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Did inflation set off the universe?

  1. Apr 16, 2013 #1
    Was it inflation that started off the universe to exist, or was it the Big Bang? The reason I ask is because from I've read is that the universe wasn't an explosion, but rather a rapid expansion. Was there a small explosion we call the big bang, then the cosmological inflation? Or was there first a smaller inflation we call the Big Bang, then a larger inflation we normally call inflation?
  2. jcsd
  3. Apr 16, 2013 #2
    The first 10-43 seconds is unknown. From there the first second is devided into epochs. The inflationary era occurs only during the first part of the electroweak epoch However the inflationary era is still described as exponential expansion of the universe.

    This link has a decent coverage of the epochs.

    http://www.physicsoftheuniverse.com/topics_bigbang_timeline.htmlg [Broken]
    Last edited by a moderator: May 6, 2017
  4. Apr 16, 2013 #3


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    Tim, I don't know of any observational evidence supporting the idea that the universe only began to exist at the start of expansion. There are models which go back before and fit the data just as well as the conventional model that breaks down right at the start.

    Beginning to exist, and not existing before a certain time, is just what some people SAY, and I don't know what they mean by it. It sounds more like myth or magic to me.

    If you do a search with keyword "quantum cosmology" in the research literature you will get a lot of research currently being done in "bounce" cosmology in which quantum effects at extreme density make gravity repellent and cause a contracting phase to rebound, and other kinds of "non-singular" cosmic models in which there is no "singularity" (mathematical model breakdown) at the start of expansion.
    The observational data is equally consistent with some of these non-singular models, where you go back in time THROUGH the start of expansion, explain the start by reference to what preceded, and continue back in time.
    The challenge is now to TEST some of these models. Derive predictions from them involving the Background of ancient light, or CMB, that can then be tested. Perhaps some models can be ruled out!

    There was an example just this past week. A couple of guys came out with a model with a bounce and said "this and this and this are our core predictions" and they challenged the observationalists to disprove their model. World class people: Paul Steinhardt (Princeton) and Jean-Luc Lehners (Paris). I can't say I'm fond of their model but it makes predictions that will be testable in fairly near future. What I like or dislike doesn't matter, ultimately what counts is making predictions and passing observational tests. If you are curious you could google "steinhardt planck 2013 results" and get the paper. The words "planck 2013 results" are in the title, referring to the recent report from Planck space observatory.

    If you want a broader sample here's a professional research literature search for quantum cosmology papers that have appeared since 2009, it is ordered by the number of times a paper has been cited in other papers (a rough measure of interest or importance)
    Last edited: Apr 16, 2013
  5. Apr 16, 2013 #4
    On the other side of the fence is the hot big bang model. The inflationary epoch is part of this model.
    In the original inflationary model derived by A. Guth. Is one where the quantum vacuum of nothing or completely devoid space. Has virtual particle production. There is two particle production models describing virtual production. the one described in A.Guths model is described as false vacuum.
    The other one is Parkers radiation.
    Later inflationary models derive from the false vacuum.
    The initial temperature created from the epochs posted above created a lot of heat.
    When the temperature of the universe dropped below 3 k matter could start forming. googling big bang nucleosynthesis will pull up related articles and links.

    The current best fit to
    observation model is the
    lambdaCDM model. Which is a
    hot big bang model.

    This article has a well rounded tutorial

    Last edited: Apr 16, 2013
  6. Apr 17, 2013 #5


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    "best" compared with what? You cite Ned Wright. What does he actually say?

    Since the Loop cosmology model reproduces the Friedmann equation that LCDM is based on, after a small fraction of a second, the Loop model gives just as good a fit to data.
    what they are now looking for is some way to derive predictions that are DIFFERENT from LCDM and which might be confirmed or refuted by more refined analysis and future data. It is a subtle and challenging job to find possible features of the CMB (say polarization) that might be different.

    Planck mission has not released the polarization part of its report, I believe. We'll see. There may also be future missions with even greater sensitivity and resolution.

    Anyway, LCDM can hardly be the UNIQUE "best fit". And the conventional LCDM suffers an embarrassing breakdown or blow-up at the very start. It cannot be trusted very near start.

    I think the essay "A Tale of Two Big Bangs" posted on the Einstein Institute website "einstein-online" is still a good thing to read about this.

    Don't get me wrong, I'm an enthusiastic fan of the LCDM! I just think it needs to be replaced by something that is just as good a fit as LCDM everywhere the LCDM is applicable, and which does NOT fail catastrophically right at the start of expansion.
  7. Apr 17, 2013 #6
    Lol as I stated early on I presented the other side of the fence or rather some of the inflationary history including some key words to search.

