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Laymans question. What happened before the big bang ?

  1. Sep 1, 2007 #1

    GUS

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    I realise without understanding maths I will be limited in my understanding of the answer. You may even point out that its the wrong question. However all I wish to know is what is currently mainstream physics view of what happened before the big bang (if there was a before) and is M theory taken seriously by the physics mainstream or is it a fringe theory ?
     
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  3. Sep 1, 2007 #2

    marcus

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    that is really two discussion threads, Gus.
    one about cosmology, and one about particle physics.

    M-theory came up in the mid 1990s as an idea or hope that would connect several string setups. But M-theory never did develop into a well-defined theory AFAIK. Maybe someone will correct me if this is wrong.

    There are no longer as many research papers written about M-theory as there used to be, like five years ago. But a certain class of theorists that we consider mainstream (publishing in major peer-review professional journals) undoubtably take it seriously!

    YOUR MAIN QUESTION seems to be about something different, namely QUANTUM COSMOLOGY. That is a totally different field from string, or M, theorizing. You can have stringy cosmology but that is not mostly what it is about.

    The QC people (quantum cosmologists) are the ones who research models of the universe that go back before the big bang.

    I looked at a bunch of QC people's publication track-record to see who the most important QC experts are----whose papers are most highly cited. And made a thread about it:
    https://www.physicsforums.com/showthread.php?t=175240

    Currently the most recent post there is #18
    https://www.physicsforums.com/showthread.php?p=1413484#post1413484

    What I am counting is how often OTHER scholars, writing in peer-review publications, cite the professional articles by each author. It is a way of finding who are the recognized leaders in the field.

    Those are the worldclass mainstream quantum cosmologists, in my estimation. Except for Reuter, they ALL HAVE IDEAS ABOUT BEFORE expansion started. Most of them have numerical models you can run on a computer, as well as equation models. Most of their models can be run back in time and thus begin to say things about conditions before.
    This is not fringe, it is what Quantum Cosmologists are supposed to do. that is what the QC field is about.

    NONE OF THE MODELS HAVE BEEN TESTED YET. It is a fairly new field. Bojowald Ashtekar and Reuter are all fairly close to being able to make predictions about what we should find by observations made in the present that could either confirm or refute their models. In all three cases they can approximately get the same results as conventional (non-quantum) cosmology so deciding will have to be based on small differences in the predictions.

    It is an exciting time in mainstream quantum cosmology right now. The field is beginning to gain prominence. In August, Bojowald had an article in the journal called Nature Physics that got a lot of attention.
     
    Last edited: Sep 1, 2007
  4. Sep 1, 2007 #3

    GUS

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    Thanks for the reply I was expecting to be flamed by lots off ticked of physisits with their quantum rays .
    Just to clarify , I was referring the M theory before the big bang where they say two branes of the 11 th dimension collided to cause the big bang as referenced in this documentary is the one I was asking about :

    http://www.tv-links.co.uk/listings/9/5239

    Its explained better here :

    http://www.historyincontext.com/Articles/Cosmology/1-BeforeBigBang.htm


    I had never heard of QC thanks for telling me a bout it Illl have a look at the links. Id love to understand the math behind this stuff. I am seriously thinking of doing a foundation and then a physics degree, its just really hard to understand it properly from a laymans perspective.
     
    Last edited: Sep 1, 2007
  5. Sep 1, 2007 #4

    marcus

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    Steinhardt is one of the people on my list (see post right before yours)

    Steinhardt "clashing branes" model is not what I think of as M-theory so when you said M-theory it threw me off track.

    Steinhardt's model is called "string-inspired" but I'm not sure how much it really involves string theory proper. There are a lot of different places where membranes occur in all different sorts of theory, so just because Steinhardt's cosmology model has them does not mean it is the same as M-theory. But that doesn't matter! Just terminology.

    So you want to know how seriously people take STEINHARDT'S cosmology!

    Now I understand better!

    Someone else may have to answer this. I personally don't take "clashing branes" at all seriously. To me it seems bizarre and cooked up.
    there is a huge amount of made-up structure---a higher dimensional world in which our lower dimension universe floats like a billowing pennant. And now and then two such lower dimension universes collide. that seems to me all made up and silly. there have never been seen any clues that this might be so.
    And it is not NEEDED. Other much simpler models like Bojowald, Ashtekar etc answer the same questions and solve the same puzzles and only need very little additional equipment.
    You dont NEED to assume unseen extra dimensions.

    But I would be happy if someone else shows up who does take Steinhardt cosmology seriously and wants to tell us about it.
     
  6. Sep 1, 2007 #5

    GUS

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    Wow Ok I see this is a subject on which there are no definate answers, thanks again for taking the time to respond. But this Steinhardt guy, I mean, hes not some kind of krank or anything is he ?

    Anyway so what you are basically telling me is that quantum cosmologists are the ones who are most looked to at the moment to explain what happened before the big bang.
     
