Precision Cosmology Defeats void Model

[CraigS]

Folks;

Here's another recent paper from Uni of British Columbia:
'Precision Cosmology Defeats Void Models for Acceleration, (July 2010)'

http://arxiv.org/abs/1007.3725

...which puts another 'popular' hypothesis to the test. (Would seem to be relevant to demonstrating Science's open-mindedness to well thought out, alternative ideas).

Unfortunately, its too big to post as an attachment, but hopefully one can get a feeling for the article from the below quotes. (You can also download a pdf from the link above).

Some interesting quotes:

The Introduction:
"The suggestion that we occupy a privileged position near the centre of a large, nonlinear, and nearly spherical void has recently attracted much attention as an alternative to dark energy. Putting aside the philosophical problems with this scenario, we perform the most complete and up-to-date comparison with cosmological data. We use supernovae and the full cosmic microwave background spectrum as the basis of our analysis. We also include constraints from radial baryonic acoustic oscillations, the local Hubble rate, age, big bang nucleosynthesis, the Compton y-distortion, and for the first time include the local amplitude of matter fluctuations, σ8. These all paint a consistent picture in which voids are in severe tension with the data. In particular, void models predict a very low local Hubble rate, suffer from an “old age problem”, and predict much less local structure than is observed."

The Conclusions:

"We have performed the most complete and up-to-date analysis of the proposal to explain the acceleration of the Universe with a large, nonlinear void. Our main results can be summarized as follows:

• Models which fit both the CMB and SNe have an extremely low local Hubble rate of h0 = 0.45 ± 0.02 and are very old, with an age of around 18.5– 19 Gyr. Both of these are inconsistent with observations.
• The radial BAO scale is suppressed in the outer void region compared to ΛCDM and is a poor fit to data.
• The Compton y-distortion constraint from COBE rules out wider, deeper voids even if the overdense shell is tuned to minimize y. Generic shells are inconsistent with the COBE limit and all void models are ruled out at high significance in conjunction with radial BAO data.
• The local amplitude of matter fluctuations is extremely low in void models, with σ8 = 0.49 ± 0.04. This is due to the suppression of growth compared to ΛCDM, and is strongly incompatible with estimates from local galaxy clusters.
• The primordial power spectrum would need to be highly tuned and far from scale-invariant in order to attempt to alleviate some of these problems. We considered running of the spectral index and a broken power law and these were insufficient to change our conclusions.
• We uncovered a class of models with multi-valued distance-redshift relations. While unusual and interesting to study, they again did not alter our conclusions.

Thus it appears that void models for acceleration are overwhelmingly at odds with several types of observations."

"Finally, we note that two of the most important assumptions in cosmology are those of the cosmological and Copernican principles. Therefore, in confronting void models, which blatantly violate both of these principles, with observations, we do more than just examine an unusual approach to the mystery of acceleration. We put the foundations of modern cosmology themselves to the test."

Great stuff !!
Cheers

[renormalised]

I'll have to read this before I can comment, but it does sound interesting. That'll have to wait, though....uni work calls.

[CraigS]

Here's another quote from the Introduction of this paper:

"However, ΛCDM appears to suffer from severe fine-tuning problems of its own and it is conceivable that unknown physics could produce the conditions necessary for such a void. Therefore, it is important to ignore our philosophical prejudices and use the available cosmological observations to decide the issue. Given the increasing scope and precision of those observations, which largely support the SMC (the standard model of cosmology), demonstrating the viability of models that depart so dramatically from ΛCDM would certainly appear unlikely. Nevertheless, the relevance of this line of inquiry extends beyond particular models of dark energy, and refuting these inhomogeneous models would, importantly, strengthen our confidence in the fundamental assumptions of our standard cosmological models. There is presently little direct evidence for cosmological-scale homogeneity, in particular."

