Wiltshire's Timescape model been refuted?

[Jorrie]

Since 2006/7, David Wiltshire published a number of papers on his "http://arxiv.org/abs/1102.2045" ", as he calls it lately (2010/11), apparently changing from the original "Fractal Bubble (FB) universe" name. I suspect that this change was due to it being confused with the "Hubble Bubble", which it has little to so with, other than offering an 'explanation' for the Hubble Bubble phenomenon. AFAIK, it has all to do with inhomogeneity and the postulate that gravitational time dilation in the clusters can cause those SN1a to appear farther than they actually are (hence apparent accelerating expansion).

My question is: has there been any refutations of his 'Timescape model', either theoretically or by incompatibility with recent observations that stood up? I could not find any such papers so far.

 

[bcrowell]

Could you provide references to the Wiltshire papers? Are they on arxiv?

 

[LithiumHelios]

http://arxiv.org/abs/1009.5855

You can find some on the arXiv. (Not that I've particularly read any of them though...)

 

[cosmik debris]

Could you provide references to the Wiltshire papers? Are they on arxiv?

I've been to many of David's seminars (i work at the same University) and I'd be interested in your thoughts on his stuff. I find it pretty interesting.

 

[bcrowell]

One thing I don't understand is why the existence of voids gives any systematic effect in supernovae's brightness-redshift relationships. I would think that the local gravitational redshifts would tend to cancel out. A photon is emitted by a supernova in a galaxy, which is at the bottom of a potential well in some high-density region of the universe like a filament or a supercluster. The photon climbs out of that gravity well, but then as it approaches our own galaxy it falls back down into our own gravity well -- so why don't the effects cancel? I'm sure Wiltshire has got this right, but I just don't understand it.

There is a review article on livingreviews on the cosmological constant http://relativity.livingreviews.org/open?pubNo=lrr-2001-1&page=title.html , but it doesn't appear to be recent enough to give any impartial analysis of the timescape model.

We have two independent sources of information about the cosmological constant: supernovae and CMB anisotropy. The paper LithiumHelios linked to focuses on the supernova evidence. I don't understand why inhomogeneity would have an effect on the CMB analysis at all...?

 

[bcrowell]

OK, maybe I get it more now.

Here's a recent analysis by an impartial observer:
http://blogs.discovermagazine.com/cosmicvariance/2010/07/29/are-you-the-center-of-the-universe/

The model says we happen to be in a void. I think the idea is that if a photon was emitted in the early universe, it was emitted before most of the structure formation happened. Therefore it didn't have to climb out of a deep potential well, but by the time it got to us, we had come to occupy a spot in a high-potential void, so there is an anomalous redshift.

 

[bcrowell]

Here is a paper that claims to refute the timescape model: http://arxiv.org/abs/1007.3725

A couple of other recent papers:
http://arxiv.org/abs/1103.2335
http://arxiv.org/abs/1104.1300[EDIT] Originally gave the wrong link.

 

[yenchin]

Here is a paper that claims to refute the timescape model: http://arxiv.org/abs/1007.3725

A couple of other recent papers:
http://arxiv.org/abs/1103.2335
http://arxiv.org/abs/1104.1300


[EDIT] Originally gave the wrong link.

Not sure if this is relevant: http://iopscience.iop.org/0004-637X/730/2/119/fulltext"
"The improved measurement of H0, when combined with the Wilkinson Microwave Anisotropy Probe (WMAP) 7 year data, results in a tighter constraint on the equation-of-state parameter of dark energy of w = –1.08 ± 0.10. It also rules out the best-fitting gigaparsec-scale void models, posited as an alternative to dark energy. "

Is Timescape model equivalent to void model?

 

[Jorrie]

Is Timescape model equivalent to void model?

As I understand it, no. The "void model" is equivalent to the "Hubble bubble model", but as I wrote in OP:

I suspect that this [name] change was due to [the TS model] being confused with the "Hubble Bubble", which it has little to do with, other than offering an 'explanation' for the Hubble Bubble phenomenon.

I understand Wiltshire to say that since we are inside a "bubble wall" (gravitational well) our locality is expanding slower than the voids, which dominate the cosmic volume. In a sense, he has different Ho (and different H(t)-evolution) for observers in different density regions. The TS model hence still favors an isotropic CMB for all observers, but (unlike the LCDM model) not at the same CMB temperature/redshift for all observers.

It seems that if his work is correct, an open inhomogeneous solution with some 33% normal+dark matter energy can give (from our POV) an apparent accelerating expansion with no dark energy required.

Wilthire's 2011 paper (or Astro-Ph letter) http://arxiv.org/abs/1102.2045" (Gravitational energy as dark energy: cosmic structure and apparent acceleration) has a particularly interesting "FIGURE 2. The effective comoving distance HoD(z) is plotted for the best-fit timescape (TS) model."

Other than misunderstandings of Wiltshire's model, I have not yet seen any refutation in the literature. Smale & Wiltshire's 2010 paper http://arxiv.org/abs/1009.5855" (Supernova tests of the timescape cosmology) answer some criticisms, but I do not understand the model well enough to decide one way or the other.

 

[Jorrie]

Not sure if this is relevant: http://iopscience.iop.org/0004-637X/730/2/119/fulltext"
"The improved measurement of H0, when combined with the Wilkinson Microwave Anisotropy Probe (WMAP) 7 year data, results in a tighter constraint on the equation-of-state parameter of dark energy of w = –1.08 ± 0.10. It also rules out the best-fitting gigaparsec-scale void models, posited as an alternative to dark energy. "

I found the http://arxiv.org/abs/1103.2976" .
I scanned it briefly, but I'm still not sure if they really address Wiltshire's TS model or just the "Hubble Bubble" type models.

E.g. they wrote: "The enhanced precision in measuring H0 also provides a strong rebuff to recent attempts to explain accelerated expansion without dark energy but rather by our presence in the center of a massive void of gigaparsec scale."

This does not seem to apply to Wiltshire, although they mention his 2007 paper in the same paragraph.

 

[cosmik debris]

Thanks for some of the comments, I'll have to do a bit of reading.

 

[Jorrie]

Not sure if this is relevant: http://iopscience.iop.org/0004-637X/730/2/119/fulltext"

It is indeed relevant. Witshire did mention Rees et al.'s H0 determination in the discussion section of his http://arxiv.org/abs/1102.2045" (Gravitational energy as dark energy: cosmic structure and apparent acceleration, 2011)

"The value of the dressed Hubble constant is also an observable quantity of consider-
able interest. A recent determination of H0 by Riess et al. [55] poses a challenge for the
timescape model. However, it is a feature of the timescape model that a 17–22% vari-
ance in the apparent Hubble flow will exist on local scales below the scale of statistical
homogeneity, and this may potentially complicate calibration of the cosmic distance lad-
der. Further quantification of the variance in the apparent Hubble flow in relationship to
local cosmic structures would provide an interesting possibility for tests of the timescape
cosmology for which there are no counterparts in the standard cosmology."

An interesting dilemma...