Shape-univ April 2003

shape-univ@cosmo.torun.pl

4 participants
6 discussions

Ten Major Challenges in Cosmology
by Andrzej Marecki 22 Apr '03

22 Apr '03

Paper: astro-ph/0304369 From: Reuven Opher <opher(a)astro.iag.usp.br> Date: Mon, 21 Apr 2003 19:47:31 GMT (16kb) Title: Ten Major Challenges in Cosmology Authors: Reuven Opher Comments: 11 pages, invited talk at Xth Brazilian School of Cosmology and Gravitation, Rio de Janeiro, July 29 - Aug. 9, 2002 [...] ----- End of forwarded message from astro-ph ----- Interesting is that "geometry and topology" is number ONE on author's (biased) list of "Ten Major Challenges in Cosmology". Seems like topology is becoming more and more "fashionable". ;) -- Andrzej

1 0

Re: inflation vs topology (fwd)
by Boud Roukema 18 Apr '03

18 Apr '03

> ---------- Forwarded message ---------- > Date: Thu, 17 Apr 2003 13:34:35 +0200 (CEST) > From: Boud Roukema <boud... > To: szajtan... > Subject: Re: inflation vs topology * Shouldn't this be on shape-univ ? i think this could be interesting for others. hi, On Wed, 16 Apr 2003, szajtan odwieczny wrote: > > > > I'm wandering if inflation scenaries of cosmological evolution, > > > discriminate the possibility for non trivial topology of the > > > universe (eg. some torus topology) of circumference smaller than > > > the hubble radius. I had short talk about that with Boud but perhaps > > > it was too short. If I understand well, in case of such non trivial > > > topolology, there should be some, outstanding (special) directions > > > in the CMB sky seen in multipole distribution just for the few > > > lowest multipoles (on the biggest anular scales). On the other hand, > > > > Well, multipoles are a *bad* way of trying to detect topology, but > > it's correct that there should be something funny in the low l > > multipoles for a multiply connected universe. > > Well, you observed the maps composed of the sum of some few first > multipoles, and ..."saw the thing". Thats what I ment. There > mae be several sky maps resulting in the same C_l spectra, and that's > why it can be difficult or impossible to get the direction from C_l > (but that's not importand.) i think we agree here. The "bad" is only a criticism of Tegmark et al's approach. Maybe "bad" is too strong. The sky maps are a little bit better than C_l spectra, and they give a hint ("clue") to topology, but not a good analysis. > > > > > one of the predictions of the inflationary models is that > > > fluctuations in gravitational potetial ( in the biggest angular > > > scales ) are gaussian and have random phases - so there should be no > > > outstanding directions in CMB. > > > > Up to the scale of the inflationary bubble, yes. > > Could you put this in full sentence ? > Do you mean that the topological radius (of eg. n-torus) is to be at least > as big as the radius of the inflationary bubble ? Yes. The physical Universe cannot be bigger than itself. > (That would be really > large radius). Maybe, maybe not. There are many, many inflationary models. > > > > > (So far there is no evidence for > > > deviations from gaussianity). > > > > There were several COBE analyses such as Pando, Valls-Gabaud & Fang: > > > > http://de.arxiv.org/abs/astro-ph/9810165 > > > > that showed non-Gaussianity. Since the WMAP map looks similar to COBE > > on large scales, i guess there should still be the same non-Gaussianity. > > > > Do you know of an article that claims Pando et al were wrong? > I didn't read that paper, but I just rely, on the papers released > along with WMAP data (eg. astro-ph/0302223 and many references therein > among others the one of Pando 98) so maeybe I should write "so far there > is no significant cosmological non-Gaussianity". And WMAP data are found > to be consistent with assumption of Gaussian primordinal fluctuations. Don't believe everything you watch/read on/in CNN/BBC/ApJ/MNRAS/A&A/... In professional astronomy research articles, people often write sentences which sound good, but are vague, misleading and sometimes simply wrong. It's not because they want to be wrong, it's just that they don't have the time to do the analysis properly and they're under pressure to publish and to conform. If you can find a WMAP analysis which shows that Pando et al 9810165 are wrong, that would be interesting. > btw. if the non-gaussianity is found then whole my work with masterthesis > is "o kant" - in a way useless - ;) If I remember well that would > be inconsistent with one of the assumptions of the cmbfast. (I don't know > about the size of the effect), but C_l couldn't be a good fluctuations > tracer, and the probability of model must have been computed directly > from the map. For an exact calculation, it's true that your analysis is probably *slightly* wrong if it assumes gaussianity on all scales. So you have to choose whether to live life in the real world and accept that your results may be nearly right, but a little bit wrong, or you could wait until there is a definite answer on topology, but this might be long after the deadline to write your master's thesis. In fact, Spergel et al 0302209 and Tegmark et al 0302496 seem to show a definite non-gaussianity on the biggest observable scales. I'm not sure if there is a way that you could include this in your analysis *without* making an assumption on the physical origin of the non-gaussianity. But maybe there is. IMHO, non-gaussianity on a big scale is not a