New cosmology - dark energy unnecessary

[Kea]

Hello Marcus, selfAdjoint, nightcleaner, Chronos, setAI and others

I think the following speaks for itself

Viable exact model universe without dark energy from primordial inflation
David L. Wiltshire
http://www.arxiv.org/abs/gr-qc/0503099

Regards
Kea

 

[selfAdjoint]

Aren't those "supersized remant perturbations" being criticized as non causal? How can something over our light horizon affect us?

 

[Chronos]

I have issues with that paper. In particular, the cosmic clock concept. It looks suspiciously like a preferred reference frame.

 

[marcus]

Ive been reading the Wiltshire paper, and also the previous one by Kolb et al that came out 10 days or so (that Wiltshire cites). Cant comment. just trying to picture what Wiltshire's talking about.

I assume there's been some discussion on SPR, but I've missed it. I'd be glad to read some lengthier responses by others.

 

[marcus]

there is a troubling numerical discrepancy, or something i don't get
for example typically you see estimates like Omega_matter = 0.27
and Omega_Lambda = 0.73

and he has a digit switched around, see for example the caption
to figure 1 on page 3
he has Omega_matter = 0.23
and Omega_Lambda = 0.77

the 0.23 is the usual estimate for DARK matter, but you have to add 0.04 for observed matter, to get 0.27
and then conventionally one says Omega_Lambda = 1 - Omega_matter = 1 - 0.27 = 0.73

so it looks like he has made a careless numerical mistake which, in itself does not affect the qualitative conclusions very much.
Or is there something I am missing?

 

[Chronos]

I thought it was just me. I had a couple of disconnects like that myself.

 

[marcus]

I'm inclined to focus on the Kolb et al paper that came out 14 March

http://arxiv.org/hep-th/0503117
Primordial inflation explains why the universe is accelerating today
Edward W. Kolb, Sabino Matarrese, Alessio Notari, Antonio Riotto
4 pages, one figure
Report-no: FERMILAB-PUB-05-024-A

"We propose an explanation for the present accelerated expansion of the universe that does not invoke dark energy or a modification of gravity and is firmly rooted in inflationary cosmology."

I think the essential ideas are in Kolb et al, and Wiltshire (as I believe he indicates) is picking up the idea from them and calculating some cases. Assuming he first saw the Kolb paper some 10 days ago he has not had much time to revise and correct, so maybe his paper is not in its final form. This does not diminish its value and importance! (but for the time being I'll devote more attention to the predecessor)

 

[marcus]

to oversimplify Kolb et al say look at this 73% which we need to have a flat universe (at large scale)
we see the universe is flat so we postulate some "dark energy" to be this 73% and fill the hole in our model

wait! they say, suppose there really is this hole. suppose the universe at very large scale IS on average flat and governed by the regular Friedmann eqn we know and love, but suppose our part of the universe is atypically thinned out so that it is matter-lean by the observed 73%

suppose a primordial quantum uneven-ness made matter (just before inflation) be unevenly distributed-----so our part got only 27% of its fair share (as we observe there is only 27% enough matter to make the universe flat, yet it is flat)-----and then suppose INFLATION expanded all that so the unevenness is now on an immense scale.

OK, this is something that seems like it would leave a signature in the CMB and that one could test by analyzing the CMB better. I am not sure about that but it seems to me that one can derive predictions from that and test it and see how it fits. (and also in principle one can wait until the observable universe is bigger and check then too but that is a long wait)

so this is probably not some fairytale multiverse untestable pipedream but probably a testable hypothesis one can plug into the regular Friedmann equation and see how it fits-------and it doesn't have any acceleration-producing dark energy so it should actually have a very distinctive look.

if I have oversimplified too much please anybody give an improved sketch of their idea

I am going to look and see who Antonio Riotto and Edward Kolb are

 

[marcus]

