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A possible Coasting Universe model vs ΛCDM

by petergreen
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petergreen
#1
Feb6-13, 12:09 PM
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Two Coasting Universe model and comparison of the ΛCDM as well as Rh = ct models with Ia supernovae, GMB and CMB events. Both theory lead to the same result and fundamentals.
[Journal references below]

First model:

Rh = ct universe

"The backbone of standard cosmology is the Friedmann-Robertson-Walker solution to Einstein’s equations of general relativity (GR). In recent years, observations have largely confirmed many of the properties of this model, which is based on a partitioning of the universe’s energy density into three primary constituents: matter, radiation, and a hypothesized dark energy which, in ΛCDM, is assumed to be a cosmological constant Λ. Yet with this progress, several unpalatable coincidences (perhaps even inconsistencies) have emerged along with the successful confirmation of expected features. One of these is the observed equality of our gravitational horizon Rh(t0) with the distance ct0 light has traveled since the big bang, in terms of the current age t0 of the universe. This equality is very peculiar because it need not have occurred at all and, if it did, should only have happened once (right now) in the context of ΛCDM. In this paper, we propose an explantion for why this equality may actually be required by GR, through the application of Birkhoff’s theorem and the Weyl postulate, at least in the case of a flat spacetime. If this proposal is correct, Rh(t) should be equal to ct for all cosmic time t, not just its present value t0. Therefore models such as ΛCDM would be incomplete because they ascribe the cosmic expansion to variable conditions not consistent with this relativistic constraint. We show that this may be the reason why the observed galaxy correlation function is not consistent with the predictions of the standard model. We suggest that an Rh = ct universe is easily distinguishable from all other models at large redshift (i.e., in the early universe), where the latter all predict a rapid deceleration."

The Rh = ct Universe
http://arxiv.org/pdf/1109.5189.pdf

Fitting the Union2.1 SN Sample with the Rh = ct Universe
http://arxiv.org/pdf/1206.6289.pdf

The Rh = ct Universe Without Inflation
http://arxiv.org/pdf/1206.6527.pdf

Angular Correlation of the CMB in the Rh = ct Universe
http://arxiv.org/pdf/1207.0015.pdf

High-Z Quasars in the Rh = ct Universe
http://arxiv.org/pdf/1301.0017.pdf

The Gamma-Ray Burst Hubble Diagram and Its Cosmological Implications
http://arxiv.org/pdf/1301.0894.pdf

[Journal refs.: Monthly Notices of the Royal Astronomical Society (MNRAS) & Astronomical Journal - IOP Science]

Second model:

The model of a flat (Euclidean) expansive homogeneous and isotropic relativistic universe in the light of the general relativity, quantum mechanics, and observations

"Assuming that the relativistic universe is homogeneous and isotropic, we can unambiguously determine its model and physical properties, which correspond with the Einstein general theory of relativity (and with its two special partial solutions: Einstein special theory of relativity and Newton gravitation theory), quantum mechanics, and observations, too."

http://arxiv.org/pdf/1301.0894.pdf

[Journal ref.: Astrophysics and Space Science]

The two theory fundamentals:

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Mordred
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Feb6-13, 12:33 PM
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Nice articles going to take me a bit to go through them
Garth
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Feb6-13, 05:52 PM
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I have argued for the benefits of the coasting cosmological model in the past.

Viz:

1. No need for Inflation; the horizon, density and smoothness problems that Inflation was developed to explain would not be there in the first place.

2. A natural explanation for the Age of the Universe = Hubble Time coincidence.

3. It alleviates any Age problem in the early universe.

4. The longer BBN epoch yields results in a higher baryon density that may explain Dark Matter as baryonic in nature. ( Must still be dark in the form of IMBHs perhaps). It would leave a Deuterium problem but resolve the Lithium Problem.

5. It would explain a low power deficiency in the CMB power spectrum when compared with the LCDM prediction.

First proposed by Kolb in 1989 as a way of avoiding Inflation A coasting cosmology , it was then taken up by an Indian team who found it a concordant alternative to LCDM. A Concordant “Freely Coasting” Cosmology, recently it has been advocated by Melia et al. in the papers cited in the OP.

