Will the new WMAP3 data challenge the assumption of a spatially flat universe?

[marcus]

I have some quotes from Ned Wright (the cosmologist at UCLA whose website and its cosmo. tutorial many of us have visited) and from George Ellis that I want to put in.

this will help give an idea of what some selected people are saying now and later on we can see if there has been any significant shift in the message.

Here is George Ellis on page 25 of his "Cosmology Issues" essay
====exerpt=====

4.2.3 Determining the RW parameters [Robertson-Walker]

Given that a RW geometry is a good description of the observable universe on a large scale, the further issue is what are the best-fit parameters that characterize it, selecting the specific universe we observe from the family of all FL models (Sec.2.1). Important observational issues are:

• Determining the Hubble parameter H_0, which sets the overall scale of the observed universe region.

• Determining the trio of the density parameter Omega_0, deceleration parameter q_0, and cosmological constant Lambda (or equivalently the density parameter Omega_Lambda), which are the major defining characteristics of a specific Friedman-Lemaitre model. The CBR data, supernova observations, deep number counts, source covariance functions, velocity measurements, and gravitational lensing observations can determine these quantities.

• Determining the sign of the curvature k, showing whether the universe has closed spatial sections and also whether it is possible for it to recollapse in the future or not. Analyses of the observations should always attempt to determine this sign, and not assume that k = 0 (as is often done).

• Various parameters are used to characterize the nature of dark matter (Sec.2.3.6) and dark energy (Sec.2.3.5). As their dynamics is unknown, these too have to be determined observationally.
=====endquote=====

It seems to me that Ellis is critical of some of his fellow cosmologists for favoring the SPATIALLY NON-CLOSED picture to such an extent that, according to him, they "often" TAKE IT FOR GRANTED. This is how I understand what he says here.

Interestingly enough today Ned Wright posted something on arxiv that sends a similar message. Let me get it.

 

[marcus]

what Ned Wright posted today

Conceivably someone reading this thread might be interested by what Ned Wright had to say about this in something he put on arxiv today:
http://arxiv.org/abs/astro-ph/0603750
A Century of Cosmology
E. L. Wright (UCLA Astronomy)
Talk presented at the "Relativistic Astrophysics and Cosmology - Einstein's Legacy" meeting in Munich, Nov 2005. Proceedings will be published in the Springer-Verlag "ESO Astrophysics Symposia" series. 10 pages with 2 figures

AS ONE OF HIS FIGURES Wright has a caricature of a cosmologist's CIRCULAR ARGUMENT: It is his Figure 1. A big circle of words evidently meant as a joke. It has these words going around the circle:

"If w = - 1, then flat LambdaCDM is a good fit to all the data. If Omega = 1 , then w = - 1 is a good fit to all the data."

He is opposed to assuming flat. Explaining this Figure 1. he says
"However, there is a very strong tendency among theorists to assume the Universe is flat when seeking w and w'. This is a logical error, since the evidence for a flat Universe comes from the agreement of the concordance LambdaCDM model with all the data. But the concordance LambdaCDM model has w = -1 and w' = 0 exactly. If w and w' are allowed to vary, then the evidence for a flat Universe must be re-evaluated. ... "

Unfortunately I have to go out now so can't finish this post but will get back to it later.

========
I'm back now. Yeah. I think to put it simply the message of what Wright says, and of his figure 1, is that IT IS NOT COOL ANYMORE TO ASSUME FLAT.

Wright is a leading cosmologist, in case any reader doesn't know----he was one of a group of top scientists in charge of WMAP----so you see his name as co-author on some main WMAP papers. But he was an important figure already before that.

=========

Eventually I will get over to the Astronomy building and talk to some grad students---in the coffeeroom or in one of their offices. So far I am going on signals i get from bigname people like George Ellis and Ned Wright, and from things like Figure 17 of the Spergel et al paper. But I would also like to talk with some of the "troops on the ground". Over the years I've done that on occasion and they (random grad students) have been very helpful. that should give additional perspective on a possible shift.

 

[Chronos]

Marcus, I agree in spirit with Ned Wright's analysis, but am reluctant to accept the conclusion. There are too many conflicting observations that cannot be ruled out. Maybe, in 100 years, the answer will become obvious. For now, I cannot accept that assertion.

 

[marcus]

Marcus, I agree in spirit with Ned Wright's analysis, but am reluctant to accept the conclusion. There are too many conflicting observations that cannot be ruled out. Maybe, in 100 years, the answer will become obvious. For now, I cannot accept that assertion.

You are heartily welcome to whatever your attitude is but I don't understand what you think is his "conclusion" or his "assertion" that you say you can't accept.

Wright is a working cosmologist who was involved in the planning execution of WMAP and in the analysis of WMAP3. He is talking about what to do TODAY, not in 100 years. Nothing visionary here.

He says that if you want to find out about w, then you should let BOTH w and Omega VARY SIMULTANEOUSLY and use the data to constrain both.
He says that you should not peg Omega = 1 and then calculate w

and he says you should not peg w = -1 and then calculate Omega.
He says, to put it simply, IT IS NOT COOL TO ASSUME FLAT i.e. to assume Omega = 1.

this could be seen as just good scientific advice to people doing analysis of data today and tomorrow.

