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Size of the Universe


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Just how big is the universe anyway??? I know that there won't be exact figures available for some time, but what is the estimate of the size of the Universe?

 

Ned Wright is one of the worlds top cosmologists and he recently came out with an estimate

 

In his recent paper he calls it the "best fit"

 

He put all the data from all different sources together

http://arxiv.org/abs/astro-ph/0701584

Constraints on Dark Energy from Supernovae, Gamma Ray Bursts, Acoustic Oscillations, Nucleosynthesis and Large Scale Structure and the Hubble constant

Edward L. Wright (UCLA)

17 pages Latex with 8 Postscript figure files. One new Table, one new Figure, and several new references added. Submitted to the ApJ

 

It comes down to saying that the best fit model space a 3-sphere with radius of curvature presently equal to 130 billion LY.

 

it is expanding so the radius of curvature is getting larger

 

His "best fit" is a slight modification of the standard picture (called "LambdaCDM") that most cosmologists use nowadays. the difference is that the standard model has INFINITE FLAT SPACE and you get the best fit to the data if you make that NEARLY flat but not perfectly flat, in which case space becomes a very large 3-sphere in other words FINITE INSTEAD OF INFINITE with, by his estimate, radius of curvature 130 billion lightyears.

 

So you can work out the circumference---the length of a great circle, or whatever you want from that.

 

Because of uncertainty in the measurments there is some errorbars and stuff, so there is some slop. which means the data is still some percentage CONSISTENT with a flat infinite space. But these days the weight of the data is mostly coming down in favor of slight positive curvature, and finiteness. nevertheless cosmologists continue using the flat model because it is simpler and they are used to it so they keep on.

 

Ned Wright is a WMAP leader, he also was supporting cast in COBE (that Smoot and Mather got Nobel for). He's one on the short list of worldclass cosmologists. he's fighting to get the nearly flat, finite case adequately considered instead of just automatically assuming flat infinite.

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Ned Wright is one of the worlds top cosmologists and he recently came out with an estimate

 

Really? For visible universe or the whole thing? I thought it was still an open question as to whether the universe was infinite in extent or not.

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Whole thing.

 

It IS an undecided question. Read my post.

there is enough uncertainty so that it still could be flat infinite.

 

indeed that has been the conventional assumption for several years (the prevailing version of LambdaCDM)

 

the point is that this is NOW BEGINNING TO BE CHALLENGED.

 

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

here is another shot in this particular war. Bruce Bassett has joined with Ned Wright.

 

Bruce Bassett and Ned Wright are both raising the warning flag and saying no the numbers DON'T work out the same. One should NOT automatically assume finite spatially flat, especially when studying dark energy.

 

Bruce Basset et al

http://arxiv.org/abs/astro-ph/0702670

Dynamical Dark Energy or Simply Cosmic Curvature?

Chris Clarkson, Marina Cortes, Bruce A. Bassett

5 pages, 1 figure

"We show that the assumption of a flat universe induces critically large errors in reconstructing the dark energy equation of state at z>~0.9 even if the true cosmic curvature is very small, O(1%) or less. The spuriously reconstructed w(z) shows a range of unusual behaviour, including crossing of the phantom divide and mimicking of standard tracking quintessence models. For 1% curvature and LCDM, the error in w grows rapidly above z~0.9 reaching (50%,100%) by redshifts of (2.5,2.9) respectively, due to the long cosmological lever arm. Interestingly, the w(z) reconstructed from distance data and Hubble rate measurements have opposite trends due to the asymmetric influence of the curved geodesics. These results show that including curvature as a free parameter is imperative in any future analyses attempting to pin down the dynamics of dark energy, especially at moderate or high redshifts."

 

 

Joanna Dunkley et al

http://arxiv.org/abs/astro-ph/0507473

Measuring the geometry of the Universe in the presence of isocurvature modes

J. Dunkley, M. Bucher, P. G. Ferreira, K. Moodley, C. Skordis

4 pages, 5 figs.

