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Big Bang

  1. Jul 16, 2008 #1
    Is it possible at the start of big bang matter and energy went faster than c?
     
  2. jcsd
  3. Jul 16, 2008 #2
    I don't think so...
     
  4. Jul 16, 2008 #3
    reasons?
     
  5. Jul 16, 2008 #4

    marcus

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    in the standard model of cosmology--based on Einstein General Relativity---it is necessary for most of the recession speeds to be much greater than c, near the beginning

    in fact it is still the case that most of the galaxies we can see are receding at speeds greater than c.
    for them not to do so would violate the Hubble law and thus and in effect violate relativity, the theory on which the model is based.

    Have a look at the Lineweaver SciAm article. The link is in my sig. It gets recommended a lot to PF newcomers, and it explains this stuff pretty well, with diagrams and simple non-mathematical language.

    (local motion is different from longrange change of distances. local motion is governed by the earlier theory of special relativity.
    the SciAm article has a reference to a 2003 Lineweaver Davis article that is also good to read about this)
     
    Last edited: Jul 16, 2008
  6. Jul 16, 2008 #5
    Wow. That articles really showed me how little I know. I still maintain that the data we obtain from space cannot be used as true observable data. If space is expanding volumetrically, then any photons traveling have also receded from each other, giving an expanded picture, creating illusions of variating gravity.

    Another maybe silly question, are the pictures we see 2 dimensional pictures I mean if length goes to zero at the speed of light, isn't there a whole other dimension that we see every day missing in the data?
     
  7. Jul 17, 2008 #6
    G'day from the land of ozzzzzz

    I came across these links,,,,,,,,,,,may I have an opinion on these.

    http://lanl.arxiv.org/abs/hep-th/0206138

    Cosmological Perturbations Through a General Relativistic Bounce

    Authors: Christopher Gordon, Neil Turok
    (Submitted on 17 Jun 2002 (v1), last revised 29 Nov 2002 (this version, v2))

    Abstract: The ekpyrotic and cyclic universe scenarios have revived the idea that the density perturbations apparent in today's universe could have been generated in a `pre-singularity' epoch before the big bang. These scenarios provide explicit mechanisms whereby a scale invariant spectrum of adiabatic perturbations may be generated without the need for cosmic inflation, albeit in a phase preceding the hot big bang singularity. A key question they face is whether there exists a unique prescription for following perturbations through the bounce, an issue which is not yet definitively settled. This goal of this paper is more modest, namely to study a bouncing Universe model in which neither General Relativity nor the Weak Energy Condition is violated. We show that a perturbation which is pure growing mode before the bounce does not match to a pure decaying mode perturbation after the bounce. Analytical estimates of when the comoving curvature perturbation varies around the bounce are given. It is found that in general it is necessary to evaluate the evolution of the perturbation through the bounce in detail rather than using matching conditions.


    http://lanl.arxiv.org/abs/astro-ph/0206287

    Topological defects: A problem for cyclic universes?

    Authors: P.P. Avelino (1,2), C.J.A.P. Martins (1,3,4), C. Santos (2), E.P.S. Shellard (3) ((1) CAUP, Porto; (2) DF-FCUP, Porto; (3) DAMTP, Cambridge; (4) IAP, Paris)
    (Submitted on 17 Jun 2002 (v1), last revised 31 Aug 2003 (this version, v2))

    Abstract: We study the behaviour of cosmic string networks in contracting universes, and discuss some of their possible consequences. We note that there is a fundamental time asymmetry between defect network evolution for an expanding universe and a contracting universe. A string network with negligible loop production and small-scale structure will asymptotically behave during the collapse phase as a radiation fluid. In realistic networks these two effects are important, making this solution only approximate. We derive new scaling solutions describing this effect, and test them against high-resolution numerical simulations. A string network in a contracting universe, together with the gravitational radiation background it has generated, can significantly affect the dynamics of the universe both locally and globally. The network can be an important source of radiation, entropy and inhomogeneity. We discuss the possible implications of these findings for bouncing and cyclic cosmological models.


    http://lanl.arxiv.org/abs/hep-th/0208086

    Bouncing and cyclic universes in the charged AdS bulk background

    Authors: Y.S. Myung
    (Submitted on 13 Aug 2002)

    Abstract: We study bouncing and cyclic universes from an (n+1)-dimensional brane in the (n+2)-dimensional charged AdS bulk background. In the moving domain wall (MDW) approach this picture is clearly realized with a specified bulk configuration, the 5D charged topological AdS (CTAdS_5) black hole with mass M and charge Q. The bulk gravitational dynamics induces the 4D Friedmann equations with CFT-radiation and exotic stiff matters for a dynamic brane. This provides bouncing universes for k=0, -1 and cyclic universe for k=1, even though it has an exotic stiff matter from the charge Q. In this work we use the other of the Binetruy-Deffayet-Langlos (BDL) approach with the bulk Maxwell field. In this case we are free to determine the corresponding mass M-tilde and charge Q-tilde because the mass term is usually included as an initial condition and the charge is given by an unspecified solution to the Maxwell equation under the BDL metric. Here we obtain only bouncing universes if one does not choose two CTAdS_5 black holes as the bulk spacetime. We provide a way of avoiding the exotic matter on the brane by introducing an appropriate local matter. Finally we discuss an important relation between the exotic holographic matter and Lorentz invariance violation.