He actually goes further and says that you should let w AND its timederivative w' AND Omega vary and try to constrain them all. To allow for the possibility that w could be changing. But the simple version of the message is to let Omega and w vary----which incidentally was what was done in Figure 17 of Spergel et al, the figure which I liked so much and discussed earlier in this thread. That Figure illustrates a simple version of what Wright advocates doing.

Wright makes this the message of his Figure 1 , and his conclusions paragraph, of the paper he put on arxiv yesterday.

I'm happy for you to be as reluctant as possible but I just want to make sure we are on the same page and both talking about the same conclusions of the same Ned Wright paper! As long as we understand what we're talking, then I'm delighted if you have a negative reaction. It illustrates what I think is a majority, or at least very common, attitude in the field----and one which Wright is addressing---and one which I think will gradually shift over the coming little while. We will see

 

[marcus]

As could be expected, since Ned Wright is a key figure in this whole business, and one of the WMAP project leaders, he is one of the co-authors of the "Implications for Cosmology" paper which is the basis for this thread.

this is the paper we call "Spergel et al".
I should put the link again, in case someone drops into this thread and wants to look at the WMAP3 results "implications for cosmology"

http://arxiv.org/abs/astro-ph/0603449
Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology

the Figure 17 is on page 50 IIRC, in case anyone wants to check it out

 

[SpaceTiger]

I attended a talk yesterday in which the speaker was discussing future methods of measuring curvature and dark energy parameters. In the next ten or twenty years, they expect to be able measure curvature to at least one more decimal place and perhaps two. The seemingly best method of doing this is with weak lensing surveys, but Type Ia supernova, cluster counting, and baryon oscillation experiments should do comparably well.

He also discussed methods of actually testing GR (which would be refreshing) by measuring dark energy parameters and then comparing the predicted and measured growth functions, which describe the growth of perturbations in a general relativistic universe.

In the middle of his talk, he flashed up your favorite graph from the WMAP3 paper, but gave no indication that he thought it was suggestive of a universe with positive curvature.

 

[marcus]

I attended a talk yesterday in which the speaker was discussing future methods of measuring curvature and dark energy parameters. In the next ten or twenty years, they expect to be able measure curvature to at least one more decimal place and perhaps two...

COOL!

In the middle of his talk, he flashed up your favorite graph from the WMAP3 paper, but gave no indication that he thought it was suggestive of a universe with positive curvature.

Fine, in a certain sense that gives us a kind of benchmark for where people's heads are, at the moment. I should really go talk to some of the local grad students. that will also give a benchmark, I can then come back later and gauge if any change.

 

[marcus]

another straw in the wind?

I don't recommend this article---on the contrary: apologize for even mentioning it---and so wrote the mention in white

http://arxiv.org/abs/astro-ph/0603690
Cross-correlation of WMAP 3rd year and the SDSS DR4 galaxy survey: new evidence for Dark Energy
A.Cabre, E.Gaztanaga, M.Manera, P.Fosalba, F.Castander (IEEC/CSIC)
5 pages, 5 figures, submitted to MNRAS Letter
We cross-correlate the third-year WMAP data with galaxy samples extracted from the SDSS DR4 covering 13% of the sky, increasing by a factor of 3.7 the volume sampled in previous analyses. The new measurements confirm a positive cross-correlation with higher significance (total signal-to-noise of about 4.7). The correlation as a function of angular scale is well fitted by the integrated Sachs-Wolfe (ISW) effect for LCDM flat FRW models with a cosmological constant (w=-1). The combined analysis of different samples gives Omega_L=0.75-0.80 (68% Confidence Level, CL) or 0.70-0.82 (95% CL). We find that the best fit Omega_L decreases from 0.82 to 0.75 (95% CL) when we increase the median redshift of the galaxy sample from z~0.3 to z~0.5. The quick drop of the measured signal with z is too fast for the LCDM cosmology. The data can be better reconciled with a model with an effective dark energy equation of state w<-1.5. Such phantom cosmology reduces by up to ~20% the amplitude of the lower multipoles of the CMB temperature anisotropies with respect the w=-1 prediction, which also brings the models closer to the observations.

I find the idea of w<-1 repugnant, as do all rightthinking ppeople I would hope. there is a strong appeal of the two ideas w = -1 exactly and Omega = 1 exactly (or 1 with a little random quantum ripple).
However these people (Spaniards, I see) find something about the WMAP3 data suggests to them w way less than -1. Even in my favorite Spergel figure 17 the 68% confidence interval for w only goes down to -1.14 and they are below that. Yuk. Is this a sign of the times?

=========================
the main paper we are assimilating in this thread is "Spergel et al", the "implications for cosmology" paper that has Ned Wright as a co-author.
I should put the link again:

http://arxiv.org/abs/astro-ph/0603449
Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology

Have another look at Figure 17 is on page 55 IIRC, to see what it would mean to contemplate the unpalatable idea that w might be less than -1.

 

[Chronos]

The best fit models proposed by Spergal et al. still suggest, without insisting that w is very close, if not exactly -1. I think that is just good science.