There are problems, but no more than the standard model that has had to invoke Inflation, DM and DE, all unconfirmed in the laboratory.

Just a thought,
Garth

petergreen
#4
Feb6-13, 06:19 PM
P: 25
A possible Coasting Universe model vs ΛCDM

First proposed by Kolb in 1989 as a way of avoiding Inflation A coasting cosmology , it was then taken up by an Indian team who found it a concordant alternative to LCDM. A Concordant “Freely Coasting” Cosmology, recently it has been advocated by Melia et al. in the papers cited in the OP.
And this:

http://www.akamaiuniversity.us/PJST12_1_214.pdf
Chalnoth
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Feb7-13, 08:43 AM
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Quote Quote by Garth View Post
There are problems, but no more than the standard model that has had to invoke Inflation, DM and DE, all unconfirmed in the laboratory.
I would say the problems are vastly, vastly greater, as the coasting model requires either extremely exotic matter or an entirely new law of gravity.
Garth
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Feb7-13, 10:22 AM
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Quote Quote by Chalnoth View Post
I would say the problems are vastly, vastly greater, as the coasting model requires either extremely exotic matter or an entirely new law of gravity.
And the [itex]\Lambda[/itex]CDM model does not? DM?? DE??

Linear expansion requires DE with an equation of state [itex]\omega = - \frac{1}{3}[/itex].

Kolb suggested K matter with [itex] p_k = - \frac{1}{3} \rho_k[/itex]

Such as might be provided by cosmic string networks.

As for an entirely new law of gravity, Self Creation Cosmology maybe??
(published in 'Horizons in World Physics, Volume 247: New Developments in Quantum Cosmology Research', Nova Science Publishers, Inc. New York)

Just a thought...

Garth
Chalnoth
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Feb7-13, 12:11 PM
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Quote Quote by Garth View Post
And the [itex]\Lambda[/itex]CDM model does not? DM?? DE??
Dark matter isn't exotic at all by these measures. And [itex]\Lambda[/itex] has been a part of GR from the beginning (though it was usually assumed to be zero).

Quote Quote by Garth View Post
Linear expansion requires DE with an equation of state [itex]\omega = - \frac{1}{3}[/itex].

Kolb suggested K matter with [itex] p_k = - \frac{1}{3} \rho_k[/itex]

Such as might be provided by cosmic string networks.
Yes. But detailed observations have now disproven the possibility that cosmic strings are a large fraction of the matter density of the universe.

I don't think you can fit the coasting universe with the CMB, at all.
petergreen
#8
Feb7-13, 04:57 PM
P: 25
Dear Chalnoth and Garth!

In the coasting universe, dark energy does not exist (Λ=0)! Only dark matter, onto which is the only possible candidate the weakly interacting axion, or the continuously and in increasing quantities generated, appearing and disappearing virtual particle pairs.
Garth
#9
Feb7-13, 05:11 PM
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Quote Quote by petergreen View Post
Dear Calnoth and Garth!

In the coasting universe, dark energy does not exist!
Well that depends on how you obtain a coasting, i.e. strictly linear, expansion.

The empty universe, the Milne FRW model, contains no source of gravitation and therefore there is nothing to decelerate it, so it expands linearly.

If matter is present (as indeed there is) then that produces a gravitational field that would decelerate the universe. To obtain linear expansion something must counter act this effect.

In the Dirac-Milne universe equal amounts of matter and anti-matter exist and it is assumed that they repel each other. The universe instantly separates out into matter and anti-matter zones and this mutual repulsion cancels out the gravitational attraction within each zone.

Otherwise you need a medium of high negative pressure, otherwise known as dark energy and they are several hypothetical candidates that might be the source of this, the cosmological constant being one of them.

I hope this helps.

Garth
petergreen
#10
Feb7-13, 05:29 PM
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Garth!

Here the negative energy is the gravitational energy! The zero-energy universe hypothesis states that the total amount of energy in the universe is exactly zero. The positive energy of the matter is exactly balanced by the negative energy of the gravitational field.

