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What is the more puzzling our universe with inflation or without it?

  1. Oct 20, 2009 #1
    Hi all,
    I know that inflation solves shortcomings of Standard big bang cosmology, but doesn't intoducing inflation puts us in another puzzle , what is the mechanism which is responsible for inflation?
    I mean what is the more puzzling our universe with inflation or without it?
  2. jcsd
  3. Oct 20, 2009 #2
    Based on GR, universe can not be static.
    2nd law of thermodynamics tells the same - just for different reasons.
    So there is no surprise... at least for me...

    There are other, much more mysterious things.
  4. Oct 20, 2009 #3


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    I take it you are raising the problem of infinite regress. Where do the turtles stop? If it is all turtles, let's restrict it to just one.

    The way I look at it is if we are correct in modelling the development of the universe as a symmetry breaking, then any prior originating state must by definition be a state of higher symmetry. And because symmetry breaking is about the emergence/addition of constraints in a system. going the other way in cosmological modellling would be a loss of constraints, the subtraction of constraints, that might restore a greater symmetry.

    So inflation would be a "good model" to the extent it removes constraints and restores symmetry. Which it does in positing an exponentially-expanding scalar energy field. Yet it also has a clunky feel.

    This would be because it is too much a single scale view. The scalar field would be tied to a particular energy and a particular number of dimensions. So would be still constrained in these ways. A more general theory would be scaleless - generalised or scale-symmetric across energy and dimension.

    So I think inflation can be treated as a model that explores in the right direction by removing some obvious constraints but does not go far enough. It does not arrive at some model of absolute, end-of-the-line, symmetry.

    But to do this, we would need a clear idea of how constraints emerge in systems, so we can then subtract them away in our modelling.

    In terms of turtles, this would be like going backwards from our present state of crisply existent turtle to increasingly vague turtleness. A successive removal of constraints, such as a requirement for four legs, leathery skin, hard shell. But what does the removal of the requirement for four legs mean in practice? Is an "n-legged" turtle more symmetrical for example? Or is it instead a "propulsion-equipped" turtle - so fins, legs, tentacles, wheels, whatever, at its four corners?
  5. Oct 20, 2009 #4

    It's all motivated by observation. If you can think of a more elegant way of fixing the observational issues that led people to assume cosmic inflation or some way of explaining the data without assuming inflation then feel free to chime in.

    The trouble is that without inflation you have to assume about five crazy things have to happen to explain the various puzzles that we see. With inflation you replace five crazy things with only one crazy thing. Getting things to the point where you have to assume only one crazy thing is quite an accomplishment.
  6. Oct 21, 2009 #5


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    Our universe could be the result of an infinite number of superimposed states. I agree we have reduced it to a more manageable number of logical states.
  7. Oct 23, 2009 #6

    A universe with Time and an arrow of time and comprehending beings in it is puzzling enough. Inflation is a very small puzzle compared to the grandeur of the other Bigger puzzles.

    When we find out this and other little "details", it's likely that we will attempt to create another universe through a Big Bang. Perhaps, billions of years from now, some intelligent creature will look to the sky at night and pray to "god".
    Last edited: Oct 23, 2009
  8. Oct 23, 2009 #7
    I believe inflation is directly proportional to the USD and the funding thus resulting has directly effected the outcome of such research. When i have more time I shall graph it out.
  9. Oct 24, 2009 #8
    I dont find anything strange with time and arrow of time (the direction of arrow of time is defined by the BB). CP violation, resulting in T-symmetry violation, or the "microscopic arrow of time" is much more puzzling.
  10. Oct 24, 2009 #9

    There has never been a Big Bang for a photon emitted at what we define to be a Big Bang. Moreover, there is no mechanism in the physical laws that separates one now from the next. And there is no law that requires time to move in one direction and not the other. The Delayed Choice Experiment and Eraser is even more troubling for the enquiring mind.
  11. Oct 24, 2009 #10
    Delayed choice experiment is trivial if you dont require a realism.

