Finite Big Bang, Infinite universe?

[Cuetek]

What is wrong with the idea that the Big Bang is a finite structure a million or more times the diameter of the visible universe, and the universe surrounds it in the same way that the visible universe surround the Milky Way?

-Cuetek

 

[mathman]

What is wrong with the idea that the Big Bang is a finite structure a million or more times the diameter of the visible universe, and the universe surrounds it in the same way that the visible universe surround the Milky Way?

-Cuetek

Nothing. Current theory about inflation describes the universe exactly that way (except for the multiple).

 

[Cuetek]

When I say "in the same way that the visible universe surrounds the Milky Way" I mean that fairly literally, like the Big Bang eventually dissipates entirely at some distant point and gives way to relatively empty space for some arbitrary span whereupon some other disposition of matter is encountered. Does inflation theory allow for at least the possibility of this type of material disposition?

 

[my_wan]

When I say "in the same way that the visible universe surrounds the Milky Way" I mean that fairly literally, like the Big Bang eventually dissipates entirely at some distant point and gives way to relatively empty space for some arbitrary span whereupon some other disposition of matter is encountered. Does inflation theory allow for at least the possibility of this type of material disposition?

You say "dissipates" to "relatively empty space" yet as is presently conceived "space" is a product of the Big Bang. So no, not as presently conceived.

ETA: I do find these assumption ripe for theoretical and possibly empirical questioning. They are however empirically consistent thus far.

 

[Cuetek]

ETA: I do find these assumption ripe for theoretical and possibly empirical questioning. They are however empirically consistent thus far.

Surely the Big Bang under the current tenets of the cosmological principle is perfectly consistent for a region at least 1,000,000 times the dia of the visible universe (based on the CMB uniformity) without modification. But for 1,000,000,000 times the vis. u.? Maybe not; For 1,000,000,000^^2 times?... Who among us seriously thinks that we won't need to modify the theory of relativity in some fashion over the next 1000 years?

As far as relativity goes, any characterization of "super-regional" material dispositions surrounding us at vast distances beyond the ultimate extent of the Big Bang would themselves presumably exhibit the same internal tensor relationship between matter and space that the Big Bang does as well as collectively exhibiting these relationships inter-structurally over whatever interstitial spans exist at such scales. We could expand into such immense interstices and perhaps be only very slightly tugged (acceleration of our local expansion profile) by the influences of such hypothetical structures, all without unduly disturbing the overall tensor relationships.

The thing that I feel behooves us to presume the extension of the material hierarchy is that it predisposes us to look for diversity beyond our current data set that has always been the case. Every time we humans have tried to devise a complete description of the cosmos we find there is a larger structure beyond the range of our instrumentation that each time reconfirms the hierarchy. Yet even though the previous cosmology always turns out to be a hierarchical subordinate of the following cosmology, we still try to terminate the hierarchy each time. Why not anticipate this process?

Formalizing the notion that there will always be more diversity beyond the limits of our examinations is the better strategy even if the hierarchy does terminate at some point. That is, if there are only two more tiers of ever larger structures beyond the Big Bang, we will be better off always searching for the next discovery and being surprised just once when the search is over, rather than falsely presuming an end to the hierarchy and having to be stubbornly convinced two more times before the search ends. It's just an efficiency thing, of course. The data will take us where it takes us, no matter what. But why not expedite the process?

 

[MeJennifer]

What is wrong with the idea that the Big Bang is a finite structure a million or more times the diameter of the visible universe, and the universe surrounds it in the same way that the visible universe surround the Milky Way?

-Cuetek

Who makes the claim the the Big Bang is a finite structure?

 

[Cuetek]

Who makes the claim the the Big Bang is a finite structure?

I do.

-<[{( Speculation Alert!)}]>-

I base my presumption of the Bayesian probability that the unbroken material hierarchy we see across 40 orders of spatial magnitude continues beyond the Big Bang. I presume the cosmological principle to apply out to many millions of times the diameter of the visible universe and the Big Bang to range far beyond that, but neither to abide indefinitely. It seems purely philosophical, but it addresses a certain psychological pathology we humans have always suffered at the limits of our understanding.

Basically this theory limits the first two axioms of the cosmological principal --(1) the homogeneous and (2) isotropic universe)-- by suggesting the following two axioms as more universal:

1) The Finite Rule: All material phenomena are finite in extent and constituent to a larger structures.

2) The Plurality Principal: All material phenomena are multiply manifest.

(numerical justification: http://www.thegodofreason.com/rules-of-discovery.pdf)

If the Big Bang were just a million times the diameter of the visible universe then we would only see one part per million difference in the homogeneity of the visible universe from one side of the sky to the other. (WMAP data only goes to about 25 parts per million resolution.)

This video poses a rationale for the above two rules:


This video offers an improvement of the Cosmological Principle:


And this video is a speculation on how we might imagine the large scale
structure of the Big Bang under the constraints of the two rules:

 

[cristo]

I do.