Antonio Riotto has 147 papers going back to 1992
Edward Kolb has 64 papers going back to 1992

In 1996 they were both at Fermilab and they wrote several paper together, so their association goes back at least that far

Kolb is still at Fermilab. Riotto is at INFN-Padua.
Both have published with some wellknown people whose names
any of us would recognize. I didnt happen to know of them---their
names didnt happen to ring a bell for me, which could just be a glitch in
my memory

National Institute of Nuclear Physics
--Istituto Nazionale di Fisica Nucleare-sezione di Padova:
a branch of INFN connected with the University of Padua

Notari is at McGill, Matarrese is at INFN-Padua

---------------

We should also plug the University of Canterbury which is where
David Wiltshire and Kea are
I have to admire David Wiltshire---he may not have invented this curious no-dark-energy cosmology, but got on it really fast. it looks like he had a paper carrying out calculations with it within 10 days of Kolb et al posting.

 

[marcus]

the LQG connection with fluffy cosmology

for me what seems like a nice thing about the no-dark-energy cosmology notion proposed by Tony Riotto and co-authors (note the outrageous use of nickname, it sounds better)

is the way it fits with Bojowald's quantized Friedmann equation.

the tony riotto idea is basically standard Freidmann-equation cosmology with inflation----it is rather classical in spirit and doesn't presume a lot of extra dimensions and branes and etc.

bojowald Loop Quantum Cosmology derives from a quantized version of the Friedmann equation (which then turns into a difference equation and doesn't suffer from the classical singularities)

so LQC is very close to the cosmological model that cosmologists are used to working with, and has been around since 1922-1924 when Friedmann wrote it

and a nice thing about LQC is that the quantized Friedmann eqn, now a difference eqn, MAKES INFLATION AUTOMATIC. that is a brief period of inflation with a graceful exit is (as Ganashyam said) "generic". it happens without finetuning the parameters, you get it in LQC over a wide range of choices of the details

so LQC seems like a good context in which to look at the Tony Riotto idea,
which depends on a quantum fluctuation affecting the energy density (or density of matter) in an instant right before inflation.
one might be able to put the quantum geometry together with the
quantum density fluctuation

Here is a recent survey of progress so far in LQC
http://arxiv.org/gr-qc/0503020
The Early Universe in Loop Quantum Cosmology
Bojowald
10 pages

"Loop quantum cosmology applies techniques derived for a background independent quantization of general relativity to cosmological situations and draws conclusions for the very early universe. Direct implications for the singularity problem as well as phenomenology in the context of inflation or bouncing universes result, which will be reviewed here. The discussion focuses on recent new results for structure formation and generalizations of the methods."

in this paper the form of the Friedmann eqn appears as eqn (1) and the quantized version appears as (13). there is a brief sketch of how to get from one to the other

 

[wolram]

All of cosmology seems to boil down to percentages, and what is in
our universes, is dark matter real, is dark energy real? I guess one
can theorise ad infinitum without concrete figures.
My guess is that observations are all that is necessary to forecast the
mass in the U, and any missing mass is due to the primordial energy
that caused creation, what that is, is what science needs to know, so
until then guessing games are the norm.

 

[marcus]

I see that someone over at SPR just posted this link to a press release

http://www.fnal.gov/pub/presspass/press_releases/darkenergy_3-16-05.html

the press item was written by someone in public relations at INFN, in italy.

Fermilab just copied the INFN release. this confirms the notion that Tony Riotto is the main author here. padova is the homeplate from which this ball has been hit, so to speak

I am wondering why I haven't seen more discussion. I could find essentially nothing on SPR.

Peter Woit called attention to the Kolb et al paper right around when it came out, IIRC, which would have been around 14 March. I will go back and see if NotEvenWrong blog has some discussion

yeah, this is just another sign of how cool Peter Woit is
he blogged this immediately, on 16 March
http://www.math.columbia.edu/~woit/blog/archives/000169.html


then Sean Carroll blogged it 22 March
http://preposterousuniverse.blogspo...erousuniverse_archive.html#111155024666490546

Peter Woit got 21 comments on his 16 March blog, and Sean got 31 comments on his blog a week later.

