Wednesday, September 04, 2019

What’s up with LIGO?

The Nobel-Prize winning figure.
We don’t know exactly what it shows.
[Image Credits: LIGO]
Almost four years ago, on September 14 2015, the LIGO collaboration detected gravitational waves for the first time. In 2017, this achievement was awarded the Nobel Prize. Also in that year, the two LIGO interferometers were joined by VIRGO. Since then, a total of three detectors have been on the lookout for space-time’s subtle motions.

By now, the LIGO/VIRGO collaboration has reported dozens of gravitational wave events: black hole mergers (like the first), neutron star mergers, and black hole-neutron star mergers. But not everyone is convinced the signals are really what the collaboration claims they are.

Already in 2017, a group of physicists around Andrew Jackson in Denmark reported difficulties when they tried to reproduce the signal reconstruction of the first event. In an interview dated November last year, Jackson maintained that the only signal they have been able to reproduce is the first. About the other supposed detections he said: “We can’t see any of those events when we do a blind analysis of the data. Coming from Denmark, I am tempted to say it’s a case of the emperor’s new gravitational waves.”

For most physicists, the 170817 neutron-star merger – the strongest signal LIGO has seen so-far – erased any worries raised by the Danish group’s claims. That’s because this event came with an electromagnetic counterpart that was seen by multiple telescopes, which can demonstrate that LIGO indeed sees something of astrophysical origin and not terrestrial noise. But, as critics have pointed out correctly, the LIGO alert for this event came 40 minutes after NASA’s gamma-ray alert. For this reason, the event cannot be used as an independent confirmation of LIGO’s detection capacity. Furthermore, the interpretation of this signal as a neutron-star merger has also been criticized. And this criticism has been criticized for yet other reasons.

It further fueled the critics’ fire when Michael Brooks reported last year for New Scientist that, according to two members of the collaboration, the Nobel-prize winning figure of LIGO’s seminal detection was “not found using analysis algorithms” but partly done “by eye” and “hand-tuned for pedagogical purposes.” To this date, the journal that published the paper has refused to comment.

The LIGO collaboration has remained silent on the matter, except for issuing a statement according to which they have “full confidence” in their published results (surprise), and that we are to await further details. Glaciers are now moving faster than this collaboration.

In April this year, LIGO started the third observation run (O3) after an upgrade that increased the detection sensitivity by about 40% over the previous run.  Many physicists hoped the new observations would bring clarity with more neutron-star events that have electromagnetic counterparts, but that hasn’t happened.

Since April, the collaboration has issued 33 alerts for new events, but so-far no electromagnetic counterparts have been seen. You can check the complete list for yourself here. 9 of the 33 events have meanwhile been downgraded because they were identified as likely of terrestrial origin, and been retracted.

The number of retractions is fairly high partly because the collaboration is still coming to grips with the upgraded detector. This is new scientific territory and the researchers themselves are still learning how to best analyze and interpret the data. A further difficulty is that the alerts must go out quickly in order for telescopes to be swung around and point at the right location in the sky. This does not leave much time for careful analysis.

With the still lacking independent confirmation that LIGO sees events of astrophysical origin, critics are having a good time. In a recent article for the German online magazine Heise, Alexander Unzicker – author of a book called “The Higgs Fake” – contemplates whether the first event was a blind injection, ie, a fake signal. The three people on the blind injection team at the time say it wasn’t them, but Unzicker argues that given our lack of knowledge about the collaboration’s internal proceedings, there might well have been other people able to inject a signal. (You can find an English translation here.)

In the third observation run, the collaboration has so-far seen one high-significance binary neutron star candidate (S190425z). But the associated electromagnetic signal for this event has not been found. This may be for various reasons. For example, the analysis of the signal revealed that the event must have been far away, about 4 times farther than the 2017 neutron-star event. This means that any electromagnetic signal would have been fainter by a factor of about 16. In addition, the location in the sky was rather uncertain. So, the electromagnetic signal was plausibly hard to detect.

More recently, on August 14th, the collaboration reported a neutron-star black hole merger. Again the electromagnetic counterpart is missing. In this case they were able to locate the origin to better precision. But they still estimate the source is about 7 times farther away than the 2017 neutron-star event, meaning it would have been fainter by a factor of about 50.

Still, it is somewhat perplexing the signal wasn’t seen by any of the telescopes that looked for it. There may have been physical reasons at the source, such that the neutron-star was swallowed in one bite, in which case there wouldn’t be much emitted, or that the system was surrounded by dust, blocking the electromagnetic signal.

A second neutron star-black hole merger on August 17 was retracted

And then there are the “glitches”.

LIGO’s “glitches” are detector events of unknown origin whose frequency spectrum does not look like the expected gravitational wave signals. I don’t know exactly how many of those the detector suffers from, but the way they are numbered, by a date and two digits, indicates between 10 and 100 a day. LIGO uses a citizen science project, called “Gravity Spy” to identify glitches. There isn’t one type of glitch, there are many different types of them, with names like “Koi fish,” “whistle,” or “blip.” In the figures below you see a few examples.


Examples for LIGO's detector glitches. [Image Source]

This gives me some headaches, folks. If you do not know why your detector detects something that does not look like what you expect, how can you trust it in the cases where it does see what you expect?

Here is what Andrew Jackson had to say on the matter:

Jackson: “The thing you can conclude if you use a template analysis is [...] that the results are consistent with a black hole merger. But in order to make the stronger statement that it really and truly is a black hole merger you have to rule out anything else that it could be.

“And the characteristic signal here is actually pretty generic. What do they find? They find something where the amplitude increases, where the frequency increases, and then everything dies down eventually. And that describes just about every catastrophic event you can imagine. You see, increasing amplitude, increasing frequency, and then it settles into some new state. So they really were obliged to rule out every terrestrial effects, including seismic effects, and the fact that there was an enormous lightning string in Burkina Faso at exactly the same time [...]”
Interviewer: “Do you think that they failed to rule out all these other possibilities?

Jackson: “Yes…”
If it was correct what Jackson said, this would be highly problematic indeed. But I have not been able to think of any other event that looks remotely like a gravitational wave signal, even leaving aside the detector correlations. Unlike what Jackson states, a typical catastrophic event does not have a frequency increase followed by a ring-down and sudden near-silence.

Think of an earthquake for example. For the most part, earthquakes happen when stresses exceed a critical threshold. The signal don’t have a frequency build-up, and after the quake, there’s a lot of rumbling, often followed by smaller quakes. Just look at the below figure that shows the surface movement of a typical seismic event.
Example of typical earthquake signal. [Image Source]


It looks nothing like that of a gravitational wave signal.

For this reason, I don’t share Jackson’s doubts over the origin of the signals that LIGO detects. However, the question whether there are any events of terrestrial origin with similar frequency characteristics arguably requires consideration beyond Sabine scratching her head for half an hour.

So, even though I do not have the same concerns as were raised by the LIGO critics, I must say that I do find it peculiar indeed there is so little discussion about this issue. A Nobel Prize was handed out, and yet we still do not have confirmation that LIGO’s signals are not of terrestrial origin. In which other discipline is it considered good scientific practice to discard unwelcome yet not understood data, like LIGO does with the glitches? Why do we still not know just exactly what was shown in the figure of the first paper? Where are the electromagnetic counterparts?

LIGO’s third observing run will continue until March 2020. It presently doesn’t look like it will bring the awaited clarity. I certainly hope that the collaboration will make somewhat more efforts to erase the doubts that still linger around their supposed detections.

127 comments:

  1. > With the still lacking independent confirmation...

