Cosmo-torun March 2010

cosmo-torun@cosmo.torun.pl

1 participants
3 discussions

cosmo workshop Fri 15:00 12.03.2010: Li and Liu arXiv:1003.1073: WMAP quadrupole = antenna direction interpolation error
by Boud Roukema 02 Aug '10

02 Aug '10

witam cosmo-torun Cosmo workshop WHEN: Fri 15:00 12.03.2010 WHO: boud TITLE: Liu and Li arXiv:1003.1073 ("The origin of the WMAP quadrupole") ABSTRACT: The WMAP quadrupole is apparently mostly a pointing error. The true quadrupole is much closer to zero. The missing fluctuations problem has just got much worse for the infinite-flat-universe hypothesis. Liu and Li arXiv:1003.1073 ("The origin of the WMAP quadrupole") have posted a very interesting article (presumably submitted to Nature, guessing from the style and length). The best estimate of the CMB quadrupole is apparently... zero! They claim that the WMAP quadrupole comes from a single error - an antenna direction representation error by half of an observational angular interval. The discussion concerns quaternions, but don't be frightened - it presumably uses the imaginary part only, to represent X, Y, Z directions. You can think of them as vectors in R^3 if you like. Order of magnitude check of their calculation: Liu and Li say that the error is by 7' and that this causes incorrect subtraction of the dipole in the time-ordered-date (TOD). The direction of the error varies as the direction of observation varies, so it's reasonable that it doesn't give a simple offset detectable by post-processing in the analysis pipeline, IMHO (though Bartek may have another opinion). The dipole is about 3.3mK (e.g. section 7 Bennett et al 2003). sin(7') * 3.3mK = 0.002 * 3.3mK = 6.7 microK Liu and Li say 10-20 microK, just slightly higher, but their Eq.(1) is a motivational equation - it is not used as an entry to their data analysis pipeline. Figures 1 and 2 should the effect very dramatically. Rephrasing what they've said: Figure 1 left: difference between Liu Li analysis, using the same wrong method that the WMAP team used. This is a check that their pipeline does the same thing that the WMAP team does. |Difference| < 2 or so microK. Figure 1 right: Liu Li using correct antenna directions on WMAP Q1 3yr data. They get a strong quadrupole! Figure 2 left: The effect of using a wrong dipole, calculated using *only the directional information* from the time-ordered-data from the spacecraft, with *no CMB data*. See paragraph 2, page 4: "only the spacecraft attitude information is used to compute d' ." Figure 2 right: official WMAP5 V+W quadrupole. Figures 1 right, and 2 left look very, very similar to Figure 2 right. There seems to be a slight difference in angular position visible by eye, but the coincidence is striking. Can we really believe that the CMB quadrupole just by chance happens to be very strongly aligned with and of nearly identical amplitude to a map made using only the time-ordered-data of the spacecraft direction ("attitude") and the spacecraft orbit around the Sun, and the Sun's motion with respect to the CMB? Since this is a Nature-type article, the authors are forced to exclude almost all interesting details from the article, but info like the spacecraft attitude quaternions and interpolation method should not be too difficult to find. * Bennett et al 2003: arXiv:astro-ph/0302207 http://arXiv.org/abs/astro-ph/0302207 * Liu, Li 2010: arXiv:1003.1073 http://arXiv.org/abs/1003.1073 The good thing about this is that it shows that a lot of very intelligent people - those in a mega-collaboration plus many outside of the official group - can spend 7 years looking closely at an important set of observational data without finding what appears to be a very elementary error in the analysis details, with a very fundamental consequence. The fundamental consequence is that a lower quadrupole makes Infeld's (1949) prediction of the equivalent of the low l cutoff due to the shape of the Universe even stronger! Liu & Li suggest an inflationary argument, but their interpretation is not what is important - they don't want the referee to make a fuss about interpretations, since their observational argument is so strong. pozdr boud

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advanced summer school on computational astrophysics at Nicolaus Copernicus University, Torun, Poland, 11-25 July 2010
by Boud Roukema 08 Mar '10

08 Mar '10

witam cosmo-torun Our colleagues in the optical group have got together with some galaxy formation people and are organising a simulation workshop this northern summer (July 2010): http://supercomputing.astri.umk.pl/ Ben Moore is one of the key people doing galaxy simulational work since a long time ago. Romain Teyssier does adaptive tree code work AFAIK - his program RAMSES is here: http://irfu.cea.fr/Projets/Site_ramses/RAMSES.html It is wolne oprogramowanie, under the CECILL licence, which is GPL-compatible under section 5.3.4 of the CECILL licence: http://www.cecill.info/licences/Licence_CeCILL_V2-fr.txt i think that many of us could be interested in participating or at least listening to a few talks. i'm sure that Michal Hanasz and the doktoranci will tell us if they prefer us to formally register or not, though of course, i'm sure there wouldn't be things like registration fees for local participants. We should think of organisers' practical side of making sure that there are enough seats or computers available, etc. but i don't expect that that would be a huge problem - e.g. eduroam access for laptops should presumably be available at the Maths building. pozdr boud

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two books for library: Schilpp/Infeld (1949); Bolejko et al (2009)
by Boud Roukema 04 Mar '10

04 Mar '10

hi Karolina, Here are two books that would be useful to buy. The first one has what seems to be the first statement of the "nothing-can-be-bigger-than-the-Universe" argument in terms of density perturbations. Apparently, the first scientist(s) to state the argument were not Starobinsky (1993) and Stevens et al (1993), but rather... a Polish physicist: Leopold Infeld in 1949! The second book synthesises recent papers on the Einstein-equation exact-solution approach to what i have repeatedly said in our cosmology group several times (and Helena is working on this :). In simple words: "the simplest explanation for dark energy may be the failure to do the maths carefully enough". (1) Albert Einstein: philosopher-scientist, edited by Paul Arthur Schilpp , 1949 (republished 1970) e.g. http://searchworks.stanford.edu/view/1066168 http://www.questia.com/library/book/albert-einstein-philosopher-scientist-b… (2) Bolejko et al 2009: Title: Structures in the Universe by Exact Methods Author: Krzysztof Bolejko, Andrzej Krasinski, Charles Hellaby, Marie-Noelle Celerier ISBN: 9780521769143 http://assets.cambridge.org/assets/bookpageresult.jsf?conversationId=1165892 The first book is apparently cheap, the second one expensive. Both would be useful IMHO. pozdr boud

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Cosmo-torun March 2010