What Is the Expansion Limit of Our Universe?

[Garth]

The problem with this kind of argument is that it ignores the reasons why there is more interest in the 'standard' model. If you look at the broad predictions of the Milne model you very quickly see that for every observation we have the theory and data are in complete conflict. Therefore there isn't much motivation for going any further with the model.

The 'standard' model is in agreement with the data in terms of broad predictions. Hence there is a good reason to investigate further. By checking the minute details we have discovered some anomalous aspects of the model in comparison with the data.

'Doing more work' on a model generally means that you are pushing the boundaries to see where it breaks. Of course we won't bother pushing the boundaries on a model that is broken from the start. Such additional work is not necessary, and indeed would not produce any additional insight. The assumption that more work may fill 'the gaps' is groundless when 'the gaps' are fundamental first order (or even zeroeth order) problems with the model.

Others would disagree with you - it seems the standard model is the one that is "a model that is broken from the start" - it is only fixed by invoking Inflation, DM and DE, all as yet undiscovered by 'laboratory' physics...

From Sethi, Kumar, Pandey & Lohiya's 2005 paper A case for nucleosynthesis in slowly evolving models

Summary

In spite of a significantly different evolution, a linear coasting cosmology can not be ruled out by all the tests we have subjected it to so far.
Linear coasting being extremely falsifiable, it is encouraging to observe its concordance ! In standard cosmology, falsifiability has taken a backstage - one just constrains the values of cosmological parameters subjecting the data to Bayesian statistics. Ideally, one would have been very content with a cosmology based on physics tested in the laboratory. Clearly, standard cosmology does not pass such a test. One needs a mixture of hot and cold dark matter, together with (now) some form of dark energy to act as a cosmological constant, to find any concordance with observations. In other words, one uses observations to parametrize theory in Standard Cosmology. In contrast, a universe that is born and evolves as a curvature dominated model has a tremendous concordance, it does not need any form of dark matter and there are sufficient grounds to explore models that support such a coasting.

Garth

 

[Chronos]

Wallace make a pursuasive argument Garth. He might be wrong, but the reasoning is pretty solid, would you not agree? The strength of the 'Standard Model' is it has very loose parameters. In fact, it even allows for additions - like the dark stuff. The evidence in favor of dark stuff is, in fact, fairly compelling. But still, the 'Standard Model' can survive without dark stuff, it merely needs a fairly severe tweak. Surely not all of physics is wrong. The bigger issue is where we draw the line. I stop at GR. GR may only be an approximation, but is much closer to dead on than any lower level physics.

 

[Wallace]

Others would disagree with you - it seems the standard model is the one that is "a model that is broken from the start" - it is only fixed by invoking Inflation, DM and DE, all as yet undiscovered by 'laboratory' physics...

Garth; Inflation, DM and DE ARE the standard model, not 'fixes' tacked onto some model, they are the model!? If you have a theoretical prejudice against these features then that is your prerogative, however the point is that the data, independently, across the range of observables, agrees with the same parameter values, with these features to a high level of precision.

As for the paper you point to, of course there will always be dissenting views to any proposition, that is human nature. I've played with the SN data myself and the Milne model is a poor fit. I don't know how else to say it since you simply disagree. I work in structure formation and I've run the Milne model and frankly you would have to be stark raving and possibly barking mad to think the results look anything like the structure data we have (such as 2dFGRS or SDSS). If you would like me to post some images I'm happy to do so.

 

[Garth]

Hi Wallace,

Yes I am familiar with structure formation in the standard model such as in the Millenium simulation.

The structure formation in that model, together with galactic cluster dynamics and spiral galaxy rotation profiles, requires more density than the standard BBN can provide, hence the need for non-baryonic DM. The smoothness, flatness, density and magnetic monopole problems of GR cosmology requires Inflation. Cosmic acceleration and spatial flatness require DE. It is this exotic non-baryonic DM, the Higgs Boson/Inflaton and DE itself that has not been discovered in the laboratory even after three decades of intense searching, which of course you know all too well.

These have become necessary parts of the standard model, therefore their continued non-detection does become a reason to consider other "dissenting" approaches.

I have no problem with that standard model so long as it is treated as provisional on these entities being discovered.