    Ned Wrights site was more for the OPs benefict in regards to being one of the sites for current cosmology tutorials. Its FAQ section is good as well as the cosmology tutorial.
    Inflationary based models does have its faults I fully agree on that. The runaway inflation problem which led to a smattering of other inflationary
    models that either try to correct or take advantage of that problem. Such models include chaotic eternal inflation, bubble Universes, etc. Both inflation and LQG have their merits and faults I readily agree on that aspect.
    Far more so than MOND can ever claim lol. Or Poplowkii's universe inside the EH scenario.
    Last edited: Apr 17, 2013
  8. Apr 17, 2013 #7
    I appreciate your answers, but they were not answers I was hoping for; that's really my fault for wording it badly. What I really want to know is if there really was a "bang" at all that contributed to the universe exisiting. The only reason I ask is because they say the Big Bang was a huge explosion that brought the universe to its ginormous size, but I thought inflation brought it to its large size. Was there the explosion of the Big Bang that was small, and then inflation that took place that made the universe its large size?
  9. Apr 17, 2013 #8
    No there was no bang. Instead its best to think of it as geometric expansion of space time.
    The big bang model does not predicts a singularity that exploded. Although lots of pop media literature will mention a singularity.
    As mentioned above no one knows what occured prior to 10-43 seconds. Marcus and I provided two lines of research into answering that question. My view is in regards to the history of the big bang model. The models I mentioned has to do with the inflatonary "universe from nothing" model supported by Lawrence R Krauss.
    In Marcus example he is describing a bounce cosmology, which is essentially a cyclic universe model. Needless to say he is far more familiar than I on LQG

    To be honest with you I never could understand where the singularity idea came from in our literature. As the false vacuum model is the earliest form of the inflationary model. It does not describe a singularity beginning. As I mentioned later inflationary models derive from the false vacuum model.

    this link provides an explanation of false vacuum.


    the link I provided above on epochs is incorrect here is the corrected link


    edit: most likely the singularity idea got stuck in historically sometime between the steady state model and the inflationary model in 1980 when Guths work first came out, either way its a relic concept that confuses people in understanding the big bang model.
    Last edited: Apr 17, 2013
  10. Apr 17, 2013 #9


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    Tim, how about you start talking about the currently OBSERVABLE PORTION of the universe. We don't know how big the whole thing is so it gets kind of vague when you try to talk about its size.
    But we can reckon the size of the portion we're currently able to observe.

    Inflation, if it happened, occurred sometime during the first second after the start of expansion. After inflation ended (if it actually occurred) the observable portion was still quite small compared with today.

    After that first fraction of a second of inflation, the universe settled down into normal ordinary expansion mode. In terms of miles or cubic lightyears or whatever, that ordinary expansion is responsible for most of the observed size and is still going on. The portion we can observe and reckon the size of is now thousands of times bigger than it was when inflation ended.
    (Thousands of times bigger is actually a considerable understatement.)

    "Inflation" has a technical meaning. It is a special technical KIND of expansion that may or may not have happened. It would have needed a special, temporary, mechanism that was exhausted after a short spurt. There are lots of good reasons to suspect it happened but we don't know for sure that it did.

    In any case the portion we can judge the size of is now thousands of times bigger than it was after inflation ended and that is an UNDERSTATEMENT.

    Does that help to answer your question?

    Would you like some actual numbers? We can give you some numbers if you wish, like the current radius of the observable part, or the estimated radius as of year 378,000. (there's fairly good information about that.)

    Inflation didn't contribute much in terms of gross overall size. But that very early expansion was very important, so if it happened inflation would have played a really important role! It matters how that initial burst of expansion occurred. Early growth stages, embryo universe time so to speak, can be very important even if the linear size scale is puny.


    You were also asking about something else, "bang" and "existence"...Would you like to try rewording you question about that?
    I agree with what Mordy said, that we have no reason to believe existence began with the start of expansion. The expansion we see around us must have started some time, with things in a very high density state. But the universe could have been doing something else before that. It could have existed in a contracting mode, or some other way. The expansion has certainly contributed enormously to the SIZE, but size is not the same as existence. Maybe it always existed. That's more philosophical.

    Expansion cosmology was christened "big bang" by an enemy of the theory named Fred Hoyle. It is is both contemptuous and misleading. It has damaged the public's understanding by giving people the mental picture of an explosion from a central point outwards into empty space. That is definitely NOT what expansion cosmology is about. Hoyle had a rival theory...
    EDIT: some unfair words about Fred Hoyle deleted (because of something Mordy wisely pointed out in the next post)
    Mordy thanks for the reminder of Hoyles good work in other areas.
    Last edited: Apr 17, 2013
  11. Apr 17, 2013 #10
    I've studied a bit on Fred Hoyle, he is after all a major contributor of stellar nucleosynthesis. This is not to be confused with big bang nucleosynthesis. stellar nucleosynthesis deals with element formation in stars. So to say his work is forgotten is not quite accurate. Unfortunately his cosmology model he supported was the steady state model. Even though Freidmann and Hubble showed that its not he was determined to find a steady state solution to explain why galaxies were getting further apart. His argument was that matter and not space was being created between galaxies.
    Its funny though that he had no objections to either Hubble or Friedmann, he simply did not like Guth's inflationary model, as according to his biography articles he felt it delved away from true science into the realm of pseudoscience. Sort of like some of todays arguments lol
  12. Apr 17, 2013 #11
    All right, thank you both! I deeply appreciate your explanations.
  13. Apr 17, 2013 #12


