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Pre-Big Bang models query

  1. Jun 25, 2008 #1
    If one has some sort of bounce scenario for BB, with preceding contraction, then for say 1 sec or 10 sec after BB, one has a certain Hubble parameter and temperture, and associated quantum description. Then for 1 or 10 sec before the BB, would it seem most likely to have the same Hubble parameter and temperture, and hence same quantum description? Wouldn't this seem consistent with Capernican Principle http://en.wikipedia.org/wiki/Copernican_principle- that is, nothing special for pre-BB stages, but rather just typical?
     
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  3. Jun 26, 2008 #2

    Chronos

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    The problem with pre-big bang scenarios is detecting an observational footprint. A few ideas have been proposed, but, none are observationally supported thus far. Lacking such evidence, the proposition the universe originated from 'nothing' is the only truly scientific explanation. That raises some disturbing implications - like a creation event - but, IMO, we must let the evidence speak for itself.
     
  4. Jun 27, 2008 #3

    Wallace

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    I disagree, the evidence we have tells us that we don't know what happened beyond a certain look back time. Therefore the only reasonable statement we can make is that we don't know what happened before this time. Hopefully we will work this out in the future, but at the moment the evidence is silent. There is as much evidence for the proposition that the Universe always existed as there is for the proposition that there was a creation event. For both propositions the evidence is the same, no evidence!
     
  5. Jun 27, 2008 #4

    hellfire

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    This does not necessarily hold. Take for example the most simple bounce scenarios in loop quantum cosmology: in the previous contracting phase the orientation of space-time is the opposite than in the subsequent expanding phase. This could have consequences on a different behavior of matter at quantum level. The models are however still very primitive and do not make any clear predictions on this.
     
  6. Jun 27, 2008 #5

    Chronos

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    I concede your point, Wallace. A universe from 'nothing' is impossible to prove, but, possible to disprove. Thus far, it has not been disproven. I agree that does not validate the proposition, merely places it no worse than in a tie for first place with all other contenders to date.
     
    Last edited: Jun 27, 2008
  7. Jul 1, 2008 #6
    I disagree. IMO the comparison was not ok. The proposition which makes sense is "we don't know what happened before the so called big bang". This sais some thing happened ore something existed. We are only acquanted with something, there is no evidence in nature for nothing which notion in nature can even not exist and of course never can be given physical sense.
     
  8. Jul 1, 2008 #7

    cristo

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    Sure, it says something happened or existed or it says that the question is not defined (i.e. there is no "before the big bang.")
     
  9. Jul 2, 2008 #8
    I am not sure whether my statement was clear enough and/or well understood, therefore I add to this "it is absolutely sure (100% true) that 'nothing' ever existed, exist or will exist, therefore it is absolulutely sure (100% true) that existence (nature) always existed, exist and will exist".
    NB and by Heisenbergs' energy <--> time relation physisists etc know that "time always existed, exist and will exist.
     
  10. Jul 2, 2008 #9
    Incoming data


    The observational footprint is here https://www.physicsforums.com/showthread.php?t=239134 The power anisotropy anomaly is telling us something. The scientists tell us it is the fingerprint of events before the big bang. I prefer to think of it as evidense of that our visible universe is not centrally located in the larger finite universe, but that's just me :wink:
     
  11. Jul 2, 2008 #10

    Wallace

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    No, the power anisotropy is not evidence for a 'pre-Big Bang' epoch. But don't take my work for it, in the thread you linked to George Jones can a link to Sean Carroll's blog about why this is not evidence for a pre-big bang epoch. Why should you listen to Sean Carroll? Because he wrote the paper on this....
     
  12. Jul 2, 2008 #11

    marcus

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    Hurk, I like what I think you are trying to say. But I think your native language is Dutch and you are having difficulty with the English.

    I think what you are trying to say is something like this "it is absolutely certain (100% true) that 'nothing' never did exist, does not now exist, and never will exist, ..."

    the rest of what you said seems clear. It comes across clearly in English.

    I don't feel like challenging the claim you are making----which I read as a claim on the logical and philosophical level----a statement about the concepts of nothingness and existence.

    I also sense that there is a submerged issue hidden in this kind of discussion. the question of time. What is time and can one have time without some dynamical material process that goes along with it? Can one have time without something material and observable that changes? Sorry, I am not philosophically sophisticated enough to pose this question in a clear intelligible way.
    ========================

    Hurk, personally I try to avoid arguing with people at a high conceptual level and I take comfort in the thought that it doesn't matter much what one's companions say or don't say regarding such verbal protocols.

