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Everything posted by Martin

  1. Jackson, thanks so much for the kind words. About Windhorst, I hope I didn't say anything critical of him! He wrote this technical paper in 1997: http://arxiv.org/abs/astro-ph/9712099 It didn't say any of the stuff that I was criticising. The professional article was fine---just gave the redshift figure 2.39. I would guess the boo-boos came from the Boston Globe August 1998 journalist (as far as I can tell, you have to pay to see the whole article). And then someone from encyclopedia.com grabbed the newspaper article. I would guess harvesting for content to put in their pay-per-view encyclopedia, which could be a job assigned to untrained people. So then it shows up 11 years later and it's kind of confusing and has large numerical discrepancies. So what worries me is how unreliable information gets churned up. Windhorst can hardly be faulted, he is probably a great guy, he is rather the victim of journalism plus encyclopedia.com steam-shovel approach to acquiring content. That's my take anyway. Didn't research it. Just an impression. So far, although I've seen stuff in Wikipedia I didn't like, I would guess it is the best general source of astrononomy information. It's a problem, the quality of what we get on the web. Takes some filtering. I also have found good articles at something by a David Darling. Maybe we should pool our favorite sources. David Darling ( http://www.daviddarling.info/ ) might be half crackpot/sci-fci nut, for all I know. But I've gotten useful up-to-date info from his "encyclopedia of science". Just a small sample so I can't vouch for his whole output. I find I keep going back most often to Wikipedia. then there are the academic outreach sites like Einstein Online and also UC Berkeley has one.
  2. Yes, it is amazing. It's beautiful. Wikipedia has an article on the Friedman equations (actually there are two equations). It is too technical for me to recommend but just so you know. G is Newton's constant. There are several different ways to measure or estimate the overall average spatial curvature. One is from microwave background temperature maps, the bumpiness. One is from galaxy counts, how they depend on radial distance or redshift. Measurements of curvature keep getting refined. One thing the Planck spacecraft that was launched last month will do is improve the measurement of curvature beyond what was achieved by the WMAP spacecraft. The Friedman equation has a spatial curvature parameter k which if you set it to zero and solve for the presentday density you get the critical density (what is needed for exact spatial flatness) and it comes out in that formula I mentioned, in terms of the presentday Hubble rate H. In 1962 California had about the best highschools of any state in the Union and US highschool education was some of the best in the world and Americans were not afraid of numbers and we didn't have to import so many overseas-trained engineers. Google has a calculator built into the search window. If you type in "1 parsec in meters" and press search it will tell you what is one parsec in meters. If you type in "(74 km/s per megaparsec)^2/G" it will probably calculate what that is in some units and tell you. I never tried that exact thing. But anyway the Google calculator knows units, so that can save trouble looking up what G is in a handbook, or what a parsec equals in kilometers. On the other hand it could be argued that it makes you strong to do it on your own without crutches etc. I used to use a physics handbook and an HP calculator but I got seduced by how easy Google is. What "we would notice" depends on how refined the measurement of curvature is. The error-bar on curvature gets translated directly into an errorbar estimate of the current density and that is how you see it published. There is a 95 percent confidence interval published last year that says we are within one or two percent of crit. I'll get the figure later.
  3. Sisyphus, who said this? "Law is par excellence the thing that wants a reason. Now the only possible way of accounting for the laws of nature...is to suppose them results of evolution." I'll give you a hint. An American philosopher. I would judge that this quote is the cornerstone of Smolin's collaboration with Unger. In physics if you simply trace observations back to the application of a physical law then you have explained nothing. The challenge is to explain the law itself. Why it is not some different law. They want to carry the understanding of nature to a deeper level. (I think.)
  4. Great picture! the dotted lines show paths of inference. Dotted lines down back into the past are inference about what was. Lines upwards are inference about what will be. All the info we have is just what is on the lightcone. So your dotted arrows of inference all have their tails on the lightcone. This picture shows exactly how cosmologists construct their picture of the universe. There are certain horizons which you didn't show. You should look up a 2003 paper by Lineweaver that is on the arxiv. He puts in more detail. However your graphics are more attractive and noobie-friendly. You should compile a looseleaf binder textbook and teach at the adult school. Cosmology for housewives and retired people. You have a really nice pseudo-crackpot style---that conceals much quite solid knowledge. Lineweaver's 2003 "Inflation and the Cosmic Microwave Background" has some nice graphics too, but very black and white and no-nonsense. http://arxiv.org/abs/astro-ph/0305179 It shows the past lightcone in two types of coordinatres so in one it is coneshape and in the other it is teardrop shape (because back into a smaller universe) Same info different graphic presentation.
  5. That is a beautiful question. You must learn how to calculate the critical density. I suspect you were educated in some place where young people are taught to calculate stuff and not to fear numbers. I long for the company of people who like to calculate stuff. Indulge me. You take the Hubble rate, say H = 74.2 km/s per megaparsec, and simply do this with it 3 c^2 H^2/(8 pi G) That is called the critical density, expressed as an energy density. The beautiful Friedman equation which describes an homogeneous isotropic universe says that if space has this density then it will be FLAT, in the sense that Euclidean 3D geometry is flat, angles of triangles adding up to 180. Volumes of spheres being (4 pi/3)R^3. and all that. If the density is significantly greater than crit, then the geometry will have some positive curvature and you will notice non-flatness. Like volumes of spheres not going with R the way you expect. Like galaxy counts by distance not being right etc etc. If the actual density is less than crit then you will notice other deviations from flat geometry. The size of the bumps in the CMB map is one way they tell. There are various ways to measure how close to flatness. So the key thing for you Purin to do is to calculate crit. Calculate the sucker! If you went to highschool in India, say, then you will experience no trouble with this. Tell me what you get. It should come out in terms of nanojoules per cubic meter. Which is the same as nanonewtons per square meter (do you see why?) which is the same as nanopascals. OK? If you have any trouble at all, like not knowing what a megaparsec is, tell me.
