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A search for traces of cosmic string didnt find much

  1. Mar 7, 2005 #1

    marcus

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    http://arxiv.org/abs/astro-ph/0503120

    Ned Wright and Amy Lo, looking thru WMAP data on the CMB
    for signature of cosmic string, largely negative.
     
  2. jcsd
  3. Mar 7, 2005 #2

    Chronos

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    Another disappointment for the string camp. This pretty hot stuff last summer - a testable predictions of string theory:
    http://www.eurekalert.org/pub_releases/2004-06/uocs-ndt061004.php
    Shortly after that press release, this rather pessimistic [albeit amusing] comment turned up on Not Even Wrong:

    "There is more chance of a ufo landing in your back yard and Elvis getting out of it than there is of this cosmic string scenario and its predictions actually coming about."

    Perhaps LIGO or the LHC will breathe some life back into to the patient.
     
  4. Mar 7, 2005 #3
    Chronos check your inbox

    I appreciate it
     
  5. Mar 8, 2005 #4
    Chronos, and Marcus, would you please educate me on the sources of your pessimism in regard to the paper Marcus listed? When I read the abstract, what stood out for me was:

    "We have searched the WMAP data for evidence of a cosmic string recently reported as the CSL-1 object, and found an ``edge'' with 2$\sigma$ significance. However, if this edge is real and produced by a cosmic string, it would have to move at velocity $\ga$ 0.94c. "

    It seems to me that they are saying they did find something. It seems to me that given the long wavelength and extreme age of CMBE, any positive correlation at all is rather amazing. The long wavelength is like looking at something with infrared imagery, and the extreme age is like looking at something, with infrared imagery, through a very thick wall. We shouldn't exactly expect to see nosehairs on the face of G-d with such an analysis. The paper referenced seems to me to be saying that there is something there, and that alone is very big news. So why, exactly, is everyone down-playing this? We now have two observations of one event using widely different technology, both suggesting the presence of a major anomaly. Maybe it isn't a cosmic string, but the evidence seems to be there to suggest something is going on.

    Please enlighten me about this. I know it is fashionable to take a (ho-hummmmm. Yawn) attitude to new information. But the nerve hairs on the back of my neck are tingling. Aren't you the least bit interested, really?

    nc
     
  6. Mar 8, 2005 #5

    SpaceTiger

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    [tex]2 \sigma[/tex] is pretty low significance for something like that.
     
  7. Mar 8, 2005 #6
    SpaceTiger

    Yes, of course it is low. The interesting thing, I think, is that there is any sigma at all.

    Long wavelength, light deformed by 12 b.y. travel. Why should we expect to find a high sigma? But I am, as Marcus and Chronos are, still withholding judgement. I don't mean to go off into the bulk! (pardon the stringy pun)

    But really, I mean it as an honest question, not rhetorical, why would we expect sigma to be high? I still cant believe the detail found in the short wavelength stuff.

    Thanks,

    nc
     
  8. Mar 8, 2005 #7

    marcus

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    I'm pleased different people take it different ways and react variously,
    that's sort of why I flagged the article. thinking some might really be interested, others not.

    earlier I tossed a thread into the pot called "Proof of String theory thru a telescope" or something like that, with a link to Motl blog where he was very excited IIRC.

    personally I think cosmic string is an interesting possibility. However if such were observed I would not immediately take it as a proof of String/M notions because the latter are looking less and less promising and more like a blind alley or a physically fruitless venture into mathematics-land.

    but my personal opinion is not the point of the thread. the point is Ned Wright did some serious checking in the WMAP data. I am going to visit his website and try to get an idea of how HE feels about it. I guess he would love to have something more positive to report!
     
  9. Mar 8, 2005 #8

    marcus

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    Shucks, I just went to Ned's site
    http://www.astro.ucla.edu/~wright/cosmolog.htm
    and looked in his "news of the universe"
    where he puts recent research/observation results he thinks are interesting

    and as far as I can see he didnt even mention this!
    must not have thought it panned out significantly
    or maybe he hasnt gotten around to updating his "news" items
     
  10. Mar 8, 2005 #9
    Hi Marcus

    I guess you are right about not getting too excited. I am going to review my knowlege of how sigma affects this interpretation.

    nc
     
  11. Mar 8, 2005 #10

    marcus

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    I have no feeling of being right or wrong. I really like the PF group-mind response. I found this thing of Ned Wright and put it out there and now we have a few different peoples reactions. I like having yours as well as my own. these things are very subjective (no right no wrong)
    a reason that PF is helpful. my wife wants to go for exercise walk up the hill, back in hour or so
     
  12. Mar 9, 2005 #11

    Chronos

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    Cosmic strings have been on the ropes [my bad] since the late 90's. The original concept predicted the CMB would be non-guassian. COBE dealt the first blow and WMAP applied the coup-de-grace. As noted in the referenced paper:
    "...the CMB anisotropieswere consistent with a Gaussian signature, while numerical simulations of all topological defects show that they would leave distinct non-Gaussian signatures in the CMB."
    The cosmic string scenario predicted they would arise from GUT phase transitions, and be abundant. Again from the paper:
    "If we expect GUT scale strings to form, one defect would be created per causal horizon. This leads to a possibility of ~13000 cosmic strings in CMB.The gravitational signatures of these strings will persist in the CMB even if the strings themselves have dissipated."

    From another recent paper:
    http://www.arxiv.org/abs/astro-ph/0410073
    Cosmic Strings Reborn?

    "Cosmic strings were very popular in the eighties, and much of the nineties,
    because they seemed to offer a neat alternative to inflation as a means of generating the primordial density perturbations from which galaxies and clusters eventually grew. In particular, for GUT-scale strings, the predicted string tension was about right to explain their magnitude. But towards the millennium their popularity waned, swept away by the avalanche of data, especially the microwave background measurements from COBE, BOOMERanG, and, more recently, WMAP. This eventually showed beyond doubt that cosmic strings or other topological defects could not provide an adequate explanation for the bulk of the density perturbations."

    The 2 sigma result [which is not very significant as noted by SpaceTiger] for CSL-1 reported by Wright & Lo is rather optimistic when you look at the overall data. For instance:
    "We have also investigated claims of a possible cosmic string detection of the object CSL-1, and found little evidence of a string at this position. For the proposed string mass... CMB temperatures at the location of CSL-1 would require the string to have been moving very relativistically, with v~0 96c. We conclude that this is unlikely,"

    While the evidence is not damning, it's a bear market for cosmic strings.
     
    Last edited: Mar 9, 2005
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