On the Time Lags of the LIGO signals

It seems that a lot of rumours are flying around on social media and elsewhere about the discussions that have been going on here in Copenhagen between members of the Niels Bohr Institute and of the LIGO scientific collaboration concerning matters arising from the `Danish Paper‘.  The most prominent among these appears to be the LIGO team and the Danish team have agreed on everything and that the Danish authors have conceded that they were mistaken in their claims. I have even been told that my recent blog posts gave the impression that this was the case. I’m not sure how, as all I’ve said is that the discussions reached agreement on some matters. I did not say what matters or whose position had changed.

I feel, therefore, that some clarification is necessary. Since I am a member of neither party to this controversy I have to tread carefully, and there are some things which I feel I should not discuss at all. I was invited to participate in the discussions as a neutral observer as a courtesy and I certainly don’t want to betray any confidences. On one thing, however, I can be perfectly clear. The Danish team (Cresswell et al.) have not retracted their claims and they reject the suggestion that their paper was wrong.

To reinforce this, I draw your attention to the fact that a revised version of `The Danish Paper’ has now been accepted for publication (in the Journal of Cosmology and Astroparticle Physics) and that this paper is now available on the arXiv. The referees raised a large number of queries, and in response to them all the revised version is almost double the length of the original.

Here is the arXiv entry page:

The main body of the paper has not been significantly modified and their main result – of an unexplained 7ms correlation in the background signal (referred to in the abstract as `noise’) – has not “gone away”. If you want to understand more, read the paper!

I’m sure there will be much more discussion of this and I will comment as appropriate when appropriate. In the meantime this remains very much a live issue.

P.S. In the interest of full disclosure I should mention that I did read over part of the revised version of the Danish paper and made some suggestions with regard to style and flow. I therefore have a mention in the acknowledgments of the final version. I was warned that I might expect some trouble for agreeing to be associated with the paper in this way but, as  Sam Spade says in The Maltese Falcon `I don’t mind a reasonable amount of trouble’…

13 Responses to “On the Time Lags of the LIGO signals”

  1. “`I don’t mind a reasonable amount of trouble’…”
    God bless you.

  2. Are the 6 mistakes in the LOSC tutorial you mentioned going to be displayed in forthcoming papers or blogs

    • telescoper Says:

      I think it’s much better if the LIGO team just corrected them. They know what the errors are. There are also errors on Ian Harry’s page which haven’t been corrected.

  3. Hi!
    I have a question, but I’m not an astronomer, so you can totally dismiss it.
    In the cross correlation of the null output streams in section 3.3, showing that 7ms is a shift intrinsic to the equipment, the templated event signal was simply subtracted.
    Is this the right thing to do?

    Working in acoustic signal processing myself, we are usually interested in finding a finite impulse response between two signals, and then remove the contribution in order to study remainder/noise. But in section 3.3 of the arxiv paper you linked, the authors are working with a size-1 FIR. Is this the standard approach?

  4. […] the contribution of gravitational waves to the detected signals./quote] See the discussion at https://telescoper.wordpress.com/2017/08/10/on-the-time-lags-of-the-ligo-signals/ I suspect that this criticism will not remain viable when a detector at a third location comes on […]

  5. Peter I read the updated paper. They are standing by their claim of phase correlations. (I thought from one of your earlier posts that they had conceded that this is error). Also they assume the acronym TOD, without explanation. I presume this is “time of detection”. Or is it something else? They also talk about a precursor and echo signal. Isn’t this same as what Afshordi and colleagues have found in arxiv:1612.00266 and arXiv:1701.03485

    • telescoper Says:

      TOD is defined on page 2. It means `Time Ordered Data’. The Ashfordi results are probably related.

      I did at one point think that the observed phase correlations were an artefact of not windowing (apodizing) the data leading to edge effects. Having looked at this myself, I am now confident this is not the case.

  6. It is interesting that LIGO developed both software and hardware fake signal injection procedures used in tandem for their “big dog” event in 2010. I wonder: Would a hardware injected fake signal in one noisy data set being partially duplicated by software injection to another noisy data set create unwanted noise correlation with uniform time delay, e.g. 7 ms?

    Sincere respect, Olav Thorsen

  7. I have some corrections to the letter by Creswell, et al. Mostly they have to do with mistakes in Appendix B related to the field of digital signal processing. I don’t think they bear strongly on the letter’s conclusions but it irks me to see blatant errors in a paper like this and feel they should be corrected.

    I cannot figure out how to contact the letter’s authors directly. Can you provide some guidance here? I would be glad to send you a copy of my inputs if you can pass it on to Creswell et al. Are you interested?


    • Just email the authors. Their addresses are easily found.

      • Okay…I’ll find those and do that. Just FYI, I think I’ve come up with a cleaning algorithm which gets rid of the correlation in residuals. Don’t get too excited just yet however…I need to see if it can pass the sniff test with Creswell et al 😉

  8. It has been nearly one year since the Creswell et all. preprint. As the origin of noise correlations with identical lag in LIGO strain data around detections to diagnostic signal lags has been unclear, I have undertaken an empirical analysis of coincident physical data from solar, magnetosphere, and ionosphere sources, with lightning data surrounding GW triggers. Progress notes for this unpublished study are available at https://fulguritics.blogspot.com. I welcome feedback and corrections, and all math, data, workbooks, and code are freely available upon request through the linked contact info. Thank you for your time.

  9. […] some time ago to clarify some points I made in previous blog posts on this issue (e.g. this one and that one). I even ended up being quoted in the […]

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