  6. Come on Widdekind. Be a gentleman and don't overdo it. It does not suggest the possible ubiquity of biology to me, for the reason I mentioned. It may suggest the possible ubiquity of biology to you. Fine But please don't keep insisting. Good discussion. You make a valid point. Seeing iron is a sign that there were supernovas. I agree. Well I'm not an expert but I would say definitely. I hear about ammonia in those clouds, and methane, and molecular hydrogen H2, and atomic H----all those are reducing species. I also hear about carbon monoxide in those clouds, which again is reducing. I would say that a reducing gascloud is the natural fart of stars. They blow off that kind of mix. It is their destiny. The nuclear fusion sequence and the periodic table of elements is just set up that way. In a different universe with different elements and chemistry and fusion reactions maybe it would be different. It would, yes, be different. But in our universe seeing a big cloud of methane is a sign that stars have been there. Just my non-expert opinion. We all need to be modest:D
  7. Just wanted to say thanks to Widdekind for starting this thread! It has stimulated quite a bit of thought and discussion. Maybe the key thing which we can learn from this is a Chem concept---the difference between an oxidizing and a reducing atmosphere, or other environment. Thanks to everybody who has contributed. I assume, from all the question marks ?? that Widdekind was intentionally making questionable statements to serve as discussion-starters. Things he didn't believe or wasn't sure about like his "Conclusion (?) " were decorated with interrogation. This simple strategy seems to have been successful. Lucaspa pointed out that some of the articles linked to are interesting. And is certainly better qualified to define the difference between reducing and oxidizing environment. Unless somebody does the general theory here (electron-donors dominate versus where electron grabbers dominate) I will give it a try. In a reducing environment, methane and ammonia are the default, the natural way for C and H and N to exist. Earth has an oxidizing environment, Mars too, and methane is not the default---so on Mars and Earth, methane and ammonia are not the default. C likes to be CO2, H likes to be H2O, and all that. Somebody want to discuss? EDIT: OK nobody handy who wants to discuss. One sign of life is chemicals that dont belong. So if you have an oxidizing environment and you see ammonia that might be a sign. But in a reducing environment where the basic default is stuff like methane and ammonia, then maybe some other chemical would be the one out of place. Maybe in that kind of environment (I'm just speculating) it would be oxygen or co2 that didn't belong. And then THEY would be a sign of life or some other departure from equilibrium. Anyone who wants to correct or comment would be very welcome. The general topic of what chemicals are signs of life, in what different environments, is interesting.
  8. You are most cordially welcome! You obviously have an excellent memory so it will be great when it is stocked with a lot of the new astrophysics and cosmology that has come out since 1998! There has been quite a revolution in cosmology in the past ten years. Thanks are due to Widdekind for starting this thread. He has a style which is very good at motivating discussion. Stimulating, sometimes provocative. A curiously good match for the group here. It certainly caused me to delve into brown dwarf lore! So thanks Widdekind.
  9. Jackson, you are quoting something from a NEWSPAPER BACK IN 1998. The date encyclopedia.com gives is August 1, 1988. But their accuracy is terrible. It is probably August 1, 1998. (Windhorst reported a 2.39 redshift radio galaxy in 1997 http://arxiv.org/abs/astro-ph/9712099 ) So a non-professional who didn't have a clue what she was doing lifted something from the Boston Globe of August 1, 1998 to obtain raw content for encylopedia.com Please try to use professional writing as sources and check the date when the thing was written. Recent, like 2005 or later, is better. In any case after 1998 when the new parameters from the Hubble Space Telescope were published. Your Boston Globe encyclopedia.com article goes like this: In the constellation Hercules, an estimated 13 billion light years away, astronomer Rogier Windhorst of Arizona State University has discovered the most distant known "near normal" galaxy. A near normal galaxy reveals itself to astronomers only as a faint radio source. This one is 10 million times too faint to be seen with the naked eye. Windhorst's galaxy has a red shift of 2.39, or 84 percent the speed of light, higher than any of its type previously identified. Red shift, caused as the motion of a distant object shifts its light toward the red end of the electromagnetic spectrum, is... That is their salespitch come-on and after that, to read more, they want you to pay. They say that redshift 2.39 means distance 13 billion lightyears and recession speed of 0.84 c. Those numbers are completely coo-coo. Would you like to get the real numbers corresponding to z = 2.39? Google "cosmos calculator". Put in the current best estimate parameters: 0.25, 0.75, 74 (that means .25 for matter, .75 for dark energy, 74 for the Hubble rate.) Then put 2.39 in the redshift box and press calculate. You will get that the distance to the object now is 18.45 billion lightyears (not 13). And the recession rate now is 1.39 c (not 0.84). If you are interested in the distance and recession rate back when the object emitted the light we are now receiving, it gives that too. The distance then was 5.44 billion lightyears and the recession rate was 1.33 c. The light travel time was 10.61 billion years. (The calculator tells you the age of the U when the light was emitted and when it was received so to get travel time you just subtract 13.39 - 2.78 = 10.61) The numbers are approximate, you can round off. The hard data here is the redshift z = 2.39. I doubt that represents the farthest anything, and it isn't clear what "normal" means. Nowadays people see galaxies way past z = 5. Some in the range 6-7 and even a few z > 7. The point is not these particular numbers. It's just that encyclopedia.com can't be trusted. They only give a taste, then they want money. They don't give links to professional sources. And it is easy to get better quality more up to date stuff. Wikipedia is not bad on a lot of things. At least it sometimes gives references to profession writing, some of which are live links.
