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Pre Big Bang universe discovered ?

  1. Jul 3, 2007 #1


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    pre Big Bang universe "discovered"?

    This has got to be sensationalist journalism. Suirely, they mean a new hypothesis, not new discoveries.

    "New discoveries have been made about another universe whose collapse appears to have given birth to the one we live in today."

    From Science Daily.

  2. jcsd
  3. Jul 3, 2007 #2


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    Dave, I think I may have posted your press release link a couple of days ago (1 July) here:

    IMO it's good advice not necessarily to take quotes or journalist's interpretation at face,
    to see what the author actually said, you need a subscription to Nature Physics
    see where it says "advance online publication: cosmology: Bojowald"
    if you click there it asks for a subscriber password

    you can't rely on any journalistic or popularized account

    so until someone shares piratecopy from Nature Physics, what we have is a longer paper that recently appeared on arxiv. Free.

    Effective equations for isotropic quantum cosmology including matter
    Martin Bojowald, Hector Hernandez, Aureliano Skirzewski
    42 pages
    (Submitted on 7 Jun 2007)

    "Effective equations often provide powerful tools to develop a systematic understanding of detailed properties of a quantum system. This is especially helpful in quantum cosmology where several conceptual and technical difficulties associated with the full quantum equations can be avoided in this way. Here, effective equations for Wheeler-DeWitt and loop quantizations of spatially flat, isotropic cosmological models sourced by a massive or interacting scalar are derived and studied. The resulting systems are remarkably different from that given for a free, massless scalar. This has implications for the coherence of evolving states and the realization of a bounce in loop quantum cosmology."

    this longer paper, of less than a month ago, has (I would guess) about the same news as the Nature Physics article, but submerged in a mass of technical detail (which camouflages new results and makes them less likely to be spotted and misinterpreted by the likes of science reporters)
    Last edited: Jul 3, 2007
  4. Jul 8, 2007 #3
    I dont quite understand what they`re saying.

    Their idea of Big bounce is a series of big bangs+big crunches(collapse) that has been going on since forever ?
  5. Jul 8, 2007 #4


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    that's only one possibility. what they are saying is much simpler than proposing a long repeated sequence of collapse-bounce.

    I'll try to say. The basic news is old (since 2001) and simply got media attention because of Nature Physics journal.
    the basic news is they have a quantized cosmology model (LQC) which gives approximately the same results as the standard unquantized FRW model that cosmologists normally use-----EXCEPT that it has a bounce at the beginning.

    It doesnt have a singularity (which is a glitch or breakdown where the classical FRW does not make sense). Instead of failing at that point, the LQC model continues on back into earlier time and shows a collapsing phase of the universe.

    This has been studied by dozens of people by now and in many different cases---also using computer simulations lately.

    It DOESN'T say where the earlier collapsing phase comes from-----maybe it is the collapse of an entire universe----maybe it is just part of a universe collapsing to form a black hole. Matter can be created in an inflation scenario following a bounce (just as in ordinary cosmology the bulk of the matter in our universe is imagined to be the result of inflation) so it doesn't have to all be present at the time of bounce. So there are various possibilities, INCLUDING the series of bounces you mentioned. But basically the model doesnt say where it all came from, it just gets rid of the singularity and replaces it by a bounce.

    Now the model needs to be checked with astronomical observation and there are several cosmologists interested in that---Magueijo, Maartens, Singh,...
    There is a growing scientific literature about LQC and about testing it. It is a good research field at the moment, lot of talented young people getting in.

    But all that is not really fresh NEWS, except the fact that it got some media notice.

    The only fresh bit of news is that Bojowald and Kagan and Skirzewski and Hernandez have recently improved the LQC model by adding an effective theory of how the quantum state evolves during the bounce and Bojowald found a kind of INDETERMINACY limiting knowledge about the prior collapsing phase (like how big it was and how much matter was in it).

    the specific form of the indeterminacy, which came out of their equations, was new----his article in Nature Physics (which caught the attention) was about finding that.
    Last edited: Jul 8, 2007
  6. Jul 8, 2007 #5
    Cant it be that all matter and energy (in whatever form or dimension or universe they were) have existed since forever? Are there physicists that take this into account? (Or is this just an "easy way out" explanation)
  7. Jul 8, 2007 #6


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    of course. Lots of physicists have assumed that. Isaac Newton thought that, as did generations of physicistis who came after him.

    but what is the interest? why bother to say it?

    Physicists are not trying to decide whether the universe was always here or not. they are into studying nittygrit detail of how it works, what causes what and how and why---all at a quantitative level.

    You seem to think that the answer to the big question is "It has always been here!" But that does not even begin to get at the really interesting stuff.

    I think maybe you heard a POPULAR MYTH that the universe began with the big bang. Famous guys spread that kind of talk around and used it to sell books, because it appeals to popular imagination.

    But, in fact, some good physicists have been trying for decades to remove the big bang blockage ("singularity" = breakdown) by improving the theory. Those guys NEVER thought that time started at that point, they always wanted to improve the model so it could crank on back to before.
  8. Jul 8, 2007 #7


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    Hell yes! Bojowald and Ashtekar are the top world-wide experts in quantum gravity---as measured by peer-review publications, and citation indices, and by who gets asked to give the survey talks and write the handbook/encyclopedia articles etc. The usual academic measures.

    and they have plenty of co-workers and young researchers in their group that they are bringing up.

    it wouldnt ever occur to any of those guys to imagine that the world began 13.7 billion years ago!

    the thing is though that simply saying that doesnt explain anything, you still have to build a numerical model of the big bang, describing conditions during when it happened and what came earlier.

    then you have to derive conclusions from your model about things we can observe with telescopes, to check the model.


    I have got to compliment you, Nick, on coming to the conclusion by yourself that the world might not have begun at that point 13.7 billion years ago. :smile: You are in good company there.
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