Very cool words .... very honest and very frank ...
and I note the last sentence, which is also a very refreshing admission.
:)
Cheers

[CraigS]

Y'know;

Apart from the message contained in this paper about how the foundations (Cosmological Principles) are themselves, continually under scrutiny and review, I was amazed about the possibility that mainstream scientists could seriously entertain the thought that we could possibly "occupy a privileged position near the centre of a large, nonlinear, and nearly spherical void".

Goodness me !! Copernicus' model was published in 1543 and yet, 467 years later, science is still wrangling with an 'Earth-centric privileged position' model!

There must be a lot of scientific types lobbying about this view for these guys to have been bothered enough to produce a serious 20 pager on it !! Good on these guys for 'getting over it - and on with it'.

Goes to show how distasteful the concept of 'Dark Energy' really is - even to scientists! I'm glad I'm not alone.

Having admitted this now, I'm also determined to understand & get more of it, in order to come to terms with the bizarre-ness of the concept (and 'get on with it').

The spherical void thing really is extreme, though.
Star Trek Stuff !!

Boldly going .... tah .. dah ...!!

Cheers

[renormalised]

Even Einstein said that the CC was his greatest blunder, and yet if the supernova data are correct, then it's an unavoidable consequence of the nature of the universe. It evolved from the BB, just like everything else and despite it being distasteful, they have to live with it.

Just like Scotty said, "Yeh canna change the laws of physics!!!!":P

Well, you can actually, but don't tell him that!!!:):P

[CraigS]

There's another dimension of thinking which I have been trying to get into words over the last few weeks .. here goes ... (oh no !!) ..

Big Bang Theory (BBT), ΛCDM (or Standard Cosmology Model), dark thingys, etc, etc are really concepts to have firmly embedded in every fibre of a cosmologist's being, because when used a 'filter', and applied to an idea, it invariably results in a clarity of thought which in turn, results in a level of comfort in positioning seemingly unintuitive, unexpected observations of the world around us.

This would seem to be because of the extraordinarily high degree of rigor and logic applied in the rationale of developing them.

Adopting the thinking also results in further (always productive, often null), investigation beyond the present understanding (regardless of how distasteful this investigation might be).

Having said this, its also healthy to not hold them so closely that it becomes one's soul belief (as though the concepts are irrevocably undeniable 'truths'). They then become religious beliefs which always end up at the same place, hence no further thinking is worthwhile. Its easy to slip into this mode and I find I have to wrestle with myself to stay away from this.

Enough philosophy !!! ... Back to me books.

Cheers

[renormalised]

Despite the protestations to the contrary from the lunatic fringe, scientist normally don't hold onto ideas or theories to the point that they become like a religious mantra. It may seem like that if you listen to some scientist speak or read some of the journals, but there's very good and sound reasons as to why scientists stick to tried and true methodologies and theories. Yes, they can be inflexible sometimes. But as a whole, most scientist are open to new ideas, so long as those ideas make sense, are verifiable and promote the furthering of knowledge.

Unfortunately, like all people, some scientists can get an idea in their heads and become dogmatically stubborn in sticking with it. It usually occurs with ideas that are pet projects of scientist and those scientists don't want to give up on their ideas. That can be well and good, but sometimes the ideas they have weren't all that viable in the first place, or they have been repeatedly refuted by the overwhelming body of evidence that's been accumulated over the years. Except for their band of followers, most of these scientist are largely ignored or just allowed to continue on with their research but aren't generally cited by anyone, except where their studies are being tested again for scientific veracity.

However, it's when scientist start to go off the deep end with unsupportable ideas, or they begin to take on the less than sound ideas of the fringe as their own, is when they become ridiculed and rebuffed.

[Robh]

From recollection, one of the ideas going around was that the Universe consisted of an infinite number of such voids. A bit like bubbles in a bottle of lemonade. So, it is not that unbelievable that we should be near the centre of one of these infinity of bubbles. If the research indicates that this is not the case then it eliminates this model.
http://ngm.nationalgeographic.com/ngm/0308/resources_who.html

Regards, Rob.

