
On the time lags of the LIGO signals - okket
https://arxiv.org/abs/1706.04191
======
sleavey
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...](http://www.preposterousuniverse.com/blog/2017/06/18/a-response-
to-on-the-time-lags-of-the-ligo-signals-guest-post/)

~~~
ISL
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...](https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102)

------
mabbo
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.

~~~
femto113
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.

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

[https://www.forbes.com/sites/startswithabang/2017/06/16/was-...](https://www.forbes.com/sites/startswithabang/2017/06/16/was-
it-all-just-noise-independent-analysis-casts-doubt-on-ligos-detections/amp/)

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...](http://www.physik.uni-
muenchen.de/aus_der_fakultaet/kolloquien/asc_kolloquium/archiv_sose17/jackson/video_jackson/index.html)

------
aaroninsf
I learned a lot from this thread. Thanks HN.

