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Big Bang v. Cyclic Universe models

  1. Jun 5, 2008 #1

    Nabeshin

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    I had the pleasure of attending a lecture given by Paul Steinhardt, a Princeton professor, regarding the big bang and cyclic universe models at Fermilab this evening. Steinhardt, having written a book called The Endless Universe, is obviously a fan of the cyclic universe camp and the main focus of the talk was to introduce this as a legitimate alternative. Both theories were discussed in the framework of string theory, particularly brane theory, and it was interesting to see how these different approaches to looking at the universe relate to the theory.

    Now, not being very much in the cosmological community, I had not realized that this was such a viable alternative to traditional inflationary big bang models. So, I would like to open the discussion up as to which you believe to be correct, why, and any current evidence which points towards one or the other.
     
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  3. Jun 5, 2008 #2
    I don't think a cyclic universe is possible because data point to an accelerating, not decelerating universe. There's not enough mass in the universe to pull back and recollapse everything into a big crunch, then big bang scenario.
     
  4. Jun 5, 2008 #3

    Wallace

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    I'm not sure that I would characterise the situation as being a choice between the Big Bang and Cyclic Universes. The Big Bang theory just says that Universe was hotter and denser in the past, up until a time beyond which we cannot observe. What happened before this is anyones guess with two possibilities being that the Universe simply did not exist before this time and that the Universe did exist but underwent some drastic change, possibly in a way it has done before (i.e. cyclic) that lead to the events we can observe.

    It comes down to semantics in a way, but I think what most cosmologists think of when they think of 'the Big Bang' is neutral on the question of cyclic universes. Big Bang theory is compatible with a cyclic universe and also compatible with a 'one shot' universe.
     
  5. Jun 5, 2008 #4

    Nabeshin

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    Ok, let me clarify the two theories which were explicitly mentioned during the lecture which I have in mind.

    1) Universe begins from nothingness, undergoes a period of rapid inflation, coasts for some 9 billion years, undergoes acceleration due to dark energy(from current evidence until the universe is completely flattened and essentially dead). (Key point here is inflation happens)

    2) Our "Universe" begins when two branes collide, producing matter out of the collision. Universe expands for some nine billion years, undergoes acceleration due to dark energy and becomes essentially uniform. Some time later, branes collide again and the process repeats. Unclear whether or not this has been going on forever or not.

    The major difference is that one requires inflation and one does not. In my eyes, these two are not compatible with each other.
     
  6. Jun 5, 2008 #5

    dkv

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    I thought Universe cannot begin from Nothingness.There was something quantum mechanical in the begining. I guess.
     
  7. Jun 5, 2008 #6

    marcus

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    I agree with Wallace. I think you have somehow been sold a false choice.
    Paul Steinhardt is a respectable scientist but few professional cosmologists go along with his cyclic brane-clash idea.
    He's a good writer and i recommend the articles at his website. I like him as he comes across in interviews and quotes.

    But his brane-clash cosmology is rather a minority thing, kind of a fantasy, but nicely executed mathematically speaking.

    Your 1) and 2) is not a real choice.
    Because your 1) is just one version how how and from what expansion may have started.
    And your 2) is just Steinhardt and there is a lot more alternative to 1) than that!

    There is no one unique "big bang theory". You should learn about the various different ideas of conditions before the big bang (the start of expansion) and the various different ideas being discussed about what led up to it.

    there is a book coming out July 1 about this, with different proposals by some 10 - 20 different top experts

    As far as I know none of them say the big bang, or expansion, started from "nothing"!
    That is how people used to talk in the 1980s if I remember right. So perhaps you should have a look at this book and get up to speed and stop saying the big bang began from "nothing"----but just realize there are different models being proposed and studied.

    Here's the book:
    http://www.amazon.com/Beyond-Big-Bang-Prospects-Collection/dp/3540714227

    I know the general direction in a lot of it and I personally reject about 80 percent of it, out of hand. Or am very skeptical anyway. You wont find much about Steinhardt's ideas. Maybe one chapter out of 15 will be brane-clash. I'm not sure if even that.

    But like it or not, you should know the range of scientifically respectable pre-big bang models. You shouldn't just hear of a random one and say "hey, that sounds nice." You should have some idea of what the menu is. I'm not criticising you. This is friendly advice :biggrin:
     
    Last edited: Jun 5, 2008
  8. Jun 5, 2008 #7

    dkv

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    where is the book ?
     
  9. Jun 5, 2008 #8

    Nabeshin

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    Well thank you for your post, Marcus. Sorry for misunderstanding this.
     
  10. Jun 13, 2008 #9
    How far as thought progressed with M-theory and a multiverse of continusly existing universes being born out of continuous bangs, some expanding into a big freeze and others collapsing into blackholes (amongst other high density outcomes)

    Is the answer not then, always existing and coming into existence (the bang) are both correct?
     
  11. Jun 14, 2008 #10

    Chronos

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    A cyclic universe is plausibe, but unlikely. No observational evidence yet favors that proposition. The best observational evidence suggests a one time event - a big bang.
     
  12. Jun 19, 2008 #11

    kxd

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    And if the infinitely big doesn't pass infinitely small?
    And if the infinitely small doesn't pass of infinitely big?
     