  10. Lee Smolin has a new article in Physics World that will shake some people up. http://physicsworld.com/cws/article/print/39306 It's primarily about time. The idea that the universe actually has a fundamental global time, that its evolution runs on. Even though as we well know from conventional relativity the time we experience is observer-dependent. But the article will also help tone down some of the "Multiverse" excesses of the past several years.
  11. Not so. I rather think the expected response to a declarative sentence followed by question-mark is denial. Example: Ulysses S. Grant, the 18th President of the United States, was a Martian? Answer: No, he was from Ohio. Journalists use this ploy: A declarative headline with a question mark is often an invitation to contradiction or challenge. This is in the Suggestions, Comments and Support section because it contains a Suggestion. Namely when a SFN member starts a thread with a patently false declaration followed by "?" that we consider the possibility that he or she is doing something constructive for us. Opening a discussion, eliciting a counterargument. If there are enough question marks showing, it could even be supposed that the person disbelieves the statement and wants to see it shot down. We've all had highschool teachers that used that didactic strategy.
  12. According to my info the first confirmed brown dwarf was reported in 1995 and they come in all ages, like stars do. http://astro.berkeley.edu/~basri/bdwarfs/index.html Simply by googling "brown dwarf" I found an article about one estimated to be about 1 billion years old. I never heard anything about brown dwarves having to be 18 or more billion years old so hearing something like that makes me curious. The standard mass range for brown dwarf is between 13 and 75 Jupiters. Less than 13 Jupiters and she cannot even fuse deuterium (D) and lithium (Li). Above 75 and she can fuse hydrogen and is considered to be a normal star. (The sun is roughly 1000 Jupiters.) In between 13 and 75, she is not a planet because she can fuse D and Li. So there is some slow faint fusion going on in the core, which is just hot and dense enough to fuse these low percentage constituents. In our galaxy, the smaller stars, less than half solar mass, are by far the most numerous. As objects, the brown dwarves are essentially just too-small stars or too-large planets---presumably formed by the same processes. They must be quite numerous as well. There are hundreds of billions of stars (most of them less than half the mass of the sun) in our galaxy. It is harder to pin down the number of brown dwarves because they are too dim to be seen at distances of more than a few hundred lightyears.* ===================== Advice: base your questions on fresh information. Assumptions remembered from 20 years back can lead to confused/confusing questions. If you want to ask a question, figure out what assumptions it is based on and in case of doubt google to find a source. This may result in your asking a better question. ====================== Your question: a genuine "do they [brown dwarves] still exist, or did they never?" Answer: There must be billions of brown dwarves in our galaxy alone. It astonishes me that someone could ask such a question. Of course they still exist, why would they go away? How could it be the case that they "never" did exist when if fact we see them. *this paper reports one of the most distant detected so far http://arxiv.org/abs/0804.1477 at around 100 parsecs or 300 lightyears. the things are so dim it is difficult to find them outside a severely restricted radius Merged post follows: Consecutive posts merged Beautifully put! But this brown dwarf business is turning out to be quite interesting. I've found David Darling's encyclopedia to be reliable in the past. Quite good on astronomy topics, when I've consulted it. Here is his brown dwarf page: http://www.daviddarling.info/encyclopedia/B/browndwarf.html ==sample excerpt== ...A surprisingly high proportion of brown dwarfs have been found as companions to low-mass (red dwarf or other brown dwarf) stars, and, within these systems, the separation between the two components is typically very small, averaging about 4 AU. This goes against the prediction by some theorists that most very low-mass stars and brown dwarfs are solo objects, wandering though space alone after being ejected out of their stellar nurseries during the star formation process. Very few brown dwarf companions of larger, Sun-like have been found inside 5 AU, a deficiency that has been dubbed the "brown dwarf desert;" however, there is no such desert associated with low-mass stars. The observations to date strongly support the idea that low-mass binaries form in a process similar to that of more massive binaries, and that the percentage of binary systems is similar for bodies spanning the range from one solar mass to as little as 0.05 solar mass. ==endquote== Low mass stars much more numerous than Sun-like ones, so in terms of overall numbers the so-called "desert" cannot be very significant. The SciAm article on B.D. an estimate of some 100 billion in our galaxy. However still a puzzle why Sun-like stars would tend not to develop B.D. companions, while lower-mass stars do. The April 2000 SciAm article is here: http://astro.berkeley.edu/~basri/bdwarfs/SciAm-book.pdf ==excerpt== More important, the Canary Islands group conducted the first useful assessment of the number of brown dwarfs in the Pleiades by counting the most likely candidates in a small surveyed area and then extrapolating the tally for the entire cluster. Their results indicated comparable numbers of stars and brown dwarfs in the Pleiades. If true in general, this would mean that our galaxy alone contains about 100 billion brown dwarfs... ==endquote== I would conjecture a possible answer to the puzzle of why massive bright hot stars like the Sun (about 2X average mass) do not tend to have B.D. companions, though less massive, more average size stars have them. the conjecture is simply that hot stars have sunlight pressure and a stellar "wind" like the Solar wind and this drives away a large part of the proto-star disk. Less massive stars have a cooler dimmer light, maybe a weaker stellar wind as well. So more of the crud from the stellar nursery can stay around and co-agulate. This kind of speculation is not my dish, maybe someone else can think of a better explanation. Widdekind does us a favor by raising an interesting topic (as usual) but we shouldn't automatically assume that he has got it right.