    I disagree with this statement. The Princeton group has written a completely independent search pipeline (https://arxiv.org/abs/1902.10341), and they have written several papers on the events they found in the O1 and O2 datasets (e.g. https://arxiv.org/abs/1902.10331, https://arxiv.org/abs/1904.07214, https://arxiv.org/abs/1908.05644). Note that some of their event candidates are the same as LIGO's official ones, but the Princeton group also claims detections that LIGO did not claim! So, it's not like a black box. The understanding for how to analyze GW data is out there, and others have independently confirmed signals of high statistical significance.

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    Replies
    1. Leo,

      No signal analysis can confirm that the signal was of astrophysical origin. You are talking about a different point than I entirely.

      Delete
    2. The discussion starts from the criticism from Denmark.
      The claim from Denmark is that we do the analysis on the same data in our own different way and find nothing. The response is that several other people have done it in their own different way and found the same results as the LIGO/Virgo analysis, and by the way, here are the mistakes that the people from Denmark have been making to get their results.
      Therefore, for how long should the criticism coming from Denmark be considered as a valid starting point?

      Delete
    3. @Vagelford: Actually, LIGO had to withdraw their published 150914 template due to the Danish critique and Rai Weiss admitted they "screwed up" the analysis (Sackler Lecture 2018). Amazingly, the new LIGO 150914 still has residual noise correlations.

      => https://arxiv.org/abs/1903.02401

      So the Danish critique still is very much relevant, even concerning 170817.

      Delete
    4. As far as I know, the initial publication had a figure which by LIGO's admission was there mainly for illustrative purposes and was not part of the actual analysis. Therefore any problems with the figure in question do not reflect on the actual data analysis.

      Furthermore, I can't say that I find it surprising that the Danish group still finds correlations if they are doing the same analysis as they did in the first place.
      I don't think that they have addressed the criticism that they received for example, here https://arxiv.org/abs/1711.00347

      Delete
    5. @Vagelford: Yes but the published figure was labeled as real (and still is), and the admission came only after the Danish critique. Plus, the original waveform template on LIGO's website also turned out to be false and got a disclaimer added. Why even publish such false data?

      The Danes have already responded to this and other critiques: https://arxiv.org/abs/1903.02401 The updated templates describe a quite different system (extreme spin, different location), which is strange, and according to the Danes, still have residual correlations.

      Delete
  2. Hi

    Great piece. But I failed to understand your statement: "We don’t know exactly what it shows."

    We see the data in the figure, what exactly is it we do not know? Why isn't that "The Data".

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    1. Drevney,

      This isn't raw data. It's highly processed data with some inferred signal overlaid. Just where exactly that signal template came from is the question.

      Delete
    2. For the glitches, they are a problem yes. But on the assumption the glitches are caused by events local to the detectors they won't be correlated between the detectors. And from that the false alarm rate from the two detectors happening to glitch at the same time can be estimated.
      There are some complications here: the noise in the detectors does change over time so you really want to use the glitches close-ish to the detections to estimate the false alarm rate (for GW150914 Ligo refrained from changing the detectors for weeks, I think, so as to collect a large sample of glitches & noise similar to what would be expected at the time of detection.) And there is limited glitch data, and mixed in with the glitches are an unknown quantity of actual gravitational wave signals, so for the better quality events it's not really possibly to calculate a false-alarm rate and instead you get an upper limit to the false alarm rate.
      The changing noise characteristics is also why I would not take the false alarm rates reported in https://gracedb.ligo.org/latest/ seriously, even if it weren't for the retractions. Better to wait for the papers.
      Really large lightning strikes affecting both detectors near simultaneously is an interesting possibility. The detectors collect a wealth of environmental data so it should be possible to check if the GW signals match up with the ionosphere going "boing" from lightning strikes. I can but presume this has been done, I don't actually know.

      Delete
    3. "But on the assumption the glitches are caused by events local to the detectors..."

      If that's what you want to show you shouldn't assume it.

      Delete
    4. Just where exactly that signal template came from is the question.

      That question is a double-edged sword. Certainly it is not clear that the signal can only be accounted for by a gravitational wave model, as that involves a claim of omniscience - that all other possible sources are absolutely accounted for by the LIGO team. In LIGO-land, the possibility of unknown unknowns is apparently defeated by self-assurance, or something.

      The matched template is, itself, one of 250,000 templates for which a match is being sought, by algorithms designed to sift a voluminous data set looking for just such a match. It is not at all clear that the signal isn't being created as much as found.

      Then there is the rather physically preposterous claim that a classical scale interferometer with 4-kilometer arms is somehow capable of measuring a signal that is 100 million times smaller than the atoms of the mirrors that supposedly detect the signal. Such a claim is physically inexplicable, but with a little creative math, I guess you can come up with a pretty picture of such a signal.

      LIGO should abandon the the gw search and try to accurately measure the speed of light in repeated trials to determine if there is a regular pattern to the variations found. That might actually be useful information.

      Delete
    5. bud rap: "Then there is the rather physically preposterous claim that [...]".

      Why is it a "rather physically preposterous claim"?

      I mean, other than that you personally find it so.

      Delete
    6. Why is it a "rather physically preposterous claim"?

      Check out Bud's other contributions here and you'll realize that conversing with him is a waste of time.

      Delete
    7. Jean Tate,

      Why is it a "rather physically preposterous claim"?

      Well, for the reason I mentioned, that the atoms of the mirror are 100 million times larger than the scale of the alleged signal and also a reason I did not mention, that all of those atoms are vibrating chaotically.

      Therefore if it were possible to concoct a physical account of how such a minute signal managed to be picked by the interferometer, you also would have to explain how the signal - supposedly a variation in the fixed length separation between the two mirrors - can even exist given that there is no fixed length separation at the scale of the atoms, let alone at a scale 100 million times smaller.

      So, if you want to explain the physics of how such a quantum scale measurement can be made with such a large piece of classical machinery, be my guest. Tell me how such a thing can be physically accomplished.

      Hey Phillip, it's OK with me if you want to prance around in your faux-scientist pose, demonstrating, again, that once your arguments from authority are set aside, you don't have two thoughts of your own to rub together. You're a poster boy for everything that's wrong with theoretical physics, Phillip.

      Delete
  3. Interesting article. Copyedit:

    "Glaciers are now moving faster than this collaboration"
    Needs a period.

    "but so-far no optical"
    "the collaboration has so-far seen"
    "so far" is not hyphenated.

    "(You find an English translation here.)"
    (You can find an English translation here.)

    "This give me some headaches, folks."
    This gives me some headaches, folks.

    (Within Jackson's speech) "and then it settles into something new state"
    Probably "some new state"

    "Think of an earthquake as example."
    Think of an earthquake for example.

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    Replies
    1. Dr Castaldo,

      Thanks for this; I have made these changes. I don't understand what's wrong with "You find" instead of "You can find" though?

      Delete
    2. Sabine, ultimately "You find" is "wrong" because it's not what native speakers of English say (or write). Today.

      Yes, some linguist can give you some nice reason why this is what such people say (however, I am not such a linguist) ...

      Delete
    3. Since you are talking about linguistic glitches I would say, inadvertently using ‘as’ in e.g. „... as example“ happens, since in German it translates as „... als Beispiel“.
      I had a same type typo here – it should have been: “What could be more non-linear then a simple threshold?”

      Delete
    4. Damn it - a hat trick typo – you are as always, as correct as possible - thanks

      Delete
    5. since in German it translates as „... als Beispiel“.