big problem for your analysis. > > > > > > > > To me these two things are contrary to each other. Mae they exist > > > together ? Can anybody shed some light on this ? > > > > If there is detectable non-trivial topology, then it's likely that if > > the data is analysed *assuming* trivial topology, then there is a > > non-Gaussian signal. > > > > > Another thing is about the size of the universe. I mean, how it is possible > > > for the universe to have topological circumferece smaller than (for example) > > > the hubble radius, when we assume that every distance has been blown by the > > > factor of 10^54 ever since the world begun ? Or maeybe these two facts also > > > remain without any mutual confict ? > > > > This is the fine-tuning problem. How is it possible for the cosmological > > constant/quintessence parameter to be approximately equal to the matter > > density parameter today (a factor of 2.3 is not much ;) rather than at > > some more "random" time in the past or future? > > "Another thing" was the same problem as the first one but attacked from > another side. My point was rather like: does the topological radius ( > circumference) grows with the inflation ? The injectivity diameter (what you call "topological radius") is comoving. So it grows with inflation. > Or it was once set by > something and doen't change in time. No, it's comoving. > ...hm, you write about the quintessence. But what does it have to do with > the inflation, and to the problem ? Let's assume the inflation is > already finished. the "graceful exit problem" suggests that we mae > consider it as finished by the time of some 10^-33 s, and in this case > dark energy has nothing to do with activity of false vacum. In the early > universe (even in radiation dominated era) the density of dark energy was > negligible small. Unitl now when it starts to be importand. I don't know > about > some fine tuning with inflation ? It's rather cosmological constant that > should be tuned. I don't know maeybe false vacum was the priomridal origin > of the quinessence which starts dominating our universe recenly :), and > this is interesting topic itself, but it wasn't the point of my question. I was including cosmological constant and quintessence together. Let's call it dark energy. Even if it was "negligibly small" at 10^-33s, it had to be just big enough, and not too big, so that today it is 2.3 times bigger than Omega_m. > > > > First some corrections: > > > > - the Guth value was (i think) 55 e-foldings, i.e. e^55 \approx 10^{24} > I wrote it from memory, but you're right, the factor is some 10^29. It > depands on how long we assume the inflation lasts. OK. > > > > - it's not "since the world begun", it's since some early time such > > as t = 10^{-33}s > of course but even if it was from the beginning (whatever that means) or > from 10^-43 s it wouldn't change anything in sizes. > 10^-33 s - 10^-43 s = 10^-33 s - 10^-35 s = 10^-33 s (approxiamately) > (but these are details) OK > > Answer: It's sufficient that the injectivity diameter ("topological > > circumference") was just a bit smaller than > > 10h^-1 Gpc/10^24 \approx 500m at t = 10^-{33}s. > Where does it come from ? (any references to read?). Do you mean "where does the injectivity diameter come from"? If you mean some ideas on quantum gravity or quantum cosmology (apparently quantum cosmology is *simpler* than quantum gravity), look up the references in the 2nd last paragraph of Section 2 of Luminet & Roukema astro-ph/9901364 > So from this I assume > that the injectivity diameter grows with time. Is that right ? > And btw. (probably it's another word, with no polish translation), but is > there some polish equivalent for injectivity diameter ? (and btw. for > fundamental polyhydron > (or something like that) as well. Request for polish translation - > anyone ? ) > > > > > Fine-tuning inflation is required to get Om_Lambda/Om_m \approx 10^0; > mmm, isn't it the problem of quintessence tuning not inflation? I guess it could be either. > > fine-tuning inflation is required for observable topology. > What do you mean ? I mean just what you're saying ;). The amount of inflation needs to be enough so that the injectivity diameter is not too big, not too small, today. Just as quintessence/cosmological constant needs to be fine-tuned (either from inflation or independently) so that it's not too big, not too small, today. > > Fine-tuning inflation is also needed for observable curvature > > (e.g. Om_total = 1.02). > fine tuning here ? probably yes, maeybe just tuning is ok. I disagree. Again this a question over many, many orders of magnitude. > As just for the flatness problem, there is no lower limit set for flatness > (upper limit for inflation duration), but if inflation lasts too > long it would never stop, or universe might get too heavy or so, and we > wouln't have cmb fluctuations at level 10^-5 which in turn might would > have catastrofical consequencies for us :). > > > > > We only know that the first one is correct - so far - but maybe all > > three are correct, and are linked. > > > ...it's a long road, just to come to terms with the above. > > b. Last time i tried to understand inflation, i ended up discovering that there was a fundamental thing that most people had forgotten - topology. Maybe if you try to understand the above, you'll come up with something else that most people (including me) have forgotten... b