Sean is waving his hands making warning motions about the Kolb et al, which he calls KNMR for the authors' initials. but that is just his gut reaction.
he linked to this news item in "the Australian" which quoted Michael Turner, also shaking his head
http://www.theaustralian.news.com.au/common/story_page/0,5744,12633934%255E29098,00.html

Sean also linked to an article in New Scientists
http://www.newscientist.com/article.ns?id=dn7167
this quotes Robert Brandenburger and also Sean himself
(who says Tony Riotto et al have a good track record, but expresses skepticism)

 

[marcus]

One of the 21 comments in Peter Woits blog about Kolb et al
was where Alejandro (fellow PF) gave a link to still another
site, the Cabi blog:
http://www.mit.edu/people/cabi/blog/2005/03/universe-accelerated-beyond-horizon.html#comments

seems to be a huge reaction to Kolb et al.
a good way to get the flavor is to read the 21 comments at Woit's blog.
eg. someone had lunch with a bunch of cosmologists and that was what they were talking about and he gives an idea of their reaction.

http://www.math.columbia.edu/~woit/blog/archives/000169.html

 

[marcus]

As I said earlier Sean Carroll blogged it 22 March
http://preposterousuniverse.blogspo...erousuniverse_archive.html#111155024666490546

and so far he got 31 comments (mostly about Kolb et al but) some were about WILTSHIRE paper, which is derived from Kolb.

Here are some comments from Carroll's blog that specifically concern the Wiltshire paper

---quote---

Wiltshire's model (gr-qc/0503099) is just weird. General relativity is a complete theory that doesn't obey Mach's principle; you're not allowed to just add Mach's principle to it. And the business about "true cosmic time" being set by the unobservable background is just not right. Clocks measure the spacetime interval, and you can always calculate it locally.
Sean, Thu, March 24, 2005 @ 10:52 pm

Surely the idea with Wiltshire's work is that CMB defines who the isotropic observers are and the CMB (even as we observe it here in our bubble) defines the true surface of homogeneity in the full universe. So when we put ourselves in the frame that gives an isotropic CMB we are putting ourselves in the full cosmic comoving frame.
Note that Wiltshire has already put out a slightly modified version of his paper after comments from Roy Kerr.
Andreas, Fri, March 25, 2005 @ 3:35 am

---end quote---

[EDIT] Aside from a couple of comments like this i have seen nothing about Wiltshire. By contrast there is tons of comment about the Kolb et al paper. I want to make clear that the Wiltshire paper, which Kea brought up, is a separate issue for me. what I think is important to form an impression of, and read opinion about, is Kolb et al, which seems in a lot of people's opinion to require comment

ABOUT THE KOLB ET AL PAPER, [/EDIT]I am beginning to form my own private opinion (which is still kind of on the fence) but still I think it's more my place to register comments by others than contribute my own

Here are some earlier papers by the authors:

http://arxiv.org/astro-ph/0410541
Cosmological influence of super-Hubble perturbations
Edward W. Kolb, Sabino Matarrese, Alessio Notari, Antonio Riotto
Four pages, no figures

http://arxiv.org/hep-ph/0409038
Effect of inhomogeneities on the expansion rate of the Universe
Edward W. Kolb, Sabino Matarrese, Alessio Notari, Antonio Riotto
19 pages, 2 figures Version 2 includes some changes in numerical factors and corrected typos. It is the version accepted for publication in Physical review D
Journal-ref: Phys.Rev. D71 (2005) 023524
*

 

[Chronos]

It's not my nature to sit on the fence. I object to absolute time and inserting a Machian interpretation.

 

[marcus]

It's not my nature to sit on the fence. I object to absolute time and inserting a Machian interpretation.