-<[{( Crackpot Alert!)}]>-

Erm... labelling your post with "crackpot alert" is not a good start. Have your read the PF rules?

 

[Cuetek]

Erm... labelling your post with "crackpot alert" is not a good start. Have your read the PF rules?

Yeah, Cristo, I've read 'em, and that's kinda why I prefaced the balance of my post. The rules say that I should discuss with informed people as to the prevailing technical realities before I post. I started this thread in order to do exactly that. As the thread developes I am inevitably prodded for further explanation of why I might be asking my original question. So, for those uninterested in my more speculative points, I warn them off with the alert. Is that a bad thing?

 

[my_wan]

I do.

-<[{( Crackpot Alert!)}]>-

I could take that as a -<[{( Speculation Alert!)}]>- iif (yes 2 i's) your rants had a thread of empirical content. I will not even let the official advisor's here get away with overstating the veracity of certain standard model claims. Why then would I give some claim from left field any consideration whatsoever. Especially one that purports to derive legitimacy from argument alone.

My personal experience when trying to actually give such ideas a fair trial is objections that it simply must be that way. Followed often by accusations of ignorance. Capernicus even prefaced his questions with such accusations. So I'll not bother.

 

[marcus]

What is wrong with the idea that the Big Bang is a finite structure a million or more times the diameter of the visible universe, and the universe surrounds it in the same way that the visible universe surround the Milky Way?

-Cuetek

When I say "in the same way that the visible universe surrounds the Milky Way" I mean that fairly literally, like the Big Bang eventually dissipates entirely at some distant point and gives way to relatively empty space for some arbitrary span whereupon some other disposition of matter is encountered. Does inflation theory allow for at least the possibility of this type of material disposition?

I base my presumption of the Bayesian probability that the unbroken material hierarchy we see across 40 orders of spatial magnitude continues beyond the Big Bang. I presume the cosmological principle to apply out to many millions of times the diameter of the visible universe and the Big Bang to range far beyond that, but neither to abide indefinitely. It seems purely philosophical, but it addresses a certain psychological pathology we humans have always suffered at the limits of our understanding.

Basically this theory limits the first two axioms of the cosmological principal --(1) the homogeneous and (2) isotropic universe)-- by suggesting the following two axioms as more universal:

1) The Finite Rule: All material phenomena are finite in extent and constituent to a larger structures.

2) The Plurality Principal: All material phenomena are multiply manifest.

It sounds to me like it doesn't belong here at PF Cosmology subforum.

Empirical science depends on theorists restricting themselves to making predictive theories. Theories that predict new phenomenal (not already predicted by previously established theory) so that they can be tested.

It is not about imagining the universe in emotionally satisfying ways, or whatever else, it is about making quantitative predictions. And at this subforum we only deal with mainstream theories of this sort. Models of the universe that appear in peer-review professional publications. We don't dream up our own models, because we are interested in learning about and studying mainstream cosmology models. Typically the focus here is on the prevailing consensus LambdaCDM model.

I think this thread will probably be locked, or moved somewhere like Philosophy. I don't know what to advise you to do. Obviously you are pushing your website with your writings and visuals about the way you fantasize the universe. It is not appropriate to do that here. I don't know where it would be appropriate for you to go.

I think the big gap in what you are talking about is you don't have any equations describing gravity, that is, describing the dynamics of spacetime geometry. You are proposing a picture of the geometry of the universe but it seems kind of vague and unmathematical. In conventional mainstream cosmology we SEE the universe evolving geometrically and that evolution is related to our best understanding of gravity. The cosmological model is based on General Relativity (which has been tested). The universe is laid out the way it is and behaves the way it does because it obeys the equation of GR.
So there are all sorts of checks and interrelated things that you can test.

 

[Cuetek]

It sounds to me like it doesn't belong here at PF Cosmology subforum.

Empirical science depends on theorists restricting themselves to making predictive theories. Theories that predict new phenomenal (not already predicted by previously established theory) so that they can be tested.

It is not about imagining the universe in emotionally satisfying ways, or whatever else, it is about making quantitative predictions.

Why does this not count as an empirical examination?

http://www.thegodofreason.com/rules-of-discovery.pdf

I only ask that you are equally diligent in restricting yourselves to my predictive theory and not "imagining the universe in emotionally satisfying ways."

My prediction is that the probability is 99% that the homogeneity of the Big Bang will dissipate and give way to a larger structure made up at least in part by other Big Bang structures.

The most obvious test of this theory would be to examine the WMAP data for a faint dipole. Such a dipole would only show up in the WMAP data if the Big Bang was in the neighborhood of 100,000 times (or less) the size of the visible universe. Based on the relative sizes of other scalar successions (say star system to galaxy) it would likely be much larger.

How is this not empirical?

 

[my_wan]

I actually read the paper.. You did say predictions, oh well. In the conclusions it admits that the assignment of priors is subjective and therefore more qualitative than quantitative.