  13. I forget, do you still have your exams ahead of you or are they done? If you still have the exams maybe we should take it easy and not talk so much. Study. Sleep. Prepare. Don't waste time on web. But if you have already taken exams, then it might be fun to look at some UK universities. Not even wait for ajb to reply. It's fun. I don't have direct acquaintance with UK universities. But I have associations with several because of interest in cosmology and astrophysics. For instance, Roy Maartens is a world-class expert and he has a Cosmology Institute at Uni Portsmouth. http://www.icg.port.ac.uk/people/staff/maartens.html When I say world-class, I mean this. He is a top expert in both the theoretical and the observational. And he brings top people to the Institute of Cosmology and Gravitation (ICG)---promising post-docs, bright young people. I don't know how is the undergraduate program at Portsmouth. I only know it is a good place for PhD students and post-docs to get ideas and do their research. Here for example Frederico Arroja http://www.icg.port.ac.uk/people/students/arroja.html Here Antonio Cardoso http://www.icg.port.ac.uk/people/students/cardoso.html These two are PhD students. There is a long list of post-docs at the ICG and also a long list of PhD students. Here is the list: http://www.icg.port.ac.uk/people/current.htm You will see on this list also that one of their post-docs in the ICG is Portuguese, he is Dr. Francisco Lobo He is interested in worm-holes and time-travel among other things (he has broad interests). Here is his picture and a list of his publications---both the professional writings and the popular articles. http://cosmo.fis.fc.ul.pt/~flobo/'>http://cosmo.fis.fc.ul.pt/~flobo/ Personally I think at this point in history there are better fields of research than worm holes and time travel! But obviously this man is not stupid, or merely a dreamer. Roy Maartens is a top cosmologist---very grounded in observation (not merely in equations). He would not have Lobo there with him at ICG unless Lobo is in some way excellent. WAIT! It says that Lobo has finished his post-doc contract at the Portsmouth ICG and he has already gone back to Lisbon! (They do not keep the list perfectly up-to-date) Lobo is now at the Lisbon CAAUL (Center for Astronomy and Astrophysics at the University of Lisbon). http://www.oal.ul.pt/caaul/en/index.html OK read carefully the list of the research interests of Dr Francisco Lobo, who is now in Lisbon but who has connections with a top Institute at Portsmouth, and see if you can visit him for a short advice about education plans. Maybe he will say not, but he might say yes. He can say if Uni Portsmouth would be a practical and beneficial place to try to get into. Perhaps he could say how best to proceed. Suggest names of people. Suggest other UK universities if there are some better for physics undergraduate studies. ==quote== Personal Data Researcher at the Centro de Astronomia e Astrofísica da Universidade de Lisboa (CAAUL). Previously, a Postdoctoral Researcher at the Institute of Cosmology and Gravitation, University of Portsmouth. MSc and PhD degrees by the Science Faculty of the University of Lisbon. Publications (links to his professional papers on arXiv, SPIRES, NASA ADS Database, citebase) News New Scientist: Comments on Time Machine at the LHC (pdf) New Scientist: Comments on cosmic time machine (pdf) New Scientist: Pioneer anomaly - Extra force in modified gravity New Scientist: Dark energy stars National Geographic: Wormoles and time travel International Herald Tribune: Back to the future: Seeking a refined theory of time New York Times: Remembrance of Things Future: The Mystery of Time Research Interests Averaged cosmologies Modified theories of gravity Dark energy models Brane Cosmology Exact Solutions to the Einstein Field Equations Lorentzian Wormholes and the Causal Structure of Spacetime Energy Conditions and Closed Timelike Curves Black Holes and Cosmology Analogue models Quantum Inequalities and Quantum Field Theory ==endquote== His office is in Building C8 of the Campo Grande of the Uni Lisboa. His email: flobo"AT"cosmo.fis.fc.ul.pt [replace "AT" with @] Here is the page for his research group http://cosmo.fis.fc.ul.pt/ (Cosmology and Gravitational Physics research group at the Uni Lisboa) This way you can see who the other people are. It is better to look at a whole group than at a single individual. Wow, look at Paulo Crawford's research interests! http://cosmo.fis.fc.ul.pt/~crawford/pc_i_05.html He also is interested in worm holes! Is this a strange Portuguese national characteristic?? Another one of the group is Paulo Aguiar, who did his undergrad work at Uni do Porto. Here is his path: Graduated in Física-Matemática Aplicada (Ramo de Astronomia) in Faculdade de Ciências da Universidade do Porto in February 1991. Master degree in High Energy and Gravitation in Faculdade de Ciências da Universidade de Lisboa in November 1994, maintaining the thesis titled: Observational Problems in the Big Bang Cosmology, supervised by Prof. Paulo Crawford. Ph. D. in Cosmology in May 2004, maintaining the thesis titled: Homogeneous Cosmologies: Observational Parameters Analysis, supervised by Prof. Paulo Crawford. Here is his photo and homepage http://cosmo.fis.fc.ul.pt/~paguiar/paguiar.html My comment is that the University of Lisbon cannot be so terrible, because this man Lobo got his Masters degree and his PhD degree both from the UL. If they were so bad, then since he is a bright energetic fellow he would have gone somewhere else. But he did the graduate work at Lisbon. That doesn't necessarily mean Lisbon is good. (What matters is how you work, not where you are.) But it can't be a complete desert either! And also Paulo Aguiar