    On the other hand, what delights me is this: what I get by a keyword search of the research literature since 2005 using keywords "quantum cosmology", sorted by how often the papers have been cited. European librarians at the DESY maintain the catalogue.
    http://www.slac.stanford.edu/spires...+date+>+2005&FORMAT=WWW&SEQUENCE=citecount(d)

    that is: the mainstream peer-review published literature that actually deals with the big bang issue, especially the papers that are highly cited, predominantly replaces the singularity by a bounce. with a prior contraction phase.

    the people who complain that quantum cosmology can never be tested don't seem to be keeping up with the literature. several papers have proposed ways of extracting predictions and testing. People who point out that QC models have not YET been tested are perfectly right!

    It is a fast-moving field. I am skeptical of statements that QC models are inherently untestable, or even that they are untestable with current types of observation such as Cosmic Microwave Background. Recent paper about this by Zygmunt Lalak, by the way.
    http://arxiv.org/abs/0807.0160
    Loop Quantum Cosmology corrections to inflationary models
     
    Last edited: Jul 2, 2008
  13. Jul 2, 2008 #12

    marcus

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    What paper? Not sure I know of an authoritative paper by Carroll on models that go back before start of expansion. I've seen some highly speculative stuff by him, but I don't think he is usually the guy that gives the invited plenary talk about this at the relevant international conferences and stuff like that.
    His online textbook on General Relativity is used. But what authoritative paper do you mean, Wallace?
     
  14. Jul 2, 2008 #13
    Here are some quotes from the link you are talking about. I have highlighted certain parts to ilustrate that while Sean stops just short of suggesting evidence of a pre big bang era he is certainly suggesting he has found evidence of what was happening in the pre inflationary era.

    --------------------------------------------------------------------------------
    A Hemispherical Power Asymmetry from Inflation

    Abstract: Measurements of temperature fluctuations by the Wilkinson Microwave Anisotropy Probe (WMAP) indicate that the fluctuation amplitude in one half of the sky differs from the amplitude in the other half. We show that such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to the homogeneity of the Universe. In contrast, a multi-field inflationary theory, the curvaton model, can produce this power asymmetry without violating the homogeneity constraint. The mechanism requires the introduction of a large-amplitude superhorizon perturbation to the curvaton field, possibly a pre-inflationary remnant or a superhorizon curvaton-web structure. The model makes several predictions, including non-Gaussianity and modifications to the inflationary consistency relation, that will be tested with forthcoming CMB experiments.

    The goal here is to try to explain a curious feature in the cosmic microwave background that has been noted by Hans Kristian Eriksen and collaborators: it’s lopsided. We all (all my friends, anyway) have seen the pretty pictures from the WMAP satellite, showing the 1-part-in-100,000 fluctuations in the temperature of the CMB from place to place in the sky. These fluctuations are understandably a focus of a great deal of contemporary cosmological research, as (1) they arise from density perturbations that grow under the influence of gravity into galaxies and large-scale structure in the universe today, and (2) they appear to be primordial, and may have arisen from a period of inflation in the very early universe. Remarkably, from just a tiny set of parameters we can explain just about everything we observe in the universe on large scales.

    The lopsidedness I’m referring to is different from the so-called axis of evil. The latter (in a cosmological context) refers to an apparent alignment of the temperature fluctuations on very large scales, which purportedly pick out a preferred plane in the sky (suspiciously close to the plane of the ecliptic). The lopsidedness is a different effect, in which the overall amplitude of fluctuations is a bit different (just 10% or so) in one direction on the sky than in the other. (A “hemispherical power asymmetry,” if you like.)

    What we’re talking about is illustrated in these two simulations kindly provided by Hans Kristian Eriksen.






    But we didn’t give up! It turns out that you can make things work if you have two scalar fields — one that does the inflating, cleverly called the “inflaton,” and the other which is responsible for the density perturbations, which should obviously be called the “perturbon” but for historical reasons is actually called the “curvaton.” By decoupling the source of most of the density in the universe from the source of its perturbations, we have enough wiggle room to make a model that fits the data. But there’s not that much wiggle room, to be honest; we have an allowed region in parameter space that is not too big. That’s good news, as it brings the hope that we can make relatively precise predictions that could be tested by some means other than the CMB.

    One interesting feature of this model is that the purported supermode must have originated before the period of inflation that gave rise to the smaller-scale perturbations that we see directly in the CMB. Either it came from earlier inflation, or something entirely pre-inflationary.
    So, to make a bit of a segue here, this Wednesday I gave a plenary talk at the summer meeting of the American Astronomical Society in St. Louis. I most discussed the origin of the universe and the arrow of time — I wanted to impress upon people that the origin of the entropy gradient in our everyday environment could be traced back to the Big Bang, and that conventional ideas about inflation did not provide straightforward answers to the problem, and that the Big Bang may not have been the beginning of the universe. I was more interested in stressing that this was a problem we should all be thinking about than pushing any of my favorite answers, but I did mention my paper with Jennie Chen as an example of the kind of thing we should all be looking for.

