Uncovering the Truth Behind LIGO's Gravity Wave Detection: A Critical Analysis

[auou]

Hi,

I was looking for a second opinion on this article regarding LIGO's gravity waves and if it made sense or not.

https://www.forbes.com/sites/starts...dent-analysis-casts-doubt-on-ligos-detections

"Analysis of the data attributed the signal to a black hole merger that happened several billion light years away. But what if there wasn't a signal at all, but rather patterns and correlations in the noise that fooled us into believing we were seeing something that wasn't real? A group of Danish researchers just submitted a paper arguing that the celebration might have been premature."

 

[Vanadium 50]

Forbes is going to be useless as a source. You should find the primary source and post it here. (And yes, I could probably figure out where it is - but it's your question)

 

[Frimus]

Here is the primary source:
arXiv.org > astro-ph > arXiv:1706.04191

 

[pervect]

A direct link to the article is https://arxiv.org/abs/1706.04191. I don't have an opinion on the paper at this point, but I thought I'd post a better link to it.

 

[auou]

Forbes is going to be useless as a source.

As a source yes, what was 'interesting' about the article was that the researchers at LIGO didn't want to respond, why?

 

[PeterDonis]

Forbes is going to be useless as a source.

Forbes in general is not a great source for scientific news, but the particular article in question was written by Sabine Hossenfelder, who is knowledgeable in the field. From skimming the primary source paper, her presentation of the issue appears to be reasonable.

the researchers at LIGO didn't want to respond, why?

According to the article, the LIGO collaboration scientists "do not agree on the methods being used and thus with the conclusions". The article also says: "A major shortcoming of the Danish group’s analysis that they [the LIGO scientists] pointed out to me is that the Danes use methods based on tutorials from the LIGO Website, but these methods do not reach the quality standard of the – more intricate – data analysis that was used to obtain the published results." So the LIGO group appears to believe that the Danish group's findings are an artifact of a flawed method of analysis, not an actual problem with the LIGO findings.

 

[auou]

So the LIGO group appears to believe that the Danish group's findings are an artifact of a flawed method of analysis …

Alright, so that was easily settled with a bit of hand waving.

I guess the Danish group might have been annoyingly more critical because LIGO resembled the pride of Denmark, LEGO (The name 'LEGO' is an abbreviation of the two Danish words "leg godt", meaning "play well")

 

[etudiant]

There is a very clear dissection of this Danish paper by Lubos Motl here: http://motls.blogspot.in/2017/06/danish-ligo-discovery-is-noise-paper-is.html

Lubos is a top notch string theorist and mathematician, his conclusion is that the paper is entirely wrong.

 

[rootone]

As far as I know the forward plan is to have multiple detectors similar to LIGO.
In that case local background noise should be easy to eliminate

 

[atyy]

There is a very clear dissection of this Danish paper by Lubos Motl here: http://motls.blogspot.in/2017/06/danish-ligo-discovery-is-noise-paper-is.html

Lubos is a top notch string theorist and mathematician, his conclusion is that the paper is entirely wrong.

Motl's main point seems reasonable to me:

"Andrew Jackson et al. is saying that "something is wrong" because "the residual noise from LIGO-LA and LIGO-WA detectors are correlated and have the same delay" but this correlation between these two "noises" shouldn't exist.

Except that this statement is wrong. The residuals aren't just noise. They're the difference between the best fit and the actual observation. But the best fit isn't the same thing as the actual gravitational wave."

One way to check Motl's argument is to see whether the blind injections also have the same feature that Jackson et al think are problematic. Alternatively, Jackson et al could check their paper by analyzing the blind injections and showing that they lack the supposedly problematic features.

http://www.ligo.org/news/blind-injection.php
http://www.ligo.org/scientists/GW100916/index.php (publicly available blind injection data)

 

[Vanadium 50]

what was 'interesting' about the article was that the researchers at LIGO didn't want to respond, why?

A. It's not published.
B. It was released Wednesday, and it's only Saturday.
C. Normally the way things happen if a formal response from the collaboration is required is that the NBI group would submit this as a comment to the journal that published the original result. This isn't, so far, what's happened.

 

[auou]

There is a very clear dissection of this Danish paper by Lubos Motl here: http://motls.blogspot.in/2017/06/danish-ligo-discovery-is-noise-paper-is.html

Lubos is a top notch string theorist and mathematician, his conclusion is that the paper is entirely wrong.

Not sure what to think of his article, he only briefly mentions what's wrong with the paper of the Danish group, and than goes on over his on own theory of 'different polarizations'.

 

[auou]

A. It's not published.
B. It was released Wednesday, and it's only Saturday.
C. Normally the way things happen if a formal response from the collaboration is required is that the NBI group would submit this as a comment to the journal that published the original result. This isn't, so far, what's happened.

