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#37
Mar2404, 02:01 PM

PF Gold
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#38
Mar2404, 03:16 PM

Astronomy
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PF Gold
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wolram thanks for adding these links to the reference thread!
the interactive tutorial on gravity is a good idea (with the mild online quizes to selfcheck understanding) the history of formation of a star like the sun was informative (at least for me) by telling central and surface temperatures at each stage and time in that stage and plotting the protostar's approach to the main sequence on the HR diagramgives a more detailed story helping imagine how the sun came into being 


#39
Mar2604, 12:19 PM

PF Gold
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#40
Apr1704, 01:28 AM

Astronomy
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PF Gold
P: 23,085

http://relativity.livingreviews.org/...es/lrr20014/
Clifford Will Confrontation between General Relativity and Experiment  http://math.ucr.edu/home/baez/physic...periments.html Tom Roberts Experimental Basis of Special Relativity (from the Physics FAQ)  these are two links that Russ says Nereid supplies in her posts responding to folks challenging GR and SR 


#41
Apr1704, 10:41 AM

P: 915

This paper seems interesting:
"Distance measures in cosmology" David W. Hogg http://arxiv.org/abs/astroph/?9905116 It must be good given that I really enjoyed the pdf course of special relativity of D. Hogg 


#42
Apr2804, 08:11 PM

Astronomy
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PF Gold
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A recent set of lectures
http://www.mpiahd.mpg.de/homes/rix/Lecture.html Rix is director of the MPI for Astronomy the lectures are winter 20032004 by Matthias Bartelmann a recent article by Alan Guth "Inflation" http://arxiv.org./astroph/0404546 a new pedagogical paper on the standard view of the early universe seems clearly written, 44 pages by David Langlois http://arxiv.org./hepth/0405053 


#43
May1404, 04:06 PM

Astronomy
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PF Gold
P: 23,085

the Friedmann equations (the basic equations of cosmology)
just to have them handy for reference: in units where c = 1: [tex]\frac{a''}{a} =  \frac{4\pi G}{3}(rho + 3p) [/tex] [tex](\frac{a'}{a})^2 = \frac{8\pi G}{3}rho  \frac{k}{a^2}[/tex] on first encounter with F. eqn. people often get confused by the fact that Greek letter rho (for density) looks like Roman p (for pressure) so I spell rho out here instead of using the symbol. The rho and p here are inclusive of all forms of energy from ordinary matter to dark energy. k is a spatial curvature term, often set to equal zero since the universe is seen to be spatially flat either exactly or to a good approximation a is the spatial scale factor in the standard cosmology metric (socalled FRW metric) and a increasing means distances between points are getting larger IOW space is expanding. The prime is its time derivative, so a' is rate of increase of a and a'' is a measure of acceleration. very sketchy discussion in cosmology almost nothing has pressure besides the dark energy and for dark energy the most commonly assumed equation of state is p_{X} =  rho_{X} (thats what you get from a vacuum energy or a constant energy density associated with the cosmological constant, the typical dark energy idea) IIRC the estimated average density for our universe at the present is about 0.83 joules per cubic km this includes the estimates of everything: visible matter, unseen matter, dark energy, light energy, neutrinos etc. this energy density accords with the observed expansion rate and the observed flatness. Dividing a'' by a makes the arbitrary length unit go away and you get a measure of acceleration that is just a reciprocal time squared. Dividing a' by a gets rid of the length unit and after squaring you have a reciprocal time squared there too. So in both equations the LHS is a reciprocal time squared. rho and p have the same units (the unit of energy density is the same as that of pressure, in any coherenent system of units) and multiplying by G will give, on the RHS as well, a reciprocal time squared the point about dark energy is that as an energy density it contributes to the slowing of expansion by contributing to rho just like any other type of energy including matter so by contributing to rho, dark energy favors contraction but dark energy is 3 times more influential as a pressure and in that way (by the negative pressure) it makes the whole RHS of the eqn positive and favors accelerating expansion 


