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New cosmology - dark energy unnecessary

  1. Mar 24, 2005 #1

    Kea

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    Hello Marcus, selfAdjoint, nightcleaner, Chronos, setAI and others

    I think the following speaks for itself

    Viable exact model universe without dark energy from primordial inflation
    David L. Wiltshire
    http://www.arxiv.org/abs/gr-qc/0503099

    Regards
    Kea :wink:
     
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  3. Mar 24, 2005 #2

    selfAdjoint

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    Aren't those "supersized remant perturbations" being criticized as non causal? How can someting over our light horizon affect us?
     
  4. Mar 25, 2005 #3

    Chronos

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    I have issues with that paper. In particular, the cosmic clock concept. It looks suspiciously like a preferred reference frame.
     
    Last edited: Mar 25, 2005
  5. Mar 25, 2005 #4

    marcus

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    Ive been reading the Wiltshire paper, and also the previous one by Kolb et al that came out 10 days or so (that Wiltshire cites). Cant comment. just trying to picture what Wiltshire's talking about.

    I assume there's been some discussion on SPR, but Ive missed it. I'd be glad to read some lengthier responses by others.
     
  6. Mar 25, 2005 #5

    marcus

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    there is a troubling numerical discrepancy, or something i dont get
    for example typically you see estimates like Omega_matter = 0.27
    and Omega_Lambda = 0.73

    and he has a digit switched around, see for example the caption
    to figure 1 on page 3
    he has Omega_matter = 0.23
    and Omega_Lambda = 0.77

    the 0.23 is the usual estimate for DARK matter, but you have to add 0.04 for observed matter, to get 0.27
    and then conventionally one says Omega_Lambda = 1 - Omega_matter = 1 - 0.27 = 0.73

    so it looks like he has made a careless numerical mistake which, in itself does not affect the qualitative conclusions very much.
    Or is there something I am missing?
     
  7. Mar 26, 2005 #6

    Chronos

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    I thought it was just me. I had a couple of disconnects like that myself.
     
  8. Mar 26, 2005 #7

    marcus

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    I'm inclined to focus on the Kolb et al paper that came out 14 March

    http://arxiv.org/hep-th/0503117
    Primordial inflation explains why the universe is accelerating today
    Edward W. Kolb, Sabino Matarrese, Alessio Notari, Antonio Riotto
    4 pages, one figure
    Report-no: FERMILAB-PUB-05-024-A

    "We propose an explanation for the present accelerated expansion of the universe that does not invoke dark energy or a modification of gravity and is firmly rooted in inflationary cosmology."

    I think the essential ideas are in Kolb et al, and Wiltshire (as I believe he indicates) is picking up the idea from them and calculating some cases. Assuming he first saw the Kolb paper some 10 days ago he has not had much time to revise and correct, so maybe his paper is not in its final form. This does not diminish its value and importance! (but for the time being I'll devote more attention to the predecessor)
     
    Last edited: Mar 26, 2005
  9. Mar 26, 2005 #8

    marcus

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    to oversimplify Kolb et al say look at this 73% which we need to have a flat universe (at large scale)
    we see the universe is flat so we postulate some "dark energy" to be this 73% and fill the hole in our model

    wait! they say, suppose there really is this hole. suppose the universe at very large scale IS on average flat and governed by the regular Friedmann eqn we know and love, but suppose our part of the universe is atypically thinned out so that it is matter-lean by the observed 73%

    suppose a primordial quantum uneven-ness made matter (just before inflation) be unevenly distributed-----so our part got only 27% of its fair share (as we observe there is only 27% enough matter to make the universe flat, yet it is flat)-----and then suppose INFLATION expanded all that so the unevenness is now on an immense scale.

    OK, this is something that seems like it would leave a signature in the CMB and that one could test by analyzing the CMB better. I am not sure about that but it seems to me that one can derive predictions from that and test it and see how it fits. (and also in principle one can wait until the observable universe is bigger and check then too :smile: but that is a long wait)

    so this is probably not some fairytale multiverse untestable pipedream but probably a testable hypothesis one can plug into the regular Friedmann equation and see how it fits-------and it doesnt have any acceleration-producing dark energy so it should actually have a very distinctive look.

    if I have oversimplified too much please anybody give an improved sketch of their idea

    I am going to look and see who Antonio Riotto and Edward Kolb are
     
  10. Mar 26, 2005 #9

    marcus

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    Antonio Riotto has 147 papers going back to 1992
    Edward Kolb has 64 papers going back to 1992

    In 1996 they were both at Fermilab and they wrote several paper together, so their association goes back at least that far

