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Penrose, Carroll, and Inflation

  1. Jun 13, 2007 #1

    George Jones

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    Without inflation, only extremely special conditions in the past produce the universe we now see. Or so the story goes.

    Penrose has long argued that conditions necessary for inflation are actually more special that the necessary past conditions without inflation. Its seems that Sean Carroll agrees with this (slides 15 and 16). Carroll seems to prefer a multiverse explanation over inflation.

    I think, however, that Penrose (nay) and Carroll (yeah) disagree on the likelihood that inflation happened, and that Penrose's position is quite non-standard. Note that the questions of 1) the specialness of necessary conditions for inflation and 2) physical evidence that inflation occurred, are quite different. Also note that in his GR book, Carroll does not mention that special conditions are necessary for inflation, so maybe:

    I have misinterpreted Carroll;
    Carroll has thought about this since writing his GR book;
    Carroll thought that this was a little too speculative for his GR book;
    or ..., etc.
     
    Last edited: Dec 14, 2009
  2. jcsd
  3. Jun 13, 2007 #2
    Great link! good call George! I read that when it was posted a few days ago. I have been really meaning to have a discussion of time's arrow on this forum and what we know and do now know.

    I don't totally understand Sean's talk.
    First, it would be great if someone could write a quick summary about the arrow of time and how that relates to entropy as well as gravitational attraction(tends to clump things together-> decreasing entropy?)
    second, what does it mean to for the equations of physics to be time symmetric?
    then, how is the arrow of time related to the multiverse theory?
    Does the multiverse explain the arrow of time in a way inflation cant'?
    what are the advantages and disadvantages?

    i'm just trying to get a good post going about this, i feel, important issue.

    thanks
     
    Last edited: Jun 13, 2007
  4. Jun 13, 2007 #3

    marcus

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    that's a very interesting talk, George. thanks for flagging it.
    the picture he ends up with has remarkable similarity the picture underlying Smolin CNS hypothesis----with universes like ours budding as baby universes and pinching off from within the event horizon of a prior black hole (which then evaporates).

    as I see it, the most consequential difference between Carroll's and Smolin's pictures is that the latter allows slight changes in the fundamental parameters of physics to occur during the bounce that creates the new universe----so in Smolin's picture the fundamental constants of physics can evolve in ways promoting higher reproductive rate. From this he is able to derive a testable hypothesis, namely that the fundamental constants are locally optimized for reproduction.

    BTW around slide 20, the top statement on the slide, which he highlights red, is
    In particular, we’re assuming that quantum gravity will ultimately teach us how to resolve all singularities.

    http://preposterousuniverse.com/talks/time-colloq-07/
    I think there's an increasing awareness among ordinary cosmologists and relativists of the progress in quantum gravity and of current exploration of ways to resolve some key singuarities that occur in the classical GR context. I am glad that Carroll took the trouble to make that assumption explicit.
     
    Last edited: Jun 13, 2007
  5. Jun 14, 2007 #4

    I thought Inflation included a multiverse, i.e. that one of the strongest arguments for a multiverse actually was inflation? The way I see it, the biggest difference between Chaotic Inflation and the CNS hypothesis is that in Chaotic Inflation, the universes (or pocket universes) are created through quantum fluctuations, while in the CNS hypothesis, the universes are created through black holes?

    Something I have misunderstood here?
    Interesting subject though. :wink:
     
  6. Jun 14, 2007 #5
    I can't understand why those fantasies remind me of the ancient people that thought the Earth was flat and carried by two big whales ... or was it elephants ? lol
     
    Last edited: Jun 14, 2007
  7. Jun 14, 2007 #6

    Wallace

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    Interesting. I really wonder though if we will ever be able to say with any certainty that any of this has merit scientifically. Still history is littered with ill-conceived quotes such as:

    'Heavier than air flying machines are impossible' (Lord Kelvin)

    and

    'We are probably nearing the limit of all we can know about astronomy' (Simon Newcomb 1888 )

    so who knows what we can discover in the future.