I don't know if you noticed but I am discussing the Kolb et al paper.
My guess is that David Wiltshire is a postdoc at Canterbury NZ and a colleague of Kea, his paper will be getting plenty of criticism from others and will probably undergo further revision.

What i would find interesting is if you have any comment specifically directed to the Kolb et al paper.

this is the one that is getting such a lot of attention in the media and the blogs.

If you ARE talking about Kolb et al, so that we are not talking at cross purposes, then you may need to help me out: Where, what page, what line, do you find something objectionable in Kolb paper?
Where exactly do do you find the Mach principle inserted in Kolb et al?

 

[Haelfix]

My take on this is the classical one. Long wave length super Fourier modes is nothing new in cosmology, in the bible for graduate students (Peacock) he talks about this at length in the CMB chapter. So in my opinion this is just trying to revitalize an old idea.

Anyway the usual counter argument about long wave length modes effecting local horizons in a non causal way is that they are distinctive quantum effects, which inflation pushes through superluminally (kinda). Classically you would be right in arguing about causality, but its not so clear in the quantum case (at least to some people). Expectation values can a priori be shown to change. But Caroll is right in another sense, small tensor perturbations tend to preserve their value provided other stress pressure effects are small. An obvious problem again is that there is nothing protecting certain other cherished constants from such effects, and indeed if this scenario is true you would expect it, but I doubt its true, and here's why:

The fundamental technical issue I have (which I mentioned on Woits blog) is best summarized in chapter 15 of Peacock. Scalar fields are very sensitive to gauge ambiguities in inflationary cosmology. And Kolb explicitly fixes his. This is dangerous because it can obscure obvious problems that might be manifest in a different gauge. The modern approach is to cast your variables in a gauge invariant manner and to explicitly work out the perturbation solutions directly, often with numerical simulation. This paper flat out contradicts those results, and thus I am skeptical.

 

[marcus]

Haelfix, thanks for taking the time to comment here, I appreciate it.
what I think is the crux here (and I wonder if your take on it changes this)
is their Figure 1.

Going by Figure 1, their model predicts that SNe Ia with redshift almost out to z = 2 should all be dimmer than expected
with that effect most pronounced in some range like 0.3 < z < 1.3
which depends on details

LambdaCDM with Lambda = 0.7 apparently predicts, again going by their figure 1, that the SNe should be dimmer than expected out to around z = 1.3 and then BRIGHTER than expected.

the way Kolb et al draw the picture, putting in a couple of extra LambdaCDM cases and intentionally or not blurring the distinction by having so many solid and dashed curves, you may not notice that there is a stark contrast between the kind of acceleration that the Lambda model gets and the kind of acceleration that Kolb et al get.

so (although not expert enough to judge) i want to see some real SNe data plotted. this might be a source
http://arxiv.org/abs/astro-ph/9906463
this is the article in Science by Steinhardt and others that Kolb cites as their reference [1] "for a review of the observational evidence for the acceleration of the expansion...see, e.g..."

I have a notion that one might be able to exclude Kolb et al simply on grounds of giving a bad fit to the supernovae! So I am going to take a look at the Science article

[EDIT] Rats! the Science article has colorful graphically stunning figures that I can't interpret and compare with Figure 1. What I need is a better article about the SNe data[/EDIT]

 

[marcus]

Yeah, look
http://www.astro.ucla.edu/~wright/sne_cosmology.html

about halfway down the page there is a plot like Kolb figure 1
that has real data on it as well as theoretical curves
and you can see that the SNe have to be brighter for around z>1.3

Kolb doesn't get that. it is a quite noticeable bad fit.

