tag:blogger.com,1999:blog-1513704378254120283.post8520482352597311505..comments2020-05-13T16:02:53.913-07:00Comments on The Trenches of Discovery: The universe as seen by Planck - Day oneShaun Hotchkisshttp://www.blogger.com/profile/04832423210563130467noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-1513704378254120283.post-34479152018818200362013-04-23T13:06:58.211-07:002013-04-23T13:06:58.211-07:00Hi Rene, yeah I agree, fig.11 looks a bit funny. T...Hi Rene, yeah I agree, fig.11 looks a bit funny. The first time I run into someone who might know the answer I'll ask them about it, but that might not be until June.<br /><br />I did ask about this on Twitter, but nobody replied with an idea.Shaun Hotchkisshttps://www.blogger.com/profile/04832423210563130467noreply@blogger.comtag:blogger.com,1999:blog-1513704378254120283.post-87161829621890675662013-04-16T16:24:08.870-07:002013-04-16T16:24:08.870-07:00Hello Shaun
I'd like to refer to my last post...Hello Shaun<br /><br />I'd like to refer to my last post. In the meantime I had a look at the Planck papers XX and XVI. From Fig.10 of XX it is easy to calculate a sigma-8 = 0.821 with the Omega-M value = 0.315 given in Planck's CMB paper XVI (Tables 2 and 5). These tables also indicate a sigma-8 value of about 0.83 which is LESS than the average sigma-value shown in Fig.11 of paper XX (about 0.86).<br />Therefore, reporting this lower sigma value in Fig.11 of XX the likelihood contours of cluster-SZ and CMB will begin to intersect. And - who knows - maybe after some corrections in cluster modeling, intersection would occur, and then, instead of saying "ignore clusters at your peril" one could say "include clusters for your profit"!<br /><br />Kind greetings from Switzerland<br /><br />ReneRenenoreply@blogger.comtag:blogger.com,1999:blog-1513704378254120283.post-37803238310000112712013-04-13T01:13:06.640-07:002013-04-13T01:13:06.640-07:00Hi Rene, thanks for the comment.
I'm a little...Hi Rene, thanks for the comment.<br /><br />I'm a little confused about your first question. You seem to be asking me for more technical detail about how the *power* spectrum is calculated, but you also seem to know all the technical details. If you want the absolute nitty gritty relating to issues of blocking out the galaxy and questions of numerical algorithms Planck use then I'm afraid I just don't know the details. Were you interested in the technical details for the *bi*spectrum? If so, then the bispectrum is simply the Fourier transform of the three-point correlation function. Sorry if that didn't help. Please feel free to ask the question again if it didn't.<br /><br />- Regarding the vertical axis in the last figure, I took that straight from Planck's paper XX, so if there is a mistake it is also theirs. Your comments seem reasonable though, those Planck contours do seem quite high. I'll keep it in mind and try to ask someone the next chance I get, but that might not be for a few months at least.Shaun Hotchkisshttps://www.blogger.com/profile/04832423210563130467noreply@blogger.comtag:blogger.com,1999:blog-1513704378254120283.post-12568397170308331282013-04-12T19:06:13.682-07:002013-04-12T19:06:13.682-07:00Hello Shaun
You write:
Bispectra
All of the curv...Hello Shaun<br /><br />You write:<br />Bispectra<br /><br />All of the curves above are called power spectra. What they essentially do is tell you how the CMB's temperature or polarisation will look if you average it over two points separated by a particular angle. If the power spectrum has a larger amplitude at a particular angle, then the CMB's temperature should look more similar over those angles (i.e. if it is hotter at one point, then it should also be hotter at another point that is that particular angle away from it). If the amplitude is smaller at a particular angle, then the CMB will look less similar over those angles.<br /><br />- Well, this is a short description, but I'm curious about the more technical details how this power spectrum is computed. I already know that the power spectrum is the Fourier transform of the 2-point correlation function, and that the measured angle on the sky is related to the multipole moment l and the wavenumber k.<br /><br />- The vertical axis of the last diagram is labeled sigma-8. I think this is not correct: the sigma-8 value can not be as large as about 0.86. The Planck paper XVI gives the best fit value of 0.8288. So the vertical axis should be labeled as in the second diagram of your post "Day Two" to make both figures consistent.. <br /><br />Greetings from Switzerland<br /><br />Rene<br />Renenoreply@blogger.comtag:blogger.com,1999:blog-1513704378254120283.post-81480899412630470852013-04-04T02:45:11.649-07:002013-04-04T02:45:11.649-07:00Hi Sarrvesh, thanks for the comment (and especiall...Hi Sarrvesh, thanks for the comment (and especially the feedback).<br /><br />Here are some answers to your questions:<br /><br />1) You should take a look at my post about the second day's talks as I go into this in a bit more detail. But the answer is that this would make the cluster based estimates of the matter density and amplitude of primordial density perturbations increase. This would bring the clusters in line with the CMB measurements. (Curiously, as I explained in yesterday's post, if Planck were just over-estimating the errors on their mass measurements then this could also be causing the discrepancy)<br /><br />2) Well, Planck isn't discrepant with *all* other cosmological measurements. It matches with WMAP and with Baryon Acoustic Oscillation measurements relatively well. That Planck and WMAP match suggests that the CMB is being measured well. Also, note that the CMB is easier to predict in models than late-universe things are. It will be very expensive to build another telescope to verify Planck's full sky measurements (though note that both ACT and SPT are measuring the same signal on smaller patches of the sky - ACT is consistent with Planck, but SPT is slightly discrepant; however I just heard a very interesting rumour about that, which I will be writing up soon). A final point I would make is that the cosmological measurements that *were* discrepant already seem to be converging on Planck's new results. We had a talk here yesterday about supernovae measurements of the expansion rate and it appears that (independently) they were already going to revise their measurements towards a lower value (which will be more in line with Planck).<br /><br />I hope that helps... do stay tuned though for the interesting stuff about Planck and SPT (I'm quite excited by what I overheard)!Shaun Hotchkisshttps://www.blogger.com/profile/04832423210563130467noreply@blogger.comtag:blogger.com,1999:blog-1513704378254120283.post-73524395290498527942013-04-04T00:23:55.169-07:002013-04-04T00:23:55.169-07:00I should first thank you for such a nice blog entr...I should first thank you for such a nice blog entry. I found it to be neither too technical nor too general; it was at the right level.<br /><br /> I have two questions concerning the Planck data release:<br /><br />1. Assuming that Planck is underestimating the mass of the detected galaxy clusters, in what way would it affect the values of the derived cosmological parameters?<br /><br />2. Given the discrepancy between Planck's results and other recent cosmological measurements, are there observations planned in the near future to confirm Planck's results?Sarrveshnoreply@blogger.com