I am interested in the fact that you have run structure formation in the Milne model. What density were you using?

Garth

 

[Wallace]

A range of densities, nothing fits too well. The problem is that we have to points in which we can normalise the growth amplitude, the CMB (via COBE and WMAP) and today (via 2dFGRS and SDSS). Without bothering with simulations, just looking at linear perturbation theory, there isn't a single set of parameters for the Milne model that gets the correct growth amplitude increase from z=1100 to z=0 as well as being consistent with $$H_0$$ and SN data (even the nearby data if we cut of the high z points that do not agree with the Milne model, and may suffer from spurious evolution effects).

We have two differential equations, the distance vs z and growth vs z. For LCDM they both get the same answer between z=1100 and z=0 for a common set of parameter values that also fits other data. The same is simply not true for the Milne model, you just don't get even close to the required growth amplitude increase for complex structures to form.

BTW: I still strongly disagree with the notion that DE and DM will only be 'real' if they can be 'detected in a lab'. If they truly only interact gravitationally this may be literally impossible to do. Does this mean they therefore cannot exist? I just don't understand the theoretical prejudice that demands that if Humans can't make it then it must not exist. A lab experiment is merely the observation of the action of some force on some substance. Astronomy is the same process. I don't understand the fingers in the ears 'LA LA LA' kind of dismissal of the evidence that is staring us in the face due to an anthropocentric notion that something can't be real unless we can play God and make some for ourselves??

 

[Garth]

Thank you for that information.

I believe the Indian team were using values $\Omega_{M}$ = 0.65 ~ 0.69 and h = 0.65 ~ 0.71.

They claim in Cosmological Constraints on a Power Law Universe:

It was also demonstrated that this model is consistent with primordial nucleosynthesis [9]. For
$\Omega$ = 0.65 and $\eta$ = 7.8 × 10⁻⁹, the model with $\alpha$ = 1 yields He⁴ = 0.23 and metallicity of the range 10⁻⁷ [11]. Linear coasting surprising clears preliminary constraints on structure formation and CMB anisotropy [10].

(emphasis mine), where reference [10] is A Concordant "Freely Coasting Cosmology"

About your second point: I am not saying that if we do not discover the Inflaton particle/DM and DE in the lab they do not exist, just that the assumption of their existence is provisional. Our conclusion that they do exist is theory dependent.

That theory (GR) may be modified, especially if/when a quantum gravity theory replaces it.

We just have to keep that in mind.

Garth

 

[Wallace]

Chinese whispers. If you look at the reference [10] all they do, as I have pointed out to you in the past, is show that 'structure can form'. We know a good deal more about structure in our Universe than merely that there is some! They do not attempt to confront the predictions of this model with data. Having done so myself I can see why, though that speaks volumes for their credibility (or lack thereof). It's not a difficult task to do.

On the Lab verification point, I ask you the question of what makes DE and DM 'provisional' theories?? There is no such thing. They are theories that best fit current data. If new data comes along and a new theory is developed (which is certainly occurring on both fronts) and the new theory fits the new data better then the theory will be replaced.

There is no reason to call a theory that is supported by the available evidence 'provisional' apart from, once again, theoretical prejudice. The existence of everything in physics is 'theory dependent' though your toaster doesn't come with a warning 'Danger: The operation of this device is theory dependent, use at your own risk'. Pointing out a banal point about the scientific method in certain cherry-picked cases and not others highlights the fundamental prejudice of the cherry-picker. It's just like Creationists poo pooing Evolution because it is 'just a theory', while happily using the theory of electricity to beam their sermons into your lounge room.

That theory (GR) may be modified, especially if/when a quantum gravity theory replaces it.

We just have to keep that in mind.

Again, no one in cosmology is not bearing this in mind. Pointing it out the way you do implies that this is not the case.

 

[Garth]

I am not disputing the standard model works well, given the addition of these necessary 'entities'. However, if the provisional nature of Inflation/DM/DE is not kept in mind then over-confidence may well close the mind to alternative possibilities.

Garth

 

[Wallace]

But why do you describe them as 'provisional'? Why are these theories any less valid than any other?