this ned wright plot is dated July 2003 and he gives his source

---quote from Ned Wright---
The data points on the above plot are from my binning of the Tonry et al. data table. The binned normal points are
<z> d(DM) sigma
0.0051 -0.228 0.174
0.0105 -0.050 0.088
0.0169 -0.026 0.059
0.0279 0.015 0.044
0.0482 -0.015 0.039
0.0870 -0.008 0.042
0.1955 0.086 0.147
0.3386 0.104 0.097
0.4351 0.246 0.058
0.5069 0.117 0.062
0.6205 -0.027 0.086
0.8210 0.259 0.133
0.9353 -0.101 0.168
1.0560 -0.128 0.270
1.1990 -0.543 0.340
1.7550 -0.448 0.415
---end quote---

you can see how the data goes negative magnitude (brighter) after around z>1.0
this is what Kolb model fails to do, it is still positive out to z = 2
this is disappointing, whatever the theoretical flaws and/or merits might be

[edit] Normanby in the next post is right. Some Kolb curves do go negative before z = 2. But still the fit is not very satisfactory. If they go up then they don't go down enough, if they go down then they didnt go up enough. they are rather flat compared with the ned wright curves and data in the page linked above[/edit]

 

[normanby25]

what about the Psi_l0 = -0.5 line. That goes negative around z=1

 

[marcus]

what about the Psi_l0 = -0.5 line. That goes negative around z=1

hello normanby25, welcome. To compare with the Kolb et al Psi = -0.5 curve you mention I want to point to this:
http://www.astro.ucla.edu/~wright/sne_cosmology.html
halfway down the page there is this figure and there is a
DASHED MAGENTA curve that goes negative right around z = 1.

It is the best fit to the SNe data of all the curves he shows there.

I am going to compare what you are talking about the " Psi_l0 = -0.5 line" to this dashed magenta curve.

this curve is for a universe with a very slight positive curvature.
so it is not the flat case that people ordinarily make their default one to consider. And it would be a finite universe.
Maybe you are the expert (I just watch cosmology as an onlooker) and you should be telling me all this and more.

and another thing, I suspect that this dashed magenta curve case is using a Omega which is more in the middle of the measured errorbar for Omega, from WMAP. The flat case that people tend to use is more off at one end of the errorbar. It is more comfortable to say 1.00 than to say 1.01, even if the measurements center around 1.01.

 

[marcus]

what about the Psi_l0 = -0.5 line. That goes negative around z=1

i see what you mean. You are talking about Kolb et al
and you refer to their figure 1, and the case Psi = -0.5 which is the
third solid curve from the top and it does indeed, when i lay a ruler on it, seem to go negative around z = 1.2

it goes up to about +0.05 magnitude around z = 0.4
and it goes negative around z = 1.2 and by z = 2 it is already magnitude increment -0.1

that is the right kind of behavior but I think that it is a rather flat curve.
it goes up in the right place (but not by much compared with the data) and it goes down in the right place, but again not by much.

let's compare it with the ned wright plots, like that dash magenta curve is already down at -1.5 at z=2, and the Kolb curve you mention is only down as far as -0.1

and the dash magenta curve at z = 0.4 is up to over +0.2
(where the data says +0.24)
while the Kolb et al curve you mention is up to less than +0.05 (hard to measure it is so small)

to summarize, the ned wright curve is 4 times more positive at z = 0.4 and it is 15 times more negative at z = 2
compared with that Kolb case you mentioned.
but the Kolb curve is comparatively flat
and the data Ned plots are not so flat

 

[marcus]

Kolb and Riotto answered by Dan Chung

Dan Chung has co-authored papers with both Tony Riotto and Ed Kolb. he evidently knows their line of research. Now he has written challenging the latest paper Kolb et al.

http://arxiv.org/abs/astro-ph/0503553
Do Large-Scale Inhomogeneities Explain Away Dark Energy?
Ghazal Geshnizjani, Daniel J.H. Chung (UW-Madison), Niayesh Afshordi (Harvard)
4 Pages, no figures

"Recently, new arguments (astro-ph/0501152, hep-th/0503117) for how corrections from super-Hubble modes can explain the present-day acceleration of the universe have appeared in the literature. However, in this letter, we argue that, to second order in spatial gradients, these corrections only amount to a renormalization of local spatial curvature, and thus cannot account for the negative deceleration. Moreover, cosmological observations already put severe bounds on such corrections, at the level of a few percent, while in the context of inflationary models, these corrections are typically limited to ~ 10^{-5}. Currently there is no general constraint on the possible correction from higher order gradient terms, but we argue that such corrections are even more constrained in the context of inflationary models."

