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60 efolds with no inflaton, no slow roll, no reheating-QEG's apt to be right

  1. Aug 12, 2007 #1

    marcus

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    60 efolds with no inflaton, no slow roll, no reheating---QEG's apt to be right

    QEG predicts the Einstein-Hilbert action of General Relativity. don't have to put it in by hand
    Starting with zero entropy it predicts the right amount of entropy after inflation.
    (essentially the measured CMB entropy)
    It gives 60 efolds of inflation without any exotic matter field---no inflaton needed---just by the natural running of the cosmological constant, also a prediction of the theory.

    Conventional inflation they put in an exotic inflaton, which causes exponential expansion, and then THEY HAVE TO CONCOCT A WAY TO TURN IT OFF, so they fantasize a special "slow roll"---a way for the inflaton to die down, put in by hand. QEG inflation naturally turns itself off as the universe expands. No device is needed to shut QEG's natural inflation down.

    In conventional inflation scenarios they have to put in some device to "reheat" after inflation. The exotic "inflaton" field has to somehow decay so as to produce a lot of energetic matter. Another device put in by hand. QEG does not require any artificial "reheating" arrangement. The running of Lambda predicted by the theory transfers the required energy to whatever matter is present.

    THIS IS AN OCCAM THING. ONE SIMPLE RG FLOW EQUATION DOES EVERYTHING. The Renormalization Group flow equation gets you Einstein Hilbert action, bare values for G and Lambda, and tells how G and Lambda change with scale---so how they run during the early universe. And provides a long classical period during which they are constant, fit to observed values.

    I think this paper changes the picture in cosmology. It lets you throw out a lot of junk put in by hand (Guth, Linde, Vilenkin etc) and one thing, which it looks like Nature is providing us, covers all the bases. Maybe you'd like to discuss the paper:

    http://arxiv.org/abs/0706.0174
    Entropy signature of the running cosmological constant
    Alfio Bonanno, Martin Reuter
    57 pages, 7 figures
    (Submitted on 1 Jun 2007 (v1), last revised 3 Jun 2007 (this version, v2))

    "Renormalization group (RG) improved cosmologies based upon a RG trajectory of Quantum Einstein Gravity (QEG) with realistic parameter values are investigated using a system of cosmological evolution equations which allows for an unrestricted energy exchange between the vacuum and the matter sector. It is demonstrated that the scale dependence of the gravitational parameters, the cosmological constant in particular, leads to an entropy production in the matter system. The picture emerges that the Universe started out from a state of vanishing entropy, and that the radiation entropy observed today is essentially due to the coarse graining (RG flow) in the quantum gravity sector which is related to the expansion of the Universe. Furthermore, the RG improved field equations are shown to possess solutions with an epoch of power law inflation immediately after the initial singularity. The inflation is driven by the cosmological constant and ends automatically once the RG running has reduced the vacuum energy to the level of the matter energy density."
     
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  3. Aug 12, 2007 #2

    Wallace

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    Nothing put in by hand hey? I think not!

    The problem with using the mythical 'Occam's Razor' approach in the way you keep suggesting marcus is that it comes down to an individuals own subjective judgment of which theory is more 'simple' in some ill defined way.

    The are a range of issues with Big Bang cosmology that need something special to occur in the early universe, this is inflation or something similar. Having realised this something needs to be put into the theory to provide a mechanism for this. This could be an inflaton field or some other mechanism such as that which you point to here. However it is achieved in some theory it is equally 'put in by hand'. You seem to like this phrase but I wouldn't mind seeing how exactly you define this. Did Newton put gravity in 'by hand' to explain Kepler's laws for instance?
     
  4. Aug 12, 2007 #3

    marcus

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    You will see what I mean if you read the paper, Wallace.

    there is a long outstanding problem of making gravity renormalizable.
    he takes a minimalist, barebones approach
    keeps the metric as the carrier of degrees of freedom, as in Einstein's original theory changes as little as possible, puts in as little as possible
    and succeeds.
    the conservatism is not MY subjective impression---it characterizes Reuter's approach and he articulates it. You just have to read the paper, if you want to discuss it.