    Time does not move, it is an illusion.
    Physical laws do not contain the definition of NOW, I think that the notion of 'NOW' emerges at the level of consciousness.
  12. Oct 24, 2009 #11

    It seems like all roads lead to a more or less similar conclusion. But if time is an illusion, then everything is an illusion. Existence requires a properly defined time scale and if the time scale is an illusion, so is existence as we perceive it. Ever since i was 9 years old, i've always had this weird feeling there was something very wrong with reality. The poor kid in me had no idea the greatest minds were trying to recover realism from a state of coma.
  13. Oct 24, 2009 #12
    No. We live in a world with 3 spacial dimensions and 1 time dimension (3S+1T)
    You can imagine a laws in some universe with say 3S+2T. it would be quite interesting.

    Also, you can imagine a uiverse 4S+0t - Universe without time. Of course, you can say that such universe is static and can not contain any 'creatures'. But what is a difference between 3S+1T and 4S? If we look at OUR universe from the bird's view (seeing the all spacetime at once) it also looks static.

    Time is special because entropy increases in some direction of time, allowing to structures to have MEMORY. If in 4D Universe without time there is a direction in space where chaos increases, then that direction can be perceived as time, even it is not.
  14. Oct 24, 2009 #13

    I don't agree about the static universe, it has to be purely informational. A static universe can never behave like our universe where everything(time, mass, distance) is relative. The only universe that fits the description and the laws of physics as we know them is an informational one. A static universe cannot behave according to the equations of GR.

    I think it's not a good idea to define time with entropy and then entropy with time. It looks like circular reasoning.

    What do you mean by chaos in a static universe? Can you give a reference?
    Last edited: Oct 24, 2009
  15. Oct 24, 2009 #14
    But our Universe IS static.
    Look at spacetime from the 'outside'
    It is called 'eternalism'
    And BTW only eternalism can explain the behavior of the matter inside Closed timelike loops

    Entropy defines ARROW of time, not time

    Here is an example:


    The picture above is static. But it becomes more and more chaotic if you move from the top to bottom.
  16. Oct 24, 2009 #15


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    This doesn't work as you are in fact requiring a time-like motion to "see" this fact. I could instead say read this pattern by jumping randomly about it, rather than moving from start to finish. And a "timeless" reading would be to average over the whole pattern at once (a non-local act).

    The only way to get spacetime straight, I believe, is to understand that it is a dichotomisation. We are separating existence in two contrasting directions. Into its locations and its "space" of changes. We are looking for what does not change - constraining existence to locales, spatial co-ordinates - and then providing a global metric for the changes the locales then construct. The local freedoms of action that can still be expressed.

    In the Newtonian system, these freedoms were inertial - straight lines. And deterministic. The global backdrop of time was constructed accordingly. Giving us a block time view, a globally symmetric arrow of time.

    Then different physical models - which still need to dichotomise change from lack of change - all do it somewhat differently. So we have GR as modified newtonian view - one that more correctly pins itself to c, instead of "massive particles at rest". QM dichotomised further into local vs nonlocal aspects of locality, and intruding uncertainty at the extemes of scale. Then thermodynamics as yet another wrinkle, one where time gains an asymmetry at the global scale because it has a memory, a history.

    Cosmology adds even further concrete constraints to the modelling - wiring in expansion and cooling as features of the local stasis~global change dichotomy.

    We actually have a clashing collection of models of space~time, or stasis~change. The way to unify them would seem to be to generalise, to reduce the features of the many to some deeper level of description. So instead of worrying about the true nature of time (or indeed space) we need to worry about the true definition of change (and stasis).

    Your illustration of a set of bits makes the usual mistake of wanting to treat one aspect of things as real, the other an illusion. So locality, stasis, is real for you, therefore time or the global motion of the reader is an illusion - or same thing, emergent.

