Cosmo-torun December 2001

cosmo-torun@cosmo.torun.pl

5 participants
9 discussions

Re: cosmo-torun
by Andrzej Marecki 20 Dec '01

20 Dec '01

Boud wrote: > PS: Anyone on the list should feel free to invite others who would > find the list useful. People can unsubscribe themselves later if they > find there's too much mail coming through. By the way: this is what I always wanted to know (but was afraid to ask before :-) if "cosmo-torun" is somehow arbitrarily limited to .torun.pl domain and serves Toruń people only or it actually means: "cosmo-torun-warszawa-paris-etc-if-you-only-want-to-join-and-share-ideas" To be more specific: how about inviting the cosmologists from CAMK, Warszawa (Staszek, Ewa, etc.). Maybe you could just take the opportunity of sitting next to them and talk to them. You know them better than I do so I leave this issue entirely to your discretion. What I particularly have in mind (if we decide to join the forces, of course) is to organise such "one-afternoon-workshops" in the future together with Warsaw people. (To this end sometimes they would come to Piwnice, sometimes we would go to CAMK, or sometimes we could meet half(?)-way, at CAMK-Toruń.) Pozdrawiam Andrzej

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introductions
by Boud Roukema 19 Dec '01

19 Dec '01

Cze�� koledzy, By now you've had a short scientific introduction from Micha� F., and I think you know, or if not, you will know after this sentence, that Andrzej Marecki and I are working on an RLAGN project for developing principles of techniques of detecting the global shape of the Universe, according to the standard, hot big bang, Friedmann-Lema�tre model. E.g. for a beginner's review see http://de.arXiv.org/abs/astro-ph/0010185 Would the others be able to introduce yourselves? You can, of course, find out who has subscribed using list commands (see HELP below), but so far, the others and what seem to me to be their cosmological/extragalactic interests are (in arbitrary order): Sebastian - interested in OCRA (one cm array project) Rafa� - interested in cosmic topology (as a sideline) Marcin/Motylek - interested in FRI/FRII evolution Micha� Hanasz - magnetic fields in low z (<< 1) AGN, but moving to high z (2-3) AGNi ?? I'll be back in Toru� in a few weeks time, and it would be nice to have a face-to-face meeting, but in the meantime, could everyone just say a few lines about their interests (correcting my above summary!), and feel free to make meta-suggestions (about the list or about how to organise discussions or work, whatever) as well as direct discussion of science. Pozdrawiam, Boud

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First "workshop" (was: Re: introductions)
by Andrzej Marecki 18 Dec '01

18 Dec '01

Witam wszystkich! Boud wrote: > I'll be back in Toruń in a few weeks time, and it would be nice to have a face-to-face meeting, To jest bardzo dobry pomysł, Boud! (It's a very good idea, Boud :-) Let it be our - very informal yet very serious in terms of scientific background - 1st "workshop". I can give a talk about what I've done recently. I'm sure, you, Boud, might be a key speaker with an "invited" talk. ;-) I, also, can be an "acting" LOC. Pozdrowienia, Andrzej

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cosmo-torun
by Boud Roukema 18 Dec '01

18 Dec '01

CC: cosmo-torun Hi Bronek, Andrzej M. and I have started up a web-supported, threaded, mailing list for people interested in cosmology research in Toru�: http://www.astro.uni.torun.pl/sympa/cosmo-torun/ Please feel welcome to subscribe! Instructions on how to do this are on the site. In spite of your not officially being a cosmologist, you have a reputation of knowing the basics pretty well... Cze�� Boud PS: Anyone on the list should feel free to invite others who would find the list useful. People can unsubscribe themselves later if they find there's too much mail coming through.

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Michal: quintessence
by Boud Roukema 17 Dec '01

17 Dec '01

Cześć, Michał Frąckowiak has been playing around with some ideas on quintessence. He suggested to me some ideas and asked if I could test these on the data that Staszek, Gary and I have already analysed. Well, creativity generally requires that you generate 100 ideas and try to throw away 99. If you end up throwing away 100, well, you have to go on to the next 100... Or you can modify the ideas and gradually come up with something unexpected. In fact, there's often something interesting enough to be worth talking about. So, let's see. ----- Michał, I'm not sure I understand your calculation. You express w as a Taylor series of (a-1), but normally this only makes sense if (a-1) is much smaller than 1. [ a is the expansion factor: coordinates can be chosen in which the Universe is static, and all the expansion is represented by a single function of cosmological time: a(t). By convention, a(t)=1 now. The Big Bang is simply the extrapolation a(t) -> 0 as t -> 0^+ , i.e. arbitrary separations between any coordinates get multiplied by nearly zero as t -> 0 from above. So outside of the Sun, a-1 is a negative number between 0 and -1. ] You wrote: > w(a)= w^(0) (a-1)^0 + w^(1) (a-1)^1 + w^(2) (a-1)^2 + ... > What is interesting, it seems absolutely sufficient to consider only the 2 > first terms in w !!! (up to z=500). Then the evolution reads: w(a)= w^(0) + w^(1) (a-1) (equation (*)) Well, a = 1/(1+z), so a-1 = -z/(1+z), so at, say, z=2, a-1 = -2/3. Are you interested in redshifts where z=0.01 or where z=2? The SNeIa data are mostly at about z=0.4-0.8, and the quasar data at about z=0.5 to z=2.4 (roughly). This makes the (a-1)^i terms decrease (in magnitude) very slowly. I can only see a rapid convergence if you already know something about w^(1), w^(2), ..., that they go very quickly to zero. Do you have in mind a quintessence model where these derivatives go to zero very fast? Or have I misunderstood? In any case, it is certainly possible for me to test equation (*) on the data, though at the moment it seems to me more likely that we would get reasonable error bars by estimating w(z=0.8) and w(z=1.4) and w(z=1.9) independently. From those three points with error bars, it would of course be easy (apart from error propagation ;-) ) to calculate w^(0) and w^(1) under the assumption that other terms can be neglected. If we could simply obtain significantly different values in the three redshift bands, this would be a big enough result, though of course it would be useful to have some theoretical comments of what that might mean. Pozdrawiam Boud

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Re: new thread: mhonarc options
by Boud Roukema 13 Dec '01

13 Dec '01

The above are just test messages. Don't take the values of Omega_m there too seriously ;-). I wonder if http links get automatically converted, e.g. my article with Staszek and Gary independently showing that Om_m is close to 0.3 and that Omega_total is close to 1 (in the sense that the Universe is about as flat as a 1 radian radius surface area of the Earth: if the Earth is nearly flat, then yes, the Universe is nearly flat): http://de.arXiv.org/abs/astro-ph/0106135

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new thread: mhonarc options
by Boud Roukema 13 Dec '01

13 Dec '01

Does reply using netscape work?

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new thread: mhonarc options
by Boud Roukema 12 Dec '01

12 Dec '01

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4th message
by Boud Roukema 12 Dec '01

12 Dec '01

now with archive.pl running as a !daemon!

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Cosmo-torun December 2001