Your first prediction stated here requires a few billion years to be a prediction. Your dipole prediction assumes an upside down picture of what is being observed. It is the past we are observing. In fact I see nothing in the dipole thinking that is not supporting the standard model.

Now you quoted marcus, "imagining the universe in emotionally satisfying ways", and turned it into a characterization of those supporting the standard model. The realities are that this model started out hotly debated and mostly rejected until new information kept strengthening it. Even so, if it could be knocked off its pedestal I and many thousands of others would fight to do it first. Your accusation is nothing more than a red herring.

You had your say, it's time to end it...

 

[Wallace]

Why does this not count as an empirical examination?

http://www.thegodofreason.com/rules-of-discovery.pdf

I only ask that you are equally diligent in restricting yourselves to my predictive theory and not "imagining the universe in emotionally satisfying ways."

My prediction is that the probability is 99% that the homogeneity of the Big Bang will dissipate and give way to a larger structure made up at least in part by other Big Bang structures.

The most obvious test of this theory would be to examine the WMAP data for a faint dipole. Such a dipole would only show up in the WMAP data if the Big Bang was in the neighborhood of 100,000 times (or less) the size of the visible universe. Based on the relative sizes of other scalar successions (say star system to galaxy) it would likely be much larger.

How is this not empirical?

We can already measure much more than you seem to realize or give credit for. Inflation predicts a particular power spectrum (or equivalently, correlation function) that describes the density field of the Universe. These statistical measures describe the amount of structure present on any given length scale. We can test these predictions against the density field seen in the CMB, and the theory passes with flying colours. We can also test it by observing the correlation function of the density field of galaxies from galaxy surveys and also the density field of dark matter through weak gravitational lensing surveys. These are less 'clean' measurements that the CMB however that do find a correlation function in agreement with the theory. This gives us confidence, empirically, that the theory has some merit.

Now, the theory doesn't cut off at the length scales corresponding to the largest lengths scales we could ever observe but instead makes definite predictions about what kind of structure is likely to be present in 'super horizon sized' perturbations (meaning structures larger than the observable Universe). We obviously cannot directly test this, however since it is a prediction from a theory that we can test at other scales we can have some (but not complete) confidence in it. The prediction is that on those large scales the perturbation amplitude is quite small, so we would not expect that the Universe outside of the observable chunk would be much different from the part we can see.

You seem to be enamored with Bayesian statistics, this is good, cosmologist now use Bayesian statistics almost exclusively since data is at a premium and we wish to make the best guess we can when things are not always obvious 'to the eye' in noisy data. But don't forget that the essence of Bayes's theorem is that your state of knowledge is always updated based on new evidence. If your theory does not include all the current evidence, including the observations that the amplitude of the correlation function reduces as lengths scales increase (so would be expected to be even smaller on super horizon scales), then it cannot be considered to be a 'Bayesian Cosmology'.

Still, I don't want to come across as being too harsh, it's great to toss different possibilities around, but the current cosmology theories weren't just dreamed up at the Pub one afternoon, they are the result of many years of theoretical and observational work by many people. Therefore it's hard to come up with something new that does a better job of explaining the data. I'm sure eventually that will happen, I suspect at least a few aspects of our current theories will eventually be drastically altered, but it's only by considering all of what we know that we can achieve any next step.

 

[Cuetek]

Now, the theory doesn't cut off at the length scales corresponding to the largest lengths scales we could ever observe but instead makes definite predictions about what kind of structure is likely to be present in 'super horizon sized' perturbations (meaning structures larger than the observable Universe). We obviously cannot directly test this, however since it is a prediction from a theory that we can test at other scales we can have some (but not complete) confidence in it. The prediction is that on those large scales the perturbation amplitude is quite small, so we would not expect that the Universe outside of the observable chunk would be much different from the part we can see.

Thanks Wallace for being patient with me. I didn't post this stuff to insult people. I just wanted some responses like yours telling me how exactly my views are naive in light of the conventional wisdom. This definitely gives me something to work with. I've searched some of your terminology and and found some papers I need to try and understand. Thanks again.

 

[Wallace]

Another useful term to look for is 'scale of homogeneity', I think that might get you quickly to the heart of the matter.

 

[Cuetek]

Now you quoted marcus, "imagining the universe in emotionally satisfying ways", and turned it into a characterization of those supporting the standard model.

If the slight was good enough for Marcus to characterize the presumption that the Big Bang may be finite as feel-good idiocy on my part, then it's good enough for me to put back to him for being so dismissive of my wanting peoples honest reaction.

I'm not refuting the standard model. I'm saying that the effort to make any model a complete and sufficient description of everything is precisely where that model will ultimately be found weakest. If this idea is cause for disdain and derision, knock yourself out.

 

[Cuetek]

Another useful term to look for is 'scale of homogeneity', I think that might get you quickly to the heart of the matter.

Oh yeah, that's it. Thanks again.