If in an expansive Universe relativistic and quantum-mechanical properties are complementary, permanent constant maximum possible increase of negative energy of gravitational field must arise and simultaneously, permanent constant maximum possible increase of positive energy of the matter must occur, which compensate each other; hence, total energy of the Universe is equal to zero. Therefore, the expanding Universe must be non-decelerative and non-accelerative, i.e., during the whole expansive evolution phase, it must expand by constant maximum possible velocity v = c. So the universe expands linearly.
Garth
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Feb7-13, 06:03 PM
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Quote Quote by petergreen View Post
Garth!

Here the negative energy is the gravitational energy! The zero-energy universe hypothesis states that the total amount of energy in the universe is exactly zero. The positive energy of the matter is exactly balanced by the negative energy of the gravitational field.

If in an expansive Universe relativistic and quantum-mechanical properties are complementary, permanent constant maximum possible increase of negative energy of gravitational field must arise and simultaneously, permanent constant maximum possible increase of positive energy of the matter must occur, which compensate each other; hence, total energy of the Universe is equal to zero. Therefore, the expanding Universe must be non-decelerative and non-accelerative, i.e., during the whole expansive evolution phase, it must expand by constant maximum possible velocity v = c. So the universe expands linearly.
The zero-energy universe (depending on how you measure energy) is the flat universe.

The expansion rate is determined by the FRW equation in which curvature effects and expansion rates are convoluted. You have to solve the equations carefully and use the equation of state to separate out the two effects. It is possible to balance the eos using a certain amount of cosmological constant, (which I take to be a form of DE) but you then have to show that that model is observationally concordant. It here that Chalnoth and I disagree.

Garth
Chalnoth
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Feb7-13, 06:46 PM
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Quote Quote by Garth View Post
The zero-energy universe (depending on how you measure energy) is the flat universe.
To be pedantic, it's a closed universe.

Quote Quote by Garth View Post
The expansion rate is determined by the FRW equation in which curvature effects and expansion rates are convoluted. You have to solve the equations carefully and use the equation of state to separate out the two effects. It is possible to balance the eos using a certain amount of cosmological constant, (which I take to be a form of DE) but you then have to show that that model is observationally concordant. It here that Chalnoth and I disagree.
Disagree how now? Because it sounds to me like you're saying I don't think the correct model should be chosen by the data. What I do say is that I sincerely doubt the coasting model can explain cosmological perturbations we see in the CMB. Crucially, early-on, cosmic strings were thought to be a potential source of cosmological perturbations. Cosmic strings have an equation of state of [itex]w=-1/3[/itex], and would produce a coasting universe. Except the pattern of perturbations predicted by cosmic string models was completely and utterly different from the pattern predicted in inflationary models, and observations demonstrated that it was the inflationary models that fit the data.

There still may be some cosmic strings, but they don't make up a significant fraction of the energy density of the universe.
petergreen
#13
Feb7-13, 06:59 PM
P: 25
What I do say is that I sincerely doubt the coasting model can explain cosmological perturbations we see in the CMB.
http://arxiv.org/pdf/1207.0015.pdf

Chalnoth
#14
Feb7-13, 07:10 PM
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It's telling, I think, that they use the first-year WMAP release to make that claim, despite this paper by the WMAP team being available at the time of writing:
http://lambda.gsfc.nasa.gov/product/..._anomalies.pdf

And the main discrepancy between the coasting universe and ΛCDM is likely to be found in the power spectrum, which is not shown in the above paper.
Garth
#15
Feb8-13, 01:46 AM
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Quote Quote by Chalnoth View Post

And the main discrepancy between the coasting universe and ΛCDM is likely to be found in the power spectrum, which is not shown in the above paper.
But there are others who might disagree.

Observational Constraints of a Matter-Antimatter Symmetric Milne Universe

A Concordant “Freely Coasting” Cosmology
The main point we make in this article is that in spite of a significantly different evolution, the recombination history of a linearly coasting cosmology can be expected to give the location of the primary acoustic peaks in the same range of angles as that given in Standard Cosmology.
Garth
Chalnoth
#16
Feb8-13, 08:46 AM
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If by disagree you mean ignoring the issue, then sure, they disagree. It doesn't count if they don't fully account for the production and propagation of the primordial perturbations.


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