Alright, this makes sense.

 

[vanhees71]

Well, I'm not an expert in data analysis, and I must say, I can't decide, what Jackson et al really did. There are many words, a nice plot and not much clear mathematical analysis there. Also, one should be as careful to believe analyses of outsiders (i.e., people who are not in the collaboration of the experiment) as one has to take criticism seriously. I hope, the LIGO group will carefully analyse how Jackson et al came to their conclusion.

Without really understanding Jackson's paper, I only can guess, what's really behind it, assuming that there's really a signal for gravitational waves there (which I still believe since I think the LIGO collaboration was very careful before publishing), what Jackson et al take as noise is the difference between the full signal (applying band filters to it) and a fit with a gravitational-wave signal for both detectors. The signal of one detector was shifted (and inverted) to match it with the signal of the other, and LIGO says that with high significance they detected gravitational waves, particularly the time shift necessary is compatible with the propagation of the grav. wave with the speed of light. Now it's clear that in such a case the difference taken as "noise" of both detectors are correlated due to this fitting procedure. It doesn't mean that the noise of the detectors is really correlated, because you don't know the true noise. That's what I guess is behind these findings by Jackson et al. Nevertheless, this must be carefully checked by experts, and I'm pretty sure, if they send their paper to a good journal, they'll send it to several referees to carefully check it (hopefully to both members of the LIGO collab. and independent experts).

 

[RockyMarciano]

what Jackson et al take as noise is the difference between the full signal (applying band filters to it) and a fit with a gravitational-wave signal for both detectors. [...]
Now it's clear that in such a case the difference taken as "noise" of both detectors are correlated due to this fitting procedure. It doesn't mean that the noise of the detectors is really correlated, because you don't know the true noise. .

Actually no, this is not solely what they take as noise, they look at the raw band filtered full signal at the relevant time window, and also to the full signal with the GW attributed signal fit substracted and get similar results(the GW fit signal is very weak compared to the full signal, there is correlation between Hanford and Louisville, with a lag of 7ms. Now this is quite shocking as only the GW signal should have this correlation. The supposed noise associated to this signal should be stochastic. If the full signal is correlated then it is no longer just the noise of a true signal buried within it, it is all signal to the extent it is correlated. And the correlated signal certainly doesn't have a shape that one can attribute to a GW.

The key point here is that the analysis by Jackson et al is done without the templates, which are a biasing element.

 

[RockyMarciano]

Not sure what to think of his article, he only briefly mentions what's wrong with the paper of the Danish group, and than goes on over his on own theory of 'different polarizations'.

The analysis by Motl is quite bizarre, first he is taking for granted that the residual noise is affected by the GW signal for reasons that (he says it himself nd asks for recognition of this basic detail that according to him has gone unnoticed for every other expert) basically contradict LIGO's own basis for their analysis leading to conclude the signal detected is a GW. And second he is working under the assumption that no other source could conceivably produce a signal like it's been detected.

 

[RockyMarciano]

According to the article, the LIGO collaboration scientists "do not agree on the methods being used and thus with the conclusions". The article also says: "A major shortcoming of the Danish group’s analysis that they [the LIGO scientists] pointed out to me is that the Danes use methods based on tutorials from the LIGO Website, but these methods do not reach the quality standard of the – more intricate – data analysis that was used to obtain the published results." So the LIGO group appears to believe that the Danish group's findings are an artifact of a flawed method of analysis, not an actual problem with the LIGO findings.

Curiously enough that's the information they have put out for people to look up and find objections to(and after thousands of citations this seems like the first group that actually has taken the effort to do a critical analysis and publish it. That's weird, as if all scientists are willing to accept such outstanding discovery just on faith), and when someone does find an objection their answer is: "Well that is not really the best place to look at. The good stuff with the right methods is only in our posession".

Even if this was the case the correct thing to do would be to release that "more intricate method", and in any case explain exactly why what Jackson et al are saying is flawed.
So far I would say the only difference in methodology is that Jackson is not using the templates, basically because one can see the signal correlation between the detectors perfectly without the templates. And the templates are an obvious biasing element when one is not convinced beforehand that the signal corresponds to a GW, which should be the starting point in any experiment that claims to be a seminal discovery.

 

[auou]

The key point here is that the analysis by Jackson et al is done without the templates, which are a biasing element.

Would you care to elaborate?

 

[PeterDonis]

the correct thing to do would be to release that "more intricate method"

I think they already have, in their own data analysis (published at the time of the announcements of GW detection). But I agree it would be nice to have a direct statement from the LIGO group in response to the Danish group's criticisms, instead of just an indirect quote in an article written by a physicist who is not part of that group.

