Universal expansion acceleration

[Jacques]

Hi

The high redshift supernovao survey came out with a supprising result: the expansion of the universe is accelerating. The first explaination proposed is that there should be an unknowed force that drive that acceleration, and cosmologist called it drak energy.

I have an other explaination using only relativity. Let me exposed the principles and observations on withch I base my reasonning.

1- Time slowing down in a gravity well. This is experimentally verified by many method. One of it involve and radiation emiter situated above a detector: the radiation is blue shifted.

2- The large scale structure of the universe is like a foam: a web of galaxies and galaxy cluster with large buble of empty space.

3- These buble increase with time due to the expansion

4- The expansion of the universe happen mainly in these bubble

 

Now from there I can deduced :

The gravity potential in these bubble is smaller than in our galaxy, so time in these bubble seen from our galaxy is faster.

When the universe was younger, these buble where smaller, so the gravity potential in these buble was bigger than today.

I dont know if you make the link now ???

OK the acceleration of the expansion of the universe is an observational illusion.

Has we go deeper and deeper in our gravitationnal well (galaxies condensing into a web) we observe the expansion of the universe happening in the bubble going faster.

I hope I made my idea clear enough and don't hesitate to ask for clarifications.

What do you think of that ? Is there some expert that can do the calculation to see if it can account for the mesured acceleration ?

Thanks

[Martin]

..

I have an other explaination using only relativity. Let me exposed the principles and observations on which I base my reasonning.

...

As we go deeper and deeper in our gravitationnal well (galaxies condensing into a web) we observe the expansion of the universe happening in the bubble going faster.

...

 

I personally cannot help you with this.

 

However I know that others have tried to do this general kind of analysis and there is a new article about it that surveys some of these attempts.

 

The general idea is that the universe has matter distributed in a web with large holes or bubbles ----big empty voids in the web. this is OBSERVED when we map out where the clusters of galaxies are. It is like what the dust does in the corners our house when I do not vacuum the dust. we call it "cobweb". this is SEEN so there is no question about it.

 

So there are some people, like you, who try to EXPLAIN ACCELERATION AS AN ILLUSION OR AS AN EFFECT CAUSED BY THE LARGE-SCALE STRUCTURE.

 

Your method involves TIME SLOWING in a deep gravity well, compared with the average universe time which would include the big typical voids in the web. But other people probably have other methods of explaining that also use the large-scale structure.

 

Personally I doubt that this works. I don't think the effect is ENOUGH to explain the observed acceleration. But I really do not know! I cannot help you check this idea.

 

So I will just give you a URL. Maybe from this recent article you can find other articles that could help.

 

http://arxiv.org/abs/0707.2153

Dark Energy from Structure - A Status Report

Thomas Buchert

Invited Review for a special Gen. Rel. Grav. issue on Dark Energy, 58 pages, 2 figures

(Submitted on 14 Jul 2007)

 

"The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein's theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effective volume scale factor, with matter and backreaction source terms. The latter can be represented by an effective scalar field (`morphon field') modeling Dark Energy.

The present work provides an overview over the Dark Energy debate in connection with the impact of inhomogeneities, and formulates strategies for a comprehensive quantitative evaluation of backreaction effects both in theoretical and observational cosmology. We recall the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of challenges and unresolved issues in connection with their observational interpretation.

The present status of this subject is intermediate: we have a good qualitative understanding of backreaction effects pointing to a global instability of the standard model of cosmology; exact solutions and perturbative results modeling this instability lie in the right sector to explain Dark Energy from inhomogeneities. It is fair to say that, even if backreaction effects turn out to be less important than anticipated by some researchers, the concordance high-precision cosmology, the architecture of current N-body simulations, as well as standard perturbative approaches all fall short in correctly describing the Late Universe."

[Jacques]

Thanks Martin

If you didn't told me that this article was related to my question, I would'nt know. I am happy to see that some cosmologist try to find other solution to the accelarating expansion, other than dark energy. I don't know the maths in the article, but I can understand that Einstein equation are for an homogenous universe, but the universe is not so homogenous...

[Martin]

Maybe I'm wrong, Jacques. I will take another look.