Phys.Rev.Lett. 95 (2005) 261303

 

"The Cosmic Microwave Background (CMB) anisotropy constrains the geometry of the Universe because the positions of the acoustic peaks of the angular power spectrum depend strongly on the curvature of underlying three-dimensional space. In this Letter we exploit current observations to determine the spatial geometry of the Universe in the presence of isocurvature modes. Previous analyses have always assumed that the cosmological perturbations were initially adiabatic. A priori one might expect that allowing additional isocurvature modes would substantially degrade the constraints on the curvature of the Universe. We find, however, that if one considers additional data sets, the geometry remains well constrained. When the most general isocurvature perturbation is allowed, the CMB alone can only poorly constrain the geometry to Omega_0=1.6+-0.3. Including large-scale structure (LSS) data one obtains Omega_0=1.07+-0.03, and Omega_0=1.06+-0.02 when supplemented by the Hubble Space Telescope (HST) Key Project determination of H_0 and SNIa data."

 

The point is not whether you like flat or don't like flat. The point is we don't know and ASSUMING FLAT INTRODUCES ERRORS.. Assuming flat encourages circular reasoning (according to Ned Wright) and makes what you do unreliable. This is how Basset et al argue, and they cite Ned Wright too:

===quote Basset===

However, we will show that ignoring Omega_k induces errors in the reconstructed dark energy equation of state, w(z), that grow very rapidly with redshift and dominate the w(z) error budget at redshifts (z > 0.9) even if Omega_k is very small. The aim of this paper is to argue that future studies of dark energy, and in particular, of observational data, should include Omega_k as a parameter to be fitted alongside the w(z) parameters.

 

Looking back, this conclusion should not be unexpected. Firstly the case for flatness at the sub-percent level is not yet compelling: a general CDM analysis [13 the Dunkley paper], allowing for general correlated adiabatic and isocurvature perturbations, found that WMAP, together with largescale structure and HST Hubble constant constraints, yields

Omega_k = −0.06 ± 0.02.

We will show that significantly smaller values of Omega_k lead to large effects at redshifts z ~ 0.9 well within reach of the next generation of surveys.

 

Secondly, Wright (e.g.[14]) has petitioned hard against the circular logic that one can prove the joint statement (Omega_k = 0,w = −1) by simply proving the two conditional statements (Omega_k = 0 given that w = −1) and (w = −1 given that Omega_k = 0). ...

 

Given that the constraints on Omega_k evaporate precisely when w deviates most strongly from a cosmological constant, it is clearly inconsistent to assume Omega_k = 0 when deriving constraints on dynamical dark energy...

===endquote===

 

the gist is that if Omega is EXACTLY ONE then it is flat and infinite. but if Omega is even slightly bigger than one, then it is finite.

And the errorbars all seem to be tilted in favor of bigger.----hence positive curved finite space: the 3-sphere

 

So the people who think this possibility should be taken seriously are beginning to raise hell and say IF YOU AUTOMATICALLY ASSUME FLAT THEN YOU SUCK AND YOUR WORK WILL RISK GETTING ERRORS, if you really want to do science then you have to consider this case too.

 

Because they really haven't been considering it besides a little marginal and lipservice. Paper after paper comes out just automatically assuming space is infinite.

 

I think Wright, Bassett and others will probably succeed in changing that.

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Ned Wright is one of the worlds top cosmologists and he recently came out with an estimate

 

In his recent paper he calls it the "best fit"

 

He put all the data from all different sources together

http://arxiv.org/abs/astro-ph/0701584

Constraints on Dark Energy from Supernovae, Gamma Ray Bursts, Acoustic Oscillations, Nucleosynthesis and Large Scale Structure and the Hubble constant

Edward L. Wright (UCLA)

17 pages Latex with 8 Postscript figure files. One new Table, one new Figure, and several new references added. Submitted to the ApJ

 

It comes down to saying that the best fit model space a 3-sphere with radius of curvature presently equal to 130 billion LY.

