Shape-univ

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176 discussions

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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Fri 01/03/2002 14h-16h Radio Obs Piwnice
by Boud Roukema 28 Feb '02

28 Feb '02

Reminder: shape-univ lecture tomorrow Fri 01/03/2002 14h-16h Radio Obs Piwnice Cze�� Boud

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shape-univ monograph course 14:00 Fri 1 Mar 2002
by Boud Roukema 22 Feb '02

22 Feb '02

Dear students, Nazywam si� Boud Roukema, jestem kosmologiem, zacz� jak adiunkt w Centrum Astronomii. This semester, I'm giving a "monograph course" on "the Shape of the Universe", or more precisely, on observational ways of trying to measure the shape of the Universe, aimed at the level of 4th year students, but 3rd years or other students are also welcome. You'll find more information on this at: http://www.astro.uni.torun.pl/sympa/shape-univ/index.html Sorry for the confusion about the starting date! Because of this, the next session will have a subject which is essentially the same as the first, unless you all think it is too easy and you already know it! So here are the details: ---------------------------------------------------------------------- Time/Date: 14:00-16:00 Friday 1 March 2002 Place: Radio Observatory main lecture room, Piwnice Goal of first lecture: * Basic concepts of curvature, topology, extra dimension as a psychological tool to help imagine curved and/or multiply connected spaces, comoving coordinates, with the aim of making sure the 4th year students (or others relatively new to cosmology) understand these. ---------------------------------------------------------------------- Two students who were there, Pawel and Andrzej, said that it was very easy, so if they can explain everything to you, we could maybe move immediately on to observational techniques. But this depends on you. Apparently there was another course on something about business and computing in the other building this afternoon. Well, the best way to learn computing if you want to be able to find a job in it and/or want to create your own software company is in the free software movement, e.g. GNU/Linux and the GNU Public Licence (GPL): http://www.gnu.org/home.pl.html http://groups.google.com/groups?group=pl.comp.os.linux If you write software for a company which is *not* protected under the GPL, and if the company fires you and you want the freedom to use this software in another company, you will not be allowed to! Not only will you have lost your job, but all your intellectual effort will be wasted. :-( And starting your own company would be much easier with free software, since you would only have to add one small new idea to the huge amount of existing free software. You would not have the cost of buying proprietary software or using an unstable, inefficient operating system full of bugs. So free software is better, z moim skromnem zdaniem... In astronomy, most of the software we use and write is more or less free software, but its commercial value is about... zero z�oty. However, if you help work on cosmology GPL software, it would be a good learning exercise. And I think that one of the best ways for you to learn about observational measurements of the shape of the Universe is to work with software that is related to observational work on the shape of the Universe. I would be happy to support students interested in doing this, and hope that both the face-to-face lectures and the shape-univ mailing list (and archive) can be used to think about this. Anyway, the content of the course is more or less: ---------------------------------------------------------------------- = Quantitative = - curvature measurements, e.g. http://de.arXiv.org/abs/astro-ph/0201092 - topology measurements, e.g. http://de.arXiv.org/abs/astro-ph/0010185 [This is the ref I promised during today's lecture. For a *lot* more detail on topology (but slightly out-of-date regarding observational research and with a few small, minor errors) is LaLu95: http://de.arXiv.org/abs/gr-qc/9605010 ] Please look for good introductions to these on the web (w po polsku lub w po angielsku), i prosz� wysylacie any links that you think are good to the shape-univ mailing list. That way, everybody else can just click and read. = Qualitative = - curvature Here's one which seems nice, but is essentially without algebra: http://www.astro.princeton.edu/~clark/ToC.html It's said to be at high school level, but it's important to develop intuition. Understanding is not just abstract symbols on paper, it's also intuitive understanding. But please provide a better link if you can! - topology - intuition Here's a good exercise for developing topology intuition: http://humber.northnet.org/weeks/TorusGames/ Don't be embarrassed to play the games - it's part of learning. ---------------------------------------------------------------------- To subscribe to the list, send an email to sympa(a)astro.uni.torun.pl and put subscribe shape-univ in the Subject: or main body. To send an email to the list, just send it to shape-univ(a)astro.uni.torun.pl . Hope to see you next Friday, Pozdrawiam Boud

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shape-univ up and running!
by Boud Roukema 21 Feb '02

21 Feb '02

<cross-post to cosmo-spotka & shape-univ> Here is the description of the first shape-univ announcement (this way this will be archived on the shape-univ archive): http://www.astro.uni.torun.pl/sympa/cosmo-spotka/2002-02/msg00004.html Several people will get a double of this message. Feel free to unsubscribe from or subscribe to one list or the other (or even both) depending on your interests, and encourage others to subscribe to those lists they feel are relevant. Hopefully see you all tomorrow! Cze�� Boud

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