 

[Cuetek]

Another useful term to look for is 'scale of homogeneity', I think that might get you quickly to the heart of the matter.

Well, gentlemen, (and MeJennifer) after carefully examining these articles on the scale of homogeneity, I don't think they are as conclusive as a few of you might imagine. I looked at some of these papers and they fall into two general categories to extend the homogeneity beyond the range of the visible universe. One category uses the recession data and another uses the CMB data.

One typical article in support of the cosmological principle is Martinez’s "Searching for the Scale of Homogeneity:"

http://www.ingentaconnect.com/content/bsc/mnr/1998/00000298/00000004/art00024

Using the red shift recession data, it claims "no hope for unbounded fractal distributions," which basically supports a total projection of the visible homogeneity. However, he bases his presumption on the two point correlation function which is dependent on the fair sample hypothesis which is itself a derivative of the cosmological principle. This is like saying, if the universe were homogeneous then it could be modeled like this and since the model is so beautifully compliant with respect to relativity then it is undoubtedly true.

This approach constitutes the same potentially true but ultimately false presumptions we have always made when characterizing the universe beyond the data at hand. We always make the presumption that the data we have is sufficient to explain "everything." This is what the cosmological principle is doing for us in modern cosmology. It makes an infinite universe compliant to a finite data set. But historically, the universe has always proven to be more diverse than is possible to determine from any finite local data set.

You may be surprised to find that there are also articles that do not explicitly support a totally homogeneous universe. Take Patricia Castro’s "Scale of Homogeneity from WMAP" which states:

http://arxiv.org/abs/astro-ph/0309320

"We review the physics of the Grishchuck-Zel'dovich effect which describes the impact of large amplitude, super-horizon gravitational field fluctuations on the Cosmic Microwave Background anisotropy power spectrum. Using the latest determination of the spectrum by WMAP, we infer a lower limit on the present length-scale of such fluctuations of 3927 times the cosmological particle horizon (at the 95% confidence level)."

Attacking the problem from a lower limit perspective is a far better strategy than presuming homogeneity and trying to indicate the absence of an upper limit. This approach addresses only what we can be confident in with respect to the local data rather than trying to corroborate an impossible thesis with a potential to range infinitely beyond the local data set.

If we were living on an electron of a hydrogen atom in the middle of the ocean, we would be perfectly justified in presuming the universe was made entirely of water molecules, and all our calculations would work perfectly, but we would still be wrong. All I'm saying is that a Bayesian examination across the widest possible spectrum of the existing data (the hierarchical structure of of the known material universe from quarks to galaxy clusters and across the history of scientific investigation) says that the universe is hierarchical and not homogeneous across all scales and that whenever we try to terminate that hierarchy is precisely where our theories have historically proven weakest. And the CP is that point of weakest presumption in modern cosmology.

For people to get upset to the point of indignation over the suggestion that the Big Bang may ultimately be a finite phenomenon is more an artifact of psychology than of science. The universe is not ours to claim total understanding beyond a reasonable projection of the data to a statistically relevant degree. That it is possible for the cosmological principle to be true is not the same thing as being inevitable.

-Mike

 

[marcus]

If the slight was good enough for Marcus to characterize the presumption that the Big Bang may be finite as feel-good idiocy on my part, .

I did not. You were not being slighted. You must not have understood. I have often discussed the possibility that standard cosmology is spatially finite, in the sense of finite spatial volume. Several of us have (I am not alone in my interest in that case.) Several threads here at the forum about this.

By itself, bigbang finiteness is hardly a revolutionary idea there is even some data supporting it (not conclusive though).

For people to get upset to the point of indignation over the suggestion that the Big Bang may ultimately be a finite phenomenon ...

Again I think you must have misunderstood the point of others' comment. I don't see anyone who responded to you acting upset or indignant at all!

It's a general observation which bears repeating that we have to distinguish between universe models that are supported in detail by data, and make quantitative predictions so they can be tested by practical observations, on the one hand, versus, on the other hand, concepts that appeal to somebody's imagination and are proposed without some currently feasible method of testing.

If you want to call the latter "feel-good idiocy" well, those are your words and it is your perogative. But I wouldn't choose such language. Practical testability of scientific theories is a serious point and, as I say, bears repeating----no one should take offense at the reminder.

 

[Cuetek]

I did not. You were not being slighted. You must not have understood.

The thread you quote form was between my_wan and myself. His exchange with me was far more contentious than yours. That he involved excerpts from your exchange with me is unfortunate in that they got tainted.

I have often discussed the possibility that standard cosmology is spatially finite, in the sense of finite spatial volume. Several of us have (I am not alone in my interest in that case.) Several threads here at the forum about this.

By itself, bigbang finiteness is hardly a revolutionary idea there is even some data supporting it (not conclusive though).

That would be the finite but unbounded model which fails in my estimate in the same manner that the infinite Big Bang model fails. Any model that serves as a complete structural description of physical reality is a psychological presumption and not a model that takes into consideration all the data. The data says we live in a material hierarchy.