[renormalised]

That was the idea. You had these voids with the galaxies and such surrounding the outsides of the voids like in a soap bubble. Within the voids themselves, there was stuff all of anything...virtual no gas or dust except for what was contained within the few galaxies that appeared to reside there. However, when viewed on the largest of scales, the voids and the walls blended in pretty much seamlessly to produce an isotropic and homogeneous distribution of matter and energy across the Universe, thereby upholding the CP. Given that there are/were an infinity of these voids and walls of galaxies across the universe, finding oneself in the centre of one of these voids, or even on the outskirts of one, would not be out of the question. However, if the interpretations of this paper are correct, then we have to reappraise the void/bubble model or abandon it entirely depending on the outcome of further observations and theory.

It's cutting it a little fine, given that there are demonstrably measurable voids present in the universe. Observations have shown this. But that's not to say that the present theory is entirely correct. Half a dozen or so voids does not an universe make:)

[CraigS]

Yep you guys are right ... "The big bang of the universe is actually similar to cell division in biology, since new universes are continuously formed. However, inflation always wipes out the circumstances of the beginning of the particular universe." -Wiki.

Just as a matter of interest where are the voids ?

Cheers

[renormalised]

Except the voids I'm talking about here are not new universes, even if they lie outside of our event horizon, they are voids within the universe itself. Remember, what we call the "universe" is not the whole universe. It's just a small section of it that we can see inside our horizon bubble. Inflation has expanded the total universe to a size enormously larger than what we can see. The Multiverse concept, that was formulated by Hugh Everret back in the 60's, is different. They are separate spacetimes that have expanded along with or budded off our universe. They're essentially separate universe that we cannot observe because their structure lies outside of our spacetime. All of the universes, including our own, "figuratively expand" within an even larger space, a superspace (space of spaces, if you will) that is a higher dimensional state than the universe that we would experience. However, the spacetime that we experience is cutoff at a macroscopic level from these higher dimensions. To us, these dimensions are "rolled" up into points smaller than a proton (actually, they're around the Planck Length in size, at least as we "see" them) but they occupy every point in our space. Think of it like this, using the old balloon analogy...if the 4D (3 spatial and 1 time dimension) space we experience is the surface of that balloon, then the rest of the other dimensions are the interior of the balloon (as well as everything exterior to the balloon). Underlying all of space are these other dimensions, but they lie outside of our spacetime. They appear small to us, exceedingly so, but in actual fact their total volume is infinitely larger than what we see. Our universe is just the frothy flotsam on the surface of the sea, so to speak.

It's awkward to visualise. Technically, we aren't expanding into anything, as we see it, because it is space itself which is expanding. However, if you were to look at it from a higher dimensional perspective, we are both expanding out of, and into, the higher dimensional space simultaneously. Try getting you head around that:)

[CraigS]

Hmmm very interesting.
It seems that there quite a few papers recently published, which are seriously enquiring into the viability of the 'voids' question.
This one seems to take the boldest steps in its conclusions, however.

So Carl you mention:
"that there are demonstrably measurable voids present in the universe. Observations have shown this."

Where are they and how are these observations made ?

Cheers

[renormalised]

One of them, the Bootes Void, for instance, is around 1 billion light years wide. How do they observe them??. From taking the redshifts of the galaxies that lie in that direction and plotting a 3D representation of their distances (see these sites...2Df Galaxy (http://magnum.anu.edu.au/%7ETDFgg/), 6Df Galaxy (http://www.aao.gov.au/local/www/6df/), SDSS (http://www.sdss.org/)). What they've found in the surveys is that the galaxies seem to be mostly concentrated in huge domains called walls....basically multi-megaparsec streams of galaxy superclusters that appear to surround what are basically nearly empty (to our perspective) areas that they call voids. It's a lot like soap bubbles...the walls of galaxies form the bubble and the interior of the bubble is the void. The Bootes Void is one of the largest they've found. Everywhere they've looked, they've seen the same pattern repeat itself over and over again. The maps on the sites I've given you will show you what I mean.