    Kolb is still at Fermilab. Riotto is at INFN-Padua.
    Both have published with some wellknown people whose names
    any of us would recognize. I didnt happen to know of them---their
    names didnt happen to ring a bell for me, which could just be a glitch in
    my memory

    National Institute of Nuclear Physics
    --Istituto Nazionale di Fisica Nucleare-sezione di Padova:
    a branch of INFN connected with the University of Padua

    Notari is at McGill, Matarrese is at INFN-Padua

    ---------------

    We should also plug the University of Canterbury which is where
    David Wiltshire and Kea are :smile:
    I have to admire David Wiltshire---he may not have invented this curious no-dark-energy cosmology, but got on it really fast. it looks like he had a paper carrying out calculations with it within 10 days of Kolb et al posting.
     
    Last edited: Mar 26, 2005
  11. Mar 26, 2005 #10

    marcus

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    the LQG connection with fluffy cosmology

    for me what seems like a nice thing about the no-dark-energy cosmology notion proposed by Tony Riotto and co-authors (note the outrageous use of nickname, it sounds better)

    is the way it fits with Bojowald's quantized Friedmann equation.

    the tony riotto idea is basically standard Freidmann-equation cosmology with inflation----it is rather classical in spirit and doesnt presume a lot of extra dimensions and branes and etc.

    bojowald Loop Quantum Cosmology derives from a quantized version of the Friedmann equation (which then turns into a difference equation and doesnt suffer from the classical singularities)

    so LQC is very close to the cosmological model that cosmologists are used to working with, and has been around since 1922-1924 when Friedmann wrote it

    and a nice thing about LQC is that the quantized Friedmann eqn, now a difference eqn, MAKES INFLATION AUTOMATIC. that is a brief period of inflation with a graceful exit is (as Ganashyam said) "generic". it happens without finetuning the parameters, you get it in LQC over a wide range of choices of the details

    so LQC seems like a good context in which to look at the Tony Riotto idea,
    which depends on a quantum fluctuation affecting the energy density (or density of matter) in an instant right before inflation.
    one might be able to put the quantum geometry together with the
    quantum density fluctuation

    Here is a recent survey of progress so far in LQC
    http://arxiv.org/gr-qc/0503020
    The Early Universe in Loop Quantum Cosmology
    Bojowald
    10 pages

    "Loop quantum cosmology applies techniques derived for a background independent quantization of general relativity to cosmological situations and draws conclusions for the very early universe. Direct implications for the singularity problem as well as phenomenology in the context of inflation or bouncing universes result, which will be reviewed here. The discussion focuses on recent new results for structure formation and generalizations of the methods."

    in this paper the form of the Friedmann eqn appears as eqn (1) and the quantized version appears as (13). there is a brief sketch of how to get from one to the other
     
    Last edited: Mar 26, 2005
  12. Mar 26, 2005 #11

    wolram

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    All of cosmology seems to boil down to percentages, and what is in
    our universes, is dark matter real, is dark energy real? I guess one
    can theorise ad infinitum without concrete figures.
    My guess is that observations are all that is necessary to forecast the
    mass in the U, and any missing mass is due to the primordial energy
    that caused creation, what that is, is what science needs to know, so
    until then guessing games are the norm.
     
  13. Mar 26, 2005 #12

    marcus

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    I see that someone over at SPR just posted this link to a press release

    http://www.fnal.gov/pub/presspass/press_releases/darkenergy_3-16-05.html

    the press item was written by someone in public relations at INFN, in italy.

    Fermilab just copied the INFN release. this confirms the notion that Tony Riotto is the main author here. padova is the homeplate from which this ball has been hit, so to speak

    I am wondering why I havent seen more discussion. I could find essentially nothing on SPR.

    Peter Woit called attention to the Kolb et al paper right around when it came out, IIRC, which would have been around 14 March. I will go back and see if NotEvenWrong blog has some discussion

    yeah, this is just another sign of how cool Peter Woit is
    he blogged this immediately, on 16 March
    http://www.math.columbia.edu/~woit/blog/archives/000169.html


    then Sean Carroll blogged it 22 March
    http://preposterousuniverse.blogspo...erousuniverse_archive.html#111155024666490546

    Peter Woit got 21 comments on his 16 March blog, and Sean got 31 comments on his blog a week later.