#44
May1404, 04:49 PM

P: 915

Here we provide you with an exercise to explore the possible universes governed by the Friedmann equation (equation (11.19) in the text). We use a simple applet to integrate the Friedmann equation for a range of models. (Note that this requires Java running on your browser.) On the applet below you can enter a value of Omega (density of the universe), a value of Lambda (the cosmological constant), and select a curvature (positive, zero, or negative). Note: This exercise provides a qualitative feel for the relative behavior of the Friedmann equation with respect to cosmological parameters. It does not provide detail models for comparison with observed cosmological values of omega or hubble time
http://astsun.astro.virginia.edu/~jh...Friedmann.html 


#45
May1504, 06:13 PM

Astronomy
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PF Gold
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sounds like fun, sol
here is a source on neutron stars including detailed accounts of the stages of Type II supernova collapse and the layer structure of a neutron star http://arxiv.org./astroph/0405262 


#46
May1704, 10:38 AM

P: 915

Thank you Marcus,
I have been developing well with this kind of information. I hope others will benefit too. http://online.itp.ucsb.edu/online/pl...orne/oh/08.gif Some will appreciate the understanding there, of all the maths. Klein's ordering of Geometires as they have been shown through Patricias link of what is required of String theory in terms of those maths would have been laying one over the other, but in the Bose Nova, a culmination? With Omega, critical density must still play a part in our understanding of this dynamical world in the classical realities? But when it comes to QM, how shall we understand the issues presented in cosmology, might also speak to QM as well? Do you "follow" Brane world collisions? 


#47
May2704, 08:45 AM

Astronomy
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PF Gold
P: 23,085

I have not downloaded thisit is a long review paper on the physics of GRB: 159 pages. It probably could be mined for answers to questions about what causes GammaRay Bursts and what GRB events are actually like. the paper has been accepted by "Reviews of Modern Physics" so I would expect it to be suitably mainstream and authoritative.
http://arxiv.org/astroph/0405503 The Physics of GammaRay Bursts Tsvi Piran 159 pages, 33 figures, accepted for publication in Reviews of Modern Physics 


#48
May2704, 08:52 PM

Astronomy
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PF Gold
P: 23,085

I was impressed by this short (11 page) paper by Daly and Djorgovski
http://arxiv.org/astroph/0405550 Direct Constraints on the Properties and Evolution of Dark Energy Ruth A. Daly, S. G. Djorgovski 11 pages, 8 figures, invited presentation from the Observing Dark Energy NOAO Workshop in Tucson It goes along with Wolram and other's interest in a skeptical appraisal of the dark energy idea. D and D have developed a method to analyse the raw Supernova data with a minimum of assumptionsnot assuming Friedmann equations or concordance modeland calculating the acceleration directly. then they can say "what assumptions, what model, would get us this observed acceleration?" in other words they proceed in a nonparametric way. they do not assume there are parameters like dark energy density and negative pressure, and try to find the value of these parameters. they assume nothing like that, they measure the accelerationredshift relation and then try to find some mechanism that will fit it. then they bring in models, like concordance model, and try them out. this is in a subtle way more difficult, but it is a commonsense approach, it is scientifically respectable to work with as few assumptions as you possibly can (and still be able to process the data, get "traction" on the slippery road of the world in other words) Ruth Daly has 22 papers in arxiv. many of them with Djorgovski. this was an invited talk at a dark energy conference. She seems to me like someone to listen to. Djorgovski is at CalTech. maybe Nereid knows of these people * 


#49
May3004, 07:45 PM

Astronomy
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PF Gold
P: 23,085

Here is a 66 page paper by Jonathan Feng
covering the interface between particle physics and cosmology http://arxiv.org/hepph/0405215 "Supersymmetry and Cosmology" In hepph, the ph stands for phenomenology, which studies the testing of theories by observation and measurement. he describes the current situation where it is cosmology, with its evidence for dark energy and dark matterand it 4 percent estimate of the fraction that is baryonmatter. that is driving particle physics and astronomy that is offering prospects for testing various models. he describes the interface between HEP and astrophysics/cosmology astroparticle physics, particle astrophysics, whatever different people call it different things. he talks about the prospective role of accelerators too, how he thinks it all fits together. it looks like an attempt at a review paper in a very new area, it is long, careful, with a lot of tables and/or graphs he's a prominent expert. probably his viewpoint is worth understanding it is a view of the nearterm future of physics, in some sense 