    The big change in thinking is instead to see that the dichotomising of reality is what is real. The effort of separating. So it is how this symmetry breaking occurs that we want to understand. The static part of reality can only exist to the extent it separates itself off from the realm of change. And likewise, the realm of change develops from all the local actions that happen, and equally, all the actions that could have happened but didn't. The causal light cone view.

    Existence is created by a process of separation, of symmetry breaking. And a good way to model that is by measuring all that did not change against all that could have changed. And put that way, it should be clear that neither aspect of what happened, what emerged (the space or the time) is illusory.
  17. Oct 24, 2009 #16
    This is not how we define "static". In a static universe, there is a timelike killing vector that satisfies the Frobenius condition. This is not the case for a Robertson-Walker universe.
  18. Oct 25, 2009 #17

    There is likely nothing to be seen from the 'outside'.
    The Delayed choice experiment on cosmological scales emphasizes the inadequacy of our assumptions of time and space. It's as if these notions don't exist at all at a sub level of reality. It really seems that we know nothing.
  19. Oct 25, 2009 #18
    1 'Outside' = so called 'birds view'. The same when you draw spacetime diagrams with lightcones

    2 What is a difference between the Delayed Choice experiment on the laboratory and cosmological scale?
  20. Oct 25, 2009 #19
    What are the chances that Inflation, taking place once or even twice, is just a 'fudge factor' that is used because of our imperfect BB model, and not a real event?
  21. Oct 25, 2009 #20

    Yes, i know what you mean. There are good hints coming from relativity, qm and cosmology that the universe does not exist when seen through a sort of god's view.

    Billions of years of time and billions of light years of distance obliterated as if they meant absolutely nothing. Do these numbers actually mean anything at all? Or are they just digits interpreted by a mind to mean what we assume them to mean?

    I don't think Wheeler got crazy in his last years. Or else, i am crazy too, along with a few other top physicsts.
  22. Oct 25, 2009 #21

    That would depend on which camp you are in. In the above scenario, you'd be in a very small minority, which shouldn't discourage you too much. Few things are absolutely certain in the current understanding of the Big Bang model.
  23. Oct 25, 2009 #22


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    It seems essential to take this aspect of QM seriously and then move on to the consequences.

    A way to make it seem less crazy is to then separate what happens betwee two locales (two particles exchanging a photon over nearly the age of the universe, from distant star to your eyeball) from the global ambience being knit by an averaging over all such events.

    So take a Cramer retrocausality seriously - time is symmetric at the level of individual events. But an asymmetric arrow of time emerges at the level of globally developing (expanding and cooling) cosmological history.

    The trick is in the averaging. Events spanning such great distances, like stars at the edge of the visible universe and your eyeball, are rare compared to the bulk of photon exchanges which will happen at much shorter spatiotemporal separations.

    So the bulk that forms the prevailing ambience - the classical way things look - is quite a dense clump of congealed events. Then photons that cross the whole visible universe are rare outliers that play out against this already existing ambience. They are quantumly averaging themselves over something that has already emerged along their way.

    OK, perhaps it still sounds crazy.
  24. Oct 28, 2009 #23
    As far as I have read, nobody really understands what kicked off the big bang ( QM and GR encounter infinities or divergences here) and nobody understands what might have triggered inflation nor just why inflation came to a halt....There are different versions of inflation and Guth's version had to be modified so inflation would stop. So a patch on inflation was required to stop it and both those patches were added to "big bang" because it did not work by itself....It's a bit like the standard model of particle physics, lots of disconnected pieces glued together, so we match observational findings....so far they work but are far from complete...

    In addition, I believe there are still issues of 'fine tuning' inflation theories...

    There are alternatives to big bang/inflation such as the ekpyrotic and other cyclic models.

    Wikipedia has some decent discussions on these issues.

    Roger Penrose in THE ROAD TO REALITY says in 28.5 "Despite the evident popularit of (inflation) I wish to give my own reasons for casting considerable doubt on the entire idea!...there will be few who are as negative as I am....if we want to know why the universe was initially so very,very special, in its extraordinary uniformity, we must appeal to completely different arguments....."
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