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B Exactly how quantum tunneling leads to a Big Bang?

  1. Mar 6, 2017 #1
    In wikipedia says that in a big amount of time quantum tunneling can create a new Big Bang. EXACTLY, how this happens.
    https://en.wikipedia.org/wiki/Future_of_an_expanding_universe ("Beyond" part)
    *note: I'm in high school, but feel free to explain this with complicate process.
     
    Last edited: Mar 6, 2017
  2. jcsd
  3. Mar 6, 2017 #2

    Orodruin

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    Please provide the page where you read this. How else are we supposed to know exactly what you read and whether it is a problem of the text itself or your understanding of it? "Read on Wikipedia" is not a valid reference here.
     
  4. Mar 6, 2017 #3
  5. Mar 6, 2017 #4
  6. Mar 6, 2017 #5
  7. Mar 6, 2017 #6
    In this case I put the specific page numbers in parentheses, the search button is your friend. : )

    Edit: You will learn on these forums that the term "Big Bang" is usually synonymous with "inflation".
     
    Last edited: Mar 6, 2017
  8. Mar 6, 2017 #7

    PeterDonis

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    No, it isn't. In inflationary models, the Big Bang is the hot, dense, rapidly expanding state of the universe after inflation ends.
     
  9. Mar 7, 2017 #8
    If it's not too off-topic, I have a couple questions to hopefully clarify my understanding from the pop-sci/Wikipedia mire, and the expert information discussed here on PF:

    Is there a more technical term for that state than "Big Bang" (Wikipedia articles say "reheating/thermalization" comes after inflation)?
    Are there size estimates for how small and large the universe was at the beginning and end of the inflationary period or is that irrelevant?

    The exponential expansion of the inflationary period seems more bang-like than rapid (though decelerating) expansion. But the more I read about this, it sounds like inflation was a "fix" for problems realized in early Big Bang cosmology, and is a necessary bridge between the Big Bang singularity and the Big Bang state.
     
  10. Mar 7, 2017 #9

    Drakkith

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    The problem is that the term "big bang" is not a technical description, but an offhand name given by an opponent of the initial theory. The term has come to have several different meanings:

    1. The absolute beginning of the universe. Prior to inflation, prior to everything.
    2. The initial expansion in non-inflationary cosmology without regard to what may have causes this expansion nor what may have come before it. In this sense the big bang wasn't the creation of the universe, but merely the initial phase of rapid expansion.
    3. The rapid expansion after inflation ends (which is an expansion process, but one of a different nature than the big bang in this context).

    I'm not quite sure, but I think there is an absolutely tiny, but non-zero, probability for all particles in the universe to quantum tunnel to a location and state similar to that of the very early universe. So instead of matter being spread very thinly throughout all of space (on average), it would tunnel to a state where all matter is highly compressed and very hot, similar to the conditions of the very early universe. Someone correct me if I'm wrong please.
     
  11. Mar 7, 2017 #10
    Thanks for the explanation @Drakkith, it sounds like my understanding was based on #2.

    From the paper:

     
  12. Mar 7, 2017 #11

    PeterDonis

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    My understanding is different. As I understand it, the tunneling in question is from a very tiny piece of ordinary vacuum--similar to the kind we have in empty space we're familiar with (note that this vacuum must have a tiny but nonzero cosmological constant, that's what the "true de Sitter vacuum" in the quote stoomart gave refers to)--to a very tiny piece of "false vacuum", i.e., a very tiny piece of the kind of stuff that undergoes inflation (in the cosmological sense). The very tiny piece of false vacuum will then inflate, creating a new universe.

    Some versions of inflationary cosmology say that this is how our universe began--that there is a sort of "background" spacetime that is always in the true de Sitter vacuum state, but due to thermal fluctuations every so often a tiny piece of false vacuum appears and inflates, and one of those tiny pieces is the piece that formed our universe.

    Another model says that the true de Sitter vacuum is the end state of every universe, and once it gets to that end state, sooner or later a thermal fluctuation will create a tiny piece of false vacuum and the whole inflation cycle starts again.

    AFAIK none of these models are experimentally testable at this point.
     
  13. Mar 7, 2017 #12

    Drakkith

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    Ah, well, I certainly trust your understanding more than mine. :wink:
     
  14. Mar 7, 2017 #13
    The following statement in the paper indicates the tunneling model is not preferred, is that still the case?

    References Phys. Rev. D 23, 347: Inflationary universe: A possible solution to the horizon and flatness problems
     
  15. Mar 7, 2017 #14

    PeterDonis

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    As I understand it, "slow roll" models that do not involve tunneling are currently preferred in inflationary cosmology, yes.
     
  16. Mar 7, 2017 #15
    Thanks guys, learned a lot.
     
  17. Mar 7, 2017 #16
    I didn't understand well the part of how quantum tunneling leads to a inflation. You said that the tunneling is similar to a vacumm or a tiny "false vacuum", but HOW does this piece of false vacuum inflate. (ok, by quantum tunneling, but HOW).


    *By the way, I really appreciate the answers.
     
  18. Mar 7, 2017 #17

    PeterDonis

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    No, it doesn't inflate by quantum tunneling. Quantum tunneling just creates the tiny piece of false vacuum (at least, according to the hypothesis under discussion--none of this has been tested experimentally). The false vacuum inflates because of the properties of the particular quantum field--an "inflaton" field--that it is a false vacuum state of; these properties are basically like those of a large positive cosmological constant, i.e., they cause exponential expansion with a very short time constant.
     
  19. Mar 7, 2017 #18
    How does quantum tunneling creates that tiny peace of false vacuum? I'm sorry if I very insistent with this, but I have to made a monograph explaining this.
     
  20. Mar 7, 2017 #19

    PeterDonis

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    In the hypothesis under discussion (which, I stress once again, is just a hypothesis and hasn't been experimentally tested, and can't really be experimentally tested with our current technology), it's the reverse of the process that ends inflation in the original "old inflation" models (like the one Alan Guth originally proposed). You have two possible vacuum states of the field, the "false vacuum" and the "true vacuum". If the field is in either state, there is a small probability for it to quantum tunnel into the other.

    Then you should be doing a lot more research than just asking questions here. You need to be looking at textbooks and peer-reviewed papers. Plenty of them.
     
  21. Mar 7, 2017 #20
    I have clear that this is just an hypothesis. But I don´t have yet a clear answer, HOW does quantum tunneling turn a false vacuum to a true vacuum, and vice versa.

    Don't worry about the investigation, I have 17 sources but non of them explain me this.
     
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