated among the competent.

The paper I cited and the author I cited beg to differ with you DrRocket. Since you've not personally isolated or identified any specific problem in his mathematical presentations or any of his work, I can only assume that your use of the term "lunatic fringe" is another of those less than ethical debate tactics to skew things your way and to take cheap shots at those you disagree with.

These fringe ideas are not based on science and should be confined to The Unexplained where they belong.

Why do you feed the need to control even legitimate debate complete with real mathematical and physical presentations? You might take a lesson from speedfreek. His rebuttals are done with real "papers" and include mathematical rebuttals along with physical explanations of that rebuttal. I'm still working my way through his full rebuttal in fact. This is "standard operating procedure" in real science and typical of a real scientific debate. Debate is healthy, particularly when it done the right way. Your way is to "attack the messenger" and to stifle debate entirely. That's not science, that's religion.

The inability to measure the expansion of space in an earth-bound laboratory is totally irrelevant.

It may be "irrelevant" to you personally and to others as well, but it is not totally irrelevant to everyone including the author I cited, nor to me personally. Since there does seem to be a viable way to explain the redshift phenomenon *without* resorting to superluminal "acts of faith", I see no reason to simply "assume" that "space" expands as you do. Your complete inability to demonstrate this idea in a controlled experiment also makes the skeptic in me wince.

How about you at least do us the favor of isolating the specific mathematical or physical problem in the paper I cited and explain to us why it's a problem in your opinion, and why you know that "Space" is expanding in spite of his simpler mathematical and physical alternatives.

The effects of the expansion are predicted by models of the universe based on general relativity (yes, Einstein's general relativity as practiced by he man himself),

His constant was set to "zero". Yours is not. The "cause" of this deviation from Einstein's GR has never been identified.

and the expansion is supported by a mountain of EMPIRICAL observational data. Even Hannes Alfven himself recognized the value of a need for careful in situ observational measurements and knoew that not all experiments can take place in an earth-bound laboratory. Your position to the contrary is neither rational nor scientific.

Huh? Hannes Alfven built on the work of Birkeland, all of which is based on "empirical testing" of concept. He agreed with none of your beliefs about cosmology, and most of mine. Please resist the urge to lecture me about Alfven or the scientific method. You don't have a leg to stand on.

I am quite aware that you will dispute all of this . We have been here before. But I also recognize that you have no idea what you are talking about and that your are pushing your personal agenda. Unfortunately that agenda has the potential to do harm to people like the OP who are trying to actually learn something about science.

In religion, they worry about "guiding the flock" and making sure nobody is "confused" by debate. Is that your agenda here as well?

If the universe is finite in age, and it began as a finite size, it must today have a finite size as well. The last time I asked you, you claimed the whole universe was once smaller than a breadbox (I think it was "less than 3cm" as I recall). That implies "finite size" and "finite age" and therefore it must still have a "finite size".

 

[michaelmozina]

First thing we need to do here is define the difference between "space" and "spacetime" in accordance with General Relativity. Space is a metric based on distance. Spacetime is a metric defined by events within space. Spacetime does not expand.

That seems to be the crux of the debate.

 

[DrRocket]

The authors question is viable. What exactly might "expand" in empty space?

It is space that expands. But that requires some explanation.

General relativity is a purely deterministic theory. You can argue that a correct theory would not be deterministic but that is a different subject. The problem here is an interpretation of expansion within the confines of general relativity. So, it is important as a starting point that we recognize that general relativity is deterministic, completely deterministic.

Space-time, the entire manifold is the entire universe, and not just space, it contains the entire history of the universe -- past, present, and future. It we had access to the whole thing there were be no mystery about the future and no uncertainty with regard to history and the past. EVERYTHING is determined in the space-time manifold. We obviously only get to see a tiny portion of the whole enchilada.

Space-time doesn't expand. It can't. That would require it to change over time and all of time is already part of it. Space-time contains all of space and all of time, and worse yet they are mixed together and not separable. That is what happens with curvature, and that is why there is relativity of simultaneity. There is no universal notion of time and no universal notion of space.