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    That is funny given that de Sitter inflation is precisely a Hoyle steady state model.
  14. Apr 18, 2013 #13


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    Hi bapowell,
    to be fair I have to correct something I said. Fred Hoyle claimed that when he introduced the term "big bang" in a BBC broadcast in 1949 it was NOT derogatory, it was intended to help the public understand the expanding universe model. Here is the other side of the story, from a Wikipedia article:
    "...Hoyle was a strong critic of the Big Bang. He is responsible for coining the term "Big Bang" on BBC radio's Third Programme broadcast at 1830 GMT on 28 March 1949. It is popularly reported that Hoyle intended this to be pejorative, but the script from which he read aloud shows that he intended the expression to help his listeners.[8] Hoyle explicitly denied that he was being insulting and said it was just a striking image meant to emphasize the difference between the two theories for the radio audience.[9]"

    I can't tell the spirit in which the term was coined and used---whatever his intent was, the term stuck.
    Last edited: Apr 18, 2013
  15. Apr 18, 2013 #14
    lol the history of cosmology is oft a funny convoluted evolution. In order to truly relate to any concordance
    model one must understand its
    history. However convoluted that research leads
  16. Apr 18, 2013 #15


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    I don't understand the points you're trying to make here. The notion of a singularity in the big bang cosmology is simple: the universe is described as expanding from a state that was much hotter and denser in the past. As you wind back the clock, the universe gets hotter and hotter, and more and more dense. On winding back far enough, you arrive at an initial point with infinite density: this is the initial singularity. Big bang models with an initial phase of inflation still suffer from this initial singularity.

    Now, professionals take this singularity as not something physical, but merely a warning that our laws of physics break down at that point. This is not surprising: as things get smaller, or of a higher energy, classical physics does not well-describe things, and we need a quantum theory. Since we do not have a quantum theory of gravity, we cannot answer what happens at the initial singularity.

    There are some ideas to extend, or change the established physics to deal with this initial singularity. This is where the bouncing cosmologies that marcus mentioned, or cosmology inspired from string theory, come in. But these are very much in development, and do not form a part of the standard cosmological model. With time, and more research, we hope to be able to answer the problem of what happened at the "beginning" of the universe.
  17. Apr 18, 2013 #16
    LQC is not necessarily cyclic in the sense of an infinite number of cycles. It is like this if and only if dark energy turns out not to be constant but is dynamical. If it can change then we could entertain the big crunch again and that would result in a singularity in classical GR that is replaced by a bounce in LQG. But if dark energy turns out to be a cosmological constant which the data currently currently supports then our universe will not recollapse and there will be no more cycles (there may or may not have been cycles in the past contracting universe).
    There are of course other models that are cyclic. Penose has one, Steindhardt has one etc.

    We know the big bang happened if you mean by the phrase "big bang" the universe began to expand just under 14 bio year ago. However what caused the universe to expand. There are many different models. Bouncing cosmologies seem to be making a comeback If you would like to see a short survey of some of these ideas, try watching this:
  18. Apr 18, 2013 #17
    Your descriptive above is 100% correct christco. The problem lies with naming that point where the maths break down as a singularity. The term singularity almost automatically paints the picture of some form of BH. That exploded.
    How much literature have we all seen stating everything started from some infinitely hot dense god particle?
    Instead of simply a hot dense state.
    How many times do we see the question.
    If the universe is always infinite size how did we start from a singularity?
    Or other related questions concerning the BB singularity.
    describing the point where the
    maths breaks down in that hot
    dense state as a singularity is
    incredibly misleading
    Last edited: Apr 18, 2013
  19. Apr 18, 2013 #18


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    I don't follow this. It is technically a singularity.
  20. Apr 18, 2013 #19


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    This is just a side-comment about language (don't let it interrupt substantive discussion). One traditional meaning of "singularity" is oddity, peculiarity. A "singular" occurrence is not a regular one.

    So the word was taken over into mathematics to refer to a mathematical formula blowing up or breaking down or for some reason failing to give meaningful numbers. And thence into mathematical sciences like physics.

    It doesn't mean "point". But when people hear the word "singularity" they sometimes get the mental image of a point, because a point is "single".
    So this reinforces the misconception of the "big bang" as an explosion from a "single point" outwards into empty space.

    The classical cosmological singularity (which refers to the failure at start of expansion of a classical vintage 1915 model which otherwise does remarkably well) is misconceived as being a tiny dense pellet or bean which exploded. This is not what "big bang theory" (standard model expansion cosmology) is about. It is a misconception caused in part by the sound, not the meaning, of the word "singularity".
  21. Apr 18, 2013 #20
    Singularity defined as a breakdown I can accept.
    I was out doing field work so could not respond earlier thanks Marcus for your post
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