Estim. dark energy up by 3 percentage points. Any reaction?

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marcus
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Main Question or Discussion Point

When people cite the dark energy fraction informally (without errorbar) and other basic parameters they often have been saying something like

Hubble 71
dark energy 73%
dark matter 23%
baryonic 4%

If I remember right, those are the default values used in the calculator at Ned Wright's website.

Now in this 7 March paper by Michael Turner et al, right in the abstract up front I see

dark energy 76%
dark matter 20%
baryonic 4%

So are these new values that one should quote informally? Given the uncertainty it doesn't seem very different to say 76 instead of 73, but even though it is just a rough estimate I'd like to be aligned with the mainest of the stream---and keep the jarring dissonance to a minimum. So what numbers to you say?

Michael Turner recent:
http://arxiv.org/abs/0803.0982
 

Answers and Replies

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Cosmology is a field I haven't studied in detail. I have only gone through it enough to know generally what cosmologist are talking about and why. For me my interest in cosmology is limited to what it can provide as a testing ground. Since I don't have any ideas (wild ass guesses) that require these parameters at the moment the ball park figure is fine with me. However, as a cosmologist, keeping abreast and using the best numbers from the best available data is important. Given the authors and the following quotes under "10.1 Take-home facts":

10.1.5 Current observational status. Taken together, all the current
data provide strong evidence for the existence of dark energy; they constrain
the fraction of critical density contributed by dark energy, 0.76 ± 0.02, and the
equation-of-state parameter, w ≈ −1 ± 0.1 (stat) ±0.1 (sys), assuming that w is
constant. This implies that the Universe began accelerating at redshift z ~ 0.4
and age t ~ 10 Gyr. These results are robust – data from any one method can be
removed without compromising the constraints – and they are not substantially
weakened by dropping the assumption of spatial flatness. <snip>
I would go with these figures.
 
cristo
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I don't really know where that figure has come from; I guess it depends on what data set you're using. I know the recent WMAP data had omega_lambda 0.74 on its own, and that shrunk to about 0.72 when including other data sets (namely the BAO and SN data). I've not read the Turner paper, though, so I can't really comment on that; perhaps someone else can?
 
Wallace
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The precise numbers still depend on which data sets are used. For instance see the series of tables http://lambda.gsfc.nasa.gov/product/map/current/parameters.cfm" that show the values obtained using WMAP5 + many different combinations of other data. The best fit values for dark energy vary between 0.7 and almost 0.8 depending on which data sets are used!

There are a bunch of extensions to the basic LCDM such as non flat models, different dark energy models etc that are also covered.
 
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