 

[marcus]

The best fit models proposed by Spergel et al. still suggest, without insisting that w is very close, if not exactly -1.

that is right. Personally I tend to assume w=-1 exactly, which would be consistent with a positive curved, spatially closed, finite, universe if you favor that picture. And also consistent with other cases as well! Essentially it just means that the dark energy corresponds to Einst. cosmological constant. But my liking to assume w=-1 is a personal bias which I try to discount and avoid infecting my judgment. One reason I do this is because of what Ned Wright says.
https://www.physicsforums.com/showpost.php?p=949832&postcount=72
http://arxiv.org/abs/astro-ph/0603750

...that is just good science

One of my guides regarding "good science" is Ned Wright, and he says to let w and Omega (and maybe even w') vary simultaneously. that is, when you are trying to estimate w (the DE EOS) you should not make any assumption about the universe being flat or not. Although the darkenergy EOS is nominally separate from flatness or spatial closure issues, they can influence each other in the calculation, so it should be treated that way when you analyze. One should make an effort to avoid prejudice about Omega when one estimates w-----in other words let them both vary simultaneously and constrain both.

In a nutshell, he says "do not peg Omega = 1 when you estimate w, and do not peg w = -1 when you estimate Omega" because they both might not be those numbers and pegging can skew the fit.

So the kind of analysis that results from doing what he says is Figure 17 on page 55, and here is a quote from the caption:

The contours show the 2-d marginalized contours for w and Omega_k based on the the CMB+2dFGRS+SDSS+supernova data sets. This figure shows that with the full combination of data sets, there are already strong limits on w without the need to assume a flat universe prior. The marginalized best fit values for the equation of state and curvature are w = -1.062 (+0.128 -0.079) and Omega_k = -0.024 (+0.016 -0.013) at the 68% confidence level.

What that says about w is that at 68% confidence it is in the interval
[-1.141, -0.874]

That is the darkenergy EOS is in an interval AROUND -1, and estimate varies roughly on the order of TEN PERCENT around -1.

this is how i might make sense if someone says " w is very close, if not exactly -1"
I don't object if they want to say it that way. In some contexts, on some days, if I am feeling right, I also would say that roughly 10% is "very close, if not exactly"

And because of my confessed bias, I am quite happy with that 68% interval around w = -1. So fine! All well and good.

But this does not say anything about SPATIAL CLOSURE, does it Chronos?

For that, if one is following Ned Wright's guidelines for good science and allowing both w and Omega to be constrained simultaneously, one gets the 68 % confidence interval for Omega which is

[1.008, 1.037]

The point is that this interval is NOT AROUND ONE.
It does not prove anything but it is CONSISTENT with some positive overall curvature and with spatial closure. So that is a possibility which it is "good science" (to use your expression) to keep in mind.

 

[marcus]

To remind readers, one bit of news from WMAP3 data was that when w (DE EOS) and curvature were simult. constrained by the data you got a 68% conf. interval for Omega that NO LONGER STRADDLED ONE.

The interval for Omega referred to is [1.008, 1.037]
Discussed in Spergel et al Fig 17 page 53. So the centipede upstairs is getting ready for bed and we heard a shoe drop.

We listen for other shoes. Will the scientific community gradually change the nuances in how it talks about this. If Omega REALLY WERE like 1.01 that would be consistent with a spatial finite universe, that is with SPATIAL CLOSURE. Like a big 3-sphere instead of infinite flat euclid 3-space.

OK, this thread is for listening for shoes drop. Don't be in a hurry, just wait. here is a little bump. what does it mean, if anything?

http://arxiv.org/abs/astro-ph/0604335
Cosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraints
Uros Seljak, Anze Slosar, Patrick McDonald
11 pages, 4 figures

"We combine the Ly-alpha forest power spectrum (LYA) from the Sloan Digital Sky Survey (SDSS) and high resolution spectra with the cosmic microwave background (CMB) including 3-year WMAP, supernovae (SN) and galaxy clustering constraints to derive new constraints on cosmological parameters. The existing LYA power spectrum analysis is supplemented by constraints on the mean flux decrement derived using a principal component analysis for quasar continua, which improves the LYA constraints on the linear power. The joint analysis reduces the errors on all parameters and prefers the simplest 6 parameter cosmological model. We find some tension between the WMAP3 and LYA power spectrum amplitudes, at the ~2 sigma level, which is partially alleviated by the inclusion of other observations: we find sigma_8=0.85+-0.02 compared to sigma_8=0.80+-0.03 without LYA. For the slope we find n_s=0.965+-0.012. We find no evidence for running of the spectral index, dn/dln k=-0.020+-0.012, in agreement with inflation. The limits on the sum of neutrino masses are significantly improved: sum(m_nu)<0.17 eV at 95% (<0.32 eV at 99.9%). This result, when combined with atmospheric and solar neutrino mixing constraints, requires that the neutrino masses cannot be degenerate, m_3/m_1>1.3 (95%). Assuming a thermalized fourth neutrino we find m_s<0.14 eV at 95% c.l. and such neutrino cannot be an explanation for the LSND results. The fit is poor even in the limit of massless sterile neutrino since the constraint on the number of relativistic neutrino species is N_nu=3.19+0.19-0.15 and N_nu>4 is excluded at 99.76%. The constraint on the dark energy equation of state is w=-1.04+-0.06. The constraint on curvature is Omega_k=-0.003+-0.006. Cosmic strings limits are G mu<2.3 10^-7 at 95% c.l."