But cosmologists have a way of separating time from space. If one makes the assumption of the cosmological principle -- that the universe is homogeneous and isotropic -- then it is possible to realize the space-time manifold as a foliation by a one-parameter family of space-like hypersurfaces. It then turns out that those hypersurfaces are spaces of constant curvature and by some results from differential geometry can be classified. When cosmologists speak of "space" they mean those space-like hypersurfaces or "space-like slices". The one-parameter that indexes the foliation serves as "time". Each space-like slice inherits from the Lorentzian metric of the full space-time manifold a positive-definite Riemannian metric, which provides a means of measuring distance in the normal fashion (being positive-definite is defines a "metric" in the usual topological sense of a distance function, which the Lorentzian metric of the full space-time does not}. Okay, so now you have a useful definition of "space" and on that space a useful definition of distance' You can also relate coordinates one space-like slice to those on another space-like slice, and hence can see distance change between "fixed points n space" as the indexing parameter, "time" changes. Expansion of space is simply a statement that the distance between "fixed points" increases over "time" as reflected in the metric that is used to measure distance. It is important to note that the metric is defined by a tensor field and therefore is a local concept. One ruler does not work throughout the space-time manifold., but rather you are given a ruler for each point and it only measures accurately near that point.

So what is expanding is space. If you laid out grid coordinates on space then you would see the grid grow. but your would not see it grow in a laboratory on earth. Why not? The expansion of space is defined by the (local) that is used to measure distance. That metric is determined by solutions to the Einstein field equations. Basically what general relativity is all about is the problem of solving for the metric given the distribution of matter and energy in the universe. The equations provide a solution in which space is expanding, on large scales. But in regions in which there is significant mass, the gravitational field prevents the expansions of space. The local solution for the metric simply does not exhibit expansion when other forces counter the tendency to expand.

So "expansion of space" means that in regions with no significant gravitational field that points move apart in time, as measured with the local metric. It is really an expansion of space itself and not an expansion of anything material within space.

 

[michaelmozina]

Space-time, the entire manifold is the entire universe, and not just space,

Isn't "space" a part of "spacetime" as well?

it contains the entire history of the universe -- past, present, and future. It we had access to the whole thing there were be no mystery about the future and no uncertainty with regard to history and the past. EVERYTHING is determined in the space-time manifold. We obviously only get to see a tiny portion of the whole enchilada.

Ok.

Space-time doesn't expand.

That seems to be the part that is in debate.

It can't.

Of course it can. Objects in motion stay in motion and as long as the objects that makeup spacetime "expand" away from a central point, "spacetime" can certainly "expand".

That would require it to change over time and all of time is already part of it.

Change over time would allow objects to "spread out" and to "expand" away from one another would it not?

Space-time contains all of space and all of time, and worse yet they are mixed together and not separable. That is what happens with curvature, and that is why there is relativity of simultaneity. There is no universal notion of time and no universal notion of space.

But somehow you "separate" them when you claim "space" expands?

But cosmologists have a way of separating time from space.

How do they do that exactly? How did you decide that "space" is separate from "time" exactly?

If one makes the assumption of the cosmological principle -- that the universe is homogeneous and isotropic -- then it is possible to realize the space-time manifold as a foliation by a one-parameter family of space-like hypersurfaces.

You seem to have a hard time accepting that this particular idea is not actually a "realization", it is a "hypothetical possibility" which you have never demonstrated in any sort of controlled way. Worse yet, you could never demonstrate such a thing in any controlled way.

It then turns out that those hypersurfaces are spaces of constant curvature and by some results from differential geometry can be classified. When cosmologists speak of "space" they mean those space-like hypersurfaces or "space-like slices".

Of course "space" and time are not separated, and this is nothing but an abstract concept that has not been empirically put to any "controlled test". How did you decide that space and time can be separated in this manner?

The one-parameter that indexes the foliation serves as "time".

If "space" can change over time, why can't the "distance" (between galaxies) simply change over time as well due to simple "spacetime" expansion? Aren't you equating distance and "space" in this definition?

Each space-like slice inherits from the Lorentzian metric of the full space-time manifold a positive-definite Riemannian metric, which provides a means of measuring distance in the normal fashion (being positive-definite is defines a "metric" in the usual topological sense of a distance function,

So "space" is nothing but a distance metric and if "space" can change over time, then surely distance can simply change over time as well, no?