    Reuter has carried out a program to renormalize gravity which was started by Steven Weinberg in 1979 (but Weinberg got stuck).
    HAVING RENORMALIZED GRAVITY HE GETS ALL THIS OTHER STUFF FREE.

    What shows the approach is good is its economy.

    When you read the paper he will point out to you where he is not putting in anything by hand----those are not my words.
     
  5. Aug 12, 2007 #4

    Chronos

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    The problem with rejecting inflation is it takes us back about 40 years to a time where many complicated and related issues were resolved by the inflationary model. Any substitute for the inflationary model needs to readdress these issue. I perceive, in this paper, Reuter realizes he has not yet conquered this mountain, and I look forward to his future works. I admire marcus's enthusiasm, but side with Wallace on the side of temperance.
     
  6. Aug 12, 2007 #5

    marcus

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    You haven't paid attention, Chronos. Reuter's model gets 60 e-folds of inflation---as much inflation, and as quickly, as anybody elses.

    I don't know how you got the notion that he is "rejecting inflation".

    So all the puzzles which inflation was originally devised to address are nicely taken care of by Reuter using just the one mechanism (the RG flow) which is a standard tool from QFT.

    Renormalization (with running coupling constants) is how they take care of infinities in QED and QCD.

    Reuter does not take anyone back 40 years (and certainly does not reject inflation :biggrin: )

    YOU would take us back OVER 40 years if you would deny him the use of the renomalization group.

    What he does is he uses that one tried and true method from standard QFT, gets it to work on gravity, and then he GETS INFLATION FOR FREE
    and is able to throw out the made-up paraphernalia (exotic matter, slow roll, reheating) that people concocted earlier to get inflation scenarios to work, not knowing how else to do it.

    Since you have things backwards, may I assume you are just talking "through your hat" in this case and have not read the paper in question?
     
  7. Aug 13, 2007 #6

    Chronos

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    Marcus, not everyone who disagrees with you is your enemy. I would prefer to chat pleasantly, not argue. There is much about Reuter's paper I do not understand - in particular initial conditions. Blow that smoke away and I will gladly sit up and listen. I know Reuter is not a crackpot, but, he needs to do more to make his idea workable . . . and I think he admits this at the end of his paper. I don't doubt you understand this stuff better than I, marcus, and no offense is intended.
     
  8. Aug 13, 2007 #7

    marcus

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    BTW you might enjoy this review of some lectures by Reuter
    http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_10.html
    It is non-mathematical, exceptionally clear, and has comment from an interested string-thinker Aaron Bergman.

    In no way do I regard you as offensive, my dear Chronos! :smile:
    It is very helpful to have your comments because they permit dialog.
    Far from wishing to offend you, I merely had to point out that your criticism was wacky.

    You implied that Reuter was rejecting inflation (which is a helpful part of the generic picture because it resolves horizon flatness and scaleinvariant structure puzzles). I had to point out that Reuter does nothing of the kind. He does not reject inflation at all! What he does is get rid of the mythological INFLATON.

    Indeed Reuter is the first person I know of to find a natural Occam-friendly MECHANISM for a really adequate inflation era that does not depend on exotic matter
    (exotic matter like the inflaton violate energy conditions and give the universe a lot of energy without saying clearly where it comes from. Reuter SAYS, and he avoids exotica)

    The reason it is Occam-friendly is that he gets all this FREE as a bonus for doing something else----there was the long outstanding problem that traditional metric gravity was NONRENORMALIZABLE. The QFT people tried for decades and couldnt get rid of the infinities. Reuter was simply trying to get rid of the infinities using techniques which work in other QFT contexts. He adapted a technique developed by Wetterich (applied successfully in other matter-type QFT situations)
    So Reuter does not "multiply the entities", he is conservative and uses the tools that are already on the bench.
    He succeeds in doing the renormalization job that everyone wanted done.
    He doesn't ADD anything to the picture. And he gets all this cosmology stuff out FREE.