======================

mean anything? not much I am afraid, more a point for the status quo this time.

It puts Omega in the interval [0.997, 1.009]
which is comfortably consistent with the idea that Omega true value is EXACTLY ONE.

 

[Chronos]

I was reading that same paper today, marcus, and left with the same feeling - wrapped in an old, handmade quilt. WMAP 3 seems to lean in the direction of closure [omega just barely above 1]. Not enough to be compelling, but tantalizingly close. In short, I still think omega is exactly 1.

 

[marcus]

...and left with the same feeling - wrapped in an old, handmade quilt...

can't say anything about Omega at the moment, but quilts are nice arent they. my wife has taken part in several handmade quilt projects---her sister is the real quiltmaker in the family

my favorite thing to read cosmology related papers in is an unbelieveably thick cushy blue terrycloth bathrobe

the centipede upstairs has a lot of shoes left to drop

 

[SpaceTiger]

mean anything? not much I am afraid, more a point for the status quo this time.

It doesn't mean much because it agrees with the standard model? We shouldn't get into the habit of de-emphasizing results simply because they produce no surprises. Remember, the Ly$\alpha$ forest is one of the best cosmological constraints we have and, as they say in the paper,

This is the strongest constraint on the curvature to date and the data continue to show no evidence for it.

 

[Chronos]

I agree with ST, marcus. Observational evidence still overwhelmingly favors the LCDM model. While anomalous observations remain to be explained [e.g., Arpianism], there are not enough to 'throw out the baby with the bath water'.

 

[marcus]

...

the centipede upstairs has a lot of shoes left to drop

here's another

http://arxiv.org/abs/astro-ph/0604616
Extending the WMAP Bound on the Size of the Universe
Joey Shapiro Key, Neil J. Cornish, David N. Spergel, Glenn D. Starkman
9 pages, 16 figures

"Clues to the shape of our Universe can be found by searching the CMB for matching circles of temperature patterns. A full sky search of the CMB, mapped extremely accurately by NASA's WMAP satellite, returned no detection of such matching circles and placed a lower bound on the size of the Universe at 24 Gpc. This lower bound can be extended by optimally filtering the WMAP power spectrum. More stringent bounds can be placed on specific candidate topologies by using a a combination statistic. We use optimal filtering and the combination statistic to rule out the infamous "soccer ball universe'' model."I still claim that the results so far don't mean very much in the sense that I plan to wait for a good deal more reaction. these links are not intended to prove anything either way. they are sampling the MWAP3 fallout.

Niel Cornish is an amusing guy. I remember 3 years or so back his paper about how the U has to be "at least this big". He had a pet monkey that appeared sitting on Cornish shoulder in a picture at his website (Cornish site, not the monkeys)

Make whatever conclusion you want. I'm just collecting some post WMAP3 papers related to the issue of Universe closure or non-closure.

==========================
for the curious, some samples from this particular dropped shoe:"...The WMAP data point to a universe with a total energy density within 2% of critical[3]. This means that even if space is not quite flat, the radius of curvature of the Universe is at least of order the size of the observable Universe, and space can be considered to be nearly flat. ..."

can be considered, I may add, to be FINITE and nearly flat------if one cares to so consider it

I don't particularly like the models with complicated topology such as the DODECAHEDRON thing. So I am glad to see them ruling it more and more out

"XI. CONCLUSION The claim that the topology of our Universe had been found to be that of the Poincaré dodecahedron does not stand up under scrutiny. The signature found in Ref. [8] disappears when one uses the proper S statistic and considers the false positive threshold. While the shape of our Universe remains a mystery, the matching circles test can be used to place a lower bound on the size of the Universe. The previous limit of 24 Gpc [4] can be extended by about 10% using filtering of the WMAP power spectrum. A full search with optimal filtering is now underway. "

more power to you, guys. So roughly speaking the U is sure to be at least some 30 billion parsecs across. Roughly 100 billion light years.

you know that you can find two points that far apart

and hey, it might be flat-out infinite too. we still don't know
in my unauthoritative opinion.

 

[SpaceTiger]

It was an interesting result after the first release, but this release just gives a 10% increase on the topology scale limit. Meh, I guess somebody had to check.

Note that this method more directly addresses the finiteness question than a measurement of the curvature. If the cosmological principle breaks down at large scales, the universe can have any curvature and still be finite. However, I think the detection of circles on the sky would definitively rule out an infinite universe.

 

[marcus]

... However, I think the detection of circles on the sky definitively rules out an infinite universe.

I agree. Thanks for the comment. As you say, circles would rule out infinite, and AFAIK they have not been seen.
(my gut reaction to circles is horror. I hope they are never observed. Rather see simple vanilla infinite than some periodic structure. but decency forbids dwelling on one's prejudices)

 

[Chronos]

I think we can safely rule out 'circles in the sky'. And I share your discomfort with that concept. But, I'm not convinced it rules out a finite, unbounded universe. My concern centers around the argument the universe very much appears to be temporally finite. Hence, I am forced to reject any argument it [the observable universe] is spacially infinite.

 

[marcus]

BTW Ned (SpaceTiger) is coming out very well as a guesser that the community would NOT show signs of shifting off the flat assumption any time soon. If that was his guess.