  13. Jun 19, 2008 #12

    Wallace

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    As discussed in this thread, Big Bang theory does not prohibit a cyclic Universe. Big Bang theory simply says the Universe around 14 Billion years ago was very hot and dense and for some reason rapidly inflated. What happened before this time is anyones guess, the observational evidence at present says nothing for or against the Big Bang being a one time thing or part of an endless cycle.
     
  14. Jun 19, 2008 #13

    Chronos

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    No argument, wallace. I haven't seen any credible observational evidence favoring a pre-BB state. That doesn't mean it isn't there. It would not perturb my world view were it found.
     
  15. Jun 19, 2008 #14
    Ekpyrotic Universe

    Just wanted to add that the name in the literature for these colliding brane models is Ekpyrotic. Below is a complicated link that returns 94 papers on the arXiv that discuss this model.

    http://adsabs.harvard.edu/cgi-bin/n...txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1

    As far as I understand, standard inflation is the theory that is in competition with these Ekpyrotic models. Standard Inflationary theory happens in 3+1 dimensions and is usually presented (in talks aimed at people who dont work on inflation = me) as the single scalar field toy model. These Ekpyrotic models occur in higher dimensional Universes with our Universe living on a brane which collides with another brane to produce the same sort of initial conditions that inflation does.
     
  16. Jun 20, 2008 #15
    Since the 'Big Bang' theory is derived from Sir Edwin Hubble's discovery of the 'red shift'...(i.e.: just run the film/universe backwards to a central point) could Hubble's evidence of the red shift also arise from a cyclic universe model?..and possibly been initially misinterpreted?

    I seem to recall a scientist, W. G. Tifft, at the university of Arizona had a an interesting angle on the red shift...quantized red shift patterns...which seemed to have no explanation. Could this evidence also point to a cyclic universe?
     
  17. Jun 20, 2008 #16

    Wallace

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    Redshift quantisation is an interesting bit of history. In the early days of cosmological surveys it was much harder to survey wide areas of the sky compared to today, so instead the early surveys were 'pencil beam' surveys that basically focused on a very small region of the sky, but took long exposures (on photographic plates) to see to great distances (high redshifts).

    Indeed, when this was done it was observed that redshifts seemed to go in waves, i.e. you might see a lot of galaxies near a particular redshift, then fewer at higher redshifts but then at an even higher value see a bunch around a similar value again. This was unexpected behavior and lead to a lot of speculation about what it meant.

    Now that we can survey wider regions of the sky the explanation has become more apparent, the Universe has large scale structure. Have a look at the attached picture which is from the 2Degree Field Galaxy Redshift Survey (2DFGRS) which was the first large scale cosmological survey. It shows clear structure in the distribution of galaxies. There a large empty voids, clusters and then filaments connecting the clusters in a web like pattern (indeed this is known as the cosmic web).

    Now, imagine that instead of this survey you just see a single line through all this structure. You would see the cyclic pattern. Near a cluster you see a lot of galaxies with similar redshifts then as you pencil beam passes through voids you see few galaxies.

    So galaxy redshifts tell us a great deal about the universe, but not any information about whether the Big Bang was a one shot thing or part of some greater cycle.
     

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  18. Jun 20, 2008 #17
    The nice feaure of the colliding brane idea is that it kick starts the universe everywhere simultaneously, so that model does not have any problem with an initially very large or infinite universe. The problem in cosmologies that are initially infinite but without branes is coordinating a start signal that is simultaneous everywhere without requiring the start signal to be superluminal. The rapid inflation idea gets rounds round this by smearing everything out so that the universe looks isotropic and homogenous everywhere in our local corner that we call the visible universe. On a much larger scale such as an infinite universe even a superluminal start signal like rapid inflation would mean that that the universe did not start simultaneously everywhere unless the inflation was infinitely fast. Of course in an infinite universe with no definable centre, to be democratic, the inflation would have to start simultaneously everywhere. It is difficult to explain that and that is where the brane theory has the advantage. However, one difficlty with the brane theory is that it postulates the collision of two infinite 2D planes and that would leave the universe with an axis. To get round that you would have to require the universe to started by the collison of two infinite 3D spheres where collison is defined as there exact superimposition. Of course, the 3D branes would have to be exempt from the laws of relativity because you can not superimpose all points of two moving spheres simultaneously because of the relativity of simultaneity. If the branes exist in another dimension and are massless then they probably do not have to obey any rules that apply in our universe.
     
  19. Jun 20, 2008 #18
    A mojor evidence of the big bang theory is cosmic microwave background radiation (CMB) which fills the entire universe. I read recently that about 1% of the static on a static televison channel can be acounted for by the CMB. Does cyclic model have any suggested or discovered evidences that support it as CMB supports Big bang? To my knowledge the only explanation of CMB radiation is that it is radiation left over from the birth of the universe ie. big bang. Does the cyclic model support the CMB theory or can it offer any further insight on CMB?
     
  20. Jun 22, 2008 #19
    My guess is that in the cyclic models each crunch would generate a new CMB as the density and temperatures would be the similar to a single big bang. However the evidence at the moment points to the universe never collapsing again due to acceleration of the expansion or due to insufficient mass relative to dark energy if you preer to see it that way. So if the the universe has been cyclic in the past it does not look like it is, this time around.
     
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