seems to be OK and he was entirely educated in Portugal! BS in O Porto, Masters and PhD Lisbon. How bad can it be? It can't be all that bad! I think I would rather be in Portsmouth. I respect Roy Maartens a whole bunch. Also King's College London has good people. Also Uni Nottingham has excellent quantum gravity people. It has John Barrett (so smart he is scary). There are several absolutely excellent places in UK, but just to keep focus let us think about Portsmouth. I wonder how the undergrad program there is. ==================== But look! Uni Lisbon has an undergrad program (Licenciatura) designed for future researchers in Astronomy and Astrophysics! Here is the description! http://www.oal.ul.pt/caaul/en/formacao/formacao.html "Em 2003 foi criado um ramo de Astronomia e Astrofísica da Licenciatura em Física permitindo aos alunos uma sólida formação nesta ciência básica. Além disso, tem constituído uma óptima aposta para alunos que desejam seguir uma carreira posterior de investigação em Astronomia e Astrofísica ou Cosmologia." And by the way here is the Erasmus coordinator, I think for studying part time at UK universities http://fisica.fc.ul.pt/erasmus.html http://fisica.fc.ul.pt/docentes/~gevansdf.html Now it is clear. You go to Lisbon and talk to Paulo Aguiar, Paulo Crawford, and maybe that hotshot dude Francesco Lobo, all of them in the group for cosmology and gravitational physics. And you ask them about Licenciatura em Física. Is it really good or not? And you ask them about places in the UK to go for the Erasmus year. Is Portsmouth good? Or is some other place better? They are all at CAAUL. You scope out the campus, maybe talk to a few students. Maybe talk to Dr Evans (the lady who coordinates Erasmus foreign study program). Steer clear of string theory, which is a trap with too many people in it and weak or non-existent experimental content. for some reason Crawford and Lobo are both interested in worm-holes and time travel. which I can't understand, but there it is. And they are in the Lisbon cosmo and gravitational physics group. And there is a link to Portsmouth, where one of my favorite people (Maartens) is. Maybe that is all I can say. Perhaps AJB will have a different perspective. You have to actually talk to students and professors directly in order to find out anything real.
  14. Nobel laureate George Smoot on observational cosmology, early universe, microwave background... General audience, charts, graphs, but no equations. http://www.revver.com/video/827006/the-history-and-fate-of-the-universe-part-1-of-9/ http://www.revver.com/video/827106/the-history-and-fate-of-the-universe-part-2-of-9/ http://www.revver.com/video/827171/the-history-and-fate-of-the-universe-part-3-of-9/ http://www.revver.com/video/832550/the-history-and-fate-of-the-universe-part-4-of-9/ http://www.revver.com/video/832599/the-history-and-fate-of-the-universe-part-5-of-9/ http://www.revver.com/video/832643/the-history-and-fate-of-the-universe-part-6-of-9/ http://www.revver.com/video/832679/the-history-and-fate-of-the-universe-part-7-of-9/ http://www.revver.com/video/832724/the-history-and-fate-of-the-universe-part-8-of-9/ http://www.revver.com/video/832788/the-history-and-fate-of-the-universe-part-9-of-9/
  15. Definitely! In fact (although the current model predicts continued expansion) it could turn out that somehow sometime in the remote future the dark energy factor may change so that (then with different parameters in the model) we get a collapse. There is currently no indication of that, no reason to suspect it. But cosmologists are naturally interested in that as a possibility and on the lookout for anything that might enable it to happen. would be interesting. We are talking tens of billions of years, not anything abrupt. For practical purposes one can ignore it. but still nice to think about. BTW i just ran across an excellent video talk about early universe and CMB: Nobelist George Smoot talking about the CMB and what things it tells us. Very skillful presentation with animated graphs, shows what bumps in the power spectrum mean, and why. Part of the "Honeywell Nobel" lecture series. http://www.revver.com/video/827006/the-history-and-fate-of-the-universe-part-1-of-9/ http://www.revver.com/video/827106/the-history-and-fate-of-the-universe-part-2-of-9/ http://www.revver.com/video/827171/the-history-and-fate-of-the-universe-part-3-of-9/ http://www.revver.com/video/832550/the-history-and-fate-of-the-universe-part-4-of-9/ http://www.revver.com/video/832599/the-history-and-fate-of-the-universe-part-5-of-9/ http://www.revver.com/video/832643/the-history-and-fate-of-the-universe-part-6-of-9/ http://www.revver.com/video/832679/the-history-and-fate-of-the-universe-part-7-of-9/ http://www.revver.com/video/832724/the-history-and-fate-of-the-universe-part-8-of-9/ http://www.revver.com/video/832788/the-history-and-fate-of-the-universe-part-9-of-9/ See what you think. It is a public lecture, so not mathematical. But Smoot is very skillful with verbal analogies and animated graphics. Great communicator. Delivers a whole lot of insight and information, on a general audience level.
  16. Good. Now I know that for you English is better than Spanish. I guess that means we should focus on UK. There may be also some courses taught in English in Denmark and/or Holland. American students who go to places like Copenhagen and Utrecht (good universities) say they do not have to learn to speak Danish or Dutch because everybody speaks English. But for simplicity let's focus on the UK. We have a UK physics graduate student here called AJB. You can write him a pm. Use lower-case letters "ajb". He will know all about the undergrad physics education in the main UK universities. I also will try to continue to help.