So "expansion of space" means that in regions with no significant gravitational field that points move apart in time, as measured with the local metric. It is really an expansion of space itself and not an expansion of anything material within space.

What is "space itself" in this definition if not simply "distance" between objects in "spacetime"?

 

[SpeedFreek]

Michael, the distinction these papers are making really is very subtle, and I feel it is not quite being fully understood here, as we are used to using the terminology in a slightly different way.

The Doc has explained in his post above, how by saying that "space itself expands" he simply means that distance has increased, which is correct. Yes, space-like slices of space-time expand, which can be simplified to saying that space is expanding, but that is not to say that it is the space "itself" is causing the expansion. The term "space is expanding" is helpful in understanding the concept, but can also be misleading if people interpret it in the wrong way. This is the point being made in "Expanding Space: The Root of all Evil?"

That seemingly quite reasonable terminology might cause unreasonable conclusions. It is true at face value, the space between two distant galaxies has grown in size, but some take it to mean the expansion of space is causing the universe to expand, rather than it being the result. It is the result of the difference between the background metrics when comparing events across space-time.

When the Doc and Derek say that space-time cannot expand, they are correct too. They are giving you a rigorous description from General Relativity. The space-like slice expands, due to the curvature of space-time. The slice is simply the way we have chosen to describe spacial coordinates. The papers that seem to say that space-time expands are putting it in those terms to mark the (some would say philosophical) difference between space-time curvature and the idea that space "itself" expands.

It is often said that the light from distant galaxies has been "stretched" by the expansion of the space it travelled through, I have said it myself many times in the past. It is a good illustration of the mechanism behind redshift and cosmological time dilation, and it is an accurate description in that any observer who co-moves with the expansion of the universe will see the wavelength of that light to be longer. The further the light has travelled through the expanding universe, the longer the wavelength that will be detected.

But the question being posed is whether anything is happening to that light because it travels through space. Is space itself expanding, stretching the light as it goes along, or is it that the metric that defines distance has changed over time, causing an apparent difference in how that light looks to us? This is the very subtle difference, if it is a difference! Are meters stretching such that 1 metre becomes 2 metres, or are more meters being introduced?

We cannot measure space without putting something in it to measure, and the reason that distant objects become more distant may not be due to something the space "itself" is doing to them. But it is also not about the difference between the "expansion of space" and kinematics. Nobody is saying the recession speeds of distant galaxies are purely relativistic Dopper effect either.

In a nutshell, all this boils down to is that we cannot actually separate space from time in any absolute way, so we have to choose a system and run with it! Are distant galaxies actually receding from us faster than light? In order to answer that, we have to be able to make a comparison using distance and time, but we know that we cannot synchronise ourselves with that distant galaxy in any way that reflects an absolute reality. We can make an idealised view using cosmological time and distance, and this tells us that for galaxies to have reached those distances, they would have been moving faster than light.

But if we consider everything at the large scales to be "lodged" within the fabric of the universe, and that fabric is stretching, then nothing is moving faster than light. We are being made more distant from other things by whatever is stretching that fabric, but nothing is moving, so special relativity and the speed of light are irrelevant. But that doesn't necessarily mean that space "itself" is stretching either. The fabric represents the "evolution" of space-time rather than expanding space.

In the context of the modern Lambda-CDM cosmology, think about the concept of a cosmological constant. It doesn't matter how much space expands, the cosmological constant stays constant. Why doesn't it "stretch" with the space, reducing its value as time passes? If it works as a "background" effect, increasing the rate at which the universe expands, is it stretching the spaces in between things, or is it introducing more space between things? Is there any difference?

 

[yevaud]

Not to mention, were it Spacetime that was expanding rather than Space, then the "value" of time would not be constant. It would be different everywhere as you traveled around, and this is clearly not the case.

 

[michaelmozina]

Not to mention, were it Spacetime that was expanding rather than Space, then the "value" of time would not be constant. It would be different everywhere as you traveled around, and this is clearly not the case.