    One comment I'd make is that science always seems hellbent on making the Universe infinitely old, almost as if we want to rid the religious of any opportunity to slot God in at t=0. The Big Bang has been thoroughly opposed since it's proposal on these aesthetic grounds. Now that the evidence for the Big Bang seems overwhelming (note I'm speaking very generally here, not taking 'the Big Bang' to neccessarily include inflation, DE etc) the race is on to show how a Universe containing a Big Bang can be part of an infinitely old picture.
     
  8. Jun 14, 2007 #7

    marcus

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    Newton's universe was infinitely old, yet he was a devout man.
    IIRC he considered his spacetime (euclidean R4, essentially) to be the Sensorium Dei
    that is, the absolute spacetime was a feature of God's mind in which God "thought" the universe.

    in a religious vision spacetime can extend infinitely backandforward and space extend infinitely in all six directions and yet the Creator be outside
    This was surely understandable to someone in the 17th century, contemporary with Newton. And I think we all realize this.

    I think the scientific impulse to get a better model that you can crank back with farther into the past, without its breaking down, is neutral from a religious standpoint.

    religious objections, if any, I would imagine to be based on a naive or imperfect understanding of theology----and perhaps of currently popularized scientific models as well

    does any theist here actually believe that his God needs a "slot" at t=0?

    I think Wallace you were smiling when you said that.
     
    Last edited: Jun 14, 2007
  9. Jun 14, 2007 #8

    marcus

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    I agree. that kind of inflation making an eternal branching tree-like bunch of universes---however you call it---is very similar to the picture underlying CNS.

    I dont think you misunderstood anything. I agree it is interesting. I don't much like Carroll's picture but some of the thermodynamic arguments he supports it with are fascinating and (to me) instructive.

    he is actually making even stronger arguments for Smolin CNS model (which he fails to discuss), where the new universe is started by a black hole instead of an extremely unlikely quantum burp.

    I think it is really interesting that Carroll's "universes like ours" appear to be spatially finite. (because the patch giving rise to them is finite, also see his slide showing the baby "pinching off" from the mama).

    I think spatial finite is coming into fashion among cosmologists, which basically means a bumpy 3-sphere. at least as a seriously considered possibility.

    Martin Bojowald has a new paper on arxiv (The Dark Side...) where he avoids the need for dark energy. Shows he can get acceleration out of Loop Cosmology without any additional assumptions, paraphernalia, junk.

    No special dark energy scalar field---just the already present matter including dark matter.

    It may turn out the need for an "inflaton" can also be avoided (to some extent early inflation is generic without any extra fields or other machinery) which conceivably could make the various "Inflation Scenarios" moot.

    it is an exciting time to be watching. maybe someone will that Carroll's thermodynamics and use it to underpin Smolin's CNS and implement Smolin's picture without fairytale "inflaton" scalar fields---but simply with QG.

    the thing that remain is to check whatever reproductive cosmology (CNS or other) against observation (which is what is stressed in Chapter 20 of the new book Universe or Multiverse published by Cambridge, edited by Bernard Carr. (It has gone on sale but amazon still doesnt have it in stock.)
     
  10. Jun 15, 2007 #9

    Chronos

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    A finite universe is unsettling, as it forces acceptance of the possibility of a creation event. I have no real problem with that scenario. Not because of any religious convictions, merely because 'creation' is at least as plausible as any infinite sequence of causal events. So why dodge the issue by playing the multiverse card [which is inherently impossible to prove or disprove]?
     
  11. Jun 15, 2007 #10

    Wallace

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    The argument from first cause is very commonly used by those attempting the futile exercise of logically proving the existence of God (note that the inverse problem is equally futile), so I wouldn't dismiss the God at t=0 idea too quickly.


    I'm always smiling :smile:
     
  12. Jun 15, 2007 #11

    Garth

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    As others have introduced the concept of the Deity may I make a comment?

    First, you cannot prove the existence of God - although an individual believer may have subjective experience of a divine presence they always have to take that interpretation of their experience as a matter of faith.

    But note I would also understand it to be the case that to take the opposite interpretation is also a matter of faith, it cannot be proven either way.

    Belief in God does not depend on there being a 'beginning', as most definitions think of God as 'eternal' so too could the creation be.

    One question that has been asked is, "What is it that breathes fire into the equations and makes a universe for them to describe?" (Stephen Hawking)
    Some may answer this question as a theist or otherwise.

    Garth
     
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