      While gramatically correct, "als Beispiel" is almost never used; it is "zum Beispiel". Prepositions have to be learned; cognates are used in different ways in different languages, and different languages often don't use the cognates for the same thing.

      Delete
    6. You can very well say something like "Lasst uns als Beispiel ein Erdbeben betrachten." oder "Ich benutze dies als Beispiel, um..." usw.

      Delete
    7. Sabine: I don't understand what's wrong with "You find" instead of "You can find"

      I am not a grammarian, but I believe it is the present tense; the difference between "You break the cup" and "You will break the cup".

      Native USA speakers talk about "the find" as a future event, because the action of "finding" has not been accomplished yet. So "you will find", "you can find", "More info can be found".

      An alternative is a direct order to take a future action: "Learn more here", "See this link", etc.

      Dungeons and Dragons uses the present tense; the Dungeon Master (DM) asks "What do you do?" and the player responds "Open the door", the DM says "You open the door and find a neatly folded green blanket. What do you do?"

      Delete
  4. > On August 14th, the collaboration reported a neutron-star black hole merger. Again the optical counterpart is missing.

    I wonder if anybody checked to see if a black hole was plausible in this direction/distance? Like, is it in the center of a galaxy?

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    1. These aren't supermassive black hole mergers that they see, they are some 10x solar mass or such. Just how the distribution looks like nobody presently knows exactly, but these objects are probably all over galaxies. Also, the location in the sky isn't precise enough to pinpoint single galaxies. Which, at this distance, may be so faint that the only reason you're seeing them is this specific event to begin with.

      Delete
  5. To what extent is the fact that the signal is detected at geographically distant locations evidence of astrophysical origin?

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    1. What this almost simultaneous detection tells you is that it's either a signal that passes very quickly through the system - consistent with it moving at the speed of light - or that it's something which is correlated on the Earth surface for other reasons. Seismic surface waves, for example, move much to slowly. There are certain electromagnetic atmospheric phenomena that might pass the bill, and you find these mentioned somewhere in the LIGO papers. I don't know if there are other things. Basically that's the kind of discussion I find to be missing.

      Delete
  6. Little typo:

    "I must say that do find it peculiar"
    Should be "I do"

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  7. Thank you, Sabine, for this interesting piece of news.

    “We can’t see any of those events when we do a blind analysis of the data."

    Does LIGO publish everything - all the raw data, signal analysis computer programs, and the final processed results. It seems to me that all these large experiments should do that. I suspect there is too much pressure to see a result after so much money has been spent.

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    1. They do publish their data after some delay and also have their codes on their website.

      Delete
    2. So is one supposed to reconcile that with the statement from Andrew Jackson?

      “We can’t see any of those events when we do a blind analysis of the data."

      Delete
    3. @David: The Danes are using a more strict, template-free search method. LIGO's template-based method includes more degrees of freedom, and hence is more prone to false-alerts.

      Delete
  8. I fail to see anything here that would compel me to say LIGO data is somehow wrong. It does not appear there is something like the "dusting" problem that hit BICEPII.

    The glitches look like something odd with coherent states of light. You can get bunching and other photon physics, or this can happen how they couple to other systems or a detector.

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  9. It seems to me that there is one key factor that you are not considering: LIGO only counts an event as a detection if the same signal appears in multiple detectors with the appropriate timing. The appearing in multiple detectors is what rules out detector errors, and the appropriate timing is what rules out terrestrial events--speed of light time delay for something traveling through the body of the Earth (earthquake waves travel orders of magnitude slower).

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    Replies
    1. Peter Donis,

      Yes, thank you, I know of this. As I said above, please demonstrate that there isn't any signal of terrestial origin that does that. Also, please explain why the high number of retractions *despite* of that.

      Delete
    2. Asking to "demonstrate that there isn't any signal of terrestrial origin that does that" is akin to asking someone to prove that invisible purple unicorns do not exist. Fact is nobody has been able to come up with a plausible terrestrial alternative.

      The high number of retractions is inherent to the nature of the graceDB alerts. To be of use these alerts need to be issued almost immediately. This means they are based of a low latency pipeline that essentially checks of there is something somewhat like a gravitational wave in the data stream and provides some preliminary estimates of what the source properties should be if it was a gravitational wave. This is bound to produce some false positives.
      Note also that a retraction does mean that an event has proven to be of terrestrial origin. Just that it's statistical significance has been adjusted down because of additional analysis and has dropped below a certain threshold. (Note that most retracted events started out with a low significance to start with.)

      Delete
    3. MvdM,

      What you say is simply wrong. The sought-for electromagnetic counterparts would be an example of such a demonstration. It's explained in my blogpost. There are other things you can think of. Eg, as someone suggested to me, you could try to demonstrate that the source is moving quickly relative to Earth, which would indicate that at least it's not coming from our planet or maybe even the solar system.

      "To be of use these alerts need to be issued almost immediately..."

      Yes, as I wrote. Why do you see the need to repeat what is in my blogpost?

      Delete
    4. Except that a electromagnetic counterpart has been found and you are dismissing it. The fact that it came later is irrelevant unless you are suggesting that the signal was inserted on purpose. If so you should say it clearly has you are making a serious accusation without having any proof.

      Finally, I am amazed that you found relevant to include the baseless opinion of a conspiracy theorist author of a book called "Fake Higs". Do you think that the Higgs was faked Sabine? Should we include also the opinion of a flat-earter just to be sure? And maybe the illuminati inserted the signal, who knows?

      Delete
    5. Sabine,

      How could you demonstrate that the source was moving rapidly relative to the earth?

      I mean there aren't going to be any spectral lines in a gravitational wave?

      Delete
    6. Sabine,

      "please demonstrate that there isn't any signal of terrestial origin that does that."

      It doesn't seem like a signal of terrestrial origin could show the right time delays from one detector to another, because a signal of terrestrial origin would be coming from somewhere in between the detectors instead of from somewhere far outside.

      "please explain why the high number of retractions *despite* of that."

      The signal timing obviously isn't the only criterion being used, and it isn't perfect anyway, so I would not expect it to be able to prevent retractions. Retractions look to me like a sign of an honest scientific effort: nobody gets everything right every time, and when you find out you made a mistake, you should make sure everyone else who is interested in your results knows that.

      Delete
    7. Luca,

      "The fact that it came later is irrelevant unless you are suggesting that the signal was inserted on purpose. If so you should say it clearly has you are making a serious accusation without having any proof."

      I am not making any "accusation" and didn't say anything about "insertion". I am pointing out that this is not meeting the requirement that the LIGO detection was confirmed, because the events happened in the wrong order. The NASA alert came *first*, then the LIGO analysis came. Also, the NASA alerts are coupled to the LIGO threshold triggers and none of us has any idea just what was going on with their analysis.

      I find it remarkable that you come here to criticize me simply for pointing out that this is not the confirmation we look for.

      "Finally, I am amazed that you found relevant to include the baseless opinion of a conspiracy theorist author of a book called "Fake Higs". Do you think that the Higgs was faked Sabine?"

      I have pointed out he is author of this book, so you know how seriously to take him. Would you rather have me raised the impression he is an expert?

      Delete
    8. Peter,

      "It doesn't seem like a signal of terrestrial origin could show the right time delays from one detector to another,"

      You are assuming that the event is passing through, which doesn't necessarily have to be the case. The only thing you need are long-range correlations either on Earth's surface or in the atmosphere. These arguably exist for several known phenomena. For all I can tell, the known phenomena don't fit the bill of the LIGO events, but as I said, that I couldn't think of something that looks similarly isn't a scientifically rigorous argument.