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

In general relativity, clocks at lower potentials in a gravitational field — such as in proximity to a planet — are found to be running slower. This gravitational time dilation is only briefly mentioned in this article; see that article (and also gravitational red shift) for a more detailed discussion.

I still need to finish reading the list of paper from Speedfreek and chew on his last post for awhile, but the notion that time is "constant" is a bit of a misconception.

 

[michaelmozina]

The Doc has explained in his post above, how by saying that "space itself expands" he simply means that distance has increased, which is correct.

But the "distance" between objects can increase simply by virtue of momentum. Suggesting that the"distance" between objects changes over time is fully acceptable based on our understanding of physics. Claiming that "space expands" is quite a horse of a different color however. Objects in motion will indeed tend to stay in motion and may indeed "spread out' over time. The "distance" between objects may change over time, but the claim "space expands" is evidently not required to explain this sort of redshift phenomenon. In fairness however I still have some reading to do on that list of papers you gave me. Thus far however there seem to be some philosophical differences, and a lot of confusion about *WHY* the distance changes over time.

Yes, space-like slices of space-time expand, which can be simplified to saying that space is expanding, but that is not to say that it is the space "itself" is causing the expansion. The term "space is expanding" is helpful in understanding the concept, but can also be misleading if people interpret it in the wrong way. This is the point being made in "Expanding Space: The Root of all Evil?"

If space and distance are being used interchangeably, wouldn't it make more sense to note that "distance" is changing over time rather than "space"? I still think this notion of taking "slices" of "spacetime" and calling is "space" is highly misleading. You can't reasonably take "slices" of one half of "spacetime" because time is not constant and can pass at different rates depending on the gravitational environment.

It seems to me that the author I originally cited is chalking this redshift up to "time dilation" rather than "space expansion", is he not?

 

[harrycostas]

G'day from the land ofozzzzzzz

It seems to me that the King does not wear invisible robes.

If the universe is expanding that it must be observable.

So! Where are the observations to show that either space or spacetime is expanding?

 

[yevaud]

It was almost a given that you would raise the issue of Time-Dilation in response. It takes approximately 1.32^-22 seconds to see where you are wrong, and that you are incorrect. You are mixing and matching two distinct and mutually separate issues. We are not discussing effects on an object traveling at relativistic velocities through space, we are discussing space itself expanding. Apples and Oranges.

 

[SpeedFreek]

The Doc has explained in his post above, how by saying that "space itself expands" he simply means that distance has increased, which is correct.

But the "distance" between objects can increase simply by virtue of momentum. Suggesting that the"distance" between objects changes over time is fully acceptable based on our understanding of physics. Claiming that "space expands" is quite a horse of a different color however. Objects in motion will indeed tend to stay in motion and may indeed "spread out' over time. The "distance" between objects may change over time, but the claim "space expands" is evidently not required to explain this sort of redshift phenomenon. In fairness however I still have some reading to do on that list of papers you gave me. Thus far however there seem to be some philosophical differences, and a lot of confusion about *WHY* the distance changes over time.

The bottom line here is that nobody has been able to so far come up with a model where everything can be described purely in terms of peculiar motion and have the model conform to the cosmological principle. The Milne model is the closest so far, but fails when applied to what we have observed. So if the galaxies are receding faster, the further we look, because objects in motion stay in motion, then they are all actually in motion directly away from this very special place in the universe that we must live in - the origin point for all that motion. So how come we are still here at that origin? Why is there not a void here, if everything has actually been moving away from this point for the history of the universe?

Yes, space-like slices of space-time expand, which can be simplified to saying that space is expanding, but that is not to say that it is the space "itself" is causing the expansion. The term "space is expanding" is helpful in understanding the concept, but can also be misleading if people interpret it in the wrong way. This is the point being made in "Expanding Space: The Root of all Evil?"

If space and distance are being used interchangeably, wouldn't it make more sense to note that "distance" is changing over time rather than "space"? I still think this notion of taking "slices" of "spacetime" and calling is "space" is highly misleading. You can't reasonably take "slices" of one half of "spacetime" because time is not constant and can pass at different rates depending on the gravitational environment.

It seems to me that the author I originally cited is chalking this redshift up to "time dilation" rather than "space expansion", is he not?