 

[Garth]

But why do you describe them as 'provisional'? Why are these theories any less valid than any other?

I am committed to the definition of a scientific study of cosmology that has grown out of the discipline astrophysics as opposed to philosophy or theology. It is astrophysics carried out on the largest scale.

Astrophysics is the knowledge of the physics of the heavenly bodies 'out there' by the understanding of the physics 'down here', in the laboratory.

Occasionally we discover something 'out there' before it is discovered in the laboratory, such as the element helium. However its discovery in 1868 was provisional until verified by Ramsey in 1895 when it was isolated on Earth. Its faint yellow spectral line seen in 1868 was first assumed to be sodium, or it could have been the absorption line of another element under the unusual conditions of the Sun's chromosphere. Of course the laboratory isolation of the new element confirmed it as Helium.

Inflation and the DM particle have been similarly discovered 'out there', I maintain that not until we have discovered these particles 'down here', say by the LHC and if the detection of an axion by Piyare Jain at the University of Buffalo is verified, their properties measured and found to be concordant with cosmological constraints, can we say that we really know what we are talking about.

Garth

 

[Wallace]

Right, so you do hold the anthropocentric view that unless we can make it ourselves we can never be sure it exists. My question stands that how is a lab experiment, in which we observe the action of something on something else fundamentally different to the observation in the cosmos of the same?

Your absurd accusation that LCDM is based on either philosophy or indeed theology(!?) does not become you. Should we ignore the evidence of the cosmos becuase of some history we wish to honour? Should we disregard what is possibly the only evidence we can ever get to study some fundamental physics because the process is somewhat different to what we have used in the past? I think the Aristoteleans had similar issues with a chap named Galileo...

 

[Garth]

Right, so you do hold the anthropocentric view that unless we can make it ourselves we can never be sure it exists. My question stands that how is a lab experiment, in which we observe the action of something on something else fundamentally different to the observation in the cosmos of the same?

How are we ever sure something exists? We have to go by our own observations, either in the laboratory or at a distance as in astrophysics. In the 'laboratory' experiment variables and other effects can be controlled, albeit with difficulty, however that cannot be said about cosmological observations.

If GR, unmodified, could be proven without doubt then its cosmological conclusions could be accepted without doubt. We both know this is not the case.

If the Higgs Boson/Inflaton and DM particle are discovered with the desired properties, then those cosmological observations could be accepted without doubt. Their verification could be 'just around the corner', however, as we both know, this has not yet happened.

Your absurd accusation that LCDM is based on either philosophy or indeed theology(!?) does not become you.

I made no such claim, if it read as such then my post was ambiguous, for which I apologise.

I was simply re-stating the basis of astrophysics as I understand it; i.e. the study of the physics of the stars and other 'heavenly bodies' based on the physics discovered in the 'laboratory'.

The motto of the Royal Astronomical Society, which was founded in1820, is "Quincquid nitet notandum". It means "Let whatever shines be recorded (lit. noted)". It is an interesting observation that some 187 years later it seems that '96%' of our discipline is about recording that which does not shine...

Garth

 

[Wallace]

So you're not prepared to consider that our understanding can evolve to allow us to probe fundamental questions that may be unanswerable 'in the lab'? Are you really not prepared to consider the implications of cosmological data because of what someone said, in a dead language almost 190 years ago?!

I'm not suggesting that DM,DE, inflation etc are locked in stone, neither is the theory of the electron, that's just the way science works. The point I'm making is that if we insist that we will never trust a result unless we can make the stuff ourselves we are potentially blinding ourselves to deeper insight that might not be accessible otherwise.

I see no justification for your position other than appealing to history. I'm not suggesting that cosmological observations, at present, 'seal the deal' but I'm am wary of the attitude that they can never do so, regardless of what we may otherwise be able to learn from the data.

This is not an idle danger. The prejudice against physical laws observed 'in the sky' but not in the lab leads to, amongst other things, the desperate promotion of clearly discordant models, such as the Milne model. Let's use the data we have to do the best we can rather than constraining ourselves for no other reason than homage to the past.

 

[Garth]

Of course I am prepared to consider the development of our understanding of questions unanswerable 'in the lab'. However, mindful of the scientific method I am just aware of the provisional nature of such understanding.