1 0

Remake of Fagundes & Wichoski (1987)
by Andrzej Marecki 17 Apr '03

17 Apr '03

Paper: astro-ph/0304290 From: Stephen Weatherley <stephen.weatherley(a)imperial.ac.uk> Date: Tue, 15 Apr 2003 20:02:03 GMT (254kb) Title: Ghosts of the Milky Way: a search for topology in new quasar catalogues Authors: S.J. Weatherley (1), S.J. Warren (1), S.M. Croom (2), R.J. Smith (3), B.J. Boyle (2), T. Shanks (4), L. Millar (5), M.P. Baltovic (1) ((1) Imperial College London, (2) AAO, (3) Liverpool John Moores, (4) Durham, (5) Oxford) Comments: MNRAS Letters, Accepted, 5 pages, 3 figures \\ We revisit the possibility that we inhabit a compact multi-connected flat, or nearly-flat, Universe. Analysis of COBE data has shown that, for such a case, the size of the fundamental domain must be a substantial fraction of the horizon size. Nevertheless, there could be several copies of the Universe within the horizon. If the Milky Way was once a quasar we might detect its `ghost' images. Using new large quasar catalogues we repeat the search by Fagundes & Wichoski for antipodal quasar pairs. By applying linear theory to account for the peculiar velocity of the local group, we are able to narrow the search radius to 134 arcsec. We find seven candidate antipodal quasar pairs within this search radius. However, a similar number would be expected by chance. We argue that, even with larger quasar catalogues, and more accurate values of the cosmological parameters, it is unlikely to be possible to identify putative ghost pairs unambiguously, because of the uncertainty of the correction for peculiar motion of the Milky Way. \\ ( http://de.arXiv.org/abs/astro-ph/0304290 , 254kb) ------------------------------------------------------------------------------ At first sight it's rather a dicouraging result - see the last sentence above. :-( but... Let's explore other approaches! :-) -- Andrzej