Yes, time dilation due to the difference in gravitational density. But that gravitational difference is due to the expansion of the universe. My personal opinion is that he is essentially saying he has found the mechanism for cosmological redshift and it is the difference in the gravitational density of the universe then, when compared with now, so we should drop the misleading idea that light is redshifted as it travels, by the expansion of the space it is travelling through. He says the redshift is caused by everything having been made more distant from everything else. He is basically describing the difference between the background metrics of then and now and saying that the change in reference frames accounts for the redshift.

It comes from the analysis of a possibly misleading view - that the expansion of space is somehow "pushing" everything apart, and stretching the photons travelling through that space as it does so. The expansion of space may be due to something that pervades all of space, or it might be nothing to do with that, it might be some other cause that has an effect on the background metric.

The idea that the motions of the galaxies can be explained purely by the idea that objects in motion stay in motion was dropped in favour of "expanding space", long before we found any evidence that the rate of expansion was accelerating as if there is a cosmological constant - expansion was adopted as soon as we found that the redshifts of distant galaxies implied superluminal recession velocities if we continued to think of it as objects simply staying in motion. Other observations, like the angular diameter distance relationship, seem to confirm that the metric that defines distance is expanding, and any attempt to attribute our observations to pure motion through space has failed so far.

 

[SpeedFreek]

So! Where are the observations to show that either space or spacetime is expanding?

Well for starters, for galaxies with redshifts higher than around z=1.5, the higher the redshift, the larger the angular diameter and therefore the closer the distance at time of emission, (objects with high redshifts were closer to us when they emitted their light, than lower redshifts objects were, when they emitted their light, in an expanding universe).

A z=7 galaxy has an angular diameter distance of 3.5 billion light years whereas a z=1.4 galaxy has an angular diameter distance of 5.7 billion light years. How can a z=7 galaxy whose light has been travelling for a very long time look like it was closer to us when it emitted its light than a z=1.4 galaxy, whose light has been redshifted a lot less?

If redshift is an indicator of how long the light from an object has been travelling, (which includes tired light!), the object whose light has been travelling longer was closer to us when it emitted its light. These observations are very difficult to explain if the universe is not expanding. The angular diameter is a good indicator of how close a galaxy was at the time the light we see was emitted. The most distant (light-travel time) galaxies look larger in the sky than galaxies whose light was emitted a lot later. So either they were a long way away and were actually really large, or they were close to us and just look large. But (simply put) a surface brightness test tells us they did not contain more mass relatively, so they must have been closer, rather than actually bigger.

Even if we completely ignore the surface brightness and conclude they were a long way away but really huge, we end up with a scenario where, if the universe were static, galaxies were initally shrinking, for around 33% of the history of the universe! We find that for the lower redshifts, objects do indeed look smaller with increasing redshift, just as one would expect. Only past a certain redshift do they start to look larger again.

But what if the motion of galaxies were purely dopplerian in nature? Well, if the galaxies are receding from us through space, the picture becomes even harder to reconcile as it implies we are actually sitting at the physical centre of an explosion of galaxies, for one thing. For everthing to have been receding faster then it emitted its light, the further away it was, and to have the fastest receding galaxies looking closer than some of the slower receding galaxies, implies either a variable speed of light, with light from distant galaxies overtaking the light from closer galaxies in order to reach us at the same time(!?) or that the faster a galaxy recedes, the smaller it will be when we see it, but only up to a certain distance, after which they inexplicably get larger again!

 

[harrycostas]

G'day from the land of ozzzz

Does it not seem funny that everything is moving away from us.

Putting little dusty Earth at the centre of it all, regardless of which direction you see.

Could redshift be an intrinsic property that gives off this error indicating that expansion is taking place.

If I'm correct than we have wasted a close to a hundred years of research.

This following links are interesting and question redshift. Thats the name of the game called science.

http://arxiv.org/abs/astro-ph/0302357

Is the present expansion of the universe really accelerating?