I believe a historical perspective is useful. In order to know where we are going it is instructive to know where we are and how we got here.

Garth

 

[Wallace]

Agreed, but what I see in the history of science is the way in which time and time again understanding stalls due to the confines of particular methodologies, for instance deductive reasoning did not permit empirical data and hence held science back from the wonders of inductive reasoning. Deductive reasoning had achieved a lot and the senses were assumed to be untrustworthy. Eventually the rules were re-written and empirical science bloomed.

That's a simplistic analysis and I'm sure I'm not telling you anything you don't know already, but when I look at the history of science I don't see anything that tells us we need to be able to make something for ourselves before we can be sure (in the scientific sense of the word) that it exists.

 

[Garth]

Actually I am not saying we have to 'make' DM or the Higgs Boson/Inflaton in the laboratory, just that we have to observe them under controlled conditions before we can be certain of their existence and nature.

The whole point of empirical science is that it is based on what is observed rather on that which is not.

Garth

 

[Wallace]

The whole point of empirical science is that it is based on what is observed rather on that which is not.

Garth

Precisely, and DM and DE have (or the effects that we currently think could be ascribed to these entities) been observed. Many times, in great detail. Observing the gravitational lensing of DM is a galaxy cluster is no different from measuring the scattering potential of a sub-atomic particle in an accelerator. We observe the effects of something we cannot see on something that we can.

Lab experiments are not fundamentally different from cosmology observations. If it is not possible to observe DM and DE 'under controlled conditions' (which may or may not be the case) do you really think we should therefore cease to study the cosmos, since 'we could never be sure' of what we discover, in which case, what is the point? That is the logical extension of your position. Cosmology says that we need DM and DE (or something that looks like them), further observations will only refine the parameters. Given this then, we should stop spending any money on cosmology until we find these in a lab, since anything else that cosmology discovers about their properties is only 'provisional'.

 

[Garth]

There is a fundamental difference between an experiment in which the conditions can be controlled, and varied, and the remote sensing of a distant object.

Of course I do not think we should cease to study the cosmos, studying and understanding the cosmos has been a life long passion for me, however we need to be mindful of our limitations.

"Cosmologists are often in error but never in doubt" - - Lev Landau

Garth

 

[Wallace]

Right, but promoting the Milne model is not being 'mindful of our limitations', it goes much further than that.

The best we can do it be as honest as possible about what the data that we can get says. If we have strong evidence for a certain physical theory then let's be happy to say so, rather than trying to squirm out of what the data says because of what we think it should say.

We can never make stars, galaxies, heck until relatively recently we couldn't test gravity other than by observing the sky. Yet we've learned a lot about these things (even if we have a long way to go).

 

[Garth]

But I am not necessarily promoting the Milne model, but as an alternative and simpler model to the standard I think it deserves consideration, alongside MOND or other possibilities.

The motivation for the strictly linear expansion model is that it does not require Inflation, the motivation for MOND is that it does not require DM. While the Higgs Boson and DM particle remain undetected 'in the lab' these alternatives deserve to be kept in mind.

If in the Milne model case, R(t) $\propto$ t, k = -1, high $\Omega_b$ ~ 0.69, low h ~ 0.65, does not produce the correct large scale structure formation over its longer developmental time, as you report, (BTW is there a published reference to this work?) then one question would be: "Is there anything that can be added to make it work? - such as non-interacting DM?"

If the MOND model requires a mechanism to make it work then what combination of additional scalar, vector and tensor fields will provide this?

If this seems 'ad hoc' then that would be a valid criticism, but no more so than with the standard model that required Inflation/DM/DE to make it work.

As a matter of personal 'preference' the model my own work throws up is R(t) $\propto$ t, k = +1, and that has its problems, I know! I am not promoting that here, as a published theory I have been allowed to discuss it in another thread.

But when others report that a simple model, such as the Milne, passes basic cosmological constraints I take interest. At least it provides an alternative to test the standard model against.

Garth

 

[Wallace]

If in the Milne model case, R(t) $\propto$ t, k = -1, high $\Omega_b$ ~ 0.69, low h ~ 0.65, does not produce the correct large scale structure formation over its longer developmental time, as you report, (BTW is there a published reference to this work?) then one question would be: "Is there anything that can be added to make it work? - such as non-interacting DM?"