My guess was different and would have been that by now i would have heard more about it. And I havent. But I expect to just have to wait longer than I at first expected, and am not discouraged.

Today, another paper

Look at Figure 2, on page 4

Shows a 68 % confidence region for Omega_matter and Omega_Lambda where sure enough the {Omega_total = 1} line DOES pass thru, but rather off to one side. So sure enough the data is CONSISTENT with the convenient usual assumption of Omega_total = 1, that is "flat".

And in their verbal treatment the "flat" case is the only one they appear to consider.

And a casual glance at Figure 2 shows that the "SWEET SPOT" of their 68% gaussian oval has about Omega_total = 1.1 roughly.

which as usual if we took it seriously would say "positive curved spatially closed" but which as usual we do not take seriously but attribute to mere vagary of the data.

the funny thing is it seems to happen all the time.The Hubble diagram extended to z>>1: the gamma-ray properties of GRBs confirm the Lambda-CDM model
C. Firmani (1,2), V. Avila-Reese (2), G. Ghisellini (1), G. Ghirlanda (1) ((1) Osserv. Astron. di Brera, Italy; (2) Instituto de Astronomia, U.N.A.M., Mexico)
5 pages, 4 figures included. Submitted to MNRAS Letters

"Tight constraints on cosmological parameters can be obtained with standard candles spanning a range of redshifts as large as possible. We propose to treat SN Ia and long Gamma-Ray Bursts (GRBs) as a single class of candles. Taking advantage of the recent release of the Supernova Legacy Survey and {\it the recent finding of a tight correlation among the energetics and other prompt gamma-ray emission properties of GRBs}, we are able to standardize the luminosities/energetics of both classes of objects. In this way we can jointly use GRB and SNIa as cosmological probes to constrain Omega_m and Omega_L and the Dark Energy equation of state parameters through the same Bayesian method that we have, so far, applied to GRBs alone. Despite the large disparity in number (115 SNIa versus 19 GRBs) we show that the constraints on Omega_m and Omega_L are greatly improved by the inclusion of GRBs. More importantly, the result of the combined sample is in excellent agreement with the Lambda-CDM concordance cosmological model and does not require an evolving equation of state for the Dark Energy."

As you recall in the WMAP3 report there was that figure with 68% confidence interval Omega_total being
[1.008, 1.037], not even around one! This is much broader and less precise, but it is around one (just a bit off to the upside)

 

[Garth]

BTW Ned (SpaceTiger) is coming out very well as a guesser that the community would NOT show signs of shifting off the flat assumption any time soon.

Is that flat or conformally flat?

Today, another paper

Look at Figure 2, on page 4

Shows a 68 % confidence region for Omega_matter and Omega_Lambda where sure enough the {Omega_total = 1} line DOES pass thru, but rather off to one side. So sure enough the data is CONSISTENT with the convenient usual assumption of Omega_total = 1, that is "flat".

(emphasis mine)

Note, it is actually the other way round - deductions from the data of standard candles and rulers, as well as CMB anisotropies, are dependent on the spatial geometry of the universe.

These data sets are indeed observed to be consistent with a spatially 'flat' geometry and it is this 'flatness' that requires $\Omega_{total} = 1$. However, THAT deduction leads to the invocation of problematic DE.

Conformally flat geometries are also consistent with these data sets, but they do not require $\Omega_{total} = 1$, and so DE may not exist after all.

Note further, the linearly expanding universe is also consistent with the distant S/N Ia data, however, such a conformally flat geometry and linearly expanding scale factor would require a modification of GR.

Garth

 

[Chronos]

If we leave out the alleged CMB anisotro[cow]pies, the puzzle box is not that difficult to solve.

 

[Garth]

If we leave out the alleged CMB anisotro[cow]pies, the puzzle box is not that difficult to solve.

Well, the puzzle box now includes problematic DE, exotic non-baryonic DM, Higgs bosons/inflatons, (all as yet undiscovered in laboratory physics), a possible age problem in the early universe, as well as a Pioneer anomaly, and the alleged axis of evil and deficient quadrupoles.


Agreed, those puzzles may be solvable, nevertheless, it is important to keep viable options open, we may never know what may lay round the next corner!

Garth

 

[selfAdjoint]

Well, the puzzle box now includes problematic DE, exotic non-baryonic DM, Higgs bosons/inflatons, (all as yet undiscovered in laboratory physics), a possible age problem in the early universe, as well as a Pioneer anomaly, and the alleged axis of evil and deficient quadrupoles.


Agreed, those puzzles may be solvable, nevertheless, it is important to keep viable options open, we may never know what may lay round the next corner!

Garth

Bolded matter is a bit of a stretch for cosmology? Why not include the non-mating of quantum and GR then, or just the whole world of things unknown in all of physics?

 

[Garth]

Bolded matter is a bit of a stretch for cosmology? Why not include the non-mating of quantum and GR then, or just the whole world of things unknown in all of physics?

Indeed, why not include the QM/GR interface in the puzzle box?

Modern cosmology is founded on both.

As I said, just as well to keep all viable options open.

Garth

 

[SpaceTiger]

BTW Ned (SpaceTiger)

My name is Nick.

...is coming out very well as a guesser that the community would NOT show signs of shifting off the flat assumption any time soon. If that was his guess.