    Now what I have NOT claimed is that Reuter is RIGHT. I am quite happy if you say "he could be wrong he could be wrong he could be...."
    Because I know that too :smile: This stuff has to be checked by comparing prediction with the actual CMB and galaxy structure that Nature has generated! There is a lot of work to be done!

    All I was saying in my post was that your CRITICISM of Reuter was wrong.
    Hope you are OK with that.

    thanks,

    Marcus
     
    Last edited: Aug 13, 2007
  9. Aug 14, 2007 #8

    Chronos

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    I admire Reuter's work, but agree - I'm not qualified to criticize it. Hell, I didn't even realize I had advanced beyond 'confused'! I perceive Reuter is trying to construct a universe without inflation - at least in the classical sense. Losing the 'inflaton' is no great loss. I never have grasped the need for 'super' particles to mediate spacetime geometry.

    BTW, your patient and considerate reply is appreciated, marcus.
     
  10. Aug 14, 2007 #9
    Last edited: Aug 14, 2007
  11. Aug 16, 2007 #10

    Haelfix

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    Marcus, you realize of course this paper generates a quintessence field, that acts for all intents and purposes just like semiclassical calculations that cosmologists use in their models (which were never designed to derive the field content, that was for the QG black box to deliver).

    There are many, many proposals in QG (whether string theory or other) that 'derives' the inflaton(s), or the quintessence field, or the Branes necessary for the ekyprotic models.

    From a phenemonology point of view, I rather dislike quintessence on general grounds and it was very close to being ruled out by WMAP. There is some parameter space left, but its starting to get a little contrived.
     
  12. Aug 17, 2007 #11

    marcus

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    the authors use a cosmological constant Lambda which is constant throughout space and time-----like the fine structure constant alpha is (normally assumed to be constant)

    the fine structure constant RUNS, i.e. varies with proximity
    if k is the proximity parameter one can write alpha(k)

    just as they write Lambda(k)

    for a particular k, Lambda(k) is the same throughout all space and time.

    I don't think one can think of the fine structure constant as a FIELD. it would be very awkward to do that.

    The authors do not use the term "quintessence" in the technical part of the paper----they use it only on page 52 at the very end, and they say "LIKE a quintessence". In effect, since they are using it as a DUMBED DOWN METAPHOR OR SIMILE to make their conclusion paragraph intuitive to people who have not read the technical part.

    But there is no quintessence field mathematics in the first 51 pages. There is just a cosmological constant Lambda(k).

    For any particular k (energy or proximity) one can get a particular Lambda(k) and one can find a "dark energy equivalent". So for intuitive purposes one can think of the Lambda(k) as a dark energy field. But it is not a real physical field and that would be an unfortunate way to think of it because it varies with proximity, not with time.

    WMAP data favors the equation of state w = -1 and therefore favors Bonanno and Reuter, since they are talking about the cosmo constant Lambda. w = -1 is what characterizes the cosmo constant.

    =================

    Haelfix, I don't see how you could have read the paper and make the above statement :smile: Perhaps you read the conclusions paragraph on page 52 and jumped to a false conclusion? Please read the paper.

    In case anyone doesn't know what a quintessence field is here's the Wikipedia article.
    http://en.wikipedia.org/wiki/Quintessence_(physics)
    ==quote==
    Quintessence (physics)

    In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. Quintessence is a scalar field which has an equation of state (relating its pressure p and density ρ) of p = wρ, where w is less than -1/3. Quintessence is dynamic, and generally has a density and equation of state that varies through time and space. By contrast, a cosmological constant is static, with a fixed energy density and w = −1.