  17. OK, I was wrong. You have visited Lisbon and it is not satisfactory. I see now that it does not have a strong undergraduate program. Let's change the focus to University of Barcelona (UB). They do have undergraduate Physics program. I get a good impression. Look here: http://www.ub.edu/fisica/en/ (that is the English version but you can choose other languages) Here at this page they have a video that shows the buildings, facilities, cafeteria, the life of the students, etc. To me the UB looks good. It is ranked #60 worldwide in natural sciences, but I would not worry about ranks like that. The important, for undergrad, is to have the desired program and to get good marks, grades. Wherever you are, work hard, compete. Then you can move on to Masters and possibly PhD at some more famous place. For undergraduate, I think Barcelona is probably as good as any other place. Also they have a connection with the MAGIC telescope on La Palma island. Actually there are now TWO of those big telescopes. Magic-II just began observing in May of this year. These are now the two largest optical mirror telescopes in the world, according to my information. So let us look specifically at the Astro department of UB. Here is ICCUB (institute of cosmic sciences of uni barcelona) http://icc.ub.edu/ The people of this institute teach courses both in the department of FUNDAMENTAL PHYSICS http://web.ffn.ub.es/ and also the department of ASTRONOMY http://www.am.ub.es/ they also have a section called STRUCTURE AND CONSTITUENTS OF MATTER http://www.ecm.ub.es/ Here I found some online self-teaching resources! It has four resources for the FIRST CYCLE people (the undergraduates) and it also has resources for the Second and Third Cycle people. These are links to stuff that you can use at home. Interactive. Computer simulation of experiments. They also have Applets for General Physics. I like this page: Recursos on-line On-line resources Dosiers electrònics de les assignatures (1er i 2on cicle) 1er Cicle: Termodinàmica (Veure última versió als dossiers electrònics) Laboratori de termodinàmica (Veure última versió als dossiers electrònics) Analisi Matemàtica I Analisi Matemàtica II 2on Cicle: Física estadística Física Atòmica 3er Cicle: Curs a la Web: "Metodes de simulació Numèrica" Fenòmens Quàntics en Sòlids Model Standard General: Applets de física (GAIU) Grup Reconegut d'Innovació Docent en Termodinàmica i Física Estadistica To reach this page you go to http://www.ecm.ub.es/ and then you see a sidebar menu and you select "recursos on-line/on-line resources" Also to get a sample of what the PhD level people are discussing and researching, I looked at the webpage for their ICCUB Journal Club (that meets every Tuesday to discuss new research). http://icc.ub.edu/p-c_journalclub/discussed.html This lists what research papers they have discussed recently. From what you have told me, you have already visited Lisbon and it is not right for you. OK I agree. What about visiting Barcelona? First explore the UB website and then write 4 or 5 emails to some people there. Then catch the train. Can you do it?
  18. Where did you get the idea that the universe is destined to contract? Was it a professional source from the last ten years? I am curious to know. Please find an online source and give us the URL web-address so that we can evaluate the source. Before 1998 (when the acceleration was discovered) it was believed that expansion was slowing. Professional cosmologists took seriously the possibility that it would eventually stop---all at the same time throughout according to their models---and reverse. Those models with collapse do not fit the data that has become available in the past 10 years, so they have been discarded. But if we did live in that kind of universe, we would see the end of expansion FIRST IN NEARBY objects---by nearby I mean within 10 to 100 million lightyears. There is no reason to expect such a slowing down/reversal to happen on a significantly inhomogeneous schedule. The universe appears to be approximately uniform. If contraction was destined to occur---if we lived in that kind of universe---then we would see SLOWING DOWN in nearby objects' recession speeds long before contraction actually began. And I mean billions of years before---in a universe resembling ours but lacking the acceleration factor, so that eventual collapse might be predicted, we would see ADVANCE WARNING in the behavior of nearby stuff long long long before actual contraction began. No. There is no rational reason to suppose that. But like I say, anything is possible! Pink unicorns could magically appear and begin to eat the stars! And for some unknown reason the unicorns could appear first only in distant locations far from the Milky Way, so that we would not see them at first! I don't know why they would take special care to avoid our neighborhood, at first, but they might! And then we wouldn't know! Anything is possible. What dististinguishes reasonable possibilities from unreasonable is that they conform to mathematical models based on tested physics laws, fitted to observation data. Merged post follows: Consecutive posts merged Well sure! The parameter was always there. If a really radical slowing had been observed they could have tried fitting the data by giving Lambda a negative value. But as I'm sure you realize, you get natural slowing even with zero Lambda, just from the matter density. I don't know. You tell me! I certainly didn't say that contraction was inconsistent with theory. Some models (which don't fit the data) actually predict contraction! So how could contraction be inconsistent? Maybe there is a verbal confusion here. Consistency is broader than implication. A theory can have several different outcomes consistent with it. Something is consistent as long as it is not ruled out, as long as it is possible with some adjustment of the the parameters.
  19. Lisbon Tech (Univ. Tech. Lisboa) looks like a good place. A lot of what DH says is very sensible. Do you live near Lisbon? What are the requirements for getting formally admitted as a student in the UTL? What is the deadline for application? For some Uni you must apply 6 months or a year ahead and the requirements for admission are very tough. What is UTL like, that way. You should forget about "worm holes and time travel" since this is not relevant to getting a solid undergraduate physics training. If you start talking about those things people will not have a high regard for you. If you think you can win admission to UTL then you should visit there and talk to the students sitting outside the building, and at the student cafeteria where they eat or have their coffee. Most universities you are allowed to AUDIT classes. You can sit in on the lectures even if you are not yet admitted as a regular student. So audit some classes. It is free, if it is allowed by the rules. You just walk into the hall and sit down. If the deadline is past for formal admission for September 2009 then you can still go and audit and read the textbooks for the college physics class and whatever else you are interested in. Try a beginning astro class. So, where do you live? Is your home in Lisbon or nearby? That would be fortunate. Or do you live in some far away place with only a minor college or university?