It wasn't exactly a "guess", I work with the people doing the experiment. The issue is not one of physical interpretation, just of interpretation of quoted errors. The community has no particular reason to question the WMAP team's interpretation of their own errors. The only way you could see a change of the community's view of "flatness" is if somebody incorporated more data or the error analysis was shown to be flawed.

And a casual glance at Figure 2 shows that the "SWEET SPOT" of their 68% gaussian oval has about Omega_total = 1.1 roughly.

which as usual if we took it seriously would say "positive curved spatially closed" but which as usual we do not take seriously but attribute to mere vagary of the data.

You're talking about a data set that only constrains $\Omega_k$ to ~20% and which includes unity in what appears to be a <50% confidence interval. By contrast, the precision of WMAP is of order a percent or two. You'd need ~100 such independent results with minimal systematics to even begin to compare to WMAP's constraint on flatness.

the funny thing is it seems to happen all the time.

Not in my experience. When WMAP was included with other data sets (such as SDSS), the vast majority of them brought the estimate on $\Omega_k$ down.

 

[marcus]

My name is Nick.
...

Of course Nick Bond! Just carelessness, sorry.

thanks for jogging my memory, which needs it sometimes. I just saw a list of your papers on arxiv
http://arxiv.org/find/grp_physics/1/au:+bond_N/0/1/0/all/0/1

Impressive! congratulations!

the search turned up 9 papers. I remember you saying you were in the PhD program at Princeton. You must be nearly done, finishing up thesis and so on.

Not in my experience...

You have such different experience of this from me, which makes life interesting.
My experience is that for some years now whenever I see ANY estimate of Omega_total it is NEVER on the downside of one.

whatever the dataset or the way it is measured it is always plain 1, or the confidence interval is LOPSIDED towards the upside (but still includes 1). Or else as in that WMAP3 case which we discussed, the confidence interval is ENTIRELY on the upside of 1 and doesn't even include 1.

One certainly doesn't want to over-interpret the data! (Seriously, no joke!) One wants to be very sober and judicious about this and refrain from attributing undue significance!

But my nagging experience is that the published confidence intervals always come out a bit upside, and never downside.

I assume that you, Garth, Chronos and so on HAVE seen confidence intervals that are lopsided downwards. Indeed one may INFER the existence of datasets that do make for such (like Sloan Digital Sky Survey) because MIXING SDSS data with WMAP3 data brings Omega down! I have seen a bunch of mixed data results tabulated in Spergel et al. As you indicate. But that is inference. the fact is, I have not seen anybody make a confidence interval (recently at least) that is on downside of one.

Maybe someone wants to supply a link?

It is curious that your experience is different.
=====================
I think we have already been through much of this discussion and there is no need to repeat.

But if you do happen to have a link to some recent published estimate of Omega that has a confidence interval downwards of one (in contrast to what I have seen), that would be something NEW for me and I would be very glad to see it.

Please give a page reference with the link. This is something that may have been staring at me all the time and my sometimes overworked eyes did not spot!

 

[SpaceTiger]

Maybe someone wants to supply a link?

The 2dF measurements of large scale structure yield an estimate of curvature that is not only low, but almost two-sigma below flat at a precision of ~5%:

http://lanl.arxiv.org/abs/astro-ph/0507583"

Refer to Table 2.

You have such different experience of this from me, which makes life interesting.
My experience is that for some years now whenever I see ANY estimate of Omega_total it is NEVER on the downside of one.

This should suggest to you that something's wrong. To see what I mean, let's just suppose for the moment that you're right about the curvature being positive and let's take the upper WMAP error bar -- $\Omega_{tot} = 1.038$. Now let's ask the question, if perform an experiment with gaussian random errors on this parameter of order 20% (as in the paper you just quoted), what fraction of the time will I measure $\Omega_{tot}>1$? The answer is about 57.5% of the time. That means that, even in the upper range of curvature suggested by WMAP, you should still see such measures give $\Omega_{tot}<1$ in 42.5% of data sets. The fact that you never see such things suggests one or more of the following:

1) Your sample is too small to be meaningful.
2) Your sample is heavily biased.
3) The measurements you're thinking of are not all independent.
4) The experiments you're thinking of suffer from systematics that always bias them greater than one.
5) The experiments have overestimated their error bars.

The last two things seem pretty unlikely to me, so you should probably consider looking into the first three.

 

[marcus]

The 2dF measurements of large scale structure yield an estimate of curvature that is not only low, but almost two-sigma below flat at a precision of ~5%:

http://lanl.arxiv.org/abs/astro-ph/0507583"

Refer to Table 2.


...
3) The measurements you're thinking of are not all independent.
...

this is an excellent one to add to the collection, thanks. It is from July 2005, so fairly recent though not the most so. Let's see what it says.
I am looking at Table 2, as you suggest. don't have time to study it at length but here's what I see it say:

the Omega_k error bar is around ?0.074 with limits +0.049 and -0.052

so as I read it the error bar is between [-0.126, -0.025]

this is reminiscent of my positive curvature benchmark Spergel et al

folks will recall Figure 17 on page 55 of the famous WMAP3 report by Spergel et al "implications for cosmology" where they gave a 68 % confidence interval for Omega_k which was
" ?0.024 +0.016 ?0.013 at the 68% confidence level."

this translates into [-0.037, -0.008]

that Spergel et al interval meant that we had Omega in the range
[1.008, 1.037]

that is the curious upside picture I see a lot of

OF COURSE THESE CONFIDENCE INTERVALS PEOPLE PUBLISH ARE NOT SEPARATE INDEPENDENT MEASUREMENTS, I am not doing statistics with them , THEY ARE ALL BASED ON THE SAME FEW DATASETS, like SDSS and WMAP which gradually get improved and people keep re-using.

