Shape-univ March 2002

shape-univ@cosmo.torun.pl

1 participants
5 discussions

holiday 29 march
by Boud Roukema 28 Mar '02

28 Mar '02

Noone has said anything about whether or not they want a lecture tomorrow 29 March, but since it is officially a University holiday, I'll assume by default that noone expects a lecture. But if anyone wants to come along and talk, feel free to do so! I'll be here (at Piwnice). Cze�� Boud

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feedback 15 March lecture?
by Boud Roukema 18 Mar '02

18 Mar '02

Cze�� wszysce (1) starting time 14:00 proposed In order that people can leave at 15:35 to catch the 15:52 bus, Andrzej proposed to start the sessions at 14:00 instead of 14:15. Everybody present was in favour, I think. In case lunch arrives late at Piwnice, we could start the lecture informally in the dining room - I see no problem with this, it could help to get people relaxed and talking informally. So, could people please be ready to start at 14:00, in the interests of 15:52-bus-catching people? Thanks. (2) Fri 15 March lecture I'm not sure if we went through enough or too much, but I realised that although there is nothing *difficult* in http://de.arXiv.org/abs/astro-ph/0106135, there are *many* details to think about. Rafa� asked about (i) what needs to be done to my programs, (ii) why can't we just use them unchanged? (ii) If we use them unchanged, then we will just get the old results, instead of exciting new results. (i) Here's a rough guess at what needs to be done: - rewrite the programmes to be more modular + add documentation - add a new routine for reproducing the photometric u-b_J-r band selection effects, so that "z-scrambling" doesn't have to be used for the "random simulations" for correlation function calculations - check that everything works fine on a subset and then calculate for the full "10K" data set on a fast computer - write input routines for the filter match selected candidate clusters in the 0.5 < z < 1 (approx) range (I'll look up the reference...) - this should directly reproduce the Omega_m - Omega_Lambda degeneracy of the SNeIa data (3) correlation functions Rafa� also asked about correlation functions. I suggest the 0106135 paper for the full details, but for an easy introduction, the following paper is probably better: http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?bibcode=1994A%26A...285..3… So for next week (14:00 pi�tek 22 marca) I'll try to prepare some information about my programs and the programs themselves... Pozdrawiam Boud

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torus/klein bottle games :)
by Boud Roukema 12 Mar '02

12 Mar '02

Cze��, Rewording what I said on Friday, this is a lecture course where instead of exams, the lecturer asks you to play games. :) Witam, zagrajcie! http://humber.northnet.org/weeks/TorusGames/ For those absent on Fri 8 Mar: we did a review of curvature for new people, and then a quick introduction to topology. This Friday (15 marca) I propose to get back to curvature (or more strictly speaking, to the metric parameters, which include Omega_m, Omega_Lambda and... w_Q, the quintessence parameter) and to explain what Staszek, Gary and I did in: http://de.arXiv.org/abs/astro-ph/0106135 and what I think can be done better and with other public data sets. I think this should be enough to give everyone a feel for what needs to be and/or can be done, and I propose that the following Friday, 22 March, we make a decision on which shape-of-the-Universe project we wish to carry out, and start discussing how to organise this, conceptual questions, programming concepts, etc. Pozdrawiam Boud PS: Pami�tajcie: ta lista jest dla wszysce - wszystko mo�e pisa� na liscie!