  20. Airbrush I was trying to do several things and messed up a detail in that explanation. Only saw it later when too late to edit and correct. I'll try to give the key idea. (It doesn't really matter, or change the picture of density waves very much, but it's good to get right) A kilo mass orbiting at earth distance from sun has less energy*, but orbits faster, than a kilo orbiting at Jupiter distance. If you take a mass, say a one ton craft in circular orbit at earth distance, and slowly try to speed it up with an ion thruster boost you will end up making it swing out farther and actually go slower. Earth goes 30 km/s around sun. If you have a craft doing that same thing and try to boost it faster you can have it end up going 25 km/s. If you put an ion thruster on the front of the craft try to slow it down, it will end up spiraling in closer to the sun and going faster. =================== Now the arm has to rotate as a whole, to keep its shape. So close in it will be going slower than standard circular orbit speed. And out away it will going faster than normal orbit speed at that distance. So take an inner star. It will be going faster and catch up. But while it is catching up and closing in it will be being pulled---like the craft with the ion thrust booster. By the time that sucker has merged into the arm it will have swung out slightly and be going slower. So it spends more time in the arm, because it is temporarily slowed down. That is what makes the traffic heavy in the arm. But it still is not completely slowed down to the same speed as the arm so it gradually passes thru, and comes out the front. OK now it is being dragged back by the gravity of the arm (the higher density)----like the spacecraft with a braking thruster---and that actually brings it back into its old orbit and speeds it up. So the inner track stars catch up with the arm and pass thru, and are slightly slowed while they are in the arm. The outer track stars, the opposite happens. The arm catches up with them, and temporarily they get speeded up, while they are in the arm. And so they stay longer in the arm than they would otherwise. And this also contributes to the congestion. The arm is essentially some self-reinforcing traffic congestion. I think we all have the right density wave picture and what I just did was repeat the story over again, but with that little gravity mechanism detail fixed. (A textbook explanation might say that orbital energy is the kinetic energy of the speed the thing has PLUS the potential energy of how far out it is. If you inject orbital energy into the system it can actually slow the thing down because the energy is flowing into the potential, pushing it out in a wider orbit and wider orbits are slower. The earth goes 30 and Jupiter, if I remember, goes 13, etc etc.) *the total energy of an orbit is the sum of the kinetic energy and the potential energy related to distance from center.
  21. Jackson, thank you for thinking of me! However, in this case I do not have much advice to give. Enigma, you should learn about current research in astrophysics observational cosmology In physics one attacks the problems that have promise of yielding results---these represent the "hot" research fields. It is not yet time to investigate time travel and worm holes. Those topics are not yet "hot", if they ever will be (we don't know.) Right now the attention of the smart people is focusing on how the universe works (cosmology) and using the new instruments to see and understand more. Right now one wants to understand dark energy, dark matter, high energy cosmic rays, gammaray bursts. After people have understood the basic physics of dark energy, the cause of the big bang, cosmic inflation, dark matter, then they may be in position to investigate more exotic things like time travel and worm holes. But right now these are more like dreams and fantasies. Observational cosmology is a good field because you have real telescopes and spacecraft observatories. You get real data. Not just ideas and equations. Here is an idea. Contact one of the young observational cosmologists at CENTRA, perhaps go and visit and talk about their research. http://centra.ist.utl.pt/ CENTRA is a branch of the IST, Instituto Superior Technico Lisboa. It also has a smaller unit at Algarve. By the way, do not undervalue Portugal. Also do not underestimate Spain, they have a share of one of the greatest new-technogy telescopes in the world. It is on the Canary Islands. It sees not visible light, but gamma rays. It is a huge mirror. It is called the MAGIC telescope. they share it with Germany and some other EU. Here are the people of CENTRA: http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=usersList&Itemid=55 See here Ana Maria Mourao (observational cosmologist) http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=userProfile&user=79&Itemid=55 See here Mario Santos (obs. cosm.) http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=userProfile&user=92&Itemid=55 See here Luis Ferramacho (obs. cosm.) http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=userProfile&user=111&Itemid=55 See here Patricia Castro (obs. cosm.) http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=userProfile&user=76&Itemid=55 Her statement of research interests is intelligent and practical, she is also personally very beautiful. Her telephone is +351 218419145 There is a list of her publications since around 1998. Good track record. Main interest is the Cosmic Microwave Background Here is another obs. cosm. http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=userProfile&user=109&Itemid=55 Another http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=userProfile&user=95&Itemid=55 Another http://centra.ist.utl.pt/index.php?option=com_comprofiler&task=userProfile&user=75&Itemid=55 There are 30 members of the CENTRA and many of them, especially the older ones, are classified "theoretical astrophysics and cosmology". But 6 of the 30, exclusively young ones, are classified "observational cosmology" This is because a lot of ACTION in observational. Amazing new instruments, able to tell us things about the shape and evolution of the universe. It is not just pure theory. You must understand theory, but you must also analyze observational data and test theory. All the people I told you, their email is listed on their page. Any young portugues who is interested in observational cosmology has the right to contact them and ask about how is the field. What are the new development in the field? What are the opening research opportunities? What are the leading institutions (say in Portugal and Spain)? I would not go outside Portugal and Spain. And if you send 5 email letters, maybe one or two will be answered. Also I would try to go to the office of some young researcher and talk personally. I have no direct knowledge of Portugal or Spain Universities. If I was a young Portugues, I would go immediately to see Patricia. Also I would love sometime to visit the MAGIC telescope on La Palma in the Canary Islands. It can see TeV photons coming from the black holes of the AGN (active galactic nuclei). TeV means trillion electron volts. Ordinary light is around 3 electron volts. These photons leave a blue trail in the atmosphere and MAGIC records the trail and figures out where the photon came from and measures its energy. It is a new kind of telescope, nothing before like this. http://wwwmagic.mppmu.mpg.de/ Portugal is not in MAGIC, but maybe Patricia Castro knows someone who is a member of the MAGIC team, perhaps someone in Barcelona that you could also talk to. Here is a list of Barcelona people who are in the MAGIC team. http://wwwmagic.mppmu.mpg.de/collaboration/members/index.html Exciting things happening. Patricia will be waiting for the data from the new Planck spacecraft that was launched last month. You should know some details about the Planck spacecraft. It will measure the CMB with greater accuracy than has ever before been possible.