    To an audience of astronomers, talk of baby universes tends to make people nervous, so I wanted to emphasize that (1) it was all very speculative, and (2) even though we don’t currently know how to connect ideas about the multiverse to observable phenomena, there’s no reason to think that it’s impossible in principle, and the whole enterprise really is respectable science. (If only they had all seen my bloggingheads dialogue with John Horgan, I wouldn’t have had to bother.) So I mentioned two different ideas that are currently on the market for ways in which influences of a larger multiverse might show up within our own. One is the idea of colliding bubbles, pursued by Aguirre, Johnson, and Shomer and by Chang, Kleban, and Levi. And the other, of course, was the lopsided-universe idea, since our paper had just appeared the day before. Neither of these possibilities, I was careful to say, applies directly to the arrow-of-time scenario I had just discussed; the point was just that all of these ideas are quite young and ill-formed, and we will have to do quite a bit more work before we can say for sure whether the multiverse is of any help in explaining the arrow of time, and whether we live in the kind of multiverse that might leave observable signatures in our local region. That’s research for you; we don’t know the answers ahead of time.

    One of the people in the audience was Chris Lintott, who wrote up a description for the BBC. Admittedly, this is difficult stuff to get all straight the very first time, but I think his article gives the impression that there is a much more direct connection between my arrow-of-time work and our recent paper on the lopsided universe. In particular, there is no necessary connection between the existence of a supermode and the idea that our universe “bubbled off” from a pre-existing spacetime. (There might be a connection, but it is not a necessary one.) If you look through the paper, there’s nothing in there about entropy or the multiverse or any of that; we’re really motivated by trying to explain an interesting feature of the CMB data. Nevertheless, our proposed solution does hint at things that happened before the period of inflation that set up the conditions within our observable patch. These two pieces of research are not of a piece, but they both play a part in a larger story — attempting to understand the low entropy of the early universe suggests the need for something that came before, and it’s good to be reminded that we don’t yet know whether stuff that came before might have left some observable imprint on what we see around us today. Larger stories are what we’re all about.
    --------------------------------------------------------------------------------------

    I have cut out large sections to avoid copyright issues so please read the full article in its original context here http://cosmicvariance.com/2008/06/08/the-lopsided-universe/
     
  15. Jul 3, 2008 #14
    I would strongly oppose such a "universe from nothing" idea, since strictly speaking a "nothing" does not even contain the possibility that there is something, let alone a universe. Of course, a vacuum does not qualify as "nothing" since it has physical properties. A real "nothing" does by definition not have any property.
    And for that matter, the idea of a "begin of time" is an equally ill proposition, since how can time begin (i.e. the occurence of a change) if there is no time yet? Introduce another (imaginary) time axis?
    Very bad constructs if you ask me. Btw. the Hartle-Hawking proposal was ruled out by observations.

    The most "natural" way for time and space to come about is to have no boundaries, no edges or otherwise topological "special points". The universal principle is that all points be treated equally.
     
  16. Jul 3, 2008 #15

    Wallace

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    I was referring to the CMB Power Anisotropy paper that Kev mentioned. Indeed the point of my post was that Carroll's paper about this was not referring to a model that goes back to before inflation(Edit: As Kev pointed out, he does hint at how this work relates to pre-inflation, but in essence this is still a theory of how inflation happened, not really a 'pre Big-Bang' theory). The point of the CV blog is to wonder at how his paper was reported in the press to be about this! Follow the link to the Cosmic Variance post and it will be clear.
     
  17. Jul 3, 2008 #16

    marcus

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    Thanks, I tracked it down and the reference makes sense to me now. Kev linked to this PF thread started by oldman:
    https://www.physicsforums.com/showthread.php?t=239134
    and oldman began thread by giving a link to this preprint where Carroll was a co-author
    http://arxiv.org/abs/0806.0377
    A Hemispherical Power Asymmetry from Inflation
    Adrienne L. Erickcek, Marc Kamionkowski, Sean M. Carroll (Caltech)
    4 pages, 2 figures
    (Submitted on 3 Jun 2008)

