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Beginning of the Beginning

  1. Sep 25, 2007 #1
    Hello


    ive been pondering lately about the big bang theory. so far as i know, mislead or not, that all the energy in the universe was derrived from a singularity in nothingness, then decided to at one point break loose and begin to form the universe. i guess my question would be what theoretically might have gone on before that? the only conclusion that i have come up with myself (which isnt directly conclusive to the question at hand) is that im thinking of time as linear, and shouldn't be thought of as beginning and ending, rather that it should be thought of as just a relative connection to objects to describe where they are. i guess the only sense to me right now is to think linear time (like a clock) is just human invention and its senseless to think of such extreme events based on human process.
     
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  3. Sep 25, 2007 #2

    marcus

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    As far as we know no singularity exists or ever existed in nature.
    When people used to talk about "the big bang singularity" it was a failure-point in the THEORY.
    a singularity is a place where a particular theory breaks down and stops computing, stops giving reasonable answers.

    some popularizers gave the public a misconception by MYTHOLOGIZING the singularity or breakdown of the main theory (General Relativity) that was being used to describe the universe----they essentially told the public a fairy story that made it seem as if the singularity was something in Nature.

    In the history of science there have been quite a few singularities which have been fixed simply by replacing the old theory (that had the failure) with a new better theory that didnt go haywire at that point. Three big examples I can think of were singularities that were fixed 80-100 years ago, by people like Max Planck and Niels Bohr.

    So now we just have to wait while the folks who are working on it fix the BigBang singularity. More exactly we wait and watch them replace General Relativity by a better theory that will give all the good results of the old but also will not break down in black holes and at the beginning of our universe expansion.

    they are making good progress and it is interesting to watch.

    A recent news item that was published about the ongoing work was by Carlo Rovelli in the August issue of NATURE PHYSICS.




    here is the Rovelli
    http://npg.nature.com/nphys/journal/v3/n8/full/nphys690.html

    here is a brief exerpt from Rovelli's commentary


    Science has frontiers; sometimes these frontiers move. One of the most impressive of science's frontiers is the Big Bang, and now a quantum theory of gravity — loop quantum gravity — is providing equations with which to explore it. Although these equations are still tentative, and rely on drastic approximations, they introduce a definite method of exploration, and are capable of describing the Universe not only close to the Big Bang but also beyond it. It is in this context that Martin Bojowald reports, in this issue, on the possibility of a peculiar limitation to our ability to observe fully the 'other side' of the Big Bang — whatever that expression might mean (Nature Phys. 3, 523–525; 2007).

    The article that Rovelli refers to here is by Martin Bojowald.
    here is the link to the full article (which is a little more technical than Rovelli's commentary)
    http://npg.nature.com/nphys/journal/v3/n8/full/nphys654.html
     
    Last edited: Sep 25, 2007
  4. Sep 25, 2007 #3

    mathman

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    Endless Universe:beyond the big bang - by Steinhardt and Turok

    The above boook (just came out) is an excellent discussion of this subject, including the authors' own theory of cyclic universe as well as the current version of the big bang.
     
  5. Sep 25, 2007 #4
    Truthfully, the best the alternative approach to explaining the birth of our particular universe would be the tale Endless Universe by Steinhardt and Turok. Though you must be aware that this is an alternative to the big bang model, rather than complimenting it , it proposes a new view.

    It basically states that we are but a small sud amongst an entire ocean of similar suds, i.e. a mere bubble in that of a megaverse. Our creation is due to the collision of two intra-universal membranes, or branes. These branes are located within a hidden extra dimension, the reason behind our inability to directly detect them. However, their collision transfered energy (into the form of a singularity), and thusly spawned our own universe. Once a brane collision occurs, the two membranes spring apart an incredibly far distance, then slowly return together and spawn a new universe. The entire process takes trillions of years to accomplish.