    http://lanl.arxiv.org/abs/hep-th/0111098
    Cosmic Evolution in a Cyclic Universe

    Authors: Paul J. Steinhardt, Neil Turok
    (Submitted on 12 Nov 2001 (v1), last revised 20 Mar 2002 (this version, v2))

    Abstract: Based on concepts drawn from the ekpyrotic scenario and M-theory, we elaborate our recent proposal of a cyclic model of the Universe. In this model, the Universe undergoes an endless sequence of cosmic epochs which begin with the Universe expanding from a `big bang' and end with the Universe contracting to a `big crunch.'
    Matching from `big crunch' to `big bang' is performed according to the prescription recently proposed with Khoury, Ovrut and Seiberg. The expansion part of the cycle includes a period of radiation and matter domination followed by an extended period of cosmic acceleration at low energies. The cosmic acceleration is crucial in establishing the flat and vacuous initial conditions required for ekpyrosis and for removing the entropy, black holes, and other debris produced in the preceding cycle. By restoring the Universe to the same vacuum state before each big crunch, the acceleration insures that the cycle can repeat and that the cyclic solution is an attractor.
     
  8. Jul 17, 2008 #7

    DaveC426913

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    Well, yes but...
    - space is mostly empty so we can see pretty far, and by knowing distances we know that extra dimension (depth)
    - other than stars, most things in space are not opaque. Certainly, much effort goes into seeing through dust and gas clouds to see what lies beyond

    This is not really a relevant factor. The length of a massive object approaches zero as the object's velocity relative to us approaches c, this is true, but we don't really encounter massive objects moving toward us at c.

    Length contraction does not apply to EM, which is what we use to observe the universe.
     
  9. Jul 17, 2008 #8

    marcus

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    I think you can get opinions on these (cyclic or ekpyrotic model) papers from other PF posters, but it would probably be better to start a thread about that.
    It doesnt fit in this discussion. If we got started about brane-clash cosmology it would divert the discussion from what the original poster was asking about.

    Turok was just appointed director of Perimeter Institute, a position of great influence. Essentially for political or social reasons this could revive some interest in the Steinhardt/Turok brane-clash business. But otherwise I'd say interest in that stuff peaked back around 2001-2003. there are now some newer pre-big-bang cosmology models that seem to have more going for them and are attracting more attention from researchers.

    A good way to gauge the current directions of research here is to do a keyword search for quantum cosmology papers and get the list ranked by CITATION COUNT, that is, the number of other research papers which cite the paper as reference.

    I would suggest you disregard anything published before 2005, or some cutoff year like that. 2003 or 2004 would work. It is a rapidly evolving field. Here is a sample keyword search of published research in quantum cosmology ranked by cites-number.
    http://www.slac.stanford.edu/spires...+DATE+>+2004&FORMAT=www&SEQUENCE=citecount(d)

    There is a book edited by Vaas, coming out April 2009, that covers all the current research approaches to what preceded and caused the big bang. It is called Beyond the Big Bang. Don't confuse it with the popular mass-audience book by Steinhardt and Turok, which I gather just focuses on their own approach to the problem and doesn't discuss newer ones.
    http://www.springer.com/astronomy/general+relativity/book/978-3-540-71422-4?detailsPage=toc
    I don't set much store by most of the solutions proposed in this book, but at least it covers the field and at this point nobody can pick winners so everything is on the table.
    Here's the amazon page about the book
    http://www.amazon.com/Beyond-Big-Bang-Prospects-Collection/dp/3540714227
    600 pages, contributions from more than a dozen different top people. I have mixed feelings. At least it is a book that will outline current thinking about what led to the big bang. Bends over backwards to be inclusive, in my view. Some of the stuff is just elaborate fantasy, and is even now going out of fashion, but he includes it anyway.
     
    Last edited: Jul 17, 2008
  10. Jul 18, 2008 #9
    Last edited: Jul 18, 2008
  11. Jul 18, 2008 #10
    ok, thanks.
     
  12. Jul 18, 2008 #11

    marcus

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    The arXiv search is your idea. It is good to learn to use that search tool, but what you have gotten in that particular case is very unselective. It isn't ranked by citation count, so there is no indication of which papers are important and getting other researchers' attention.

    So that particular arXiv search might be more confusing than helpful. Also it gets a huge number of hits.