 

it is expanding so the radius of curvature is getting larger

 

His "best fit" is a slight modification of the standard picture (called "LambdaCDM") that most cosmologists use nowadays. the difference is that the standard model has INFINITE FLAT SPACE and you get the best fit to the data if you make that NEARLY flat but not perfectly flat, in which case space becomes a very large 3-sphere in other words FINITE INSTEAD OF INFINITE with, by his estimate, radius of curvature 130 billion lightyears.

 

So you can work out the circumference---the length of a great circle, or whatever you want from that.

 

Because of uncertainty in the measurments there is some errorbars and stuff, so there is some slop. which means the data is still some percentage CONSISTENT with a flat infinite space. But these days the weight of the data is mostly coming down in favor of slight positive curvature, and finiteness. nevertheless cosmologists continue using the flat model because it is simpler and they are used to it so they keep on.

 

Ned Wright is a WMAP leader, he also was supporting cast in COBE (that Smoot and Mather got Nobel for). He's one on the short list of worldclass cosmologists. he's fighting to get the nearly flat, finite case adequately considered instead of just automatically assuming flat infinite.

 

Warming, this post of mine is typed by someone with less then desirable education in physics.

 

That aside, if the dimensions as posed for a finite universe are giving, then would it be safe to assume that forensically such can be studied in terms of natural phenomena?

 

I mean did this take into account the big bang giving such dimensions, or are these dimensions constant or not influenced by the big bang?

 

If influenced by such then my idea is that the time it took to reach its dimensions should be able to be studied indirectly via other natural phenomenon, such as formations of galaxies possibly? Another example to the point, would the size of the universe be able to be studied in an evolutionary sense?

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....

 

I mean did this take into account the big bang giving such dimensions, or are these dimensions constant or not influenced by the big bang?

 

If influenced by such then my idea is that the time it took to reach its dimensions should be able to be studied indirectly via other natural phenomenon, such as formations of galaxies possibly? Another example to the point, would the size of the universe be able to be studied in an evolutionary sense?

 

that is what they call "structure formation". It is one of the handles they have on the universe---fitting the observed rate of cluster and galaxy formation to their model.

 

As he indicates in the title, Wright took into account structure formation data as well as everything else that's been measured accurately enough so you can fit a model to it.

 

"Constraints on Dark Energy from Supernovae, Gamma Ray Bursts, Acoustic Oscillations, Nucleosynthesis and Large Scale Structure and the Hubble constant"

 

Check out his website: the dude is one of the most competent cosmologists out there. If he sets out to get the best fit to all the useful data, that's what he'll do.

http://www.astro.ucla.edu/~wright/cosmolog.htm

 

http://www.astro.ucla.edu/~wright/intro.html

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Just how big is the universe anyway??? I know that there won't be exact figures available for some time, but what is the estimate of the size of the Universe? ...

 

That's right, there AREN'T exact figures, and space might be infinite so there wouldn't be a well-defined size.

But increasingly there are indications that space might be finite.

And there IS an estimate. You asked about an estimate.

 

To make a brief answer...

 

You can think of it as a bumpy threesphere with radius 130 billion light years.

Bumpy because matter deforms geometry a little, so local concentrations of matter like clusters of galaxies make the sphere a bit bumpy. But overall still like a sphere.

 

Estimates like this are not to believe in. they are preliminary. the real information is always the errorbar, not the central point of the errorbar which you might call the "best fit" point. Like, if I had to choose a most likely, I would certainly choose this. But nobody is forcing me to choose!---so I reserve judgment and believe only the errorbar (the statistical range of possibilities)

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;325751'']Very interesting, thanks Martin.

 

Thanks also to you Tycho! Without acute listeners, nothing worthwhile would get said. There IS interesting stuff going on in cosmology these days happily enough.:)

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