    This is but an incredibly abridged rendition of their actual book, though if you are at all interested in what I have said, you definitely should pick up Endless Universe. It is most definitely very different from any other scientific literature in circuit right now.
     
  6. Sep 26, 2007 #5

    SpaceTiger

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    The cyclic universe is generally considered to be an alternative (still viable) to inflationary theory. The most important observable difference between this and standard inflation is that it lacks a gravitational wave background. Such a background could be detected directly in gravity wave detectors or indirectly by its impact on the CMB power spectrum, but it will be at least 5-10 years before the latter can be achieved.

    "Standard big bang theory" is ill-defined, but usually doesn't encompass the singularity problem or early universe theories (such as inflation and the cyclic universe). The reason for this is primarily historical, I think, as the debate used to be about "big bang" vs. "steady state" theories. Perhaps "expanding universe" would have been a more appropriate label for the former, but it did eventually win out and we now think of it as the standard framework for post-inflation cosmology.
     
  7. Sep 26, 2007 #6

    Garth

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    Hi ST!

    Just to point out that the "Steady-State Theory" also had an (exponentially) expanding universe.

    The enlarging voids between the galaxies being in-filled by the continuous creation of atomic hydrogen. This hydrogen then went on to form more galaxies and hence conforming to the Perfect Cosmological Principle.

    There would not have been a 'beginning', in this model the universe always 'was', it simply 'existed'. Unfortunately the model could not produce enough helium or the CMB.

    Garth
     
    Last edited: Sep 26, 2007
  8. Sep 26, 2007 #7

    hellfire

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    The evolution of our known universe started from an initial state that cannot be described by general relativity in terms of the dynamics of classical space-time. It requires the consideration of quantum effects in the description of the gravitational field. Without further knowledge of the properties of this state or its causes, classical cosmology assumes a finite age of the universe and tells us about the time past since then.

    The question is, however, what happens to time and causal evolution as soon as one tries to find a quantum mechanical and complete description of this initial state. Does the notion of time break down same as the break down of the space-time continuum of general relativity? Or is time a more fundamental thing?

    This question should be answered by a theory that describes the origins of the universe taking quantum effects into account. However, most of the models of quantum cosmology assume a time evolution that is selected a priori in the classical theory, making very bold assumptions about the real degrees of freedom of the quantum theory on which they should base. Some of these models (loop quantum cosmology, pre-big-bang, etc.) predict an extension of the time evolution beyond the classical singularity. However, the notion of time in a theory unifying general relativity and quantum mechanics is very subtle and still lacks of a clear interpretation.

    Why do we assume that the current models of quantum cosmology have something to do with reality? Probably because this is the only thing we have till now, and, moveover, the features of these models are interesting enough to consider that they might arise naturally in a complete theory of quantum gravitation. But still the current models that go beyond the classical singularity are very primitive in this sense.
     
    Last edited: Sep 26, 2007
  9. Sep 26, 2007 #8
    thanks for all the input, and thanks marcus for the npg link. i was wondering, though, that if the endless universe theory that seele brought up had something to do with another theory ive heard of. It states that a black hole in universe 1 formed a white hole in this universe, which then took energy from universe 1 and transported it through the throat thus bringing it to our universe. i thought it may be a good model on how black holes exist without breaking thermodynamics principles, but then again thats what hawkings radiation (i beleive) is all about
     
  10. Sep 26, 2007 #9
    if you could, can you post a link that would describe these models? i should really get a grasp on quantum theories and stop relying so heavily on general and special relativity, or at least understand the conflicts that quantum mechanics has with classical ideas such as time.
     
  11. Sep 26, 2007 #10

    hellfire

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    You can visit the last 7 entries of my blog in PF. There you will find a summary of the most relevant models and some references to papers.
     