 

[Nik_2213]

Doesn't help that there's only two LIGO stations.
Issue may soon resolve itself given that several countries are now building 'LIGO-alike' GW observatories. Looks like the Chinese pair will be on-line first. This should provide a tetrahedron of detectors, giving both a longer base-line and better 3D direction finding. Okay, given the configuration, some angles will have much better error-bars than others but, as other stations come on-line, coverage will improve...

 

[protonsarecool]

Direct answer from one of the LIGO postdocs:
http://www.preposterousuniverse.com...the-time-lags-of-the-ligo-signals-guest-post/

 

[RockyMarciano]

Would you care to elaborate?

Templates are good basically when you are working with signals you are totally sure of, not in a experiment where you are trying to reject the null hypothesis that the signal you get comes from a specific source and has a specific waveform, because the sigma you get is very different. And besides the september 2015 signal is very clear without the need of templates. What the paper discusses is the analysis of the signal and its waveform, not that there is a clear correlated signal.
Ths is in the video of a talk by Jackson that is linked in your OP link, so there you can listen to it much better explained.

 

[RockyMarciano]

Direct answer from one of the LIGO postdocs:
http://www.preposterousuniverse.com...the-time-lags-of-the-ligo-signals-guest-post/

The problem I see with this response is that it seems to completely miss the point of the paper "On the time lags of the ligo signals". The paper doesn't question at all the existence of a correlated signal of the 2015 event, it is even visible by eye in the band filtered full signal just by zooming into the appropriate power, the spike is there and is shifted by 7ms between the detectors, and yet most of the response by Harry seems to be arguing there is no doubt there is a signal. But the paper questions the analysis of the shape of the signal, not its existence.

The main argument is technical and about the use of colored signal by Jackson et al instead of the noise whitened signal to conclude the noise is not random and it is also correlated. And again, evidently noise whitening, which of course presupposes what is noise and what is not noise, will destroy the phase information and randomize it, but it is that phase info of the full signal correlated by 7ms in the detectors which needs to be explained. So the answer appears as really naive in assuming beforehand what is noise and what is not according to the theoretical templates.
Once again I recommend besides reading the paper to listen to the video of the talk by Jackson linked in the Forbes page, to at least be clear on what the authors of the critical paper are saying.

 

[auou]

Once again I recommend besides reading the paper to listen to the video of the talk by Jackson linked in the Forbes page,

http://www.physik.uni-muenchen.de/a...rchiv_sose17/jackson/video_jackson/index.html

 

[websterling]

Once again I recommend besides reading the paper to listen to the video of the talk by Jackson linked in the Forbes page, to at least be clear on what the authors of the critical paper are saying.

A link to the video can be found on this page-
Understanding the LIGO gravitational wave event (GW150914)

 

[auou]

what is noise and what is not noise, will destroy the phase information and randomize it, but it is that phase info of the full signal correlated by 7ms in the detectors which needs to be explained.

The GW signal was part of the whole noise bundle, next they matched the two GW signals over each other, so of course the whole noise bundles started to match as a whole as well.

You could look at the whole noise signal as a body and the GW's as the skeleton, if you than match two skeletons than the bodies will also correspond. Or am I missing something?

It also seemed there was only one such strong signal, at the two detectors over a long time period and they both where in a 7ms time span. That is a clear match.

The only valid excuse seemed to be the thunderstorm, maybe ignited by a heavy dose of Cosmic Rays that was also felt by those two detectors? Donno.

 

[RockyMarciano]

I don't think the paper points to a specific source, it certainly suggests that an EM terrestrial origin can not be ruled out in the light of their analysis, but I think their main point is that the instrument itself is not reliable if it can be shown that there are correlations between the detectors not associated to events. In this respect the example of how the calibration lines in the vecinity of 35Hz are correlated the right time shift and match the event peaks is disturbing.

 

[Victor Ray Rutledge]

Quotes from the references given previously, ". A clear distinction between signal and noise, therefore, remains to be established, in order to determine the contribution of gravitational waves to the detected signals." And then, "When the first LIGO discovery was released in February 2016, I downloaded the raw data from both LIGO detectors sampled at 4096 Hz, wrote and ran all the required codes in Mathematica (that did especially the filtering of frequencies and the whitening), and discovered my own LIGO gravitational wave. I am absolutely certain that the probability that such clear signal-like events occur by chance is negligible. Also, the gravitational waves are the only conceivable signal that can make the delay between the two detectors this small. Any seismic or similar process would almost certainly lead to a much longer delay, basically because the vibrations would spread through the Earth by the speed of sound etc." Now I looked deeper, and found " when I combined the two signals (with the shift and the inversion), and normalized it so that this function has the usual standard deviation of one, I got a signal that exceeded 6 sigma at least at three independent enough places. So I think that the local significance level is close to 6 times the square root of three which is over 10 sigma." This was enough to convince me that the controversy is intensely complex, and related not so much to the data, as to the interpretation thereof. From the Danish submission, I will quote as follows, " Specifically, we analyze correlations in the calibration lines in the vicinity of 35\,Hz as well as the residual noise in the data after subtraction of the best-fit theoretical templates. The residual noise for the two more recent events, GW151226 and GW170104, exhibits equivalent behavior with respect to each of their time lags. A clear distinction between signal and noise therefore remains to be established in order to determine the contribution of gravitational waves to the detected signals." This says, to me, that they found no clear distinction, between signal and noise, or, stated differently, they couldn't find the same artifact in the signals, and thus wonder if it is there. I'm just wondering if they didn't know how to look for it.