    Many models of quintessence have a tracker behavior, which partly solves the cosmological constant problem. In these models, the quintessence field has a density which closely tracks (but is less than) the radiation density until matter-radiation equality, which triggers quintessence to start having characteristics similar to dark energy, eventually dominating the universe. This naturally sets the low scale of the dark energy.

    Some special cases of quintessence are phantom energy, in which w < −1, and k-essence (short for kinetic quintessence) which has a non-standard form of kinetic energy.

    The name comes from the Classical elements of the ancient Greeks, where a pure "fifth element," the aether, was thought to fill the Universe beyond Earth.
    ==endquote==

    quintessence is a field that varies thru time and space,
    by contrast, Bonanno and Reuter's
    Lambda(k) is static, with a fixed energy density and fixed w = -1
     
    Last edited: Aug 17, 2007
  13. Aug 17, 2007 #12

    marcus

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    Just had to quote this :smile:

     
  14. Aug 17, 2007 #13

    Haelfix

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    Eh? If their CC runs, it acts for all intents and purposes like quintessence. Of course there is time dependance, they use lambda(k) where k is an energy scale that is a function of spacetime, they even make the time dependance explicit on page 12,15 by some cutoff.

    I didn't read the conclusion at all, I flipped through the paper (and actually I just read the conclusion and they say exactly what I am telling you now :p ). They are talking about cosmologies with decaying CC, and they even link papers that discuss FRW models with quintessence.

    This paper isn't interested in the exact model building of quintessence, rather its a derivation from Reuters first principles of the consequences of a running RG enhanced CC. He 'derives' if you will from quantum principles a semiclassical solution with fixed boundary conditions of one class of quintessence (one that happens to be studied a lot actually). The only thing he can't pin down, is the regime when the RG flow approaches a singularity, so there you are back to model building by hand.
     
  15. Aug 17, 2007 #14

    marcus

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    not a quintessence
    for YOUR "intents and purposes", if you can't see the difference, but not for mine :smile:
     
  16. Aug 17, 2007 #15

    Haelfix

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    This is very silly, maybe you call a time varying cosmological constant something different, but I call it quintessence, and so does everyone else including the authors of the paper.
     
  17. Aug 17, 2007 #16

    marcus

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    their cosmological constant Lambda(k) is not time varying, and they do not call it a quintessence field except metaphorically

    they say it acts LIKE a quintessence field, when you plug a time-varying k(t) into it.

    however that is a solution, corresponding to the scalefactor of the universe a(t).

    they do not get to pick k(t) by hand and the result of pluging it in just gives an approximate result.

    The important point is that they arrived at Lambda(k) (actually back in 2001 or earlier) WITHOUT ANY COSMOLOGICAL CONSIDERATIONS, by studying the renormalization group flow (RG flow) for gravity.

    I have put a picture of the RG flow for gravity (Einstein-Hilbert projection of the infinite dimensional space of actions) as my avatar. You can see the fixed point, which shows how gravity is renormalizable, as a kind of whirlpool curl. This gives the limit as k --> infty.

    Letting k go to infty gets you the "bare" values of G and Lambda---their values at the bigbang time.

    IIRC after the observable universe is a few centimeters wide, G and Lambda no longer change. They are for all practical purposes CONSTANT at their present classical values.

    Anyone who wants to learn about the RG flow for gravity can find the original figure of the RG flow in
    http://arxiv.org/hep-th/0110054.

    The point is that the RG flow and its fixed point is something physical in nature which they DISCOVERED (rather than making up to fit some astronomical data). Once they discovered it, they were able to get inflation FOR FREE, without adding any assumptions, extra dimensions, junk, imaginary structure.
    They just took what was already commonplace in QFT (running constants), added NOTHING, found the fixed point that renormalizes gravity, and get all the rest putting nothing in by hand

    I wouldn't be surprised if when Reuter realizes how apt people are to confuse a running constant with a field, that the preprint is revised, before publication, to make clear that Lambda(k) and G(k) are mathematically NOT the same thing as a "quintessence field".