    Sean is waving his hands making warning motions about the Kolb et al, which he calls KNMR for the authors' initials. but that is just his gut reaction.
    he linked to this news item in "the Australian" which quoted Michael Turner, also shaking his head
    http://www.theaustralian.news.com.au/common/story_page/0,5744,12633934%5E29098,00.html

    Sean also linked to an article in New Scientists
    http://www.newscientist.com/article.ns?id=dn7167
    this quotes Robert Brandenburger and also Sean himself
    (who says Tony Riotto et al have a good track record, but expresses skepticism)
     
    Last edited: Mar 26, 2005
  14. Mar 26, 2005 #13

    marcus

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    One of the 21 comments in Peter Woits blog about Kolb et al
    was where Alejandro (fellow PF) gave a link to still another
    site, the Cabi blog:
    http://www.mit.edu/people/cabi/blog/2005/03/universe-accelerated-beyond-horizon.html#comments

    seems to be a huge reaction to Kolb et al.
    a good way to get the flavor is to read the 21 comments at Woit's blog.
    eg. someone had lunch with a bunch of cosmologists and that was what they were talking about and he gives an idea of their reaction.

    http://www.math.columbia.edu/~woit/blog/archives/000169.html
     
    Last edited: Mar 26, 2005
  15. Mar 26, 2005 #14

    marcus

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    As I said earlier Sean Carroll blogged it 22 March
    http://preposterousuniverse.blogspo...erousuniverse_archive.html#111155024666490546

    and so far he got 31 comments (mostly about Kolb et al but) some were about WILTSHIRE paper, which is derived from Kolb.

    Here are some comments from Carroll's blog that specifically concern the Wiltshire paper

    ---quote---

    Wiltshire's model (gr-qc/0503099) is just weird. General relativity is a complete theory that doesn't obey Mach's principle; you're not allowed to just add Mach's principle to it. And the business about "true cosmic time" being set by the unobservable background is just not right. Clocks measure the spacetime interval, and you can always calculate it locally.
    Sean, Thu, March 24, 2005 @ 10:52 pm

    Surely the idea with Wiltshire's work is that CMB defines who the isotropic observers are and the CMB (even as we observe it here in our bubble) defines the true surface of homogeneity in the full universe. So when we put ourselves in the frame that gives an isotropic CMB we are putting ourselves in the full cosmic comoving frame.
    Note that Wiltshire has already put out a slightly modified version of his paper after comments from Roy Kerr.
    Andreas, Fri, March 25, 2005 @ 3:35 am

    ---end quote---

    [EDIT] Aside from a couple of comments like this i have seen nothing about Wiltshire. By contrast there is tons of comment about the Kolb et al paper. I want to make clear that the Wiltshire paper, which Kea brought up, is a separate issue for me. what I think is important to form an impression of, and read opinion about, is Kolb et al, which seems in a lot of people's opinion to require comment

    ABOUT THE KOLB ET AL PAPER, [/EDIT]I am beginning to form my own private opinion (which is still kind of on the fence) but still I think it's more my place to register comments by others than contribute my own

    Here are some earlier papers by the authors:

    http://arxiv.org/astro-ph/0410541
    Cosmological influence of super-Hubble perturbations
    Edward W. Kolb, Sabino Matarrese, Alessio Notari, Antonio Riotto
    Four pages, no figures

    http://arxiv.org/hep-ph/0409038
    Effect of inhomogeneities on the expansion rate of the Universe
    Edward W. Kolb, Sabino Matarrese, Alessio Notari, Antonio Riotto
    19 pages, 2 figures Version 2 includes some changes in numerical factors and corrected typos. It is the version accepted for publication in Physical review D
    Journal-ref: Phys.Rev. D71 (2005) 023524
    *
     
    Last edited: Mar 26, 2005
  16. Mar 26, 2005 #15

    Chronos

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    It's not my nature to sit on the fence. I object to absolute time and inserting a Machian interpretation.
     
  17. Mar 26, 2005 #16

    marcus

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    I dont know if you noticed but I am discussing the Kolb et al paper.
    My guess is that David Wiltshire is a postdoc at Canterbury NZ and a colleague of Kea, his paper will be getting plenty of criticism from others and will probably undergo further revision.

    What i would find interesting is if you have any comment specifically directed to the Kolb et al paper.

    this is the one that is getting such a lot of attention in the media and the blogs.

    If you ARE talking about Kolb et al, so that we are not talking at cross purposes, then you may need to help me out: Where, what page, what line, do you find something objectionable in Kolb paper?
    Where exactly do do you find the Mach principle inserted in Kolb et al?
     