I just so far didnt see confidence intervals favoring the downside. Not really surprising either. And I am curious did anybody else?

===============

Nick thanks so much for the new paper! I will add it gratefully to my collection.

As far as I am concerned we are not arguing and this is partly repetitious. But here you have given me something new and I am glad!

Please explain it to me and interpret, if you so desire.

 

[marcus]

this is an excellent one to add to the collection, thanks. It is from July 2005, so fairly recent though not the most so. Let's see what it says.
I am looking at Table 2, as you suggest. don't have time to study it at length but here's what I see it say:

the Omega_k error bar is around -0.074 with limits +0.049 and -0.052

so as I read it the error bar is between [-0.126, -0.025]

..

The nice paper Nick kindly provided is this one first posted July 2005

http://lanl.arxiv.org/abs/astro-ph/0507583
Cosmological parameters from CMB measurements and the final 2dFGRS power spectrum
Ariel G. Sanchez (Cordoba), C. M. Baugh (Durham), W. J. Percival (Edinburgh), J. A. Peacock (Edinburgh), N. D. Padilla (Catolica), S. Cole (Durham), C. S.Frenk (Durham), P. Norberg (ETH, Zurich)

MNRAS, in press. Minor revision after referee's report. 22 pages, 18 plots. Colour figures for talks (including additional plots which do not appear in the paper) can be downloaded from this http URL
Monthly Notices of the Roy.Astron.Soc. 366 (2006) 189-207

From Table 2 of this paper one gets a confidence interval for Omega_k
of [-0.126, -0.025]

this is the same all-negative interval situation that was so remarkable in Spergel at al, and seems to be yet another case of positive curvature---that is of Omega being on the upside of 1.

If one treats this Table 2 estimate the same way one treated Spergel, one gets this for Omega_total
[1.025, 1.126]

that is a little more marked than the Spergel WMAP3 thing of
[1.008, 1.037]

So far I don't see how this contradicts my general impression of how the papers keep leaning towards positive largescale curvature. I could very likely be missing something. Dont have time to study the whole paper and these damned minus signs and double negatives keep buzzing around like flies.

But anyway, I treat it exactly like I did Spergel et al, praying that they are using the same notation, and that's how it comes out.

 

[SpaceTiger]

So far I don't see how this contradicts my general impression of how the papers keep leaning towards positive largescale curvature.

It doesn't, that's my mistake. The analysis actually includes the WMAP data (which is by far the strongest constraint on the curvature), so it would be surprising if it didn't end up leaning in the same direction.

OF COURSE THESE CONFIDENCE INTERVALS PEOPLE PUBLISH ARE NOT SEPARATE INDEPENDENT MEASUREMENTS, I am not doing statistics with them , THEY ARE ALL BASED ON THE SAME FEW DATASETS, like SDSS and WMAP which gradually get improved and people keep re-using.

Well, actually, some of them are independent (such as the Firmani et al. measurement you cited), so you'll have to be more precise about what you're thinking of when you say they all favor a closed universe. If most of the measurements you're thinking of are not independent, then I'm curious as to why you think they support your case. As you can see from Table 11 in the WMAP3 paper, all but one of the combined data sets brings the estimate on curvature down, suggesting that the high value of $\Omega_{tot}$ comes primarily from the WMAP data...

 

[marcus]

Hi all, here is another paper in the trail of fallout in the wake of WMAP3 that has to do with the closed universe issue.

http://arxiv.org/abs/astro-ph/0605709
How Many Universes Do There Need To Be?
Douglas Scott, J.P. Zibin
6 pages, 1 figure

"In the simplest cosmological models consistent with General Relativity, the total volume of the Universe is either finite or infinite, depending on whether or not the spatial curvature is positive. Current data suggest that the curvature is very close to flat, implying that one can place a lower limit on the total volume. In a Universe of finite age, the 'particle horizon' defines the patch of the Universe which is observable to us. Based on today's best-fit cosmological parameters it is possible to constrain the number of observable Universe sized patches, N_U. Specifically, using the new WMAP data, we can say that there are at least 10 patches out there the same volume as ours. Moreover, even if the precision of our cosmological measurements continues to increase, density perturbations at the particle horizon size limit us to never knowing that there are more than about 10^5 patches out there."

these people are at UBC Vancouver
douglas scott has 94 papers on arxiv mostly all published (all I saw were)
zibin has 5 up, all published, 4 co-authored with scott and one solo.
I don't know Scott by reputation, so I have to go by something and papers will do.
(some other authors mentioned on thread, such as Neil Cornish, i know from earlier
things so don't have to be so crude)

=================
so far what I am saying, all I can say, is something that doesn't officially MEAN anything. and that is the obviously true fact that so far, looking at published confidence intervals for Omega, what I PERSONALLY HAVE SEEN in my casual reading is either all on the upside of one, or if it brackets one, then it is quite noticeably overbalanced on the upside. This is more of the nature of an *odd fact* than anything else.