Authors: R. G. Vishwakarma (IUCAA)
(Submitted on 18 Feb 2003 (v1), last revised 2 Jul 2003 (this version, v3))

Abstract: The current observations are usually explained by an accelerating expansion of the present universe. However, with the present quality of the supernovae Ia data, the allowed parameter space is wide enough to accommodate the decelerating models as well. This is shown by considering a particular example of the dark energy equation-of-state $w_\phi\equiv p_\phi/\rho_\phi=-1/3$, which is equivalent to modifying the \emph{geometrical curvature} index $k$ of the standard cosmology by shifting it to $(k-\alpha)$ where $\alpha$ is a constant. The resulting decelerating model is consistent with the recent CMB observations made by WMAP, as well as, with the high redshift supernovae Ia data including SN 1997ff at $z= 1.755$. It is also consistent with the newly discovered supernovae SN 2002dc at $z=0.475$ and SN 2002dd at $z=0.95$ which have a general tendency to improve the fit.

and

http://arxiv.org/abs/0903.0866
The Physics of Cosmic Acceleration
Authors: Robert R. Caldwell, Marc Kamionkowski
(Submitted on 4 Mar 2009)

Abstract: The discovery that the cosmic expansion is accelerating has been followed by an intense theoretical and experimental response in physics and astronomy. The discovery implies that our most basic notions about how gravity work are violated on cosmological distance scales. One simple fix is the introduction of a cosmological constant into the field equations for general relativity. However, the extremely small value of the cosmological constant, relative to theoretical expectations, has led theorists to explore a wide variety of alternative explanations that involve the introduction of an exotic negative-pressure fluid or a modification of general relativity. Here we briefly review the evidence for cosmic acceleration. We then survey some of the theoretical attempts to account for it, including the cosmological constant, quintessence and its variants, mass-varying neutrinos, and modifications of general relativity, such as scalar-tensor and $f(R)$ theories and braneworld scenarios. We discuss experimental and observational tests that may allow us to distinguish between some of the theoretical ideas that have been put forward.

 

[SpeedFreek]

G'day from the land of ozzzz

Does it not seem funny that everything is moving away from us.

Putting little dusty Earth at the centre of it all, regardless of which direction you see.

Not if the cosmlogical principle is correct. It would be really odd if we were actually at the centre of things, yes, but we are not.

Could redshift be an intrinsic property that gives off this error indicating that expansion is taking place.

If I'm correct than we have wasted a close to a hundred years of research.

The idea of redshift being intrinsic has been thoroughly investigated and dismissed, see http://www.astro.ucla.edu/~wright/tiredlit.htm for more information.

This following links are interesting and question redshift. Thats the name of the game called science.

Please read the papers you are posting, as neither deny that redshift is due to the expansion of the universe. They simply question the evidence for the acceleration of that expansion (which is fair enough, the observational evidence is not outside of the error bars yet). You do not seem to understand what you are talking about, unfortunately. Both papers are simply questioning whether the expansion is accelerating or not. They do not question whether the universe is expanding, they both fully accept it.

If you want to argue whether the known expansion is accelerating or not, that is another, completely different, question.

 

[michaelmozina]

It was almost a given that you would raise the issue of Time-Dilation in response. It takes approximately 1.32^-22 seconds to see where you are wrong, and that you are incorrect. You are mixing and matching two distinct and mutually separate issues. We are not discussing effects on an object traveling at relativistic velocities through space, we are discussing space itself expanding. Apples and Oranges.

You seem to "assume" that we are necessarily discussing two different things here, but ultimately both ideas begin with the premise of a changing "distance/time" (dd/dt) between objects. The premise of the paper I cited suggests that what you are describing as the "expansion of space" can also be mathematically described as a time dilation effect and a very real movement of objects that are in fact traveling through (empty) space and moving further apart over time. The fact that "distance" might be "changing" over "time" does not necessarily require that "space expands" over time. In the paper I cited, it is "spacetime" itself that is expanding (the actual galaxies) and SR and time dilation is used to explain this same redshift effect. You percieve these to be separate concepts, but the redshift effect can be explained both ways, meaning they can be one and the same idea. The "distance" between objects is simply "changing over time" in the final analysis. The only thing that non-zero constant does in the GR formula is to increase the distance between objects it says nothing about "cause" of this expansion. Time dilation effects are in fact what the author uses to explain some of the redshift phenomenon, particularly the highly redshifted galaxies. As SpeedFreek points out, there *must* be some sort of "expansion" occurring based on the angular size of highly redshifted objects, but it's not a given that "space" (physically undefined) actually "expands". It could be "spacetime" itself that is "expanding".