  22. Piltdown, that is a strange question. Would you please give us a link to a website where you saw information like that? Right now, I don't see how to put what you say into contact with reality. It sounds like you have read something on some website and then garbled it. If I could read what the source actually said, I would have a better chance of making sense of it.
  23. You are asking about two different things---black hole spin, and on the other hand, spiral galaxy form. They are unrelated, but both are interesting topics. Lots of galaxies have supermassive black holes and yet the galaxy is not of the spiral type. There is no connection. Airbrush gave you a good lead if you want to read up on black holes. So the other question is about spiral structure----why do some galaxies have it? How does it work? (It is not about stars spiraling down a plug hole! You can have spiral structure in a galaxy without a black hole. The stars in a spiral galaxy are not spiraling in towards the center. There is a different explanation for what maintains the pretty pattern.) So how does it work? Here is a comparatively hard Wikipedia discussion http://en.wikipedia.org/wiki/Density_wave_theory Here is a much easier (dumb-down) version by an astronomer named Alice. Alice likes to explain things so everybody feels they get it. http://alicesastroinfo.wordpress.com/2008/10/29/density-waves/ I audited a course by Frank Shu years ago, the guy who discovered how spiral arms of galaxies work, I'm pleased to say. It wasn't about this topic specifically, just a general astro course. He's an encyclopedia. The story goes like this. Stars orbit the galactic center. Inner stars take less time to go around, they cover more angle per unit time (just like in solar system inner planets orbit quicker). Stars further out from center take longer to go around, cover less angle per unit time. Suppose that just by random motion a region of higher than average density develops in the outer galaxy. It will tend to progress around faster than the stars at that radial distance because its gravity pull slows down the stars ahead of it that it is overtaking. And then since they are slower once they are inside the (proto-arm) region they tend to fall behind. Then once they are out and it has moved ahead of them the arm's pull speeds them up again. So the region of hightened density has passed thru a neighborhood of stars, momentarily concentrating them, and then left them behind, still traveling at the same speed as they had before. Something similar happens in the inner part of the galaxy except there the stars are going faster than the arm (the region of higher density) and they catch up with it. Spend some time in it, and then move on out in front. Like you are driving on the freeway and you catch up to a clog-traffic section that is moving slower, and you gradually get thru it, and then you speed up again and are in the clear. So an arm is constantly gaining some stars and losing other. It does not stay comprised of the same stars. It is a temporary concentration that forms a stable pattern. There is no net effect on the stars. they just keep on orbiting around the center of the galaxy for ever and ever, as if the spiral arm pattern weren't even there. Periodically getting caught up in heavy traffic, like on the freeway, and then getting out, and then after another cycle getting caught in it again, and so on. You can learn more detail from Alice Astro Info and from Wikipedia.
  24. Acceleration is not consistent with that one particular early version of GR with zero cosmo constant, and it is consistent with several other versions of GR. This is one of the things that makes the discovery of acceleration exciting. It enables and motivates choice. I guess everybody knows that acceleration is consistent with the original GR, that Einstein put a positive cosmo constant into. But fewer people are aware of another GR which he proposed in 1919, called "unimodular" GR. It is very interesting. The cosmo constant occurs in it in a way that I think is more natural. Unimodular is now attracting some attention. Acceleration was discovered in 1998, that's when the two key papers were published. If you would like to study what the situation was about the cosmo constant before that, there is a paper by Nobel laureate Steven Weinberg, from 1989, called "The Cosmological Constant Problem". It seems that there were always mainstream figures who did not take for granted that it was zero. Raphael Sorkin predicted a small positive value back in the 1980s, based on quantum gravity theoretical grounds. It's interesting. If you look carefully at what the smart mainstream people were doing, that parameter was always there. It didn't have to be added in 1998 as a "fix". But you are welcome to think of it as a fix, if that pleases you. After all, what is one adjustable parameter in an otherwise very elegant theory? Here's the latest paper on unimodular GR (the 1919 invention, a dark horse contender) http://arxiv.org/abs/0904.4841 Merged post follows: Consecutive posts merged Piltdown, I don't understand your question. What are you implying or suggesting?
  25. Well there are several modern models of what led up to the big bang. None of them involve a "singularity", of course. At this point it's hard to choose. Not enough data. But there is a kind of stampede of researchers going into studying the Loop Cosmology "bounce" model. And abandoning some of the others. That doesn't mean the bounce is true, just that it is currently the most attractive to researchers. Progress is being made, new papers come out frequently. We'll see. I should make the general observation that in science you don't get absolutely certain answers. What you get are models, which if they pass observational tests, gradually accumulate credibility---based largely on their track record of making correct predictions. And if they fail a test they are ruled out. Preference also depends somewhat on their simplicity and consistency. If two models make equally good predictions people tend to prefer to use the simpler one (with the fewer assumptions and adjustable parameters.)
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