      "Retractions look to me like a sign of an honest scientific effort..."

      You are missing the point. I did not say there is a problem with having a large number of retractions. As a matter of fact I said the opposite. I said I want an explanation. We do not know what is going on. That is the problem. Saying "oh, nothing to worry" is not an explanation.

      Delete
    9. Sabine,

      I do not see how the order of the alarm has any relevance. Those data are recorded, collected with completely independent methods and as far as I understand publicly available. If the analysis of the LIGO data finds a gravitational wave event consistent with the simultaneous EM event then it is a strong physical corroboration. I don't see how the order of the discovery should make any difference as the LIGO and EM data were collected independently anyway.

      I do think that if you report the opinion of a crackpot in your blogpost concerning doubts over LIGO you implicitly recognize that his opinion has relevance to this conversation. It doesn't, he is not a expert and he has a track record of conspiracy theory. It seems to me that you used him for letting out a baseles accusation of data fabrication without making the accusation yourself.

      Delete
    10. Luca,

      Unzicker is not a "crackpot," he is a science writer. I have used information I took from his article that probably took him effort to obtain, hence I credit the source. What about this is it that you cannot understand?

      As to the order of the alerts. In science we ask for predictions to avoid fooling ourselves. That's how it works. I do not think LIGO should get away with lesser standards. I am surprised I even have to defend that.

      Delete
    11. The problem with order is always cherry-picking, if you are certain an event occurred and there should be something to find, then you look hard for it.

      This is fine for developing a hypothesis that Y is preceded by X, undoubtedly it is how the human brain works. But the only true test is to see if every X is followed by a Y, and that in turn must be supported by a sufficient quantity of X's to make a statistical argument that the pattern holds and is not due to chance. Which also demands computing the likelihood of observing X.

      And if every X is not followed by a Y, that needs to be explained too, what can impersonate X? And if most observed X's are not followed by a Y, and you've only got one or two Y's preceded by X, then those could be due to chance; it is certainly not a reliable claim to say X predicts Y, or to claim Y is always preceded by X (two different claims).

      An after-the-fact match is a plausible thing to thoroughly investigate and find out if it is statistically reliable, but that's it. It is not a win.

      Delete
    12. Cataldo,

      I do not know how that data looks like th but if it is a typical GW waveform as we already saw before, consistent between the detectors and consistent with the EM location the chance of being a random fluke just because the knew where to look is astronomically small. The data is there we can simply run the analysis and draw our conclusions. The order of the alarms has nothing to do with the data.

      Delete
    13. Sabine

      Could you please enlighten me how the observation of an EM counterpart demonstrates that there doesn't exist a terrestial source that would show up almost simultaneously in multiple detectors and produce a chirp? (Because that was what *you* were asking for in your reply to Peter Donis!)

      Delete
    14. Regarding the order of the alerts. The opposite order would be just as problematic. If Fermi, went back to their data and found a coincident signal with a GW event that they had not found before, that would not be very convincing. (This in fact happened after GW150914. Fermi found a simultaneous "signal" they had not found before at approximately the same time and in the (huge) error box for the event. Unsuprisingly, nobody gave that much significance.)

      The situation we got for GW170817 was pretty much the best you are gonna get. The low latency pipelines for both experiments produced alerts, close enough together that realistically speaking it was impossible to launch a target search in that time frame. Also the data streams for both LIGO and Fermi are publically available, so anybody can independently search the each data stream for significant events and check if they will line up.

      Finally, the joint GW and X-ray triggers, triggered a joint prediction that there should be certain type of transient source observable in other wavelengths in a very particular patch of the sky. Such a source was found a couple of hours later, right where it was predicted.

      Delete
    15. @MvdM: Good points!

      The Fermi 150914 post-hoc candidate is a nice example. Several papers were written back then about whether binary black holes may in some cases produce a gamma-ray burst.

      170817 hopefully isn't the best we get, because 170817 wasn't an automatic prediction by LIGO: their first skymap came 4.5h after Fermi and Integral data was already avaible, and after several manual procedures (such as removal of a huge glitch that would normally count as a false-alert).

      Also there was not really a "joint trigger": LIGO triggered 6 minutes after Fermi due several delays, some of them still unexplained, and in one detector only.

      Finally, a sucessful automatic EM counterpart prediction, at the right place, time and distance, would certainly erase any doubts re terrestrial noise.

      After four years, LIGO still hasn't achieved that, but maybe/hopefully it will until the end of O3. Ideally LIGO should do so several times, to ensure it's not just functioning, but reliably so.

      Delete
    16. @Luca: The template-based search method is prone to error. LIGO already had to withdraw their published 150914 template due to the Danish critique, Rai Weiss admitted they "screwed up" the analysis. With 170817 (and all other LIGO candidates), the template-free Danish method doesn't even find a GW signal.

      So at least one successful automatic counterpart prediction is the minimum we should expect of LIGO. They haven't achieved that within four years, but they still may until the end of O3.

      Delete
  10. "Glaciers are now moving faster than this collaboration" That's only due to climate change. :)

    ReplyDelete
  11. I got into Gravity Spy some time ago (it is fun, but one of the more challenging Zooniverse projects). As a classification project, it's as good as they get. Some glitches were well-understood even before the project started (e.g. "violin mode harmonics"); others were tracked down later. I do not know how much effort, by the LIGO team, is being devoted to finding the causes of the remaining "cause unknown" glitches.

    Also, as far as I know, the "glitch classes" are homogeneous ... each class has just one cause, and no cause produces more than one class of glitch (this assumes unambiguous classes, which is, for the hard-core Gravity Spy folk, true).

    ReplyDelete
  12. Bee - just a heads up, you're being shredded on Hacker News (https://news.ycombinator.com/item?id=20881986) Best, AS

    ReplyDelete
    Replies
    1. So there's a guy who did his PhD on LIGO who doesn't like what I say. I'm not surprised. And then there's another guy who tries to claim I have an "anti-computer bias", which is possibly the most stupid "criticism" I have ever gotten.

      This type of ad-hominem bullshit stands in the way of progress because it discourages criticism.

      Delete
    2. "This type of ad-hominem bullshit stands in the way of progress because it discourages criticism."

      I agree, but since others have pointed out typos etc, I would suggest "ad feminam". :-)

      Delete
  13. The imprimatur of the Physics Nobel will make it nearly impossible to challenge the Ligo results--the establishment has put its seal of approval on this enterprise, and it's irrevocable.

    But there's a real danger now that some hucksters will sell imaginary data as exciting physics in their PhD theses, and no one will be the wiser.

    ReplyDelete
    Replies
    1. "The imprimatur of the Physics Nobel will make it nearly impossible to challenge the Ligo results--the establishment has put its seal of approval on this enterprise, and it's irrevocable."

      That is just complete bullshit. There are a number of papers, published in the leading journals, questioning the 2011 Nobel Prize in physics (the m-z relation for type Ia supernovae).

      Delete
    2. Philip H,

      You didn't have to go back to 2011. This blog post is about the "challenges" to the 2017 prize. The point is they're unlikely to lead to anything--this is just empty chatter by the outsiders, which might actually qualify as bullshit, but I won't be judgemental.

      Delete
  14. It's worth noting that, in addition to electromagnetic signals, both neutrino and cosmic ray signals (~coincident with the GWR ones) have been looked for. AFAIK, to date, no such signal has been found, either from an individual LIGO(+VIRGO) GWR event, or from various stacking analyses.