    What I suggested (besides just looking at the TOC of the new book Beyond the Big Bang) is the slac.stanford link---a spires database search.
    (In your post the spires link is broken. I fixed it in what I quoted. Here it is again:
    http://www.slac.stanford.edu/spires...+DATE+>+2004&FORMAT=www&SEQUENCE=citecount(d) )

    It is ranked by citation count so one can get something just by scanning the titles and abstracts of the first 10 or 20 and seeing what they are about. I wouldn't advise trying to read so much material---too much work and it would take too long.

    The idea is to see what researchers in the field are currently thinking about and working on, and which people's ideas are currently getting the attention of other researchers and being cited. It is good to be aware of because there may be reasons why things are moving in one direction rather than another. Nobody would say that ideas are right merely because they are currently attracting interest (most ideas in science historically turn out to be wrong!) but it helps to get this kind of perspective.

    BTW you can change the date cutoff in the spires search to get an idea of what USED to be considered important in quantum cosmology. The search I gave the link for was restricted to papers written after 2004 (it says DATE > 2004 in the search window).
    Suppose we change that to read DATE < 2000, so we only get papers published before 2000.
    http://www.slac.stanford.edu/spires...+DATE+<+2000&FORMAT=www&SEQUENCE=citecount(d)
    Now, if you look you see a whole different bunch of authors and ideas. It shows that there has been a big shift in what is highly cited and a big change in the direction of quantum cosmology research.

    this is just an introduction to the spires tool. play around with it to learn more
     
    Last edited: Jul 18, 2008
  13. Jul 19, 2008 #12
    G'day from the land of ozzzzzzzz

    Thank you very much Marcus.

    Years gone by, I thought I knew, but! now it seems that I know extremely little.

    This is going to take years of reading,,,,,,,,,,,smile,,,,,,,,,,,,so be it,,,,,,,,,,its alot of fun and discovery.


    On another topic:
    I was researching Z-pinch and the formation of jets from compacted matter.

    This is an eye opener, not just for the formation of jets, but! the process of compacting matter, such as Neutrons.
     
  14. Jul 20, 2008 #13
    Is pre-big bang not the same thing as the end of this universe? I mean: Would studying the end of the universe not be the same as what happened just before the big bang? I guess only if the universe would be oscillating.

    Any thoughts on this?
     
  15. Jul 20, 2008 #14

    marcus

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    That is a good guess! Several researchers have thought that was worth looking into.
    That oscillating model, repeated collapse-bounce-reexpand-recollapse is the subject of one of the papers that comes up in that slac-stanford spires search. It is the k=1 case.

    They ran a computer quantum cosmology model that reproduced that picture remarkably well. And also they derived analytical solutions, which backed up the computer sims.

    But that doesnt prove that this is what happened. You have to realize that the stage people are at now they are looking at various mathematical models of what COULD have happened, and studying each model carefully to learn all they can. People are not yet at the point where they can choose one sole model and say this is what happened.
     
  16. Jul 20, 2008 #15

    marcus

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    Look Peter, since you are interested in the oscillating case I want to show you something. Here is the Spires search I was talking about. You should knw how to do thisL
    http://www.slac.stanford.edu/spires...+DATE+>+2005&FORMAT=www&SEQUENCE=citecount(d)

    Wht this gives is the most influential QC papers published since 2005---what the most active researchers are working on---what they are using as references in their own work.

    You look down to the #5 paper there and it will be about what you are talking.
    It says5) Loop quantum cosmology of k=1 FRW models.
    Abhay Ashtekar (Penn State U. & Utrecht U.) , Tomasz Pawlowski, Parampreet Singh (Penn State U.) , Kevin Vandersloot (Penn State U. & Portsmouth U., ICG) . IGPG-06-12-1, Dec 2006. 43pp.
    Published in Phys.Rev.D75:024035,2007.
    e-Print: gr-qc/0612104
    ... Cited 45 times
    ... Abstract and Postscript and PDF ...


    the k=1 FRW models are the universes that don't continue expanding forever, they collapse. So the QC people have found that with quantized gravity the collapse leads to a bounce. So in this paper you will see the result of repeated universe bouncing over and over again.
    and they will report what they found with their computer sims.

    they found it always bounces when the density gets to a certain critical level. they found the SIZE of the universe does not have to be awfully small. Depends on what you start with. If you are big with a lot of matter to start with, then you can reach the critical bounce density while you are still quite large by our human standards. they talk about that some, as I recall. It has been a while since I read the paper.

    If you want to read the whole paper, just click where it says PDF. If you just want a short summary, click where it says Abstract.
    Spires is the greatest thing since sliced bread obviously :biggrin:
     
  17. Jul 20, 2008 #16
    I feel like that space density has something to do with space expansion. The oscillation would then be more like a sawtooth oscillation, which would explain the perception of a big bang. Is that computer quantum cosmology model that you mentioned showing something like that, or is it more like a sinus wave oscillation?

    Added: Thanks Marcus, I'm going to read that!
     
  18. Jul 20, 2008 #17
    See my latest post (#101) on the Superluminal Recesssion thread.

    Jon
     
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