 

[Chronos]

I don't know if you noticed but I am discussing the Kolb et al paper.
My guess is that David Wiltshire is a postdoc at Canterbury NZ and a colleague of Kea, his paper will be getting plenty of criticism from others and will probably undergo further revision.

What i would find interesting is if you have any comment specifically directed to the Kolb et al paper.

this is the one that is getting such a lot of attention in the media and the blogs.

If you ARE talking about Kolb et al, so that we are not talking at cross purposes, then you may need to help me out: Where, what page, what line, do you find something objectionable in Kolb paper?
Where exactly do do you find the Mach principle inserted in Kolb et al?

My bad, I was still thinking about the Wiltshire paper. So far as Kolb et al goes, I have a hard time picturing what, if any observable consequences would result from super Hubble fluctuations. On the other hand, since they originated, or at least passed through our Hubble bubble, I'm not sure they can be ruled out. My gut feeling is it would show up as inexplicable anisotropies in WMAP data [which appears a possibility] and as anisotropic acceleration in supernova data [which is not apparent].

 

[marcus]

So far as Kolb et al goes, I have a hard time picturing what, if any observable consequences would result from super Hubble fluctuations. ...

you were already skeptical of this Kolb/Wiltshire gambit some posts back when I was still on the fence.

I have tentatively gotten down (my *** gets sore sitting on the fence)
and joined you on the skeptics side.
It doesn't look to me like Kolb et al gets a goot fid to the supernovae data.
So I am not going to cudgel my poor wits over whether it is kosher theoretically or not.

Dan Chung has responded to Kolb et al. that should be interesting

 

[Haelfix]

Yea you are right its not that great a fit, the interesting thing is that a priori second order inflationary perturbation theory can in principle give corrections of order one. Ok so not quite, but what about order 3 and later orders?

From Distlers blog he cites a recent paper by Flanagan which we talked about at coffee break today. The consensus was that it was pretty damning observationally, regardless of the other subtle issues involved.

http://arxiv.org/abs/hep-th/0503202

 

[Chronos]

Yea you are right its not that great a fit, the interesting thing is that a priori second order inflationary perturbation theory can in principle give corrections of order one. Ok so not quite, but what about order 3 and later orders?

From Distlers blog he cites a recent paper by Flanagan which we talked about at coffee break today. The consensus was that it was pretty damning observationally, regardless of the other subtle issues involved.

http://arxiv.org/abs/hep-th/0503202

According to the source marcus had in mind [I think], the higher order perturbations are even more tightly constrained than the 2nd order ones - which are too small to be significant - as also noted by Flannagan in the parper you referenced. Here is the paper by Chung:

Do Large-Scale Inhomogeneities Explain Away Dark Energy?
Authors: Ghazal Geshnizjani, Daniel J.H. Chung (UW-Madison), Niayesh Afshordi (Harvard)
http://arxiv.org/abs/astro-ph/0503553

 

[Chronos]

Here is another paper I came across today commenting on Kolb et al:
Can superhorizon cosmological perturbations explain the acceleration of the universe?
http://arxiv.org/abs/astro-ph/0503582

 

[hellfire]

Does the primordial power spectrum place a constraint on the strength of the superhorizon modes? Superhorizon modes which are too strong (may be strong enough to drive the expansion of space) might be statistically too improbable, asuming a gaussian random field of perturbations. It seams that this issue is treated in the last section of Kolb’s paper, but it is unclear to me. Any help?