  12. Sep 26, 2007 #11

    marcus

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    you are most welcome!

    about the black hole budding a new universe out the back door, so to speak,
    that idea attracted a lot of interest and has been discussed quite a bit here and elsewhere.
    the key step needed to make a pure daydream into a scientific theory is to formulate it in some way not contradicted by what's already known and that you can derive a testable PREDICTION from

    a scientific theory (as distinct from a speculative philosophy) has to bet its life on some future measurement that we don't already know how it will turn out
    and if it turns out to be not what the theory said then the theory is dead.
    to be science it has to be predictive, and that means risking being wrong. (being falsifiable by some test not covered by something already on the books)

    So yes, the idea that black holes could sometimes form new universes, new expanding regions of spacetime---maybe it is all one thing, it just branches like a tree---that is an OK idea and Lee Smolin has written a book about it called The Life of the Cosmos.
    http://www.amazon.com/Life-Cosmos-Lee-Smolin/dp/0195126645/

    the key thing is does it make testable predictions! Smolin argues that it does: there are things we can look for that could help decide if that sort of thing actually happens, and which if you look and find they are contradicted would disprove the idea

    he calls the idea "CNS" for cosmological natural selection----because whenever you have a reproductive mechanism there is a chance of some kind of biological evolution---regions that make more babies come to dominate the population...----so it might lead to spacetime and its laws being adapted to forming abundant stars and therefore the chance of a lot of black holes.

    but the important thing is not whether the CNS idea is appealing, but whether it can be tested and then whether it survives testing. (there is a sort of natural selection that operates with scientific theories too :smile: )
     
    Last edited: Sep 26, 2007
  13. Sep 26, 2007 #12
    The idea of interuniverse connectivity through a black hole seems valid, of course like you said, just a daydream, no proof. but (correct me if im wrong) i would believe that if black holes connect universes together, it would cancel hawkings radiation, because (again correct if wrong) hawkings radiation is a scapegoat for allowing black holes to exist because of laws of thermodynamics, and instead of energy being radiated, it would be transported via the throat to a different universe, if that makes some sense.
     
  14. Sep 26, 2007 #13

    marcus

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    I think you are raising questions which are currently unanswerable. Maybe someone else would like to reply---but I think some of these issues, like the extent of applicability of the energy conservation law (does it require an observer, or a bounded isolated system, or does it apply globally to the broadest extent imaginable) may not be resolved at present.

    A big question that can be raised about any reproductive cosmology scheme---like the one where black holes bud off into new bigbangs----is "where do you get the energy for the next universe?"

    That could turn out to be a fatal flaw in the idea (but I doubt it will.) It also has been tentatively answered in various ways. The usual "inflation scenarios" that cosmologists imagine to resolve certain puzzles exhibit, at least superficially, a massive violation of energy conditions. Inflation theorists have various ways of evading that problem.

    One reaction is to say "it doesnt take any energy to produce a universe" because at the same time that it is creating itself it is falling into the well of its own gravity (Alan Guth calls this "the ultimate free lunch" :smile:) so it acquires an energy DEFICIT, by being deep in the hole, that equals the energy invested in its material existence. Its positive mass-energy is canceled by its "negative gravitational energy". And the universe's total energy is ZERO, your internet name, right? :biggrin:

    My attitude is wait-and-see. I am not convinced by inflation scenarios and by these "free lunch" arguments. But highly respected scientists like Alan Guth have made them their stock in trade. I think things will get a lot clearer in the next couple of years, as Quantum Gravity and Cosmology mature.

    A lot of what we have so far is either speculative (occasionally with missing pieces) or else is based on vintage 1915 General Relativity (the classical pre-quantum theory) which is really inadequate for this job and has to be replaced by a quantized version.

    Sorry for the longwinded post---the main message is its a waste of time to worry about those things now when the experts dont know for sure, just keep watching QG gradually develop and be patient.
     
    Last edited: Sep 26, 2007
  15. Sep 27, 2007 #14
    no need for apologies better longer than short... the "free lunch" arguments as you say seems interesting. ill have to look more into that. heh i should have read what i posted more carefully as it does sound like it would be unanswerable, pretty much purely imaginable
     
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