Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Big bang, big crunch?

  1. Dec 11, 2005 #1
    big bang, big crunch???

    I have a couple questions. The big bang happened and now the universe is expanding, and It will at some point contract and begin back at where and what it was at the big bang. Is that correct? Now, after it crunches it will bang again. Is it going to produce the same outcome? will, or can things happened exactly the same way again and again? I mean exactly the same, with earth and life and everything. The way I reason this is that afcter the big crunch we will be back at the start with a singularity that would be the same one as when the big bang happened because obviously we haven't accuired any new matter or anything to make the big bang singularity any different, and what governed the outcome of the universe, all kinds of rules and things, so why did things happen in the order they did and why or why couldn't it happen exactly the same again. I could take this as far as thinking i could be typing this same question in billions of years and billions after that too.
  2. jcsd
  3. Dec 11, 2005 #2
    Well, to start with, no one is sure if there will ever be a big crunch, or crush, or whatever.
    Secondly, the "new" singularity will probably be different, because, well, I ma currently too tired to explain and think up why, but I think it will.

  4. Dec 11, 2005 #3
    what would make the new singularity different? everything we have in the universe now is a result of the big bang and everything would be crunched back into a singularity again? how would it be different?
  5. Dec 11, 2005 #4
    Well, positioning? The sole fact that i am moving my fingers now, changes the positioning of matter. The positioning will therefore be different in the new singularity. OK, it's a singularity, and I honestly hardly know a thing about them, but this sounds reasonable to me.
  6. Dec 11, 2005 #5


    User Avatar
    Gold Member

    Maybe. We’re starting to think maybe not. The negative curvature makes it look like it will never contract again.
    We like to think so, but there is nothing whatever that suggests it to be so. Virtual particles appear out of utter vacuum and annihilate again. There is some speculation that the creation of our universe is a freak.
    Infinitesimally small fluctuations (possibly HUP) have been enormously magnified to produce the heterogeny we see today (including all the galaxies and stars). There is no reason to assume they will happen the same way again. It is as likely that the next universe will not even support the existence of electrons whizzing around protons, let alone the existence of life as we know it.
    That heterogeny at the outset. The Higgs field was frozen at a non-zero value.
    Brian Greene’s book ‘The Fabric of the Cosmos’ explains this pretty well in layman’s terms.
    Last edited: Dec 11, 2005
  7. Dec 11, 2005 #6
    I guess my main problem is why things thus far have happened in the way and order they have. The universe probably could have had many different outcomes why did it have this outcome? Do any of you belive in randomness? can anything be random isn't there always a previous event that molds the future events. Even with yourselves why did you get the genes you have it was directly influenced by how the universe formed but what has guided things to happen the way they did???
  8. Dec 11, 2005 #7
    I may not being clear simply I don't know why the universe formed the way it did this time so i don't see any reason why it couldn't form the same way again
  9. Dec 11, 2005 #8
    Hmm... You might want to have a look at Chaos Theory.
  10. Dec 11, 2005 #9
    I read some about chaos theory but i didn't get any answers out of it other than things appear chaotic and aren't really and that there are things we can't predict long term like weather and the universe becuase there are too many tiny fluctuations that would need to be considered and there is no way to consider them all. I know that my question is not able to be answered I guess I am just looking for other peoples take on it
  11. Dec 11, 2005 #10


    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    No, it is not correct, waderoo.
    We are very far from knowing that this will happen.
    There are several mathematical models that fit the data reasonably well and which people take seriously and NONE of them predicts a crunch AFAIK.

    The simplest and most commonly used model, in cosmology, is called the "Lambda-CDM" model. It does NOT predict crunch. It is sometimes called "the consensus model" or words to that effect, because so many people accept it as the best fit so far.

    So whoever told you crunch must have been misinformed or out of date.

    AFAIK a new model could come along and predict crunch, but ever since about 1998 the accepted story is "Lambda-CDM" and it does not predict crunch.

