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Speaking of Statistical Significance!
Check out this new submission to arxiv.org.
http://arxiv.org/abs/1506.01354 "Marginal evidence for cosmological acceleration from Type Ia supernovae" The paper calculates that the significance for cosmological acceleration based on post-1990s SN Ia data is less than 3-sigma. Counter-arguments? |
#2
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Speaking of Statistical Significance!
Le 05/06/2015 21:08, Robert L. Oldershaw a écrit :
Check out this new submission to arxiv.org. http://arxiv.org/abs/1506.01354 "Marginal evidence for cosmological acceleration from Type Ia supernovae" The paper calculates that the significance for cosmological acceleration based on post-1990s SN Ia data is less than 3-sigma. Counter-arguments? The first author of that paper (Mr Nielsen) specializes in data analysis. Other papers by him in Arxiv show him as a very mathematically minded astronomer. In another paper he develops a math system for better images for the SAMI survey, in 2011 he publishes "PyWiFeS: A Rapid Data Reduction Pipeline for the Wide Field Spectrograph (WiFeS)", he worked in the CANDELS survey too. The article about the supernova is VERY difficult to follow, but what I understood means he uses new data about supernovae to put the supposition that "the universe"'s expansion is accelerating into a statistically more solid basis. And then he realizes that the "acceleration" disappears! What is interesting too in that paper is to see how sweeping generalizations dominate cosmology. After seeing a few birds, cosmologists start screaming immediately that the spring has arrived... When cosmologists speak about "the universe", it would be better that they have a reasonable sample size to backup their claims! |
#3
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Speaking of Statistical Significance!
In article , "Robert L.
Oldershaw" writes: Check out this new submission to arxiv.org. http://arxiv.org/abs/1506.01354 "Marginal evidence for cosmological acceleration from Type Ia supernovae" The paper calculates that the significance for cosmological acceleration based on post-1990s SN Ia data is less than 3-sigma. Counter-arguments? False dichotomy. You seem to be assuming that either this new paper is completely correct or the old conclusions were completely correct, i.e. if one believes the latter then one must find some argument to show why the former is wrong. It's not so clear-cut. First, looking at FIG. 2 in the new paper, an accelerated universe is still MUCH more likely than a non-accelerated universe. Their claim is that, when all uncertainties are taken into account, that one can't strongly rule out a non-accelerating universe. OK, but, again, even their new analysis has an accelerating universe much more likely than a non-accelerating universe. However, a non-accelerating universe compatible with the supernova data would have a very low Omega and a very low lambda (which could even be negative, though they don't explore this). However, there is a huge amount of evidence, COMPLETELY INDEPENDENT of any supernova data, which points to the concordance model with Omega=0.3 and lambda=0.7. According to this new paper, this is still a very good fit to the supernova data, much better than any non-accelerating universe. A paper like this would be really interesting only if it presented data which ruled out the concordance model. Even then, the conclusion would probably be that something is wrong with the supernova data, because the alternative would be that several other independent cosmological tests are all wrong and nevertheless agree. Summary: They show that the uncertainties in the supernova-data analysis might have been overestimated, but even so the concordance model is still a good fit and acceleration is much more likely than not. |
#4
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Speaking of Statistical Significance!
In article , "Robert L.
Oldershaw" writes: Check out this new submission to arxiv.org. http://arxiv.org/abs/1506.01354 "Marginal evidence for cosmological acceleration from Type Ia supernovae" The paper calculates that the significance for cosmological acceleration based on post-1990s SN Ia data is less than 3-sigma. From a completely different point of view, my latest paper (arXiv:1505.02917) also argues that uncertainties in the cosmological parameters are larger than is generally assumed. |
#5
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Speaking of Statistical Significance!