 

[SpeedFreek]

The premise of the paper I cited suggests that what you are describing as the "expansion of space" can also be mathematically described as a time dilation effect and a very real movement of objects that are in fact traveling through (empty) space and moving further apart over time.

Just as long as we all understand that subtle difference I referred to earlier, and that is that the movement of objects cannot be thought of as "very real" in any global sense. You can break them down into lots of little patches of very real motion with SR, and try to stitch them together with cosmology, but you still get apparently superluminal recession speeds.

From Is space really expanding? A counterexample

"In an empty universe, ‘public-space’ recession velocities are not only superluminal for sufficiently large redshifts; they are even unbounded. Does it imply violation of special relativity in cosmology? Of course not. Apart from anything else, deriving Equation (26) we have used nothing except special relativity! Constancy of the speed of light, and subluminality of the motion of massive bodies, applies only to inertial frames. However, ‘public-space’ distance is a hybrid of distances measured in different inertial frames, all in relative motion. Since the resulting vrec is not measured in any single inertial frame, there is no violation of special relativity (Davis 2004)."

And he finishes with this:

"There is neither absolute space, nor expanding space. All that matters is the cosmic substratum and its relative motions. A truly Buddhist enlightenment."

In Expanding Space: the Root of all Evil? (the most insightful paper, in my opinion) it is referred to as the cosmic fluid, but they are both essentially referring to the FLRW solution and in all cases we have a metric expansion of the universe that conforms to the cosmological principle. From that paper:

"To illustrate how short this pragmatic formalism falls of being platitude, one need look no further than Abramowicz et al. (2006), in which a thought experiment of laser ranging in an FRW Universe is proposed to ‘prove’ that space must expand. This is sensibly refuted by Chodorowski (2006b), but followed by a spurious counter-claim that such a refutation likewise proves space does not expand. The exercise is futile: what matters on a technical level are predictions for observable quantities, which of course are the same regardless of how the problem is pictured and what co-ordinate system is chosen."

And on the subject of superluminal recession velocities:

"If we mean by superluminal that the motion described in the coordinates of the Minkowski (or conformal Minkowskilike) frame defined by extending the local inertial frame of an given observer is greater than unity then everyone agrees that this does not occur. On the other hand, if we take the FRW co-ordinates it is clear that there is no limit on the recession velocity: if we choose to call this superluminal motion, then it indeed occurs. The debate seems to boil down to whether this should or should not be given the name ‘superluminal’ but crucially the physical predictions made by either camp will be identical. What matters is not what we call the phenomenon but whether the understanding an individual has of a given term reflects reality and it is clear that not all the authors mentioned above held common meanings of the term superluminal."

(my emphasis in italics)

So where are we? Well Chodorowski hasn't posted his paper showing how it all stitches together yet, but as long as we understand that none of this affects the underlying picture in any way, it just affects how we should describe that picture to people who don't fully understand the mathematics of General Relativity. This is why people who do understand the mathematics properly say things like we cannot meaningfully separate space and time except at the local scale.

 

[yevaud]

Michael, you are simply mixing together two disparate things. On the one hand, we're discussing the expansion of space itself; on the other, you throw in time-dilation experienced by a mass moving at a velocity sufficient to experience it, within that space-time. They are two entirely different things.

 

[harrycostas]

G'day from the land of ozzzzz

Speedfreak said

The idea of redshift being intrinsic has been thoroughly investigated and dismissed, see http://www.astro.ucla.edu/~wright/tiredlit.htm for more information.

Mate you cannot consider that as thoroughly investigated and as evidence.

Wright has no understanding of compact matter, jet formation and dipole fields creating abnormalities in redshift.