I PERSONALLY HAVE NOT SEEN and am still looking for an example of a paper that actually shows a confidence interval on the downside of one, or way leaning in that direction.

I would be delighted if anyone can show me a paper with that.

Meanwhile, we wait and keep casual track of the fallout as time and interest permits.

========================
hope everyone understands that I am not intending to "make a case" that the universe is closed or to argue that it is closed. I am a watcher of events in physics and cosmology and I anticipate a shift in the views of mainstream cosmologists. I expect it will take a while and may be shown by them becoming more open to considering various possibilities. I am waiting with some interest to see what happens.
I wonder, for example, if there will be more papers appearing like the one here by Scott and Zibin

this thread is not intended to persuade anyone of anything I am happy if everyone keeps their opinions exactly as they are! it is more of an observational thread, keeping track of the fall-out. Nobody is being encouraged to change their mind!

 

[Chronos]

The problem with 2df and SDSS, IMO, is z ~ 2 is pretty much the observational limit for 'ordinary' galaxies. With few exceptions, most are too faint to be observed much beyond z~1. AGN's, GRB's and likewise freakishly bright events are the only windows that remain observationally accessible. The puzzle box does not easily yield its secrets.

 

[marcus]

The problem with 2df and SDSS, IMO, is z ~ 2 is pretty much the observational limit for 'ordinary' galaxies. With few exceptions, most are too faint to be observed much beyond z~1. AGN's, GRB's and likewise freakishly bright events are the only windows that remain observationally accessible. The puzzle box does not easily yield its secrets.

Chronos, I am delighted that you found the Scott and Zibin paper interesting enough to contribute a comment! I do not fully grasp the relevance of what you say to their paper (assuming you intend any) but I do readily acknowledge the difficulty of basing estimates of curvature, and of Omega, on ordinary galaxy counts.

fortunately, the Scott and Zibin paper is not based on galaxy counts, but on the microwave background. what they say is nice and clear and easy to remember.

they say look at the volume of the OBSERVABLE UNIVERSE, this is something that hellfire or others here could swiftly estimate as a certain number of cubic lightyears.

they say that they have learned from the WMAP3 data that THE VOLUME OF THE WHOLE UNIVERSE IS AT LEAST TEN TIMES LARGER THAN THE VOLUME OF THE OBSERVABLE UNIVERSE.

It might of course be infinity times larger, but at least it is TEN. that is sort of nice to know, is it not?

maybe I could do an OOM on the volume the current radius of the current observable is about 40 billion LY, so we just cube that ( 64,000 billion billion billion cubic LY) and multiply by 4 (which is the same as 4/3 pi) and we get 250 x 10³⁰ cubic LY, anyway some large number like that: 2.5 x 10³² cubic LY.

the exact number doesn't matter. what Scott Zibin claim to show is that the total volume of the entire universe not just what we see but EVERYTHING---ALL THE SPACE THERE IS---is at least 10 times bigger volume than that. at the present moment of course, because that is when we are measuring and estimating.

it expandeth apace, so the volume will be larger in the future as result of expansion, but at the moment we know it is at least that large a volume---and of course it may be infinite.

 

[Chronos]

Chronos, I am delighted that you found the Scott and Zibin paper interesting enough to contribute a comment! I do not fully grasp the relevance of what you say to their paper (assuming you intend any) but I do readily acknowledge the difficulty of basing estimates of curvature, and of Omega, on ordinary galaxy counts.

fortunately, the Scott and Zibin paper is not based on galaxy counts, but on the microwave background. what they say is nice and clear and easy to remember.

My intent was to point out they conveniently ignored known galaxy counts [e.g., SDSS] and extrapolated a very speculative result.

they say look at the volume of the OBSERVABLE UNIVERSE, this is something that hellfire or others here could swiftly estimate as a certain number of cubic lightyears.

they say that they have learned from the WMAP3 data that THE VOLUME OF THE WHOLE UNIVERSE IS AT LEAST TEN TIMES LARGER THAN THE VOLUME OF THE OBSERVABLE UNIVERSE.

So what? These 'unobservable' universes sound like a 'landscape' to me. But, your point is clear. The gratuitious insult did not go unnoticed.

It might of course be infinity times larger, but at least it is TEN. that is sort of nice to know, is it not?

It is a nice speculation. I just disagree with the reasoning.

maybe I could do an OOM on the volume the current radius of the current observable is about 40 billion LY, so we just cube that ( 64,000 billion billion billion cubic LY) and multiply by 4 (which is the same as 4/3 pi) and we get 250 x 10³⁰ cubic LY, anyway some large number like that: 2.5 x 10³² cubic LY.

the exact number doesn't matter. what Scott Zibin claim to show is that the total volume of the entire universe not just what we see but EVERYTHING---ALL THE SPACE THERE IS---is at least 10 times bigger volume than that. at the present moment of course, because that is when we are measuring and estimating.

Circular reasoning is the first thought that comes to mind.

it expandeth apace, so the volume will be larger in the future as result of expansion, but at the moment we know it is at least that large a volume---and of course it may be infinite.