The bulk of physical reality has repeatedly proven to be hierarchical even though we repeatedly try to terminate that hierarchy every time we devise some new theory by devising one that can be a potentially "complete" model. If we admit that the hierarchy is more likely, that means that we can never know the full extent of the structure. Using all scales that we have ever comprehensively examined is a more complete template for predicting the nature of the mega-scaled universe, than is taking the largest physical behavior we can see and devising some model that could exist as we always have in the past (crystal sphere, island universe, big bang)

I say that the Big Bang is a finite structure (of at least a million times the diameter of the particle horizon and probably much more) that is in turn constituent to a greater structure just like every other physical phenomenon ever examined. The expansion of spacetime could easily be the relaxation of the curvature of space from the cataclysmic reversal of a cosmic scaled black hole that belched up our local universe (or wormhole punched by a massive black hole as Hawking proposed).

Again I think you must have misunderstood the point of others' comment. I don't see anyone who responded to you acting upset or indignant at all!

My_wan was fairly indignant to the point of saying that I should stop posting He said: "You had your say, it's time to end it."

It's a general observation which bears repeating that we have to distinguish between universe models that are supported in detail by data, and make quantitative predictions so they can be tested by practical observations, on the one hand, versus, on the other hand, concepts that appeal to somebody's imagination and are proposed without some currently feasible method of testing.

If you want to call the latter "feel-good idiocy" well, those are your words and it is your perogative. But I wouldn't choose such language. Practical testability of scientific theories is a serious point and, as I say, bears repeating----no one should take offense at the reminder.

Both can be feel good idiocy. Certainly the scientific method is far less prone to such characterization, but not immune from it. The three tenets of the cosmological principle are ultimately impossible to corroborate, they are only disprovable.


I say that the bulk of the evidence for what exists in the mega-scales beyond the particle horizon lies in the 40 orders of magnitude of hierarchical consistency, not in the single order of magnitude at the scale of homogeneity of galactic clustering. Put yourself on an electron in the middle of the ocean and you would swear that the homogeneity of water molecules was absolute by all practical observations at larger scales. But you would be wrong. The material hierarchy of the subatomics in your local nucleus would continue beyond the ocean in the form a the planets etc.

-Mike

 

[MeJennifer]

Another reason I can think of why knowledgeble people might want to stay away from the phrase "expansion of space" is that FRW universes have zero Weyl curvature. In fact they only have Ricci curvature and Ricci cuvature does not even apply to vacuum regions.

 

[BoomBoom]

I say that the bulk of the evidence for what exists in the mega-scales beyond the particle horizon lies in the 40 orders of magnitude of hierarchical consistency, not in the single order of magnitude at the scale of homogeneity of galactic clustering.

The trouble with this is that, even if it were true, it would be beyond our observational threshold. So to assume this is the case is idle speculation, just as assuming it is not the case is also speculation.

It makes logical sense to me, but without any evidence, science doesn't have anything to say about it...as it shouldn't.

 

[navneet023]

well...i wanted to ask one thing...everybody's saying that the expanding universe is like a inflating balloon...wid galaxies nd everyting as points on the the balloon...can u tell me wats inside of the baloon...??

one more thing i'd like to ask ... like where is our universe expanding...where...where is it placed...where was the super dense super hot infinitely unstable point placed from which everyting came out...?

Plz...I know m sounding like an idiot...but i thought the same wen i was asking myself these questions...

 

[Cuetek]

I say that the bulk of the evidence for what exists in the mega-scales beyond the particle horizon lies in the 40 orders of magnitude of hierarchical consistency, not in the single order of magnitude at the scale of homogeneity of galactic clustering.

The trouble with this is that, even if it were true, it would be beyond our observational threshold. So to assume this is the case is idle speculation, just as assuming it is not the case is also speculation.

It makes logical sense to me, but without any evidence, science doesn't have anything to say about it...as it shouldn't.

To say that we have no evidence about it is not exactly true. We have generally the same type of evidence we use to establish the cosmological principle. That is we either project the two orders of magnitude (one order was a little skimpy) of the homogeneity we see at the largest scale out indefinitely or we project the 40 orders of magnitude of the material hierarchy out indefinitely. If the cosmological principle is good science, so is the the hierarchical principle.

That one of those projections allows a very specific field for us to project makes it seem more "reasonable" but there is actually less data to support it (2 orders of magnitude). That the other projection is conceptually vague the instant it begins to diverge from the homogeneity we presume in the first projection makes it no less accurate as far a projections go. That is to say, in both cases we are talking about the unknown, but not without any evidence.

The only real difference it should make in science is in what we expect to find. If we expect to find homogeneity we won't look very hard for any faint asymmetries in the CMB and recession data. And we should look just as hard for inhomogeneity as we do for homogeneity (the bulk of publications on the subject are looking for homogeneity).