 

YES You are right! I got the wrong paper by mistake. I am in a hurry and can't stop to be sure, but I think this paper may be the right one:

 

http://arxiv.org/abs/gr-qc/0702082

Cosmic clocks, cosmic variance and cosmic averages

David L. Wiltshire

72 pages, 5 figures,

(Submitted on 15 Feb 2007 (v1), last revised 1 Mar 2007 (this version, v2))

 

"Cosmic acceleration is explained quantitatively, purely in general relativity, as an apparent effect due to quasilocal gravitational energy differences that arise in the decoupling of bound systems from the global expansion of the universe. 'Dark energy' is recognised as a misidentification of those aspects of gravitational energy which by virtue of the equivalence principle cannot be localised, namely gradients in the energy associated with the expansion of space and spatial curvature variations in an inhomogeneous universe, as we observe. Gravitational energy differences between observers in bound systems, such as galaxies, and volume-averaged comoving locations within voids in freely expanding space can be so large that the time dilation between the two significantly affects the parameters of any effective homogeneous isotropic model one fits to the universe. A new approach to cosmological averaging is presented, which implicitly solves the Sandage-de Vaucouleurs paradox. When combined with a nonlinear scheme for cosmological evolution with back-reaction via the Buchert equations, a new observationally viable quantitative model of the universe is obtained. The expansion age is increased, allowing more time for structure formation. The baryon density fraction obtained from primordial nucleosynthesis bounds can be significantly larger, yet consistent with primordial lithium abundance measurements. The angular scale of the first Doppler peak in the CMB anisotropy spectrum fits the new model despite an average negative spatial curvature at late epochs, resolving the anomaly associated with ellipticity in the CMB anisotropies. A number of other testable consequences are discussed, with the potential to profoundly change the whole of theoretical and observational cosmology. [Abridged]

 

See also this webpage of David Wiltshire:

http://www2.phys.canterbury.ac.nz/~dlw24/universe/

 

" Dark energy has been described as the biggest problem in cosmology. In new work, I suggest that we have been looking at the problem in the wrong fashion. Dark energy is not the internal energy of a mysterious fluid, but a misidentification of those aspects of cosmological gravitational energy which by virtue of the equivalence principle cannot be localised: gradients in the kinetic energy of the expansion of space, and spatial curvature variations. These are important aspects of gravitational physics in a universe, which at the present epoch is very inhomogeneous, dominated by voids.

 

I use the formalism of Thomas Buchert in taking account of back-reaction in the evolution of Einstein's equations, but take the extra essential step of asking how our own measurements are related to volume average ones. One crucial insight is that gravitational energy, and clock rates, are defined with respect to a notion of infinity. I specifically develop the notion of finite infinity, as suggested qualitatively by George Ellis in 1984. Bound systems where space is not expanding, including all galaxies, live within finite infinity, but volume average positions in freely expanding space lie beyond it - there is a difference in gravitational energy and spatial curvature between the two locations. The differences were initially miniscule but are large today. Taking account of the initial conditions set by primordial inflation at the time of last scattering, when the cosmic microwave background was laid down, a quantitative model of the universe is developed. It appears to be viable.

 

Relative to bound system observers, ideal observers at volume average positions in voids will measure an older age of the universe, a lower mean temperature for the cosmic microwave background, and a smaller angular anisotropy scale. These differences can be systematically quantified. On account of the variance in clock rates volume average observers in voids measure no apparent "cosmic acceleration", but observers such as ourselves in bound systems do.

 

The mystery of dark energy is explained purely in Einstein's theory, through a deeper understanding of those parts of general relativity, which Einstein himself recognised as being difficult: the understanding of gravitational energy, given that space itself is dynamical and may contain energy and momentum. "

 

THESE TWO AUTHORS CITE EACH OTHER. Buchert, the one I first gave link, cites Wiltshire, who cites Buchert back. But probably the Wiltshire paper is closer to what you had in mind.

 

I don't know anything that I can be sure is exactly right, but at least Wiltshire is trying to explain the appearance of D.E. without actually having D.E.

 

Please try this one and if it is not right, tell me and I will look again.

[Jacques]

Thanks Martin

I didn't readed the article yet but the abstracts are realy about what I thought.

Next thing I am wondering, does it mark the end of dark energy ?

How long will it take for that simple explaination to be accepted ? Will it be accepted ?

I was able all by myself, only with logic, deduce that possible explaination about dark energy. If no cosmologist had thought about it, the chance that my idea survived is almost null.

Thanks again Martin

[losfomot]

I am loving this thread. Dark energy was always a pain in the ass.

 

At first glance I would tend to agree with Martin that the effect would be too small to account for the acceleration that we see, but what do I know? Maybe a big crunch is still possible, though we've been fooled into deducing the opposite?