    "Measurements of temperature fluctuations by the Wilkinson Microwave Anisotropy Probe (WMAP) indicate that the fluctuation amplitude in one half of the sky differs from the amplitude in the other half. We show that such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to the homogeneity of the Universe. In contrast, a multi-field inflationary theory, the curvaton model, can produce this power asymmetry without violating the homogeneity constraint. The mechanism requires the introduction of a large-amplitude superhorizon perturbation to the curvaton field, possibly a pre-inflationary remnant or a superhorizon curvaton-web structure. The model makes several predictions, including non-Gaussianity and modifications to the inflationary consistency relation, that will be tested with forthcoming CMB experiments."
    =====================

    edit: I was just replying to you, Wallace. Now I see that Kev has given the title of the paper (though not the arxiv link) and also the abstract. Now I understand your reference, but still don't quite see Kev's point. Carroll talks informally and blogs some about pre-big-bang, or at least pre-inflation, stuff. He is far from the only person doing that these days. There seems to be a tenuous connection with the 4-page paper he wrote with Kamionkowski describing an inflation scenario capable of producing anisotropy. I don't see him as representative of any leading pre-big-bang school of thought. Maybe Kev can explain.

    If one is going to talk about the main pre-big-bang models under consideration, shouldn't one list ideas covered in Rudy Vaas's book?
    Or maybe that isn't the intent?
     
    Last edited: Jul 3, 2008
  18. Jul 3, 2008 #17

    marcus

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    Hi Zankaon, I think what you conjecture is right. You are asking specifically about bounce models of the big bang. You are asking in those models is there time reversal symmetry at some level.

    The answer is yes. Ive seen published results both from computer runs and from analytical models and both show the same behavior. There is a quantum wave function describing the size of the universe---Stephen Hawking called it "the wave function of the universe" which is a bit overdone. And typically they start with a semiclassical state that is peaked at a certain classical size. And they evolve the quantum state through a bounce. And it stays peaked. The quantum state (at least of the size or scale parameter) looks the same before as after. The bounce is symmetric.

    It is pretty robust, they have run their model many times with many different parameters and cases---it behaves the same. The bounce always seems to happen when the density of matter gets to be about 80 percent of Planck density, when quantum effects overwhelm classical gravitational attraction and gravity becomes repellent.

    One way to read about this is to do this Stanford database search for recent quantum cosmology research and glance at a few of the first articles listed----the search gives the top-cited articles first---they will all be about bounce.
    http://www.slac.stanford.edu/spires...+date+>+2005&FORMAT=WWW&SEQUENCE=citecount(d)
     
  19. Jul 3, 2008 #18

    marcus

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    I remember this occurred in the original Bojowald model circa 2001.
    I am not aware that it happens in the models used since 2005.
    Do you have a reference to some recent (since 2005) work?
    One used to say that space turned itself inside out at the bounce, but now, I may be missing something, one doesn't. Please give a reference and correct me if I am wrong.

    Quantum cosmology changed radically around 2005 with the "new dynamics" papers, and also the introduction of solvable analytic models that confirmed the computer modeling. Don't think there is orientation reversal, but I could be wrong.
     
  20. Jul 4, 2008 #19

    Chronos

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    I'm uncomfortable with bouncing models. Drifts in physical constants between bounces would, IMO, wreak havoc after an infinite number of bounces. An inexplicably singular, expanding universe is at least as appealing and observationally consistent, IMO. No one has yet pointed out the 'finger in the sky' that refutes this conjecture.
     
  21. Jul 4, 2008 #20

    Wallace

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    I think I'll reserve judgment. This whole field is still very new and who knows what potentially observable 'fingers in the sky' the theoretical work might one day predict, leading to some hard evidence one way or the other.

    For now I think it is important to stress that we have a very good model of the Universe that describes the history of the Universe between now and almost 14 Billion years ago. Whether beyond this 'time did not exist' or rather that the Universe was in some other state is at present unknown.

    On the one hand, we shouldn't put to much emphasis on this question since it only adds to the common confusion that 'Big Bang theory' is all about the 'Bang' part, whereas in fact this is the only bit that present BBT says nothing about. When people learn this they often feel disappointed in some way, which is a shame. As I say, we need ensure people instead marvel at how successful the current theory is in being able to describe almost 14 Billion years of history very well with a remarkably simple model.

    On the other hand, we do need to look into the question of pushing our understanding even further back in time (or even to the 'beginning' of time if that is what the theory and data ends up telling us exists). We should definitely avoid making judgments one way or the other based purely on an individuals philosophical bent or gut feeling. Lets be honest, the data is (at present) silent on these questions.

    Taking the position that one option is 'uncomfortable' and therefore should be discounted until other options are refuted is a poorly motivated position. At present the only reasonable position is acknowledged ignorance. This doesn't mean we shouldn't ask the questions, indeed it makes them particularly interesting to consider and hopefully progress can be made.

    As I said at the start, I reserve judgment until there are definite observational signatures worked out theoretically and we have the capacity to make a reasonable attempt at looking for these signatures.
     
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