[CraigS]

Well, that's fascinating !! Had a cruise thru those sites. I was aware of the 2df, 6df and Sloan surveys, but did not relate them to the void issue.

The Wiki link, (I hate referring to Wiki all the time but it does hasten the comms), gives a quick 3d snapshot also:

http://en.wikipedia.org/wiki/Void_(astronomy)

-Twenty three documented voids, according to it. (Not quite a universe but a reasonable hint, though).

Fascinating that the authors of the paper do state:

"However, ΛCDM appears to suffer from severe fine-tuning problems of its own and it is conceivable that unknown physics could produce the conditions necessary for such a void."
and
"These all paint a consistent picture in which voids (theories) are in severe tension with the data".

So voids might exist, (23 already observed), due to unknown physics (according to the theory & observation test datasets applied in the paper), and the SCM doesn't support that we live inside one, or that one of the right size could exist in the first place, so the observed acceleration of the observable universe comes back to a Dark Energy driving force as the theory of best fit.

What a classic !!

Love it !

Cheers

[renormalised]

The condition for forming the voids and the walls of galaxy must have been set during the very earliest stages of the BB. It's probably a reasonably safe bet that the anisotropy seen in the CMB (cold and warm patches) is a relic of those conditions. It would also be fairly safe to say that it was the inflationary period that stretched those differences out to what we see today...the voids and the walls.

[higginsdj]

I have to chuckle somewhat when I see title's like 'Precision Cosmology'. That sounds like an oxymoron to me given that the field is based solely on theory built on top of other theory and almost no observational evidence.....

[renormalised]

Well, there is observational evidence. However, some is still a bone of contention and not everyone agrees on all the salient points. With some things though, it's pretty iffy and some of the theory isn't tied down as well as it could or should be. Precision Cosmology, though, I think is a bad choice of words. However, when you're working on the cutting edge of knowledge, you can expect things to not be so rock solid because it's changing all the time.

[higginsdj]

I didn't say there was none - just not much and what there is points to something which then can only be theorised. ie theory based on theory based on theory. Thats not a very solid foundation for a field of science!

Don't get me wrong, I know we have to start somewhere - I was just commenting on the use of 'precision' in the context of cosmology :)

[renormalised]

There's more observational evidence than you may think, but it depends on what you're observing, or what you're observing specifically for.

That's what I was commenting on as well. It was a poor choice of words.

[CraigS]

The term 'Precision' was what drew my attention to the paper in the first place (because of the 'oxy-moron-ness'). And I found it's content highly worthwhile.
Perhaps 'Precision' is a new marketing term in Cosmology !

:)

Cheers

[renormalised]

Don't go giving them any ideas!!!!:):P

Next minute, the journals will be flooding with "precision" articles!!!!:):P

Like...

"Precision Measurements of Doppler Drift upon Cosmological Redshifts at 2<z<4"

"Precision Cosmological Models for Anomalous Flow in the Direction of...."

blah blah:):P

[CraigS]

Oh but we've only just started ...

"The Precise Cosmological Forces of Canine Driven Terra Forming";
"The Precise Dimensions of Gravity Attributable to Cosmological Bacteriological Enzymes".

Disgraceful sending up my own post !! Especially when I've spent the day on my next 'project' ...
"The Precise Cosmological Applications of Gravitation Lensing"
It should be a beauty for this audience !!
:P
:)
Cheers

[Jarvamundo]

+1

It's as if they wave their opened palm across your face, and a jedi mind trick...

"precision cosmology"

I agree funny as all!

Kinda also works with "dark energy" "dark matter" "quark star" "worm holes"



more gold

+1

great comments, good questions.

[CraigS]

Pretty judgemental !!

[Jarvamundo]

precisely?

[CraigS]

A marketing term !!

[Jarvamundo]

sold, take my money

[CraigS]

Nah .. I've already got some !