2 1

Re: inflation vs topology
by szajtan odwieczny 16 Apr '03

16 Apr '03

> > I'm wandering if inflation scenaries of cosmological evolution, > > discriminate the possibility for non trivial topology of the > > universe (eg. some torus topology) of circumference smaller than > > the hubble radius. I had short talk about that with Boud but perhaps > > it was too short. If I understand well, in case of such non trivial > > topolology, there should be some, outstanding (special) directions > > in the CMB sky seen in multipole distribution just for the few > > lowest multipoles (on the biggest anular scales). On the other hand, > > Well, multipoles are a *bad* way of trying to detect topology, but > it's correct that there should be something funny in the low l > multipoles for a multiply connected universe. Well, you observed the maps composed of the sum of some few first multipoles, and ..."saw the thing". Thats what I ment. There mae be several sky maps resulting in the same C_l spectra, and that's why it can be difficult or impossible to get the direction from C_l (but that's not importand.) > > > one of the predictions of the inflationary models is that > > fluctuations in gravitational potetial ( in the biggest angular > > scales ) are gaussian and have random phases - so there should be no > > outstanding directions in CMB. > > Up to the scale of the inflationary bubble, yes. Could you put this in full sentence ? Do you mean that the topological radius (of eg. n-torus) is to be at least as big as the radius of the inflationary bubble ? (That would be really large radius). > > > (So far there is no evidence for > > deviations from gaussianity). > > There were several COBE analyses such as Pando, Valls-Gabaud & Fang: > > http://de.arxiv.org/abs/astro-ph/9810165 > > that showed non-Gaussianity. Since the WMAP map looks similar to COBE > on large scales, i guess there should still be the same non-Gaussianity. > > Do you know of an article that claims Pando et al were wrong? I didn't read that paper, but I just rely, on the papers released along with WMAP data (eg. astro-ph/0302223 and many references therein among others the one of Pando 98) so maeybe I should write "so far there is no significant cosmological non-Gaussianity". And WMAP data are found to be consistent with assumption of Gaussian primordinal fluctuations. btw. if the non-gaussianity is found then whole my work with masterthesis is "o kant" - in a way useless - ;) If I remember well that would be inconsistent with one of the assumptions of the cmbfast. (I don't know about the size of the effect), but C_l couldn't be a good fluctuations tracer, and the probability of model must have been computed directly from the map. > > > > To me these two things are contrary to each other. Mae they exist > > together ? Can anybody shed some light on this ? > > If there is detectable non-trivial topology, then it's likely that if > the data is analysed *assuming* trivial topology, then there is a > non-Gaussian signal. > > > Another thing is about the size of the universe. I mean, how it is possible > > for the universe to have topological circumferece smaller than (for example) > > the hubble radius, when we assume that every distance has been blown by the > > factor of 10^54 ever since the world begun ? Or maeybe these two facts also > > remain without any mutual confict ? > > This is the fine-tuning problem. How is it possible for the cosmological > constant/quintessence parameter to be approximately equal to the matter > density parameter today (a factor of 2.3 is not much ;) rather than at > some more "random" time in the past or future? "Another thing" was the same problem as the first one but attacked from another side. My point was rather like: does the topological radius ( circumference) grows with the inflation ? Or it was once set by something and doen't change in time. ...hm, you write about the quintessence. But what does it have to do with the inflation, and to the problem ? Let's assume the inflation is already finished. the "graceful exit problem" suggests that we mae consider it as finished by the time of some 10^-33 s, and in this case dark energy has nothing to do with activity of false vacum. In the early universe (even in radiation dominated era) the density of dark energy was negligible small. Unitl now when it starts to be importand. I don't know about some fine tuning with inflation ? It's rather cosmological constant that should be tuned. I don't know maeybe false vacum was the priomridal origin of the quinessence which starts dominating our universe recenly :), and this is interesting topic itself, but it wasn't the point of my question. > > First some corrections: > > - the Guth value was (i think) 55 e-foldings, i.e. e^55 \approx 10^{24} I wrote it from memory, but you're right, the factor is some 10^29. It depands on how long we assume the inflation lasts. > > - it's not "since the world begun", it's since some early time such > as t = 10^{-33}s of course but even if it was from the beginning (whatever that means) or from 10^-43 s it wouldn't change anything in sizes. 10^-33 s - 10^-43 s = 10^-33 s - 10^-35 s = 10^-33 s (approxiamately) (but these are details) > > Answer: It's sufficient that the injectivity diameter ("topological > circumference") was just a bit smaller than > 10h^-1 Gpc/10^24 \approx 500m at t = 10^-{33}s. Where does it come from ? (any references to read?). So from this I assume that the injectivity diameter grows with time. Is that right ? And btw. (probably it's another word, with no polish translation), but is there some polish equivalent for injectivity diameter ? (and btw. for fundamental polyhydron (or something like that) as well. Request for polish translation - anyone ? ) > > Fine-tuning inflation is required to get Om_Lambda/Om_m \approx 10^0; mmm, isn't it the problem of quintessence tuning not inflation? > fine-tuning inflation is required for observable topology. What do you mean ? > > Fine-tuning inflation is also needed for observable curvature > (e.g. Om_total = 1.02). fine tuning here ? probably yes, maeybe just tuning is ok. As just for the flatness problem, there is no lower limit set for flatness (upper limit for inflation duration), but if inflation lasts too long it would never stop, or universe might get too heavy or so, and we wouln't have cmb fluctuations at level 10^-5 which in turn might would have catastrofical consequencies for us :). > > We only know that the first one is correct - so far - but maybe all > three are correct, and are linked. > ...it's a long road, just to come to terms with the above. b.

1 0

inflation vs topology
by szajtan odwieczny 15 Apr '03

15 Apr '03

I'm wandering if inflation scenaries of cosmological evolution, discriminate the possibility for non trivial topology of the universe (eg. some torus topology) of circumference smaller than the hubble radius. I had short talk about that with Boud but perhaps it was too short. If I understand well, in case of such non trivial topolology, there should be some, outstanding (special) directions in the CMB sky seen in multipole distribution just for the few lowest multipoles (on the biggest anular scales). On the other hand, one of the predictions of the inflationary models is that fluctuations in gravitational potetial ( in the biggest angular scales ) are gaussian and have random phases - so there should be no outstanding directions in CMB. (So far there is no evidence for deviations from gaussianity). To me these two things are contrary to each other. Mae they exist together ? Can anybody shed some light on this ? Another thing is about the size of the universe. I mean, how it is possible for the universe to have topological circumferece smaller than (for example) the hubble radius, when we assume that every distance has been blown by the factor of 10^54 ever since the world begun ? Or maeybe these two facts also remain without any mutual confict ? bartek

2 1

where the WMAP map is (the linear combination)
by boud 02 Apr '03

02 Apr '03

The linear combination WMAP map is here: http://lambda.gsfc.nasa.gov/data/map/ilc/ http://lambda.gsfc.nasa.gov/data/map/ilc/map_ilc_yr1_v1.fits I can email anyone packages for reading this in - the "healpix" software is non-free software - i haven't put my version online since it's "non-free" in the Debian sense, though i would be happy for help to make it "free" (GPL compatible etc) if someone had the time... (or if i have 2-3 days free) For now, it's probably not a priority. boud

1 0

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

Shape-univ April 2003