    This is not a very stringent constraint ... after all, the only unambiguous astrophysical point sources of neutrinos are the Sun and SN1987a :-)

    ReplyDelete
  15. How does Ligo decide when the objects in a detected merger are black holes or neutron stars?

    ReplyDelete
    Replies
    1. LIGO does not decide a thing. If there are waves of space the interferometer just contracts and expands its arms so there is a small change in how light interferes. The deciders are human.

      Kip Thorne laid a lot of ground work on PN computations of gravitational waves. The calculations for the merger of black holes, say of comparable mass, predicts a different character for detected waves than for supernovae or for mergers with neutron stars.

      Delete
  16. Good morning, everyone,
    It seems to me that Sabine is giving a new idea, let's measure the speed of movement of the source, and maybe we will find that these signals come from our solar system?
    Thank you Sabine for your blog useful to the entire scientific community.
    NAP

    ReplyDelete
    Replies
    1. Not my idea! It was mentioned to me by Dan Falk.

      Delete
    2. Ha! OK Dan Falk I know, he's a good science journalist and he has a good heart.
      I read an article (n.a.p.pagesperso-orange.fr/downloads/alexandreelbezestoryeditedmiseajourdu7nov2018.pdf) could you tell us what you think, it seems a little opaque to my understanding?
      NAP

      Delete
  17. Clearly what we need is a much bigger detector. Recent calculations suggest that the masses of the supersymmetric black hole mergers we want to see will be firmly within the range of the next-biggest-detector and we should spend all our time and money making the next one up.

    ReplyDelete
    Replies
    1. ESA is planning to launch LISA, three spacecraft forming an equilateral triangle with sides 2.5 million km long. It will look for gravitational waves produced by massive black holes.
      I am really excited to see the results of this and it will not have the same problems with interference as LIGO. Unfortunately we have to wait till 2034.

      Delete
  18. Thanks a lot for that captivating update.

    ReplyDelete
  19. Maybe the researchers can still identify all terrestrial sources, but not all the consequences. GW170608 is an example of that.

    ReplyDelete
  20. In a recent congress on gravity, one of the bosses from LIGO explained how earthquakes affect their measurements. But you do not need to be a specialist to know about these issues: in a public web site, everything is explained. I wish I could write the link to this web site, but it seems that there are problems in this blog with the links (at least I had one problem in my last comment).
    In general, this post looks more like a mental straw than a straight seek for clarity. Sabine, have you contacted (and doublechecked with) any lad at LIGO before writing this post?.

    ReplyDelete
  21. There is a paragraph in your post that I don't understand. You say

    "For most physicists, the 170817 neutron-star merger – the strongest signal LIGO has seen so-far – erased any worries raised by the Danish group’s claims. That’s because this event came with an electromagnetic counterpart that was seen by multiple telescopes, which can demonstrate that LIGO indeed sees something of astrophysical origin and not terrestrial noise. But, as critics have pointed out correctly, the LIGO alert for this event came 40 minutes after NASA’s gamma-ray alert."

    It seems to me that a late alert doesn't matter much. I expect the LIGO collaboration puts sufficiently accurate timestamps on their data that you can check if the gravitational wave event and the optical counterpart occurred at the same time. The only alternative would be
    1. Chance, that can be estimated,
    2. Fabricated data.

    Are you including the possibility that the collaboration added fabricated data to be able claim the existence of a GW event?

    I'm sorry, I think I missed something in the line of arguments in that paragraph from your post.

    ReplyDelete
    Replies
    1. dlb,

      I am afraid you missed the point. We want to know whether LIGO's method of identifying events is any good. For this it is not helpful if they go look for the event *after* they know it's supposed to be there. And so-far, in all cases where the LIGO alerts came first, no one else saw anything.

      Delete
    2. Does it matter that much if the early detection system is good? The main point of content here is if the measured GW are genuine, not if LIGO early detection works well.

      Delete
    3. "Are you including the possibility that the collaboration added fabricated data to be able claim the existence of a GW event?"


      The ideal would be external observers (i.e. people without internal access to the experimental apparatus) to not need any level of trust.

      As it stands, the point is not only about the public alert, but the triggering of the detectors involved. Fermi-GBM triggered roughly six minutes before Hanford/LIGO, with Fermi's prior trigger being accessible to LIGO.

      To point it out is not to imply malfeasance - it is just to conclude that causality is not foolproofing the timeline of events.

      Delete
    4. Sabine, as a point of clarity I suggest you note that the published data shows the gamma ray burst was detected 1.74 seconds after the Gravitational wave was detected (https://iopscience.iop.org/article/10.3847/2041-8213/aa920c/pdf) --which is consistent with proposed astrophysical mechanisms. The timing of when the alerts were released to the public is a separate issue.

      Delete
    5. @VanceH: Actually, it was detected 6 minutes after the Fermi GRB trigger, but apparently found 1.74 seconds before.

      Delete
  22. Not bound by sober inference, I thought of some of those other things science has shrugged off -- like the premature detection of gravity waves in the ‘60s, then finding exotic excess emissions from curium bombarded uranium, with more recent evidence of energetic particle showers seeming to have originated from below -- and so wonder whether it’s what her scratching at glitches has loosed.

    ReplyDelete
  23. The problem here is that you cannot isolate the detectors to parameterize them. Even if you can identify some sources of noise, it must be verified by other means. For each detector individually, you can parameterize the sensitivity and the resolution. With two detectors, you can identify synchronized events and record the stats. But you have no way to be sure a signal is coming from space. To do this you have to assume something a priori. Only with three detectors with a statistical ensemble you may discriminate the origin. So, a single event can never be significant unless you have more detectors or another astronomical observation.

    Let`s say you have three detectors, A, B and C. First you define what you considered as valuable correlations. Then you gather the data for each pair A-B, A-C and B-C. Now with these stats, you may deduce what stats you should get if you combine all the detectors. Any excess measured in the correlations of the three detectors compared to your expectation must be considered to be coming from space. So, to claim a detection, you need three detectors and an ensemble of observations. Each individual event is not significant unless you have an external detection.

    I think Ligo truly detected GW but my confidence is just a lower.

    ReplyDelete
  24. As noted above, you cannot prove that there are no unicorns. Trying to exclude all imaginable and unimaginable source of signals will never succeed as there are more sources imaginable than can ever be excluded by evidence.

    "But, as critics have pointed out correctly, the LIGO alert for this event came 40 minutes after NASA’s gamma-ray alert."

    The delay between the merger and the gamma ray burst was 1.7s. This means that the distance between the source of the gravitational waves and the earth and the source of the gamma rays and the earth differ by at most 1.7 light seconds. That is one falsifiable prediction that holds up for the two source to be the same.

    There are suggestions that the detected signals are not astrophysical but "terrestrial".

    A significant fraction of events are detected by all three detectors, two in North America and one in Europe. That does restrict the possible sources considerable. The disturbance has to move with the speed of light and must be such that it can reach all three places unimpeded by the curvature of the earth to give the right type of signal.

    Some people suggest that there is some statistical fluke in the noise that is picked up as a signal. If that would be the case, the number of simultaneous three detector events would be only a small fraction of the the number of simultaneous two detections. That is not what is seen. The difference in two and three simultaneous event detections is what is expected from the lower sensitivity of the Virgo detector.

    ReplyDelete
  25. Hi SABINE. !!!

    Have a moment.
    will keep it in English.

    Again, I don't know how you
    do what you do.

    Thank You for Your Work.