#50
May3004, 07:54 PM

Emeritus
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PF Gold
P: 5,534

Straight from Physics Napster:
Astronomy and Cosmology General: Added 3/27/03 Publications of the Astronomical Society of Australia Added 3/28/03 Space Physics From Oulu, Finland. Astronomy Dot Net The name says it all. Cosmology: Added 3/27/03 Cosmological Models From LANL arXiv. Astrophysics: Added 3/27/03 Internal Dynamics of Globular Clusters From LANL arXiv. Simulators: Added 3/27/03 Astronomy Software for PC and... Relativity Special Relativity: Added 3/27/03 Lecture Notes on Special Relativity Added 3/28/03 On the Electrodynamics of Moving Bodies By Einstein, from Fourmilab. Does the Inertia of a Body Depend on Its Energy Content? By Einstein, from Fourmilab. Special Relativity by David Hogg—nice book. Added 7/11/03 Special Relativity Questions Answered by Virginia's Astronomy Department. Essay on the Twin Paradox General Relativity: Added 3/27/03 Lecture Notes on General Relativity From LANL arXiv. Added 3/28/03 Lecture Notes on General Relativity by Prof. Sean Carroll, Univ. of Chicago. Added 7/11/03 Sidelights on Relativity By Einstein. Special and General Relativity EText From Mount Allison University (in progress). Other: Added 3/27/03 The Physical Basis of the Direction of Time This could have gone either in the Quantum or Relativity section. I flipped a coin, and here we are. Added 3/28/03 Living Reviews in Relativity An online journal. 


#51
Jun404, 02:57 PM

Astronomy
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PF Gold
P: 23,085

Stanford/SLAC puts out lists of topcited articles each year
the 2003 topcites are out and there is a special review of the Astrophysics list by Scott Dodelson http://www.slac.stanford.edu/library...h_review.shtml 


#52
Jun704, 07:11 PM

Astronomy
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PF Gold
P: 23,085

http://arxiv.org/abs/astroph/0406139
A Quantum Approach to Dark Matter Authors: A. D. Ernest Comments: To be published in "Progress in Dark Matter Research" Nova Science Inc. New York "This work develops and explores a quantumbased theory which enables the nature and origin of cold dark matter (CDM) to be understood without need to introduce exotic particles. The quantum approach predicts the existence of certain macroscopic quantum structures that are WIMPlike even when occupied by traditional baryonic particles. These structures function as dark matter candidates for CDM theory on large scales where it has been most successful, and retain the potential to yield observationally compliant predictions on galactic cluster and subcluster scales. Relatively pure, high angular momentum, eigenstate solutions obtained from Schrodinger's equation in weak gravity form the structural basis. They have no classical analogue, and properties radically different from those of traditional localised matter (whose eigenstate spectra contain negligible quantities of such states). Salient features include radiative lifetimes that can exceed the age of the universe, energies and 'sizes' consistent with galactic halos, and negligible interaction rates with radiation and macroscopic galactic objects. This facilitates the formation of sparsely populated macroscopic quantum structures that are invisible and stable. Viable structure formation scenarios are based on the seed potential wells of primordial black holes formed at the e+/e phase transition. The structures can potentially produce suitable internal density distributions and have capacity to accommodate the required amount of halo dark matter. The formation scenarios show that it is possible to incorporate structures into universal evolutionary scenarios without significantly compromising the results of WMAP or the measurements of elemental BBN ratios." 


#53
Jun2704, 06:24 PM

P: 915

Grzegorz Wardziński offers all the abstracts of the latest papers in Astroph in Arxiv, all in the same page. The section is called Astroph for busy people. Wonderful!
http://www.camk.edu.pl/~gwar/astroph.html 


#54
Aug104, 12:15 PM

Astronomy
Sci Advisor
PF Gold
P: 23,085

turbo points out that Aunt Nettie
has an explanation for why grass is green it is trying to get a message back to its home planet. http://www.dearauntnettie.com/archiv...hives0105.htm (dont believe this! it may be intended as a joke) 


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