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particle horizon vs event horizon
by Boud Roukema 06 Mar '02

06 Mar '02

The simplest definition I found of the difference between the particle horizon and the event horizon is here: http://iapetus.phy.umist.ac.uk/Teaching/Cosmology/Metric.html The particle horizon is defined as the largest comoving distance from which light can have reached us - today. The event horizon is defined as the largest comoving distance from which light will ever reach us - at any time in the future. To have an event horizon, a universe needs to expand "very quickly", e.g. in a de Sitter universe, whose scale factor follows a pure (positive) exponential: http://nedwww.ipac.caltech.edu/level5/Watson/Watson6_1.html Apparently the definitions come from Rindler (1956, MNRAS, 116, 662): http://nedwww.ipac.caltech.edu/level5/Seitter/Seitter3_2_2.html but the figure is not clear to me. Boud

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next lecture Fri 8 Mar
by Boud Roukema 04 Mar '02

04 Mar '02

Cze�� wszysce, On Friday 1 March we started from the beginning again, going through comoving coordinates and curvature, with an added touch of history. Where did Euclid spend 30 years studying geometry and writing an extremely good review paper? Cairo, Africa. That's where zero curvature geometry models come from. Western scientific culture is fundamentally African. [Anyone want to search for http refs?] Who developed and introduced algebra and the Hindi decimal system to the West? An Arabic-speaking Iranian scientist born in... Khiva, Uzbekistan, hence known as al-Khwarizmi, who spent a lot of his life in Baghdad: http://www.mscf.uky.edu/~carl/ma330/project2/al-khwa21.html So, the "gor" in algorithm comes from "Khiva" in Uzbekistan. http://www.ati-uzbekistan.com/english/uzbekistan/touristcentres/khiva.htm So Western scientific culture is equally Asian. (Do you really want to do physics using roman numerals? VIII + I = IX ?) Modern "Western" science involves a mix between thinking in terms of geometry (African), decimal numbers (Indian), algebra (Arabic culture) and algorithms/software (Arabic/Iranian/Uzbek), though of course there are some European and North/South American contributions too... IMHO, observational cosmologists tend to think in terms of numbers and software, theoretical cosmologists tend more to think in terms of algebra (in the more modern concepts of algebra, calculus etc.). We discussed whether people would prefer (1) continuing lectures in a similar more or less traditional style, or rather (2) move on to a research project involving some hands-on code-writing and observational data. ** standard ruler project ** The particular project ("standard ruler project") I propose is a rewrite of the code of http://de.arXiv.org/abs/astro-ph/0106135 and application of the same analysis to a larger superset and to different observational data sets, and using more refined observational corrections in order to get more signal out of the data. Anyone contributing will have their name on any publications resulting from the work (unless they choose not to!). This relates to the shape of the Universe in the sense that - Omega_m, - Omega_Lambda and - w_Quintessence can be thought of just as parameters of the metric which convert [right ascension, declination, redshift] into 3-dimensional comoving positions. If I understood people's comments right (please feel free to correct me), the initial preferences were: (1) Bart (2) Marcin, Rafa�, Micha�, Sebastian Since we didn't cover topology during Friday's session, what would seem to match both preferences is: - 1 more or less conventional lecture (next week) on topology - following lecture as introduction to the material sufficient for understanding the standard ruler project and together discussing how we could divide the work (code writing, debugging, paper writing) ** "Archeops - topology project?" ** Micha� asked about the possibility of writing software for topology work. This is certainly possible, but it's less clear that it would result in publications or observational detections. I think that the Grenoble people would be happy to have someone contribute to programming work for Archeops analysis, and that in return, we could do topology analysis, but this would be a *much* bigger scale project (in terms of programming effort, coordination, and... politics) than the standard ruler project. Comparison local parameter vs topology projects: definite exciting result if result, then how important standard ruler YES moderate to big Archeops topology NO big to huge effort (programming, coordination, politics) standard ruler easy in a few months, IMHO Archeops topology heavy, over 12 months Hmmm.... There is also a very easy, quick topology project which should lead to a publication relating to a principle for detecting topology. :-) Let's call this: ** "roots of the identity project" ** The ultimate decision should be from the students - I personally will do the standard ruler project sooner or later. Sooner would be better, but later is also OK. I will also do the roots of the identity project, when I have a spare moment... Think about it, discuss it on this list, and at next Friday's meeting after going through a topology introduction we can see what people think. Pozdrawiam Boud

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Shape-univ March 2002