We devise all sorts of expectations and calculations based on the cosmological principle that work out fine. But just because we can make an idealized model of a homogeneous universe that works mathematically, is not sufficient to rely on it beyond the range of data at hand. This is true for either case, but, if you don't look for another possibility, you're not likely to find it and the truth is, in a thousand years from now, we will have found all manner of things that weren't like we thought they'd be.

You might have the tendency to look at it as a purely philosophical question since we are talking about the nature of the universe beyond our ability to confirm. But the fact is, we have a much more extensive field of evidence in the material hierarchy than we do in the homogeneity of the galactic clustering and the cosmological principle is not considered to be merely philosophical. This makes the hierarchical principle at least as compatible with the scientific method as is the cosmological principle.

-Mike

 

[BoomBoom]

But just because we can make an idealized model of a homogeneous universe that works mathematically, is not sufficient to rely on it beyond the range of data at hand. This is true for either case, ...

I agree. I think there are a lot of assumptions out there that are accepted as fact, and I feel like science should be a little more skeptical about things we have no evidence of. I like caveats such as the universe "could be" like this instead of saying it "is" like this in cases where there remains an element of doubt and a lack of visual evidence.


That said though, if the universe is as you suggest, would this be a possible explanation for dark energy? If there was a whole lot more matter out there beyond our expanding "local" universe, would the gentle tug of it's gravity be enough to explain DE?

 

[Cuetek]

well...i wanted to ask one thing...everybody's saying that the expanding universe is like a inflating balloon...wid galaxies nd everyting as points on the the balloon...can u tell me wats inside of the baloon...??

It's just an analogy, the whole balloon thing. It's a two dimensional representation (the skin of the balloon) of a three dimensional issue (visible universe). The inside of the balloon is not part of the analogy. A better analogy is the raisin cake analogy where as you cook the dough the whole cake expands with each of the raisins getting further and further away from each other.

one more thing i'd like to ask ... like where is our universe expanding...where...where is it placed...where was the super dense super hot infinitely unstable point placed from which everyting came out...?

Plz...I know m sounding like an idiot...but i thought the same wen i was asking myself these questions...

Not at all, navneet (at least not to me). I'm not really sure why the cosmological principle was adopted, but it was, and since it was adopted the only way a perfectly homogeneous universe could expand was if all of it was expanding equally. If this was the case then, even if the universe is infinite, it started out as both infinite and as a cosmic egg singularity. In which case, there was no prior context to this process. It started out both infinitely dense, yet infinitely vast in the instant of it's initiation. If it's not infinite then it's a closed universe that curves back on itself at some staggering volume, "outside" of which there is no existence.

Sounds totally whacky right? I think so too, although a great deal of math has been dedicated to describing just such a universe. But I have a more pedestrian model that might make sense to you, even if most of the other members of the Physics Forum will disagree strongly with it's tenets.

Since all material phenomena that we have comprehensively examined are finite in extent and constituent to larger structures I contend that the Big Bang is ultimately a finite phenomenon itself in a much larger surrounding materially hierarchical context just like the rest of everything else we ever discovered proved to be. And since black holes and the Big Bang are the only two phenomena that are associated with singularities, I suggest that the Big Bang is an enormous black hole that went kablewy.

If you were to examine a 13 billion light year wide section of a trillion trillion light year wide exploded black hole you might realistically expect to see everything around you appear to be heading away from everything else. Yet, ultimately it would be expanding "into" the surrounding context just like you imagine an expanding phenomenon to behave.

And since every physical phenomenon we ever comprehensively examined proved to be only one example of a class of similar phenomena, I would say that the surrounding context into which we are expanding might well be expected to have other really big black holes scattered about as well as some small fraction of them getting ready to go kablewy. Collectively (along with perhaps other similar scaled elements) these black holes might be expected to form even larger structures in an ongoing hierarchical universe that we will never be able to fully explore, much less characterize.

Such a universe would virtually eliminate the ability for us to ever understand and model it. It would be permanently beyond our ability to fully fathom (just like it always has been). This inability to comprehensively describe the universe is psychologically challenging for science to admit, but it is almost inevitably true as the history of science clearly indicates. It is, however, easier for me, personally, to imagine such a universe than to imagine the Big Bang as currently characterized.

-Mike

 

[Cuetek]

I like caveats such as the universe "could be" like this instead of saying it "is" like this in cases where there remains an element of doubt and a lack of visual evidence.

That said though, if the universe is as you suggest, would this be a possible explanation for dark energy? If there was a whole lot more matter out there beyond our expanding "local" universe, would the gentle tug of it's gravity be enough to explain DE?

Dark energy to me is more probably a product of our misinterpreting vast scale circumstances that affect our local disposition. Dark energy is not as certain a theory as, say, relativity, and as such, to me it belongs in the category you suggest above with an element of doubt formerly associated with it.