I haven't published this stuff, I just ran some models once to have a squiz. I don't think it's worth publishing since it's a pretty obvious result. I'm sure there are some older (~ 2dF heyday) papers that would have some figures, I'll see what I can find. As for adding DM, my simulation were with DM, as far as most N-body simulations go matter is matter, whether dark or baryonic (people do add 'gas physics' and 'star formation' in some studies but the way to do this rigorously is not yet established). So no, DM doesn't throw Milne a life line.

If this seems 'ad hoc' then that would be a valid criticism, but no more so than with the standard model that required Inflation/DM/DE to make it work.

The problem with MOND is that you need to have a different theory of gravity to fit each galaxy or cluster, since the same parameters do not fit each galaxy. Now that is what I call ad hoc! DM and DE are not ad hoc in this way, since the whole reason it is sometimes known as the 'concordant' model is that the same parameter values work for every data set. That's an incredibly powerful and significant result and far from 'ad hoc'.

But when others report that a simple model, such as the Milne, passes basic cosmological constraints I take interest. At least it provides an alternative to test the standard model against.

Garth

You can always find papers to support pretty much any position. You need to go a little deeper than the abstract to see if the claims are valid though and unfortunately several papers you have pointed myself and others to on this topic have been fairly shoddy to say the least. Science is not a democracy, I'm not discounting these paper because they are in the minority numerically, but they do not demonstrate their claims with any rigour (at least not that I have seen).

 

[Garth]

Nevertheless, even if present alternatives fall short, I continue to maintain that the mainstream interpretation of cosmological observations must be taken as 'provisional' until the existence of these dark particles/energy is confirmed under controlled conditions.

Garth

 

[Chronos]

Cosmology is always provisional. We can't create planets in the laboratory, but most agree they do exist. Right now, the preponderance of evidence is in the concordant court. And it looks pretty firm. While a single observation could unsaddle that horseman, none have yet suceeded. I think it fair to concede the concordance model is a reasonable approximation. But that does not diminish your efforts, Garth. Asking a few hard questions is always worthwhile. The concordance model does not always yield answers, but is not demonstrably false. I don't mind walking along the fence row, but am reluctant to climb it.

 

[Garth]

Of course, I agree with that statement.

However an over-confidence placed in the mainstream model may discourage effort that may put in developing other alternatives.

The reason it is good to have other viable alternative models is that they provide something against which the main model may be tested. The nature of both the main model and an alternative determines what questions should be asked and what experiments are worthwhile.

Witness the question about whether the $800 million spent on the Gravity Probe B experiment was well spent or not.

Garth

 

[Voltage]

...The problem with MOND is that you need to have a different theory of gravity to fit each galaxy or cluster, since the same parameters do not fit each galaxy...

Can you tell me where I could find out more about this, Wallace?

 

[Garth]

Can you tell me where I could find out more about this, Wallace?

Perhaps?

Angus, G. W.; Famaey, B.; Zhao, H. S.: Can MOND take a bullet? Analytical comparisons of three versions of MOND beyond spherical symmetry

Abstract
A proper test of modified Newtonian dynamics (MOND) in systems of non-trivial geometries depends on modelling subtle differences in several versions of its postulated theories. This is especially true for lensing and dynamics of barely virialized galaxy clusters with typical gravity of scale a0. The original MOND formula, the classical single-field modification of the Poisson equation, and the multifield general relativistic theory of Bekenstein (tensor-vector-scalar, TeVeS) all lead to different predictions as we stray from spherical symmetry. In this paper, we study a class of analytical MONDian models for a system with a semi-Hernquist baryonic profile. After presenting the analytical distribution function of the baryons in spherical limits, we develop orbits and gravitational lensing of the models in non-spherical geometries. In particular, we can generate a multicentred baryonic system with a weak lensing signal resembling that of the merging galaxy cluster 1E 0657-56 with a bullet-like light distribution. We finally present analytical scale-free highly non-spherical models to show the subtle differences between the single-field classical MOND theory and the multifield TeVeS theory