 

[Chronos]

I don't like superhorizon modes because they are not meaningful in our Hubble bubble. And theoretically they appear to be invalid according to more recent sources [see links]. Don't get me wrong, I find emergent models appealing. But, I think this one is a dead end.

 

[hellfire]

I don't like superhorizon modes because they are not meaningful in our Hubble bubble.

I think it is not consistent to argue that superhorizon modes cannot exist, if one accepts the standard cosmological model. Superhorizon modes are a natural consequence of inflation and the current model for formation of large scale structure relies on this: Classical perturbations are produced from quantum fluctuations in a de Sitter background by modes with wavelengths larger than horizon size during inflation, which were frozen at a nonzero value and re-entered the horizon after subsequent expansion of space. If superhorizon modes existed then, why shouldn’t they exist now? It seams to me that it would be a coincidence if the production of superhorizon modes had lead to modes which are exactly less of equal to the current Hubble length.

And theoretically they appear to be invalid according to more recent sources [see links].

May be I overlooked this, but I did not find arguments against superhorizon modes in the referenced papers. Could you specify, please?

 

[Chronos]

That was an admittedly poor choice of words. The existence of superhorizon modes is not an issue, just the effects.

 

[Kea]

corrected version

Version 4 is now available:

Viable exact model universe without dark energy from primordial inflation
David L. Wiltshire
http://www.arxiv.org/abs/gr-qc/0503099

 

[marcus]

Version 4 is now available:

Viable exact model universe without dark energy from primordial inflation
David L. Wiltshire
http://www.arxiv.org/abs/gr-qc/0503099

In the acknowledgments section of version 3 he only thanked one colleague (Roy Kerr) but now he must have received many helpful comments because in version 4 he thanks many more people. Ten, if I counted correctly, including some who are well known to us.

 

[ohwilleke]

Wiltshire's paper is basically doing what tired light, intrinsic redshift and other redshift relation doubters have been looking for, but have failed to do in a convincing way. It hypothesizes that there is a flaw in the standard redshift-distance relation, and that this flaw makes much of the unexplained weirdness in cosmology (in Wiltshire's case dark energy, cosmic accelleration, WMAP implication of early structure formation, and large scale curvature of any meaningful amount) vanish in one fell swoop.

Wiltshire also has the virtue of, at least Wiltshire claims, doing what Kolb did the hard way with an exact solution, rather than a lot of physicist approximations and hand waving.

Wiltshire's justification for the standard redshift-distance relation flaw basically flows from an assumption that the super-horizon universe has a particular density, and that our existing models do a poor job of matching the data to a time scale that makes sense for that data as a result.

One wants to root for Wiltshire. A non-weird cosmology is very attractive. Throw in a 4D LQG, which gets rid of the multi-dimensional weirdness and the abundant undiscovered particle predictions of M-theory, eliminates the singularities of GR, and which also has a non-abelian gravity which in turn could imply something like MOND (and hence eliminate the need for dark matter), and you get to a place where you can describe the observed phenomena of the universe with a formalism that doesn't make your head explode or imply a lot of new phenomena that we've never seen. Everything starts to make sense in a fairly straightforward way.

Of course, this makes most of what the mainstream science press and a super-majority of the cosmology and string theory (i.e. theoretical quantum physics) community has said for the past couple of decades sound like wacky hallucinating conjecture, but hey, lifes a b--- and then you die.

On the other hand, the standard redshift-distance relation has held up very robustly thus far in the face of numerous flawed attempts to explain away the weirdness that this model implies when you look at the data, and it is difficult to believe that this relation can really be disturbed by something as modest as some modest assumptions about the density of matter-energy in a super-horizon region. Isn't the relation more robust than that? Hence, serious skepticism is in order. I can't follow the math in Wiltshire rigorously enough to see if there is a conceptual flaw in his argument for a conversion between a "measured Hubble constant" and a "true Hubble constant". But, there are plenty of people who are capable of doing so, and since the Kolb paper has attacted so much attention, and Wiltshire himself appears to have received so many comments in a fairly short time period, one would hope that this could be sorted out fairly quickly.