I am a Bayesian. I use Bayesian logic in suggesting that the full scale material hierarchy is a better template than the single scaled homogeneity. If the material hierarchy persists then there must also persist a hierarchy of forces beyond the four we know to organize the ongoing structures. Dark energy to me seems to be a good candidate for the small scale emergence of the next force in line that exerts after gravity in the direction of larger scales.

But I also think that there are so many potential scenarios involving normal gravity like enormous gravity waves or proximity of large background gravity fields (black holes) at vast scales that may even serve explain the acceleration of the expansion as an artifact of our transition through these background circumstances. At any rate, I think science doesn't pay enough attention to the possibilities of diversity at larger scales in addressing issues like DM and DE.

-Mike

 

[mysearch]

Cosmology: State-of-Play?

Hi, it is not my intention to divert this thread, but some of the previous posts seem to be touching on the general state-of-play of cosmology. I think many newcomers to cosmology, like myself, are initially seeking to gain some general understanding as to what aspects of the standard model are supported by verified science and what might be more honestly classified as speculation, although mathematical hypothesis might be the preferred term.

In fairness to the mainstream, this situation is often compounded by the myriad of ideas from `free-thinkers`, which while I would not like to see suppressed in this forum, must ultimately substantiate their views by the same rigor expected of mainstream science. If not, an already confused situation simply becomes ever more confused via yet more unsupported speculation.

This said, the purpose of this post was to get the opinion of an article, which I hope is not considered too tangential to the current discussion that I recently came across as I continue my own reading into the issues surrounding cosmology. I have included an extracts from the article and a link to the full article below. At face value, the comments seem quite negative, but the author Dr. Richard Lieu seems to be a respected professor of physics at the University of Alabama. However, rather than just accepting his comments, I would be interested in the opinions of some of the members of this forum, especially those working in this field, who may want to respond to this article:

http://arxiv.org/PS_cache/arxiv/pdf/0705/0705.2462v1.pdf

Abstract: Astronomy can never be a hard-core physics discipline, because the Universe offers no control experiment, i.e. with no independent checks it is bound to be highly ambiguous and degenerate. Thus e.g. while superluminal motion can be explained by Special Relativity, data on the former can never on their own be used to establish the latter. This is why traditionally astrophysicists have been content with (and proud of) their ability to use known physical laws and processes established in the laboratory to explain celestial phenomena. Cosmology is not even astrophysics: all the principal assumptions in this field are unverified (or unverifiable) in the laboratory, and researchers are quite comfortable with inventing unknowns to explain the unknown. How then could, after fifty years of failed attempt in finding dark matter, the fields of dark matter and now dark energy have become such lofty priorities in astronomy funding, to the detriment of all other branches of astronomy?

Conclusion: Cosmologists should not pretend to be mainstream physicists, because there is only one irreproducible Universe and control experiments are impossible. The claim to overwhelming evidence in support of dark energy and dark matter is an act of exaggeration which involves heavy selection of evidence and an inconsiderate attitude towards alternative models with fewer (or no) dark components. When all evidence are taken into account, it is by no means clear that LCDM wins by such leaps and bounds.

 

[Cuetek]

Hi, it is not my intention to divert this thread, but some of the previous posts seem to be touching on the general state-of-play of cosmology.

I guess I started this thread and IMHO your contribution is spot on. I am woefully lacking in the mathematical chops sufficient to assert some of my more intuitive conclusions. Having some credentialed commentary inserted into the discussion to formalize some of the intrinsic uncertainties involved in modern cosmology is exactly what this thread needs.

Later -Mike

 

[yuiop]

By itself, bigbang finiteness is hardly a revolutionary idea there is even some data supporting it (not conclusive though).

The latest data suggests Omega is about 1.02 suggesting a closed universe but there is sufficient error despite billionds of dollars spent on reasearch that a universe with Omega exactly =1.00 and flat is not excluded. As I understand it Omega =1.00 implies an infinite universe and Omega >1.00 implies a finite universe. What I want to ask here is if the cosmological constant changes that interpretation? Does a cosmological constant of greater than zero suggest a universe with total Omega less than 1.00 can be finite or vice versa?

 

[marcus]

...As I understand it Omega =1.00 implies an infinite universe and Omega >1.00 implies a [spatially] finite universe.

I agree. I think your understanding is right. I put in the word spatial to make it clear.

What I want to ask here is if the [positive] cosmological constant changes that interpretation?

No it doesn't AFAIK. The cosmological constant we see evidence of, and most people mean when they say that, is positive. so for clarity I put that in. It doesn't change the spatial finiteness or infiniteness.

If Omega > 1 then it's spatial finite and even if you put in Lambda it is still spatial finite.

If Omega = 1 then it's spatial infinite and even if you put in Lambda it is still infinite.

Same for Omega < 1.