    Lambda essentially means "dark energy" and CDM means "cold dark matter"

    So when you hear people talk about dark energy and dark matter they are usually talking about a model with no crunch.

    the local experts like SpaceTiger---who is an insider with excellent qualifications---can confirm or correct this. it's true as far as I know
  12. Dec 11, 2005 #11


    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    So since crunch is not predicted, waderoo, the other stuff in your post is sort of speculative and "what-if"

    it is based on the premise of big crunch leading to another expansion phase.
    this kind of thing is STUDIED THEORETICALLY in cosmology, and especially nowadays in a new branch of cosmology called "Quantum Cosmology" and it is often called a BOUNCE and sometimes it is called a "Big Bounce"------like a Big Bang, but where the model has a prior contracting phase that reaches a maximum density allowable in the quantum model and bounces and starts expanding.

    sometimes elements (special forces, fields, particles) are put into the model which we do not know if they exist, just to make the bounce work.

    Please understand that this bounce business is very very theoretical and speculative compared with comparatively well-understood and tested things like the LambdaCDM.

    the LCDM describes the universe we know in the simplest possible way we can describe it (already a bit complicated, but comparatively simple).
    and the LCDM does not even foresee a crunch!

    the Bounce theorizing is a totally different kettle of fish. it involves much more new ideas and often involves the conjecture that THE UNIVERSE WE KNOW BEGAN WITH A BOUNCE----that a prior contracting stage actually led up to the big bang which we know about!

    And according to this picture, the prior contracting stage could even have been produced by the gravitational collapse of a star----forming a black hole in a prior universe. there are scientific papers about this by reputable, respected people (Ashtekar, Bojowald, Modesto, Hussain, Winkler, Date, Singh...). but it sounds pretty strange doesn't it? So you have to decide DO YOU EVEN WANT TO GET INTO THIS ONE?

    this new picture says that for various reasons a big bounce does not even have to be produced by the crunch of a prior universe, it can simply be produced by a MERE BLACK HOLE collapse in a prior universe.

    so even though our universe is not slated to collapse in a crunch (according to the widely accepted model) it could STILL produce subsequent universes by the bounce mechanism---according to this rather new and speculative theoretical picture
  13. Dec 11, 2005 #12


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I suppose it depends on what you're willing to call "take seriously". Dr. Paul Steinhardt has a model he calls the Cyclic Universe in which the universe undergoes a repeated big bang -> big crunch cycle. It involves no inflation, but is so far consistent with observations. It's certainly not the most popular model, but it presents a welcome challenge to the many-parameter, explain-any-observation inflationary models.
  14. Dec 11, 2005 #13
  15. Dec 11, 2005 #14
    If the Cyclic Universe is ture is it possible our universe went already went thorw a big chunch and a big bang befroe.That could explain how the bigbang happend it, frist with everthing in it being the size of a basketball and then big bang happend which created the universe and caused it to expand?
  16. Dec 11, 2005 #15


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Well, I'm definitely not an authority on the cyclic universe, but the way I understand it, he's saying not only that our universe has already been through a big crunch before, but that we've been through an infinite (or, at least, very large) number of such cycles.

    As with any theory of the universe, however, you have to introduce some set of unjustified initial conditions. In conventional theory, the big bang itself is an example such an initial condition. In the cyclic universe, he basically invokes colliding branes, but requires that the branes be parallel and homogeneous. There will always be something that's left unexplained. In theoretical cosmology, much energy is devoted to debates about which theory requires the smallest number of arbitrary assumptions, with the unspoken understanding that minimizing the number of free parameters in the model will make it more likely to be true.

    Does the cyclic universe explain the big bang? Yes, in a way, but then what explains the existence and orientation of the colliding branes?
  17. Dec 12, 2005 #16
    A good start is here;http://arxiv.org/abs/hep-th/0108187
    then here:http://arxiv.org/abs/hep-th/0109050

    and thus:http://arxiv.org/abs/hep-th/0111030

    with an informal explination here:http://arxiv.org/abs/astro-ph/0204479

    and a recent interesting paper here:http://arxiv.org/abs/hep-th/0408083

    There are many other papers that detail Crunch-Rip-Bang scenarios.
  18. Dec 13, 2005 #17
    I notice that Brian Greene, in his Fabric of the cosmos, is pretty definite that the Steinhardt and Turok cyclical model will ultimately run down due to entrope build up and quantum mechanical considerations.

    I was surprised - he is usually so careful, that I guess this must be the definite opinion on their contention that the cycles are eternal.

    Is this so?
  19. Dec 13, 2005 #18
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Big bang, big crunch?
  1. Big Bang vs Big Crunch (Replies: 2)

  2. Big Crunch (Replies: 2)

  3. Big Crunch (Replies: 9)