 

[Chronos]

v4 is a definite improvement in my mind [which is not necessarily a good sign]. Some of my issues with the initial release have been placated. I still have difficulty grasping the consequence of super horizon fluctuations within our Hubble bubble. I am stuck on the notion this is like trying to view IR wavelengths through a UV filter. I wonder though, is the intent to suggest that accelerated expansion is an illusion created by interference fringes in the super horizon fluctuations? The assertion our observable bubble was causally connected to the bulk universe prior to inflation is also troubling. I can't shake the feeling there is something paradoxical about being causally connected to unobservable regions of the universe. I will, however, allow that I may be a little too narrow minded of what constitutes being observable.

 

[ohwilleke]

Chronos, I see the intuition your getting at and in the same vein wonder if the effect Wiltshire proposes doesn't imply superluminal gravitational action.

 

[Kea]

Just Out

Exact model universe fits type IA supernovae data with no
cosmic acceleration
B.M.N. Carter, B.M. Leith, S.C.C. Ng, A.B. Nielsen, D.L. Wiltshire
http://www.arxiv.org/abs/astro-ph/0504192

9 pages, 5 figures, aastex

Abstract:
The unexpected dimness of Type Ia supernovae at redshifts z <~1 has over the past 7 years been seen as an indication that the expansion of the universe is accelerating. A new model cosmology has been proposed by one of us [gr-qc/0503099], based on the idea that our observed universe resides in an underdense bubble remnant from a primordial epoch of cosmic inflation. Although there is no cosmic acceleration, it is claimed that the luminosity distance of type Ia supernovae data will nonetheless fit the new model, due to systematic effects. In this paper the hypothesis is tested statistically against the available type Ia supernovae data by both chi-square and Bayesian methods. The model gives good agreement if the density parameter, Omega_0, is taken to be the density in ordinary baryonic matter only. If low Omega_0 parameter values are accepted, then the model would dispense with both dark energy and non-baryonic dark matter, and an alternative explanation would be required for galaxy rotation curves and dynamical measurements of Omega_0 on the scales of clusters of galaxies.

 

[ohwilleke]

If low Omega_0 parameter values are accepted, then the model would dispense with both dark energy and non-baryonic dark matter, and an alternative explanation would be required for galaxy rotation curves and dynamical measurements of Omega_0 on the scales of clusters of galaxies.

:!) It will be very interested to see what informed reviews have to say about this theory. or or or

But, enough with the decedant smilies already.

 

[Kea]

The following webpage is under construction:

Open Bubble Model Cosmology by D.L. Wiltshire

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

 

[Kea]

New

New versions now available:

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

Greetings
Kea

 

[Kea]

new paper

Structured FRW universe leads to acceleration: a non-perturbative approach
Reza Mansouri
http://www.arxiv.org/abs/astro-ph/0512605

From abstract:
We propose a model universe in the matter dominated phase described by a FRW background with local inhomogeneities, like our local patch, grown out of the primordial fluctuations. Our local patch consisting of different structures is approximated as an inhomogeneous cosmic fluid described by a LTB metric embedded in a background FRW universe. Within the exact general relativistic formulation, the junction conditions for the only possible matching without a thin shell at the boundary, neglected so far in the literature, constrains the model in such a way that the luminosity distance-red shift relation mimics a FRW universe with dark energy. Therefore, the dimming of SNIa is naturally accounted for in such a structured FRW universe.

 

[Chronos]

I read that paper and agree it's an interesting idea, Kea. It appears not to require those annoying, ad hoc parameters.