 

[marcus]

The latest data suggests Omega is about 1.02 suggesting a closed universe...

reference to latest WMAP data here:
https://www.physicsforums.com/showthread.php?p=1636651#post1636651

95 percent confidence interval for Omega using WMAP5 + SN + BAO
is [0.9929, 1.0181]

That's on page 6 of the WMAP5 paper reporting implications for cosmology. If you just base it on WMAP data you get something about the same as that. This just happens to be what you get if you include the other two datasets.
BAO (baryon acoustic oscillation data) depends on galaxy surveys and SN is supernovae.

On page 4, figure 2, of the same paper they give a lower bound for the radius of curvature of space, assuming it is a 3-sphere, that is the 3D analog of the surface of a balloon. the estimate is 104 billion lightyears.

that is the radius of the balloon-analog is AT LEAST that much. so you can figure the circumference that corresponds to 104 billion and it is at least that.
and you can calculate the 3D volume and it is at least that volume---at the present moment.

the formula for the 3D volume of a 3-sphere is 20 x R³ where R is the radius of curvature. we don't assume an extra dimension in which the R exists as a real distance, it is just a quantity describing the overall average curvature. 20 is meant as the rough value of twice pi-square.

I think if you asked for a 70 percent confidence interval you would get something entirely > 1. Probably centered around 1.01 and something like
[1.004, 1.016] just guessing. They published something like that with the WMAP3 data a couple of years ago. But this time, with the WMAP5 data, they only gave this 95 percent interval that spills over a little bit into Omega < 1.

 

[yuiop]

Please take a look at http://www.astro.ucla.edu/~wright/triptych-SNe-CMB-BO-H0-75.gif" .

In the text Ned states "Clearly if one assumes the Universe is flat the supernovae favor w = -1.3 which leads to a "Big Rip". But if one looks only at the concordance between the four datasets, the standard flat ΛCDM model with w = -1 is preferred."

To me, there is no concordance between the supernova data and the other 3 datasets. I have attached a modifed version of ned's image which I have converted to black and white, enlarged and added coloured centrelines for each dataset to make the concordances clear. If you look at the rightmost image with w=-1.3 then there is a very good coincidence of 3 out of 4 of the datasets if we ignore the supernova data. No adjustment of the equation of state parameter w can make the supernova data coincide with the other data and trying to make it match makes the other 3 data sets diverge. It surprises me that that Ned chose the centre picture with w=-1 as the best fit and his choice seems to be based on a desire to choose a fit that is on the flat Omega=1 line. I have highlighted the coincidence point in the w-3 image with a white and red dot. Why doesn't anyone else mention what a bad fit the supernova data is with the data from other sources?
The best fit in my opinion is the Omega>1 and w= -1.3. If you look at http://www.astro.ucla.edu/~wright/Wm-Wv-wMAP5yr-wSNe.gif" from the same webpage which is based on 2008 data it can be seen that that the Supernova data by itself puts Omega in the 1.3 range which is miles away from the flat universe line.

 

[marcus]

Please take a look at http://www.astro.ucla.edu/~wright/triptych-SNe-CMB-BO-H0-75.gif" . ...

that page is interesting several ways. Thanks for mentioning it, Kev. I understand that the plots you focus on come right at the end and are concerned with the DE equation of state. Should one think of it simply as w = - 1, or contemplate some other possibility like w = -1.3?

You also distrust the alleged concordance among CMB+BAO+SNe, where it looks like the first two agree all right but SNe is out of line.

I can see what you are talking about, but my reaction is (you might say) more conservative.

What I see happening with the Ned Wright page is more than just asking about w, the EOS.
He is looking at the Kowalski etal (April 2008) paper. And he isn't satisfied with it because he doesn't think they considered enough different cases. So he re-analyzes their SNe data. He rebins it. He adds new cases and plots different color solid and broken curves.

I went back and looked at the Kowalski etal 2008 paper that was Ned Wright's starting point
=========================

I can't give you a single clear response, but I did notice something in Kowalski etal TABLE 6 on PAGE 23. Instead of just assuming flat Omega = 1 as they usually do, they included a BEST FIT case allowing Omega to not be exactly equal to one.
and they got a best fit of Omega = 1.009
with a range of about [1.00, 1.02]
This is best fit for all the datasets: SNe + BAO + CMB.

What I see Ned Wright doing, on the page you linked, is primarily trying more cases where Omega is allowed to be > 1. He augments Kowalski etal analysis to be more openminded. The central figure on the page---the one he appends all those tables to---is called "332 SNe SCP Union Catalog"
Where he says "The dashed magenta curve is the best closed dark energy dominated fit to the supernova data alone."

To me the dashed magenta looks like better fit than the solid magenta and I think that is one of the ideas that Ned Wright is getting across with that figure.

Particularly since for the case z = 1.55 the sigma, shown by the vertical uncertainty bar, is so large that hitting the centerdot means relatively little.
I pay more attention to the nearly exact hits at z = 1.275 and z = 1.367, with much smaller sigma. The table right after the figure duplicates the information so we know what numbers he is plotting. food for thought.