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#21
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Static universe - revisited
On Fri, 06 May 11, Steve Willner wrote:
I haven't gone back to check this, but as long as x1 gives s uniquely, it should be fine. Goldhaber et al. show stretch values ranging between 0.8 and 1.2, and at first glance your numbers seem to show lower scatter. My numbers are in that range, with some outliers to 0.75 and 1.3. Those SNe with z0.05 average a stretch of 0.923 so if I normalize the whole data to that, then the following 0.1z bins have: z=0.0 -- avg stretch of 1.000 z=0.1 -- avg stretch of 1.028 z from 0.2 to 0.9 -- avg stretch of 1.055 z from 1.0 to 1.4 -- avg stretch of 1.081 ..... so there is indeed a small dependency of stretch on z. Eric Flesch wrote: ... we should expect a Malmquist-caused correlation. How big do you expect it to be? Given that rest-frame stretch often reaches 1.25, I'd expect that to be the average value for the high-z objects. Neither the redshift nor the stretch depends on cosmology; both are directly measured from the data. Well, the stretch has the z component removed. I'm not saying it shouldn't, but I think there's evidence that too much is removed. These observations, if normalized to Malmquist expectations (so that the high-z SNe should have average rest-frame stretch of ~1.25), would yield a redshift-stretch of about 2/3 of what is assumed. This would be a significant discovery, and I think it's viable, if only the researchers would consider it and not treat it as a closed book. There are several competing groups working on the supernovae, so if there were any obvious errors, most likely someone would have caught them. That's no guarantee, of course, but merely asserting "something must be wrong" is not useful. Yes, I did not fully analyze the data for my previous posting, because I had a specific model in mind. So in the finest scientific tradition, I worked out what stretches my model would yield, then checked it against the real data. A swing and a miss! So to assert something is wrong is all I can do at the moment -- I don't agree it's not useful, surely it's the first step to finding something better. Eric Flesch |
#22
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Static universe - revisited
In article ,
Eric Flesch writes: My numbers are in that range, with some outliers to 0.75 and 1.3. Those SNe with z0.05 average a stretch of 0.923 so if I normalize the whole data to that, then the following 0.1z bins have: z=0.0 -- avg stretch of 1.000 z=0.1 -- avg stretch of 1.028 z from 0.2 to 0.9 -- avg stretch of 1.055 z from 1.0 to 1.4 -- avg stretch of 1.081 .... so there is indeed a small dependency of stretch on z. OK, that's reassuring. Given that rest-frame stretch often reaches 1.25, I'd expect that to be the average value for the high-z objects. I don't see why. To quantify the expected Malmquist bias, you'd have to know exactly how all the data were obtained. They are not from the same or even similar surveys. SWNeither the redshift nor the stretch depends on cosmology; both are SWdirectly measured from the data. Well, the stretch has the z component removed. I'm not saying it shouldn't, but I think there's evidence that too much is removed. Dividing by 1+z is just a mathematical operation. You could use any other measure of the decline timescale. (Other SN groups do in fact use different measures.) The point is that s, or more generally the timescale for decline, is measured directly from the data; there is no cosmological assumption whatsoever in the measurement. These observations, if normalized to Malmquist expectations (so that the high-z SNe should have average rest-frame stretch of ~1.25), would yield a redshift-stretch of about 2/3 of what is assumed. If you are claiming that unusually bright (large-s) supernovae are missing from the distant sample, that seems difficult to believe. More likely would be faint (small-s) supernovae systematically missing from the nearby samples, but you'd have to look in detail at the surveys to find out whether that's happening. (Personally I doubt it, but I could be wrong.) For derivation of the cosmological parameters, I don't see any reason the supernova samples have to be complete or even unbiased. All that is needed is the assumption that nearby and distant supernovae that have the same timescale and color are the same, and therefore the absolute magnitudes of the distant supernovae are known. There are subtle ways that assumption could be false -- among them dependence on galaxy type or metallicity -- but I don't see Malmquist bias as an issue. If you have an unusual cosmological model you want to test, you need to work out what it predicts for timescale and for distance modulus and see whether it fits the data. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#23
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Static universe - revisited
In article , Steve Willner
writes: There are several competing groups working on the supernovae, so if there were any obvious errors, most likely someone would have caught them. That's no guarantee, of course, but merely asserting "something must be wrong" is not useful. Indeed. At the beginning, the two big groups were working with different strategies, different observations, different data reduction etc. The fact that they got essentially the same results made their claims (which some pundits were sceptical about at first) more believable. I think they later reduced each other's data. Also, none of them set out to find what is now the "standard model" of cosmology. In fact, many were quite sceptical. This is clearly a case of the observational data changing what people believe to be the best model. |
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