    ReplyDelete
  26. It's a great problem if science runs more and more in the direction of experiments with an overwhelming part of data manipulation before interpretation. And more and more expensive experiments with little chance of independent reproduction.

    People tends to cheat (or choose hopeful interpretations) if their jobs are in danger. And the data manipulation parts give more than enough possibilities ...

    And the international science community seems to be more and more one clique ...

    ReplyDelete
  27. Or let's say it this way: There are only a few people in science with high reputation which would be able to break through with fundamental criticism. And this people have no interest to do so.
    And any other people only have a future in science, if they support the common standpoints.

    Science becomes more and more politics and scientists act more and more like politicians.

    ReplyDelete
  28. Hi Sabine,
    Why are you afraid to answer me? I have asked you this question several times, and still without answers.
    Thank you for your scientific courage, which is rare in the scientific community. Please answer our question.
    NAP

    ReplyDelete
    Replies
    1. What question? I don't know what you are even talking about. Look, I get several hundreds of questions and comments a day. Sometimes I miss a few. Give me some slack.

      Delete
  29. What are Donald-Fauntleroy-Duck waves, and why should LIGO be able to detect them? A Donald-Fauntleroy-Duck wave is a wave with shape resembling that of the famous Donald Duck. I elaborated templates for detecting Donald-Fauntleroy-Duck waves that could emerge from the raw data noise. LIGO should be able to detect Donald-Fauntleroy-Duck waves, because their events are as probable as those of gravitational waves. Seriously, there is a gap between what LIGO tell us they have observed and the real source (or sources) of the telling. That gap is called scientific method. Scientific truths don't need believers, just verifiers. The LIGO's telling is: "believe us, what we have observed are gravitational waves". But, why should I trust you? Is that science? The gap, guys, they cannot avoid the gap.

    ReplyDelete
  30. The Ligo blog post is really interesting news. Gravitational wave detection is quite a new business, and I would not expect, that the analysis of the observed events is already correct, since comparison with observations requires a lot of fine tuning and quite delicate assumptions. We already know this from the analysis of HEP data at LEP and elsewhere. LIGO is the the very first experiment, which has seen gravitational waves at all. Hope, that further experiments will follow. It's a new window and a big chance for deepening our physical knowledge.

    ReplyDelete
    Replies
    1. Exactly this. They are the first to learn how to extract these signals from the data. Hence you want to make sure that what they are extracting is what they claim it is.

      Delete
    2. I would never trust in the results of a single experiment too much. There have been four experiments at LEP in combination with SLD studying the Z_0 resonance. LIGO is only the very first experiment detecting gravitational waves. This is good for a Nobel Price anyway. The interpretation of the measured data should be treated with scepticism. I remember the "dark matter" detection of DAMA/LIBRE for example... Further gravitational wave experiments are hopefully to come...

      Delete
    3. How does the "single experiment" argument apply here? By now it is 3 detectors, at 3 separate locations, using from slightly to quite different technologies and one of them is being run by a quite different team in their own way. Will a 4th detector resolve this issue? A 5th?

      Delete
    4. @Vagelford: Would 5 detectors solve the issue? No, because it could still be noise correlations. There may even be more false-alerts, if you count all possible two-detector pairings.

      But obviously, 5 detectors could provide a much more precise (automatic) EM counterpart prediction, which can be verified more easily.

      Delete
    5. Well, in that sense then, reality could merely be noise correlations, albeit very persistent ones.

      Delete
    6. As always in science, it's a question of verifiability and falsifiability. Falsifying LIGO is quite difficult, but EM counterparts can be verified quite easily.

      Delete
  31. I feel like you are completely discounting the fact that the data is open and thousands of non LIGO people are crunching it and working with it constantly.

    On a thematic note: Are there any large science experiments you have faith in?

    ReplyDelete
    Replies
    1. I am not "discounting" anything and I wish that instead of trying to psychoanalyze me you would think about what I wrote.

      I have faith in pretty much any other large science experiment, thanks for asking.

      Delete
    2. I apologise. How did I psychoanalyze you? I will certainly read what you wrote again.
      I still think that the question you are asking would be raised by a number of other scientists as well by this point. I am sorry I upset you. What physics are you excited or enthusiastic about?

      Delete
    3. You did not "upset" me. I am pointing out that your question about my "faith" is off-topic and irrelevant.

      "I still think that the question you are asking would be raised by a number of other scientists as well by this point."

      Yes, you would think so, wouldn't you.

      Delete
  32. As an observational cosmologist with no particular involvement in LIGO, I will explain why GW 170817 is almost certainly genuine: it is true the GRB signal was known in real-time to LIGO. However the GRB signal provided much cruder sky position and essentially no distance information; but LIGO did predict the sky position and distance consistent with the later optical/NIR transient AT2017gfo, _before_ the transient discovery. If the GW signal were a "false positive", even ignoring the time coincidence they also had to luck-out at about 1-in-30 on the sky position AND c. 1-in-100 on the distance, (since the optical transient is by far the closest out of c.100 short GRBs followed-up to date, but there is nothing unusual in the gamma-rays to flag that). This requires a crazy string of coincidences in time,position and distance so you can pretty much dismiss the "false positive" idea.

    Now, turning to the non-detections in LIGO 03: no real surprise. For the one "good" BNS candidate S190425z , the 90 percent sky area is a huge 7500 sq.deg (maybe one detector was offline?); finding something 16x fainter than AT2017gfo in that huge area within the few days before it fades is almost hopeless. For the NS-BH candidate S190814bv, the search area is only 30 sq.deg, but as noted it is 7x more distant than 170817. If it were "only" 50x fainter it could well have been found by now, but if there's less ejected material, another factor of 3 or 10 down in intrinsic luminosity would take it too faint for the visible searches.

    Bottom line: GW170817 was real, but unusually close and easy to spot the EM counterpart. For more distant events it gets a _lot_ harder to find the EM counterpart. Might take a year or two before the next nearby NS-NS merger with EM counterpart shows up; that will close down the debate.

    ReplyDelete
    Replies
    1. Hi Will,

      You raise very important points, but it's more complicated.

      The distance to AT2017gfo could never be determined by telescopes, not even an association to a globular cluster of supposed host galaxy NGC4993 was found. So a foreground or background object still cannot be fully excluded.

      Also, by the time LIGO published its 30deg2 skymap, both Fermi AND Integral data was avaible for 4.5 hours, and the LIGO skymap was placed approx. at the center of the COMBINED Fermi-Integral (triangulated) skymap.

      Moreover, even the apparent time association with the GRB trigger can be questioned: a template-free search-method (as proposed by the Danes) finds a signal that is consistent with no GW signal at all.

      Finally, the fact that no counterparts have been found in O3 certainly is a surprise to LIGO, as they initially expected to detect 50, later 10 BNS mergers in O3, of which 20% with a precision of 30deg2 or less. Currently confirmed are zero. There may certainly be reasons for this, but it means there is still no independent confirmation.

      Bottom line: after four years, LIGO has not yet achieved a successful automatic counterpart prediction. Theoretical FAR values are not reliable, as LIGO already had to retract a BNS candidate with a FAR of 1 in 5 billion years as noise.

      Delete
    2. Your point is important and most probably GW170817 was a real detection. That said, it is worth to review any possible counter-arguments.

      LIGO's skymap was sent only after Earthly observers already had information from both Fermi and Integral GRB data, making it possible - at least in principle - that such data could be used to fine tune LIGO's data. As we can see in the ApJL multimessenger discovery paper, LIGO's skymap very nicely fits into the smaller patch of the sky of joint Fermi-Integral data, see figure 1:

      https://iopscience.iop.org/article/10.3847/2041-8213/aa91c9

      And the collaboration does have the tools to reverse engineering GRB data in order to guide GW analysis.