    Again---although I don't expect Haelfix to "get it"---the running constants in their model do not vary with space and time, they vary with the proximity scale parameter k. (and in fact they were found to be essentially constant except for very large k relevant to IIRC around the first second of the big bang.)
     
    Last edited: Aug 17, 2007
  18. Aug 17, 2007 #17

    Haelfix

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    "they say it acts LIKE a quintessence field, when you plug a time-varying k(t) into it."

    Oye, thats exactly the scenario he is running, we are dealing with a cosmological solution here. lambda(K(x)), is a *field*. Generically, no different than any other field.

    "The important point is that they arrived at Lambda(k) (actually back in 2001 or earlier) WITHOUT ANY COSMOLOGICAL CONSIDERATIONS, by studying the renormalization group flow (RG flow) for gravity."

    Yes, I know, I studied the papers long before then actually. One thing, has nothing to do with the other.

    "They are for all practical purposes CONSTANT at their present classical values."

    Just *like* quintessence.

    The point is, he's derived a theory of quintessence. The only difference is his quintessence *field* is a quantum effect, and leads him to derive boundary conditions, whereas the usual one is a *field* thats put in by hand and studied at the semiclassical level.

    Theres nothing mysterious going on, as much as you try to make it seem like there is.
     
  19. Aug 17, 2007 #18

    marcus

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    it pays to not be sloppy with math notation and in particular
    it pays to not confuse mathematical objects which are different

    the renormalization group flow is defined on a space of action functionals ("theory space")

    Lambda(k) is a trajectory of this R.G. flow

    it is not even remotely defined on spacetime:smile:

    a field like a quintessence field, by contrast, is a function defined on spacetime and except in degenerate cases it VARIES with space and time.
    what most people call a quintessence also has equation of state w NOT equal to -1, and indeed w may vary.

    I think it does PF posters a disservice to confuse a RG flow trajectory with a quintessence. They are QUITE different. If I gave you a quintessence field you would have no clue as to how to construct an RG flow trajectory from it.

    So it severely misleads PF posters to dismiss a flow trajectory Lambda(k) which is something deep and not made up, by saying "Oh, that is just a quintessence!"

    That means posters, if they are misled by this, are apt to fail to appreciate the RG flow idea.

    Thanks for the discussion BTW Haelfix. I think your position misguided---apt to mystify anyone who takes you seriously---but the discussion allows us to air some important issues!
     
    Last edited: Aug 17, 2007
  20. Aug 17, 2007 #19

    marcus

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    Readers who want the real underlying nitty-gritty behind this lively discussion should have a look-listen here:
    http://www.matmor.unam.mx/eventos/loops07/talks/PL3/Reuter.pdf
    http://www.matmor.unam.mx/eventos/loops07/talks/PL3/Reuter.mp3

    download the slides (pdf) first and then turn on the audio and scroll thru the slides following the audio point by point. it is really illumniating. the first half is about how they discovered the RG fixed point for gravity, and tested it for a number of years

    then the second half of the talk is about how they have recently been applying it to cosmology and explaining various things---like inflation, and the amount of entropy in the universe. good stuff. :biggrin:

    You will see the picture of the RG flow that I just made my avatar if you look on page 10 of the pdf slides file.
     
    Last edited: Aug 17, 2007
  21. Aug 17, 2007 #20

    Haelfix

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    "it is not even remotely defined on spacetime"

    The only mystifying thing is why you think that, its simply incorrect. You better believe the cosmological constant is defined on spacetime, its true in general relativity, its true in field theory and its true in this case too.

    You do know what the improved renormalization group is right? Its a set of differential equations that generates a method to improve perturbation theory to capture some nonperturbative elements. You essentially are *generating* these elements by the action of these equations (a flow) to the renormalized lagrangian of the theory. Lambda(k) shows up there under Reuters cosmological formalism, and it acts just like any other term in the lagrangian (read its defined on spacetime).
     
    Last edited: Aug 17, 2007
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