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yuiop
yuiop is offline
#7
Aug13-08, 04:11 AM
P: 3,967
Quote Quote by Chronos View Post
Not sure where you are coming from, kev. Can you clarify how CMB and cluster data is discordant with supernova data? The Perlmutter study is pretty convincing, IMO.
Hi Chronos,

Have a look at the attached image which shows how the concordance diagrams should look if the supernova data really was in accordance with the the other data and contrast my diagram with the concordance diagrams using real data here and here from Ned Wrights cosmology page. http://www.astro.ucla.edu/~wright/sne_cosmology.html

The centre of the supernova error ellipses should coincide with where the other data cross over, but in order to do that I have had to artificially adjust the supernova data in the left diagram to agree with other data if Omega(total) is assumed to be about 1.02

In the right hand diagram I have had to move all the other datasets to coincide with the supernova data which by itself suggests Omega(total) is about 1.30. That also requires adjusting the Hubble parameter in the second diagram to about 60 which is indicated by the vertical blue line. The vertical line also represents Omega(mass) and that is sometimes estimated from cluster data and includes normal matter and dark matter. Omega(mass) has had to be adjusted to about 0.4 to agree with the supernova data which differs from the value of under 0.3 for the standard LCDM model. The CMB line has had to be moved considerably too. The slightly tilted magenta lines represents data from Baryon Acoustic Oscillations. The supernova data also suggests lambda is about 0.9 which is significantly larger than the value of about 0.7 stated for the standard LCDM model.

Also have a look at this "delta distance modulus v redshift" diagram by Ned .The binned supernova data at about Z=1.15 is so far off the best fit lines that even the error bar does not come anywhere near the model lines. The solid magenta curve which represents the flat dark energy model (which is pretty much the standard LCDM model) depends on the binned supernova data at about Z=1.6 which has a huge error bar. If the binned supernova data at Z=1.6 is ignored then the dashed magenta line is the better fit and this is the line Ned calls the "Closed Dark Energy Model". Although Ned does not state what value of Omega(total) he is using for the closed model it looks more like the figure of 1.3 that I mentioned earlier than the standard figure of about 1.02 +/- 0.2 or even 1.01 +/- 0.1 that is often quoted.

The next Ned diagram shows Gamma Ray Burst data alongside supernova data. The best fit dark energy closed model for the supernova data is a long way of the best fit flat model for the GRB data. There is also a large deviation of the flat model from the GRB data at Z<1.0 so again it is hard to draw a definitive conclusion. Ned also shows a dashed blue line that suggests an evolving supernova model brings the supernova data into better agreement with the GRB data and the flat model.

Also note that the first Ned Wright diagram I mentioned earlier (that is located at the bottom of his supernova cosmology webpage) shows Ned's attempts to get the various data sets to agree by adjusting the equation of state parameter (w). He does not succeed in getting the supernova data to exactly agree with the CMB/BOA/Hubble datasets for any value of w. The small green ellipse at the centre of the supernova error ellipses never coincides with the other datasets. It is a pity Ned does not show the GRB data on the concordance diagrams but I would be willing to bet it matches the other 3 datasets much better than the supernova data.
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