In article , jacobnavia
writes: The article about the supernova is VERY difficult to follow, but what I understood means he uses new data about supernovae to put the supposition that "the universe"'s expansion is accelerating into a statistically more solid basis. And then he realizes that the "acceleration" disappears! Wrong. Look at FIG. 2 in the paper. The difference between these and most other papers on the topic is that a non-accelerating universe is not ruled out at more than 3 sigma. However, even in this analysis, the accelerating universe is is much more probable. FIG. 2 has the dotted "no acceleration" line. BELOW that line there is deceleration, above it there is acceleration. The paper can be summarized as "While previous analyses ruled out non-acceleration at more than three sigma, this analysis places weaker constraints, but an accelerating universe is still strongly preferred by the data". Nothing disappears! What is interesting too in that paper is to see how sweeping generalizations dominate cosmology. After seeing a few birds, cosmologists start screaming immediately that the spring has arrived... Wrong. The concordance model is called such because many lines of evidence point to it. Even if the supernova data indicated strongly a non-accelerated universe and ruled out an accelerated one, one would still have to explain why so many other tests point to the concordance model. When cosmologists speak about "the universe", it would be better that they have a reasonable sample size to backup their claims! Again, wrong. Sure, when the sample size increases, better statements can be made. However, if the error bars are calculated properly, then smaller samples result in larger error bars, all else being equal. The point of the paper is that the error bars have been underestimated in the past. |
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Speaking of Statistical Significance!
Le 06/06/2015 20:26, Phillip Helbig (undress to reply) a écrit :
Nothing disappears! Excuse me but precisely the problem is that you were arguing not so long ago that any result below 5 sigma was meaningless. Of course it doesn't disappear, I wrote that too quickly. But below 3 sigma it is no longer a relevant result isn't it? |
#7
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Speaking of Statistical Significance!
In article , jacobnavia
writes: Le 06/06/2015 20:26, Phillip Helbig (undress to reply) a écrit : Nothing disappears! Excuse me but precisely the problem is that you were arguing not so long ago that any result below 5 sigma was meaningless. Of course it doesn't disappear, I wrote that too quickly. But below 3 sigma it is no longer a relevant result isn't it? One could argue that it isn't. Of course, a 3-sigma or 5-sigma cutoff is arbitrary. Were there no other evidence for the concordance model, then this result (assuming it stands up; I don't know if the paper has been refereed yet nor where it was submitted) probably wouldn't convince many people. However, what this paper does NOT claim is that a non-accelerating universe is favoured by the data. The data still clearly favour an accelerating universe, though not as strongly as before, and a non-accelerating universe is marginally allowed, whereas before it was ruled out at well more than 3 sigma. |
#8
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Speaking of Statistical Significance!
Le 08/06/2015 09:09, Phillip Helbig (undress to reply) a écrit :
Were there no other evidence for the concordance model I posted here on April 13th in the "Dark energy doesn't exist?" thread a result that implied otherwise: quote The authors conclude that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than initially reported. end quote There is mounting evidence AGAINST dark energy. jacob |
#9
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Speaking of Statistical Significance!
In article , jacobnavia
writes: Le 08/06/2015 09:09, Phillip Helbig (undress to reply) a écrit : Were there no other evidence for the concordance model I posted here on April 13th in the "Dark energy doesn't exist?" thread a result that implied otherwise: quote The authors conclude that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than initially reported. end quote There is mounting evidence AGAINST dark energy. OK, let's assume the supernova stuff is wrong. Please explain why all the other tests which indicate the concordance model a) are wrong and b) just happen to agree with each other. Again, there are a couple of papers claiming that the supernova error bars might have been overestimated or whatever. Does anyone know the status? Have they been peer reviewed? (If so, this does not mean they are correct, but it means they have passed a hurdle of unknown height.) It is one thing to say that the supernova error bars have been overestimated. If so, then the change will be a larger allowed region of parameter space, perhaps including non-accelerating universes, negative cosmological constant, or whatever, but the best-fit value probably won't change. It is something else to say that there is some systematic source of error which distorts the results. If the latter, then it is strange that one still gets a good fit with (some other) cosmological model: with only two parameters to fit, and several hundred data points, one might think that no conventional cosmological model should give a good fit if something were really wrong. |
#10
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Speaking of Statistical Significance!
In article , jacobnavia
writes: Le 08/06/2015 09:09, Phillip Helbig (undress to reply) a écrit : Were there no other evidence for the concordance model I posted here on April 13th in the "Dark energy doesn't exist?" thread a result that implied otherwise: quote The authors conclude that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than initially reported. end quote There is mounting evidence AGAINST dark energy. Suppose things were reversed. Everything supports what you believe, then ONE observation goes against it, at less than 3 sigma. Would you believe it? Would you speak of "mounting evidence"? No. You would probably say "one tentative result is not enough to convince me". The situation now is that essentially all observations support the concordance model, then one observation looks to be a bit less secure. Yet you tout this as indicating "dark energy doesn't exist" or whatever. The universe is what it is, regardless of what anyone believes it to be or wants it to be. The only thing which is important is a proper interpretation of observations. ALL observations. |
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