 

[Dr_Zinj]

Like Vanadium50 said above. It's not reasonable to expect an immediate reply. 6 weeks to 90 days is more likely for them to think about the objections, double check their work, and formulate a response.

 

[auou]

Any seismic or similar process would almost certainly lead to a much longer delay, basically because the vibrations would spread through the Earth by the speed of sound etc."

There was a heavy storm exactly in between the two detectors at the time of the detection. These might be related to Cosmic Rays and 'big bursts of x-rays and gamma rays':

On the other hand, the case of thunderstorms and lightning is slightly different. Unlike the spark chamber, the electric fields inside the thunderstorm do not appear to be big enough to initiate a spark, so in order for Gurevich's mechanism to do the job, he had to suppose that there were many, many charged particles passing through the storm at once. Because cosmic-ray air showers do not produce enough particles by themselves, Gurevich postulated that the thunderstorm gave the cosmic-ray shower a boost by increasing the number of energetic electrons through an exotic process called "runaway breakdown."

Runaway breakdown occurs when the drag force that electrons experience moving through air is less than the electric force acting upon them. In such cases, the electrons will "run away," gaining very large amounts of energy. As the runaway electrons collide with air molecules, they generate other runaway electrons plus x-rays and gamma rays, resulting in an avalanche of high-energy particles. Instead of rocks in a landslide, think of the runaway electrons as shrapnel tearing up a path through the storm cloud. According to the Gurevich model, this conductive path is what causes lightning.

Runaway breakdown can create large amounts of high-energy electrons, as well as x-rays and gamma rays. Interestingly, we know that runaway breakdown works for the low electric fields already seen inside thunderstorms. We also know that it does sometimes happen right before lightning, because we can see big bursts of x-rays and gamma rays shooting out of thunderstorms. In fact, these gamma rays are so energetic and so bright that they have been observed from outer space, 600 kilometers (373 miles) above Earth's surface. - https://www.scientificamerican.com/article/experts-do-cosmic-rays-cause-lightning/

 

[Dukon]

is the black hole density of the universe known? theoretically or observationally (experimentally)?
Given the volume of the universe (known) and the density of black holes in it (question above) then the probability for a collision should be calculable.

So far this GW observation result is once in whatever time period the GW detectors have been up (when did LIGO become first operational and has it been live 100% ever since?) The time period of LIGO activation should be used with the single observation to back out the density of black holes in the universe if it is not known by other methods already. Has this calculation been done or published already? If so where. Can someone do this calculation and post it here?

Maybe given the density of black holes in the known universe an the known universe volume the number of such observations predicted agrees with the number actually observed by LIGO. If the given BH density is not known in advance then it can be inferred by the number of BH collisions observed in the finite time LIGO has been live.

My guess and hunch is that the BH density is much bigger and implies more such collisions as actually occurring than have been observed by LIGO in the time it has been operational. If this is true then it means the efficiency of the LIGO detector is very low but has there been already an adequate explanation by LIGO for why their detection efficiency is low (if it is low)?

Has LIGO group discussed this aspect of their observations? Is this new, old or irrelevant for some reason?

 

[Sue Rich]

Since the black hole merger was a billion light years away, isn't it probable the event actually happened a billion or millions of light years ago?

 

[auou]

Since the black hole merger was a billion light years away, isn't it probable the event actually happened a billion or millions of light years ago?

That's exactly the case, but we put the date on it that we detected it.

 

[Mister T]

Doesn't help that there's only two LIGO stations.
Issue may soon resolve itself given that several countries are now building 'LIGO-alike' GW observatories.

No doubt it's better to have more observations, but it has yet to be shown that the issue raised in the article is of any significance. What's needed is a response from members of the LIGO team to that claim.

 

[Mister T]

Since the black hole merger was a billion light years away, isn't it probable the event actually happened a billion or millions of light years ago?

Travelling at the speed of light, it takes 3 billion years (of time) to travel 3 billion light years (of distance).