This paper is quite interesting

http://arxiv.org/abs/0806.4481
Hubble's Cosmology: From a Finite Expanding Universe to a Static Endless Universe

Authors: A.K.T. Assis (Institute of Physics `Gleb Wataghin' University of Campinas, Brazil), M.C.D. Neves (Departamento de Física, Fundação Universidade Estadual de Maringá, Brazil), D.S.L. Soares (Departamento de Física, ICEx, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil)
(Submitted on 27 Jun 2008)

Abstract: We analyze Hubble's approach to cosmology. In 1929 he accepted a finite expanding universe in order to explain the redshifts of distant galaxies. Later on he turned to an infinite stationary universe due to observational constraints. We show, by quoting his works, that he remained cautiously against the big bang until the end of his life.

I will comment on this once you had a chance of seeing it and getting the gist of it.

 

[SpeedFreek]

You will note I did not say Neds webpage was a thorough investigation, I said to see that page for more information on how tired light has been thoroughly investigated and dismissed. So which of the studies he cites are in error?

Why are Edwin Hubbles outdated views at all relevant here? We all know he was never happy with the expanding universe model. That paper is just an unpublished review of his beliefs (with very faint and hard to read type, no less!).

When are you actually going to start citing peer reviewed papers that actually back up what you are saying? Show me a published and peer reviewed paper with a viable tired light model - you will have trouble because nobody has come up with a viable tired light model.

 

[yevaud]

One important fact: papers held at ArviX are not, per se, necessarily peer-reviewed. They may have been previously at another academic institution, but here they are merely vetted by a loose advisory committee at Cornell.

Though that should be taken into consideration as well.

 

[SpeedFreek]

Yes, if they are peer reviewed they show a journal reference on their arXiv title page.

 

[aphrodites]

Ok ive notticed that a lot of you guys are saying that the big bang is the explosion into space when really its the explotion fo space itself. the big bang occured some 13.7 billion years ago and dark energy was what slowed the expansion of our universe. and only about 100,000 years later our universes elements balanced out and 300,000 years after the big bang mater started to form. the big crunc is one theory but another theory would aso be the big rip where dark matter takes over riping all the galaxies apart and destroying every solarystem and star.

 

[xXTheOneRavenXx]

Ok ive notticed that a lot of you guys are saying that the big bang is the explosion into space when really its the explotion fo space itself. the big bang occured some 13.7 billion years ago and dark energy was what slowed the expansion of our universe. and only about 100,000 years later our universes elements balanced out and 300,000 years after the big bang mater started to form. the big crunc is one theory but another theory would aso be the big rip where dark matter takes over riping all the galaxies apart and destroying every solarystem and star.

Of course they understand these concepts aphrodites. The issue at hand is whether or not space or space-time is expanding...to my understanding of the discussion. IF we say that space-time expands, would this not also suggest Time is expanded as well? I know from what I have read many do not believe Time expands at all, but rather space expands over time. As well, I am wondering how the speed of light IS considered constant by several. Doesn't the speed of light change depending on the substance to which it passes through? If this IS the case, then wouldn't this also play a factor in the red-shift calculations as well? Don't worry, lol I am aware nothing can travel at the speed of light regardless on the substance light passes through. But on the scales of the universe, would not this play a vital role in the necessary calculations necessary to depict accurate distances?

 

[Saiph]

Aphrodites: Welcome to SDC! Nice post, though I'll point out you have Dark Matter and Dark Energy's roles flipped.


Raven: I'm not sure how an expansion of time fits into universal expansion. It's actually an odd idea I haven't run across before, nor have I had myself...though it's a very good question as relativity treats space and time as two values you can convert between (essentially).

As for the speed of light being constant: There are a few researchers out there that are trying to figure out what it would mean, cosmologically, if the speed of light does change over time or depends upon the size of the universe. One article I saw a few years back said a guy was proposing such a change in this universal constant as a mechanism behind inflation.

Don't mistake it's being a universal constant in a vacuum with it's differing speeds in a physical medium however. Light traveling through, say water, is actually ******** by the EM fields of the atoms. Another way of looking at it is in the photon sense. Photons that travel through a medium are absorbed, then re-emitted and the decrease in the speed of light is due to this lag time between absoprtion and re-emmission by the atoms in question. In the free and open vacuum between atoms, the photon travels at C.