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On the time lags of the LIGO signals (arxiv.org)
65 points by okket 124 days ago | hide | past | web | 6 comments | favorite



There has been a reply from Ian Harry - a postdoc within LIGO who was involved in the data analysis for the discovery - on Sean Carroll's blog. To quote the blog:

"In Creswell et al. the authors take LIGO data made available through the LIGO Open Science Data from the Hanford and Livingston observatories and perform a simple Fourier analysis on that data. They find the noise to be correlated as a function of frequency. They also perform a time-domain analysis and claim that there are correlations between the noise in the two observatories, which is present after removing the GW150914 signal from the data. These results are used to cast doubt on the reliability of the GW150914 observation. There are a number of reasons why this conclusion is incorrect: 1. The frequency-domain correlations they are seeing arise from the way they do their FFT on the filtered data. We have managed to demonstrate the same effect with simulated Gaussian noise. 2. LIGO analyses use whitened data when searching for compact binary mergers such as GW150914. When repeating the analysis of Creswell et al. on whitened data these effects are completely absent. 3. Our 5-sigma significance comes from a procedure of repeatedly time-shifting the data, which is not invalidated if correlations of the type described in Creswell et al. are present."

http://www.preposterousuniverse.com/blog/2017/06/18/a-respon...


Point #3 is important. Time-shifting significance estimation is powerful in this context.

As the event rate is expected to be very low, almost all the data acquired are noise. Any true gravitational-wave signal must match within ~10 milliseconds of lag between LIGO Hanford and LIGO Livingston.

One can shift the clocks of one detector with respect to the other over months of data to look for a matching non-coincident detection. The rate at which those occur allows the straightforward determination of a data-driven false-alarm rate, independent of the analysis technique used.

Figure 4 is the relevant one: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061...


I think it's important to remember that this isn't a personal attack on LIGO. This is just science doing it's thing.

It is always critical to try your damnedest to disprove the results you get that are what you want to get. Let your friends try, let your enemies try, and thank them whether they succeed or not.

Otherwise, you're using science to prove yourself right rather than using it to become right.


No, but it's not far off that: it feels like self-promotion by fabricating criticisms of an immensely popular project. IMO the core suggestion of the paper--that noise is somehow correlated across different sensors separated by thousands of miles--is substantially more extraordinary than the LIGO experiments themselves (whose findings are well supported by decades of theory), so the possibility that this paper's results stem from anything other than flawed methodology seems vanishingly small.


A bit less technical explanation of the criticisms by Sabine Hossenfelder in Forbes:

https://www.forbes.com/sites/startswithabang/2017/06/16/was-...

Andrew D. Jackson, one of the authors if this paper, recently held a presentation at the LMU:

http://www.physik.uni-muenchen.de/aus_der_fakultaet/kolloqui...


I learned a lot from this thread. Thanks HN.




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