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Different laws after a big crunch/big bang

  1. Jul 30, 2006 #1
    Hello everyone. First off, I'm no astrophysist, but I'd been reading around and thinking about something.

    From what I gather, eventually the universe will contract back down to singularity (probably?) and there will be another big bang, creating another universe (this is all from my basic understand of cosmology...which is limited). Anyways, after the next big bang, does anyone have any idea if the same laws of physics that exist now will hold, or will the be changed based on some random fluctuations at the start of the universe? For example, could the law of conservation of energy no longer apply, or maybe F=ma will become a square fuction like F=ma^2 or something? Basically, I guess what I'm wondering is, are the laws we have now going to be around after the next big crunch/bang cycle? Forgive my ignorance on these topics...but thank you!
  2. jcsd
  3. Jul 31, 2006 #2


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    hello pete
    If you are new at the cosmology subforum, welcome.
    I think this is an intelligent question to be asking. In my private opinion it is a LEADING EDGE question. But I would ask it differently.

    (BTW since it is a leading edge question you probably are not going to get any satisfactory answer but if you know science that is normal----sometimes what matters is just to try to phrase the question as coherently as possible----because the community has not gotten to the point of answering yet)

    Current consensus cosmology DOES NOT FORESEE A FUTURE CRUNCH for our universe. Some people talk about it but the consensus view sees expansion continuing indefinitely. But there may have been a PRIOR CRUNCH before the big bang. That is certainly possible.
    So you might want to restructure your question so it does not sound like you are asking "what will happen when our universe does its big crunch, will the physics laws change?"

    There is an idea in quantum cosmology of a BOUNCE that quite a number of people have been studying recently and that can occur in various contexts, like black holes and also at big bang time. some professional journal papers have already been written considering the ways that physical constants might change during a bounce I am thinking of one by Gambini which does this, although I am not sure I like the paper or would follow his approach.

    The laws of physics that you are talking about are governed to a considerable extent by the ratios that go into them called fundamental dimensionless constants. and these fundmental proportions are things like alpha "fine structure constant" which if it were different we would have different chemical elements----maybe OK ones, or maybe icky, or maybe all radioactive. You probably know alpha and have thought or read about this. There are several dozen key proportions like that and they go into the basic laws and have a major influence on things.

    Changing the coefficients that go into the laws would, if you did it enough, seem to even change the qualitative nature of the laws themselves.

    So one way to picture a slight random change in the laws is to imagine a slight random change in the basic constants.

    And this is what some people have been doing. the basic constants (like alpha the electromagnetic coupling strength) seem to be built into the fabric of spacetime itself so if you SQUASH SPACETIME and then let it bounce and re-expand, might that not randomly alter some of the basic ratios and proportions that are built into it?

    I remember that Rodolfo Gambini had a paper about that.
    It was too technical for me to recommend it. You could find it on arxiv.org. I think the date was like 2003 or 2004.

    Anyway, it is extremely speculative but professionals DO consider these things. It is not just for crazy people. The main trouble is that studying quantum cosmology bounce is still fairly rudimentary.

    Actually probably the wisest thing would be simply to read the latest papers on the bounce, and temporarily set aside the question about whether the laws or the constants could change.

    Abhay Ashtekar is an authority on that. I will fetch a link in the next post.
    Here is a related paper by Rudy Vaas
    Last edited: Jul 31, 2006
  4. Jul 31, 2006 #3


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    here are Ashtekar's recent papers
    look at titles to get an idea of his current interest and research direction

    Ashtekar is a world expert on quantum cosmology. Last week
    he gave the main talk on his field to a plenary session of THE international conference on Gen Rel and Cosmology---something that happens every 3 years called the MARCEL GROSSMANN meetings on

    That was last week in Berlin (the location changes every 3 years)
    You can watch a video of Ashtekar's talk if you are curious.
    Anyway he is the recognized world expert on the non-string approach to quantizing General Relativity so that it gets rid of the big bang and turns it into a bounce

    a smooth quantum transition from a prior gravitational collapse thru a strange condition where gravity turns repulsive (at very high, or Planck, density and temperature) and on through to an expansion phase (virtually indistinguishable from the earlier "Big Bang").

    this can be modeled on a computer----as Ashtekar has his grad students and post-doctoral fellows doing----and he gets plots of a DETERMINISTIC EVOLUTION OF A WAVE FUNCTION for the universe's geometry.

    this is recent work and I would urge getting to know about it.
    But Ashtekar has never said a word AFAIK about the fundamental physics constants changing during this transition.:smile:
    He might have, if he were more the speculative type. But he is actually pretty slow and cautious and qualifies what he has to say carefully etc. etc. Like senior scientists are supposed to.

    my advice for right now is learn what you can about how the bounce is modeled and forget about the laws changing. In a few years they will get to that part, or they may very well. But for now it is a challenging enough business just to model the bounce and derive observational TESTS SO THAT YOU CAN CHECK IT. The model should leave some subtle imprints, a "signature" on the CMB that can be looked for----in order to confirm or falsify the model. That has to come first and then one can think about what could happen during the Planck regime transition.

    At any event you brought up some interesting issues.

    if really interested, look on page 27 of this
    where it says
    " If this is born out by detailed numerical calculations, one would conclude that quantum geometry in the Planck regime serves as a bridge between two large classical regions. Space-time may be much larger than general relativity has had us believe. "

    if interested in watching videos of last week's Marcel Grossmann talks ("MG11" conference)
    scroll down to "Publications" "conference live-line"
    select the timeslot 25 July 11-13
    and fastforward to halfway thru (Ashtekar's was the second talk in that slot)
    you can fastforward simply by dragging the timepointer

    if you just want the part of the talk where he talks about bang turning out to be bounce then drag the time pointer until it says 1:28
    that part of the talk is only about 6 minutes, from 1:28:40 to around 1:24
    the total in that timeslot is 2:27, so you have to drag the timepointer a little more than halfway across
    if you want just that part.
    Last edited: Jul 31, 2006
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