      I am *not* stating they have done so, but only pointing out that skeptical external observers can not know better.

      Delete
    3. To Guest: yes you are correct that there's no actual redshift for AT2017gfo. However, the association with NGC4993 is very convincing: first, galaxies outside the Local Group and closer than 50 Mpc cover very roughly 0.1 percent of the sky, so a chance alignment is a (different) improbable coincidence. Next, what are the alternatives... if the host of AT2017gfo were a more distant galaxy, NGC4993 is smooth and near-transparent, so a background galaxy should show up as a fuzzy blob superposed on NGC4993 after the AT faded - not seen. An unseen background galaxy would need to be very faint e.g. many Gpc distant, but then implying a very extreme luminosity for the AT. The last possibility is no host galaxy, but extragalactic transients with no host galaxy are very rare. Result: it is almost certain that AT2017gfo was inside NGC4993, independent of the LIGO data.

      Re the rates, 50 NS-NS events predicted in LIGO O3 must be a typo/mistake - the projections were roughly 1.6x range and 4x more events per time than O2, but the real gain in O3 is slightly below projections. Given one NS-NS event in 7 months in O2, this would scale to about 1 NS-NS event per 2 months in O3, with a large uncertainty, so there is no anomaly on rates.

      To Clovis: re the gamma-ray position, theoretically yes, practically no. In 2017 the Fermi team had 9 years of experience tuning their GRB locations; to theorise that the LIGO team, with little experience of gamma-rays or spacecraft, had a secret magic algorithm that improved the gamma-ray-based position by 10x in 5 hours is not realistic.

      Delete
    4. @Will: An association with NGC4993 is certainly likely, but not certain. But even if the distance is correct, LIGO was still 4.5h after Fermi and Integral, had a 50% distance uncertainty, and of course knows all the cosmographic data of the target region. So the distance alone doesn't prove a GW measurement.

      To remove any doubts, LIGO should simply provide one or two automatic counterpart predictions.

      The 50 NS-NS wasn't a typo, it was LIGO's initial published expectation. They scaled it down prior to O3 to 10. As you say, no anomaly, but no confirmation either.


      Re gamma-ray position: no need for a "secret magic formula", since the GRB triangulation algorithm is published knowledge. Moreover, NASA-Fermi and LIGO have a common working group, even their detection pipelines are coupled.

      So you see, it's a little more complicated than many assume. But as I said, LIGO can easily defuse any doubts by providing a few automatic counterpart predictions. 170817 clearly didn't meet that basic requirement.

      Delete
    5. Will: Ligo has been running programs to search for GW by GRB guidance since the early days, when they had not sensitivity enough to rule out signals without further input. You can look around for Leo Singer papers on the matter. He is also a key person in charge of the skymap produced on 170817.

      Again, I am not making accusations, but pointing out the technical expertise Ligo has to correlate GRB and GW analysis is not mere speculation.

      Delete
  33. Wouldn't it be ironic if the glitches turned out to be the most important data, pointing to some profoundly novel and unexpected feature of the universe? They might actually be worth some close examination and analysis.

    ReplyDelete
    Replies
    1. I have since learned that all the glitches so far fall into eight distinct categories. So you have hundreds of such events, but they fit into a limited number of distinct types of event. That's at least interesting...

      Delete
    2. Glitches are deeply analyzed and the cause of many glitches are known. The information about their causes is used to mitigate the glitches by filtering them out from the data and by fixing the problem in the detector. Glitch investigation and mitigation is an important part of increasing the detector sensitivity. The same time there are several glitches with unknown causes, these glitches cannot be vetoed from the astrophysical searches.

      In Gravity Spy we see many different type of glitches, volunteers classify glitches by morphology in order to prepare training sets for the machine learning algorithm (supervised learning, deep convolutional network) as well as to find the new types. Using the output of Gravity Spy the detector characterization group investigate the origin of glitches. There were 200K+ auxiliary data channels during O2, during O3 there are even more. These auxiliary data channels are used to monitor the detector and its environment, and all these data are used for analyzing the glitches by the detector characterization group. So yes, the glitches are very deeply analyzed.

      Delete
  34. For many years I have been analyzing geophysical data in search of extremely weak signals of constant frequency. That's why I'm very surprised that it was possible to extract tiny signals from the noisy LIGO data. To represent the magnitudes: Signals significantly exceeding the noise level (SNR> 20 dB) can not be overlooked. It becomes difficult when the mean amplitudes are about the same (SNR = 0 dB). Then the measurement time must be much longer than the (constant) oscillation period.

    At SNR = -20 dB (signal amplitude = 10% of the noise amplitude), the detection succeeds only if the frequency is exactly known and *constant*. In addition, the signal should be repeated several times so that the records can be added in phase. At SNR <-30 dB, neither these tricks nor elaborate selective filters help to detect the signal. Matched filters never reach the quality of narrowband filters.

    Now it is claimed that LIGO succeeded in detecting a *variable* frequency signal at a SNR = -60 dB, even though it lasted only a few milliseconds, had no agreed starting time and was never repeated. Incredible!

    ReplyDelete
  35. Seems like a reasonable summary: https://www.quantamagazine.org/studies-rescue-ligos-gravitational-wave-signal-from-the-noise-20181213/

    ReplyDelete
    Replies
    1. These have already been refuted: even with updated templates, the residual noise correlations are still there. Moreover, the updated templates have quite different source localizations than the original one. => https://arxiv.org/abs/1903.02401

      Delete
  36. Sad to say, there is so much sniping of eachother's work in this field that it's not surprising we are in this state of affairs where nobody is sure of what's correct. The inquisitive nature of science has been replaced with an all out competitive brawl, resulting in a stalemate on results. Competition does not always produce the best product, especially in science (basic game theory, multiple winners). Cooperation, on the other hand, seems to work a lot better in cognitive ventures (the Nash equilibrium, etc.).We have to change the reward structure in science if we want better results.

    ReplyDelete
  37. But, as critics have pointed out correctly, the LIGO alert for this event came 40 minutes after NASA’s gamma-ray alert.

    Not to mention the fact that there are gamma-ray burst events recorded daily. Since there have been no additional associated GW events, that leaves 170817 and its electromagnetic counterpart looking like a coincidence rather than a correlation.

    ReplyDelete
  38. Sabine,

    There are experiments that show the force of gravity can be decreased by shielding an object with a “sheet” of light (micro waves too). The experiments showed that gravity – in relation to rest mass – is a push force, generated by vacuum space around as a result of the existence of rest mass.
    Because rest mass is the result of local decreased scalars of the Higgs field I suppose that gravitation – in relation to rest mass – is created by the vectorized flat Higgs field (vacuum space). However, vectors created by vectorized scalars are not limited by the speed of light, they act instantaneous (Newtonian gravity).

    If 2 neutron stars merge there is no doubt that both neutron stars have rest mass (local decreased scalars). But will the collapse create gravitational waves? It is GR that predicts gravitational waves but because GR translates everything into amounts of energy, there is no certainty that the proposed gravitational waves are “truly gravitational” at all. If the upper limit of the detected gravitational waves is the speed of light it seems to me that the detected gravitational waves are a type of electromagnetic waves. Is there any clarity about the kind of quantum field that creates the LIGO waves? Because the delay of the gravitational wave of the 170817 neutron star merger in relation to the observed NASA’s gamma ray alert can be interpreted as a mass wave (the transfer of a local topological deformation of the structure of the electromagnetic field).

