Is the Friedmann Space-Time Observable Without Dark Energy?

[fresh_42]

I'm not quit sure whether we had this paper here already, since it is a couple of weeks old. I've seen it here
https://phys.org/news/2017-12-dark-energy-mathematicians-alternative-explanation.html
and I'm somehow fascinated by the idea to get rid of dark energy as only explanation of current observations. Unfortunately the full text doesn't seem to be freely available, but here's the abstract and some of our members might have access to the journal. Also the long review process is a bit surprising (to me).
http://rspa.royalsocietypublishing.org/content/473/2207/20160887

Abstract
We identify the condition for smoothness at the centre of spherically symmetric solutions of Einstein’s original equations without the cosmological constant or dark energy. We use this to derive a universal phase portrait which describes general, smooth, spherically symmetric solutions near the centre of symmetry when the pressure p=0. In this phase portrait, the critical k=0 Friedmann space–time appears as a saddle rest point which is unstable to spherical perturbations. This raises the question as to whether the Friedmann space–time is observable by redshift versus luminosity measurements looking outwards from any point. The unstable manifold of the saddle rest point corresponding to Friedmann describes the evolution of local uniformly expanding space–times whose accelerations closely mimic the effects of dark energy. A unique simple wave perturbation from the radiation epoch is shown to trigger the instability, match the accelerations of dark energy up to second order and distinguish the theory from dark energy at third order. In this sense, anomalous accelerations are not only consistent with Einstein’s original theory of general relativity, but are a prediction of it without the cosmological constant or dark energy.

• Received December 5, 2016.
• Accepted October 24, 2017.

Is there hope that there's something to it, or is it just another unrealistic solution of EFE?

 

[phyzguy]

Attached is a copy of the paper. I'm still digesting it.

Edit: Sorry, I removed the paper due to copyright concerns. Post #3 has the arXiv version.

 

[kimbyd]

I'm not quit sure whether we had this paper here already, since it is a couple of weeks old. I've seen it here
https://phys.org/news/2017-12-dark-energy-mathematicians-alternative-explanation.html
and I'm somehow fascinated by the idea to get rid of dark energy as only explanation of current observations. Unfortunately the full text doesn't seem to be freely available, but here's the abstract and some of our members might have access to the journal. Also the long review process is a bit surprising (to me).
http://rspa.royalsocietypublishing.org/content/473/2207/20160887

Is there hope that there's something to it, or is it just another unrealistic solution of EFE?

I think the preprint is here:
https://arxiv.org/abs/1412.4001

The text of the abstract is quite different, though the title is identical, which leads me to think that there have been very substantial revisions in the above published version. But I would wager to guess the core idea remains.

This sounds like it's one of a class of models that have been proposed for many years that attempt to explain the apparent accelerated expansion by claiming that our galaxy lies very close to the center of a gigantic low-density region. I don't think these ideas really have much chance of fitting current data in detail. Here's an older paper that describes how such models fail to match the data:
https://arxiv.org/abs/1007.3725

Ultimately, the probability that this model overcomes the problems of older void models is very low. Further causes of concern:
1. The preprint has garnered zero citations. That indicates it picked up zero interest in the community.
2. The published article came two years after the preprint, with large revisions. This isn't necessarily troubling, but it isn't good.

 

[wolram]

https://www.sciencedaily.com/releases/2017/12/171214100859.htm

Does anyone have this paper, it seems intriguing to do without Dark Energy.

Date:
December 14, 2017
Source:
University of California - Davis
Summary:
Three mathematicians have a different explanation for the accelerating expansion of the universe that does without theories of 'dark energy.' Einstein's original equations for General Relativity actually predict cosmic acceleration due to an 'instability,' they argue in a new paper.

 

[PeterDonis]

Here is the preprint on arxiv.org:

https://arxiv.org/abs/1412.4001

 

[PeterDonis]

Does anyone have this paper

If you know the title of a paper (which for this one is given in the science daily article, at the bottom), you can almost always find a preprint by Googling the title with site:arxiv.org.

 

[Dennis Plews]

I have often wondered whether the general theory predicts a pull or push. This article seems to suggest that the answer is push. That is to say gravity is not an attractive force but a repulsive force of spacetime that pushes matter towards regions of space that are dominated by matter and energy in which volumes the spacetime expansion is locally retarded by the local mass/energy density. Is this a reasonable interpretation?

 

[PeterDonis]

I have often wondered whether the general theory predicts a pull or push.

It depends on the stress-energy tensor.

This article seems to suggest that the answer is push.

No, it's suggesting that the amount of "pull" varies from place to place, whereas in the standard FRW model without dark energy it's the same everywhere. The model suggested in the article has no dark energy, so there is no "push" anywhere. (See below for further comment on the terms "pull" and "push".)

gravity is not an attractive force but a repulsive force

Gravity is not a "force" at all in GR; it's spacetime curvature. What you are calling "pull" and "push" are just different types of spacetime curvature. Objects moving solely due to spacetime curvature feel no force; they are in free fall. That's equally true for a universe without dark energy and a universe with dark energy.

 

[wolram]

If you know the title of a paper (which for this one is given in the science daily article, at the bottom), you can almost always find a preprint by Googling the title with site:arxiv.org.

Thank you Peter