    Last edited: Mar 26, 2005
  18. Mar 27, 2005 #17

    Haelfix

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    My take on this is the classical one. Long wave length super fourier modes is nothing new in cosmology, in the bible for graduate students (Peacock) he talks about this at length in the CMB chapter. So in my opinion this is just trying to revitalize an old idea.

    Anyway the usual counter argument about long wave length modes effecting local horizons in a non causal way is that they are distinctive quantum effects, which inflation pushes through superluminally (kinda). Classically you would be right in arguing about causality, but its not so clear in the quantum case (at least to some people). Expectation values can a priori be shown to change. But Caroll is right in another sense, small tensor perturbations tend to preserve their value provided other stress pressure effects are small. An obvious problem again is that there is nothing protecting certain other cherished constants from such effects, and indeed if this scenario is true you would expect it, but I doubt its true, and heres why:

    The fundamental technical issue I have (which I mentioned on Woits blog) is best summarized in chapter 15 of Peacock. Scalar fields are very sensitive to gauge ambiguities in inflationary cosmology. And Kolb explicitly fixes his. This is dangerous because it can obscure obvious problems that might be manifest in a different gauge. The modern approach is to cast your variables in a gauge invariant manner and to explicitly work out the perturbation solutions directly, often with numerical simulation. This paper flat out contradicts those results, and thus I am skeptical.
     
  19. Mar 27, 2005 #18

    marcus

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    Haelfix, thanks for taking the time to comment here, I appreciate it.
    what I think is the crux here (and I wonder if your take on it changes this)
    is their Figure 1.

    Going by Figure 1, their model predicts that SNe Ia with redshift almost out to z = 2 should all be dimmer than expected
    with that effect most pronounced in some range like 0.3 < z < 1.3
    which depends on details

    LambdaCDM with Lambda = 0.7 apparently predicts, again going by their figure 1, that the SNe should be dimmer than expected out to around z = 1.3 and then BRIGHTER than expected.

    the way Kolb et al draw the picture, putting in a couple of extra LambdaCDM cases and intentionally or not blurring the distinction by having so many solid and dashed curves, you may not notice that there is a stark contrast between the kind of acceleration that the Lambda model gets and the kind of acceleration that Kolb et al get.

    so (although not expert enough to judge) i want to see some real SNe data plotted. this might be a source
    http://arxiv.org/abs/astro-ph/9906463
    this is the article in Science by Steinhardt and others that Kolb cites as their reference [1] "for a review of the observational evidence for the acceleration of the expansion....see, e.g...."

    I have a notion that one might be able to exclude Kolb et al simply on grounds of giving a bad fit to the supernovae! So I am going to take a look at the Science article

    [EDIT] Rats! the Science article has colorful graphically stunning figures that I cant interpret and compare with Figure 1. What I need is a better article about the SNe data[/EDIT]
     
    Last edited: Mar 27, 2005
  20. Mar 27, 2005 #19

    marcus

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    Yeah, look
    http://www.astro.ucla.edu/~wright/sne_cosmology.html

    about halfway down the page there is a plot like Kolb figure 1
    that has real data on it as well as theoretical curves
    and you can see that the SNe have to be brighter for around z>1.3

    Kolb doesnt get that. it is a quite noticeable bad fit.

    this ned wright plot is dated July 2003 and he gives his source

    ---quote from Ned Wright---
    The data points on the above plot are from my binning of the Tonry et al. data table. The binned normal points are
    <z> d(DM) sigma
    0.0051 -0.228 0.174
    0.0105 -0.050 0.088
    0.0169 -0.026 0.059
    0.0279 0.015 0.044
    0.0482 -0.015 0.039
    0.0870 -0.008 0.042
    0.1955 0.086 0.147
    0.3386 0.104 0.097
    0.4351 0.246 0.058
    0.5069 0.117 0.062
    0.6205 -0.027 0.086
    0.8210 0.259 0.133
    0.9353 -0.101 0.168
    1.0560 -0.128 0.270
    1.1990 -0.543 0.340
    1.7550 -0.448 0.415
    ---end quote---

    you can see how the data goes negative magnitude (brighter) after around z>1.0
    this is what Kolb model fails to do, it is still positive out to z = 2
    this is disappointing, whatever the theoretical flaws and/or merits might be

    [edit] Normanby in the next post is right. Some Kolb curves do go negative before z = 2. But still the fit is not very satisfactory. If they go up then they dont go down enough, if they go down then they didnt go up enough. they are rather flat compared with the ned wright curves and data in the page linked above[/edit]
     
    Last edited: Mar 27, 2005
  21. Mar 27, 2005 #20
    what about the Psi_l0 = -0.5 line. That goes negative around z=1
     
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