    ReplyDelete
  39. It looks like the LIGO and Virgo collaborations have recently attempted to answer these concerns here: arXiv:1908.11170. I've skimmed it, and it appears that addresses many of the concerns you've raised. It also points to a large body of prior technical publications which outline details of signal processing and techniques for understanding and suppressing glitches.

    ReplyDelete
    Replies
    1. And which of my concerns do you think this paper addresses?

      Delete
  40. What if glitches are some sort of spacetime bubble (think of Alcubierre's) passing by the Earth? Can we rule out something so exotic like this?

    ReplyDelete
  41. Inter-detector lag restrictions were relaxed between Livingston and Hanford from c|~3,000 km (~10 ms) to ~0.67 c (~15 ms); this particular laxity invites us to view the LIGO time codes as correlated to clock errors and trigger|strain latency. These joint conditions are not accounted for in false alarm rate estimation, especially as all O1, O2, and O3 reported triggers are accompanied by synchronized cloud-ground global lightning discharges within this 0.67 c restriction during event windows,themselves coherent with space weather indices as recorded by ACE and GOES, as well as geomagnetic/geoelectric ground stations.

    Why these uniquely coincident terrestrial states are absolutely ignored by all LIGO-Virgo investigations into fundamental physics of gravitational waves is telling.

    LIGO-Virgo magnetometers are generally inoperative and always saturated during event triggers. These onsite magnetometers are the sole safeguard, with power system and clock error analysis, against conflation of global coherent chirp transients with desired non-EM signals. All of these local ground, interplanetary, and solar datasets can be readily accessed by LIGO and their "glitch group," and should be applied earnestly to assessment of rather simplistic noise taxonomies prescribed hitherto.

    0.67 c is a LIGO-Virgo recurring spin parameter central tendency for putative source remnants, as spin is degenerate in LIGO signals with other key parameters, which are merely model-assumed. No measurement of actual group velocity is possible: c is merely assumed due to expectation of this value and selection of lag restrictions between detectors that preserve this criterion. 0.67c, however, is a fairly precisely calculated rate for many terrestrial shocks from magnetospheric mode dipolarization that can affect global gravitational wave detectors no differently than supposed GW triggers (arguably exactly as all LVC non-retracted triggers given their physical identity), as many LIGO publications declare and study. Conclusions remain unchanged: "reduce noise," and "we're working on it."

    Single detector triggers are not only permitted, but are indeed the expressed goal for refinement of absolute confidence.

    A single detector trigger was reported for O3 as the most recent with respect to this comment, S190910h, with false alarm rate of 1.13 per yr. These abuses of method (single detector triggers, 15 ms LIGO max lag) is admitted in customary subdued fashion in December, 2018 O1-O2 LIGO-Virgo catalogue that added 4 new events (all within ~25 days at end of O2 during some rather exceptional foreground magnetospheric ground
    coupling conditions), also elevating LVT151012 to GW151012 and increasing confident triggers from N=6 to N=11.

    ReplyDelete
  42. Sabine Hossenfelder wrote (at 12:48 PM, September 04, 2019):
    > the LIGO/VIRGO collaboration has reported dozens of gravitational wave events: [...]
    > But not everyone is convinced the signals are really what the collaboration claims they are.

    > [...] the question whether there are any events of terrestrial origin with similar frequency characteristics arguably requires consideration

    Does the (additional) question also require consideration whether LIGO/VIRGO have experienced detection events of astro-physical origin, which were not (or at least not exclusively) due to gravitational waves having passed their "freely swinging" 4th pendulum stages (as they claimed), but instead (or at least partly) due to their entire detector equipment (as well as the entire earth) being suitably gently and coherently shaken, pushed or "forced to swing" ?

    Are the LIGO/VIRGO detector systems capable of distinguishing the passage of a gravitational wave from detector equipment being suitably shaken, if either of these occurences can induce the same strain "chirp" signal, matching some signal template ?

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  43. What of this?
    http://news.mit.edu/2019/ringing-new-black-hole-first-0912

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    1. @JB: If LIGO's initial signal analysis is false (as the Danes claim), all of these follow-up theoretical analyses are false or unfounded, too. With 150914, in particular, LIGO had already to admit that their published signal was inaccurate (see Nov 2018 article by the New Scientist).

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    2. Completely unaffiliated scientists from a number of different institution using their own methodology. I'll grab my tinfoil hat.

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    3. @JB: Actually, the lead author is from the MIT LIGO Lab, and the analysis is based on the very same data still disputed by the Danes and some others. So, no need for your tinfoil hat, this time :-)

      Interestingly, LIGO's best-fitting 150914 waveform still hasn't been published, so an independent verification of their analysis is impossible anyway.

      But let's just hope LIGO achieves a first successful automatic counterpart detection before the end of O3 that removes any remaining doubts.

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  44. Not at all. If the intitial signal analysis is false, that would imply that whatever is there in the datastream is either pure noise or the artifact of some terrestrial source. In both cases, doing consistency tests on the signal weakens the liklihood of such alternative hypotheses.

    If the signal is not actually from a black hole merger, but from some terrestrial source that merely somewhat mimics a black hole merger, than there is absolutely no reason to expect that any "overtones" in the ringdown should be consistent with the fundamental frequency of the ringdown, or the final mass and angular momentum inferred from the inspiral.

    Consistency, of various parts of the signal make any alternative hypotheses (ranging from "this was not an astrophysical event" to "the merging objects were not black holes") significantly less likely.

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    1. @MvdM: Well, the lead author of the overtone paper is actually from the MIT LIGO lab, so this was hardly a fully independent re-analysis, but based on LIGO's initial analysis, which in turn is based on LIGO's half a million theoretical waveform templates.

      150914, detected during the final engineering run, is such a perfect and strong SNR outlier that few people believe this was just (detector) noise. If it's not an astrophysical signal, it may be some terrestrial impulse, or "something else", as LIGO itself initially suspected.

      More interesting than unverifiable black hole ring-down overtones would be spin-down GWs from known pulsars, but as you know, LIGO didn't detect any from the 221 pulsars examined.

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    2. I never said nor implied that this was in any sense an independent re-analysis. I just pointed out that the hypothesis that this was indeed a signal from a black hole merger leads to a very concrete falsifiable prediction for the ringdown overtones.

      If this was indeed a terrestrial signal of "something else", than there would be no reason to expect the overtones to be exactly those predicted by GR for a black hole merger.

      Consequently, measuring the overtones and finding that they agree with GR, further strengtens the argument that this is indeed a signal from a black hole merger rather than "something else".

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    3. @MvdM: I didn't say a terrestrial signal OF something else, but OR something else. That something else could very well be a theoretical GRT black hole waveform, but it still needn't be of astrophysical origin.

      Until LIGO achieves at least one successful automatic counterpart detection, this is very difficult to rule out, unfortunately.

      And as the authors of the overtones paper state, the 150914 "engineering run" signal is currently the only signal strong enough to test the hypothesis.

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    4. @Guest: Are you suggesting it could be a black hole merger here on Earth? To create a strain the size of the GW150914 signal those black holes should still have total mass of trillions of kgs. It seems unlikely that such an event would have gone otherwise unnoticed.

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    5. @MvdM: No, this is not what I'm suggesting :-) But let's leave it here and simply hope LIGO will achieve a first automatic counterpart prediction before the end of O3 that removes any remaining doubts about its functionality and reliability. Unverifiable black holes, astrophysical or not, aren't going to do that, anyway.

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