Milgrom, Mordehai:http://adsabs.harvard.edu/abs/2007a...he mass discrepancies in tidal dwarf galaxies

Abstract
I consider in light of MOND the three debris galaxies discussed recently by Bournaud et al.. These exhibit mass discrepancies of a factor of a few within several scale lengths of the visible galaxy, which, arguably, flies in the face of the cold dark matter paradigm. I show here that the rotational velocities predicted by MOND agree well with the observed velocities for each of the three galaxies, with only the observed baryonic matter as the source of gravity. There is thus no need to invoke a new form of baryonic, yet-undetected matter that dominates the disc of spiral galaxies, as advocated by Bournaud et al.. I argue that the presence of such ubiquitous disc dark matter is, in any event, rather unlikely on other grounds.

Garth

 

[Chronos]

I think GPB was a bad idea. But my opinion is irrelevant. I don't get a vote on these projects. The results were mostly known before that mission. I'd have rather seen the money spent on the Hubble telescope.

 

[Garth]

I think GPB was a bad idea. But my opinion is irrelevant. I don't get a vote on these projects. The results were mostly known before that mission. I'd have rather seen the money spent on the Hubble telescope.

Which is a good example of what I was saying:

However an over-confidence placed in the mainstream model may discourage effort that may put in developing other alternatives.

The reason it is good to have other viable alternative models is that they provide something against which the main model may be tested. The nature of both the main model and an alternative determines what questions should be asked and what experiments are worthwhile.

Witness the question about whether the $800 million spent on the Gravity Probe B experiment was well spent or not.

If you think the mainstream model and the theory it is based on - GR - is so well established, then there is no need to test it, and the money so spent is wasted.

IMHO if the final results from that experiment are exactly those predicted by GR then at least that would falsify a whole sheath of alternative theories.

However the hint of a non-GR result, (see http://einstein.stanford.edu/content/aps_posters/APS_talk_Everitt.pdf page 21), at present seen through the noise of unexpected experimental error makes the next few months exciting!

Garth

 

[Wallace]

Can you tell me where I could find out more about this, Wallace?

If you're still interested, check out the papers Garth suggests in post #61. As I've said the issue with MOND, and these two papers are a reasonable example, is that you need to tweak the paramters of the gravity theory for each system studied. So the parameters used in each paper, that find that MOND is a good fit, are different. Use the theory of gravity of one paper with the other and the fit would not be as good.

There are many many papers that detail the best fit parameters for the LCDM model across a wide range of data sets. The MOND crowd are still operating as they did years ago, taking individual systems and constructing ad hoc parametrisations to fit them. What really needs to be done is the let the MOND parameters vary and confront the predictions with the full data set (at once) to arrive at the best fit MOND model for the Universe. If this fit could be shown to be concordant with all available data (as has been done with LCDM) then things will become very interesting. The fact that MONDians have not attempted (to my knowledge) this kind of open and thorough analysis makes me very suspicious. This is the first thing I would do if I was to look at MOND.

Before anyone suggests that this would be too much work for a few mavericks to attempt, I really don't think it would be that hard. Take somthing like http://cosmologist.info/cosmomc/" , adjust the SN likelyhood for the MOND m vs z prediction, modify the CMB code for MOND and your pretty much done. Even ignoring the structure data, which may be a bit tricker to handle with MOND, you would get a good idea of how well MOND can independantly handle these two data sets, and have an idea of how well constrained the gravity parameters are, so if the marginal distributions of the gravity parameters are wide that's pretty clear evidence that either physial laws are not homogenous or that MOND isn't a good theory.

 

[Pakbabydoll]

ok yea I am totally lost... I take my first physics class this fall and have read some basic physics books but these calculations went right over my head.. can you email me and explain please?

 

[Chronos]

It's not too much work, Wallace, as you probably know. The efforts to date simply have not been . . . convincing. And I'm not insisting they must be at this time, just pointing out they have a long row to hoe before MOND can be considered a serious contender.

Footnote for Garth: I agree the research was useful and may produce useful new science. I only object to the price tag. But hindsight is 20-20. The money was mostly spent before the new results were derived. Damned if you do, damned if you don't. I'm thinking of putting that on my resume to NASA . .