    Last edited: Sep 1, 2007
  7. Sep 1, 2007 #6

    marcus

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    No indeed! He is a fine scientist. I like his other work (not the brane-clash cosmology idea) and respect him very much. He is at Princeton (and one of the best theoretical physicists they have, I believe.) Also I like his public statements about issues of general interest. he is well-spoken, serious, incisive.

    But his cosmology was just some brainstorm that he and Turok had a long time ago. Steinhardt is mostly working on other things now, I think. I think interest in brane-clash cosmology is dying down lately.

    He will probably make some money off it though, because he has a POP-SCI book about it called "Endless Universe" that just came out recently. It will sell in the mass market even if the researchers are losing interest.

    And I could be wrong! Brane-clash cosmology might suddenly get hot and make predictions and turn out RIGHT :rofl: after all. We can't tell what will happen with research, it's wilder than the stock market!

    YES!!! quantum cosmologists on my list, including Steinhardt but also including Veneziano (a genuinely stringy "pre-big-bang" model, but somewhat old now) and also Bojowald Ashtekar etc.
    If you find others with RECENT HIGHLY CITED PAPERS in the peer-review literature, please tell me and I'll check them out. I'd like to add to the list. but I am not interested in work done back in 1980s or 1990s----those older ideas seemingly did not work out.
     
    Last edited: Sep 1, 2007
  8. Sep 1, 2007 #7

    GUS

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    Great , your response exceeded my expectations so thanks again.
    If you get the time please watch this documentary. Its made for the BBC and explains why I assumed there was a relationship between pre big bang, brane clashing, M theory and string theory because thats what the documentory seemes to suggest. Id appreciate your opinion though see now it may be a bit out of date :

    http://www.tv-links.co.uk/listings/9/5239


    cheers,
    Gus
     
    Last edited: Sep 1, 2007
  9. Sep 2, 2007 #8

    Chronos

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    String theory is not popular these days, quantum cosmology is. But both share a common problem - observables. It is not clear either theory can produce the kind necessary for validation. Part of the problem is assumptions. String assumes a background. Thus is deemed not background independent. But QC also assumes a background of sorts - albeit mathematical. QC has the edge at present - it is less background dependent. Call it a classical bounce, but ST may reemerge. It's the kind of theory that cannot be wrong. Liking it is optional.
     
  10. Sep 2, 2007 #9

    XVX

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    I only made it to about 10 minutes into that video. It's too MTVish with a lot of sloppy statements.

    :)
     
  11. Sep 5, 2007 #10

    GUS

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    So someone on another forum is comparing string theory to "intelligent design" in that its nonsense with no evidence . Is this a fair comparison to make ?
     
  12. Sep 5, 2007 #11

    marcus

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    Gus this is an interesting question and, I think, an important one. However it is difficult to discuss freely in a science-focus forum. PF works as well as it does because the categories are kept to rather consistently (with some amusing exceptions).

    the thing is, the Baconian tradition of Empirical Science is only about 400 years old and like democracy or the rule of law or tolerance of free speech or whatever other tradition it requires good faith and understanding. And it is fragile like any other human tradition.
    So we need to every now and then think about what science is, how it works, how differences of opinion are resolved within the tradition, and what makes a theory PREDICTIVE.

    Comparisons like the one you mentioned are like knife sharpening stones that you use to keep the distinctions sharp. there are ways that stringy thinking IS like pseudoscience because even after 40 years it does not risk falsification by empirical observation
    (although passionately believed in by its community of believers, who have done a considerable amount of proselytizing.)
    and there are ways in which stringy thinking is NOT like pseudoscience.
    so by having this kind of discussion you rub the blade of science on the stone of the comparison and keep it sharp.

    But it seems like a discussion to have in the context of a "philosophy of science" forum.

    I'll just say one thing, two things. Smolin's book The Trouble with Physics...and What Comes Next is absolutely great on these issues. Buy it! or get the local public library to get a copy and borrow it. Fascinating book with in-depth discussion of this.
    that was the second thing. the first thing was that to be a scientific theory something must bet its life on the outcome of a future experiment---it must risk falsification.
    If a theory is so amorphous it can accomodate any outcome of experiment not already ruled out by previous theory then it is not predictive. to be predictive it has to DISpredict something. So for example GR was published in 1915 and immediately made prediction that could have falsified it, and already GR was tested in 1919 at the next available solar eclipse. It survived the test. And has continued to survive every test people have devised.

    It is already tendentious to call stringy thinking by the name "string theory". the name itself is pretentious. Gerard 't Hooft has made this point in a book of his, entertainingly. Stringy thinking is a framework, or a collection of approaches, or work-in-progress. But it is not a theory in the traditional sense. A scientific theory, to the best of my knowledge, must predict some definite result of a doable experiment thereby putting itself at risk of refutation.

    That is about all I feel I can say in the context of this particular subforum. If you want to pursue it and start a discussion in the Philosophy forum about present challenges to the scientific method or whatever---string thinking and the anthropic principle?----let us know in case anyone wants to drop in. I don't know if you could get up a discussion there but I think it would be the place to try.
     
    Last edited: Sep 5, 2007
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