What’s Up with LIGO?
backreaction.blogspot.com
backreaction.blogspot.com
> But, as critics have pointed out correctly, the LIGO alert for this event came 40 minutes after NASA’s gamma-ray alert.
I was there the day of, when this alert went out, and the reason for that delay was that one of our detectors had its data vetoed due to a loud glitch minutes earlier and our European counterparts, Virgo, had problems getting us their data in a timely manner. As a result of that, and the fact that we had human-in-the-loop checks for everything that went public, our first announcement was slow and poorly localized, with improved data products being released throughout the day. All of this is well-described in our publications [0] on the event and can be corroborated by any one of hundreds of scientists who know what they are talking about.
[0] https://www.ligo.caltech.edu/page/detection-companion-papers
I've been following her writing for a long time, and it seems that writing a book about how "naturalness" hasn't been very good for particle physics got her somewhat radicalised, having far more scepticism than what seems warranted.
When BICEP2 was announced in 2014 Hossenfelder wrote "some people say this is wrong, I'll just say what it might mean" and then never returned to the topic with a full post as far my searches can tell. Now some danes wrote a paper with a pretty large technical flaw and LIGO representatives where a bit rude to a theorist asking about said paper and apparently this is a controversy good enough for at least 3 posts about how shaky the detections are...
But if you follow the link in that statement, it leads to a previous post of hers (from November 16, 2018), which concludes:
"Basically, I feel reassured in my conclusion that you can safely ignore the Italian paper [which questions the NS-merger]."
It's more than a little odd to imply that there has been potentially meaningful criticism of GW170817 by referring to a post in which she herself concluded that there hasn't.
Leaving aside the question of why there was a "delay", this is a fundamentally incoherent and meaningless critique on Hossenfelder's part. (Well, unless you want to take seriously the implication that the LIGO team could have used that 40 minutes to create a fake alert to go with the gamma-ray alert.)
As long as we have reason to believe (and we do) that the LIGO data record is valid, then when the alert was issued is irrelevant to whether it is "an independent confirmation of LIGO's detection capacity."
(The detection of neutrinos from Supernova 1987A was reported about two weeks after the optical detection of the supernova [optical detection: 24 February 1987; Hirata et al. Kamiokande paper submitted to Physical Review Letters in early March of 1987]. So I guess we should question whether neutrinos from SN 1987A were ever really detected?)
At sufficient precision, every experiment will face unknown non-gaussian stochastic fluctuations. It is the single most-important job of an experimentalist to discern how to accurately assess the uncertainty in a measurement. LIGO's false-alarm-rate approach to significance estimation is data-driven and, to me, compelling.
The false-alarm-rate approach uses a simple fact: any detector signals at different observatories separated by more than an Earth-light-crossing-time cannot be a gravitational wave. By placing time-shifted signals from the two (or three) detectors into the gravitational-wave analysis pipeline, one can determine the accidental-detection rate, no matter what kinds of glitches might occur. Detections and candidates are reported with such a data-driven false-alarm rate.
Gravitational-wave searches, in the context of the post, are searches for transient disturbances in the detectors. Glitches are initially-unexplained transients. It is, in general, folly to believe that any instrument capable of sensing, in one second, an object's displacement by 1/20,000th of a proton diameter won't see the occasional unexplained transient. It is, as mentioned above, essential that a scientist using such an instrument credibly assesses measurement uncertainties.
If you are a gravitational-wave skeptic, keep your ears open for binary-neutron-star mergers. A simultaneous bang-and-a-flash are nigh-impossible to fake. I'm a skeptical experimentalist (experimentalists are skeptical, as a species), and I've found GW170817 sufficiently-compelling so as to remove any remaining doubt that LIGO/LVC has seen gravitational waves (They almost certainly discovered the site of the R-process at the same time! What more do you want?). As neutron star observations accumulate, the case will only get more compelling. All of us are waiting for the next bang-and-a-flash, as the potential for discovery and wonder is enormous.
Most of the claims in this article have been refuted elsewhere, and I am sure current LIGO scientists will jump in here to further refute its claims.
The matter of "retractions" is, for example, not a fair criticism. LIGO generates automatic low-latency notifications of potential detections in order to allow optical telescopes and other detectors to aim at the location of the potential event. Upon further analysis -- which takes time and can't be done at low latency -- many of these event notifications are downgraded. These retractions should not diminish your confidence in LIGO. Indeed, the team fine tunes the "false alarm rate" to avoid sending out too many false positives while not missing real events.
The gravitational wave community is _extremely conservative_ in its scientific statements, and you can be assured that every scrutiny has gone into the analysis of detected events and the associated papers. The LIGO detections should not be considered controversial. There is 30+ years of science behind them, and the effort of thousands of professional scientists.
The post itself explained this...
>> "The alerts must go out quickly in order for telescopes to be swung around and point at the right location in the sky."
The rest of your criticism doesn't really match up with the post for me either. (See "I do not have the same concerns as were raised by the LIGO critics", etc.)
> 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.
This has been solidly debunked by several independent groups. Here's the first Google result I found on the topic:
https://www.quantamagazine.org/studies-rescue-ligos-gravitat...
> 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.”
I'm not sure what this is about -- it sounds like some off-hand remark taken out of context -- but the numerous, extremely detailed follow-up publications, not to mention that the public data release, should clear up any ambiguities.
https://www.ligo.caltech.edu/page/detection-companion-papers
> "Since April, the collaboration has issued 33 alerts for new events, but so-far no optical counterparts have been seen. "
That should say that no NEW optical counterparts have been seen. GW170817 was a stunning success wherein a neutron star collision was observed by LIGO in gravitational waves and by numerous optical detectors.
https://www.ligo.caltech.edu/page/press-release-gw170817
> The number of retractions is fairly high partly because the collaboration is still coming to grips with the upgraded detector.
True. These aren't really "retractions," but low-latency event notifications that are downgraded on further analysis.
> With the still lacking independent confirmation that LIGO sees events of astrophysical origin
False. GW170817.
> "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."
This is simply a conspiracy theory. Note that the author (Mr. Unzicker) claims that CERN, a completely separate experiment and group of people, was subject to the same kind of conspiracy.
> And then there are the “glitches”.
LIGO data is indeed very non-stationary (in the spectral sense) and contains various instrumental artifacts. A great deal of effort is put into understanding these effects.
https://web.archive.org/web/20180911150844/http://911encyclo...
http://s3.amazonaws.com/nasathermalimages/public/video/prete...
> False. GW170817.
One observation does not independent confirmation make. Obviously from context Sabine doesn't mean independent in the independent group sense as the observation itself is collaborative and there aren't exactly other ligos around.
Why are you so defensive?
> there aren't exactly other ligos around
One of the three currently operating GW detectors is Virgo, of a different design and build by different people, in Italy. It's true that LIGO and Virgo collaborate extensively.
https://commons.m.wikimedia.org/wiki/File:GW170814_signal.pn...
While I'm not a signals expert... I'm not exactly convinced.
https://www.gw-openscience.org/about/
There are eleven peer-reviewed published papers on this event, in addition to a complete public release of the time series data.
https://www.ligo.caltech.edu/page/detection-companion-papers
I'm ruling out a SN origin on the basis of the (at least) dozen of direct observations that show it isn't.
The more one knows about software, the less one trusts it, absent independent corroboration. Especially, software coded by grad students. Software engineering is a discipline of its own not generally taught them.
https://www.popularmechanics.com/military/a6384/debunking-91...
A false positive is a lot better than a false negative here.
Only if the cross correlation frequency is higher than the autocorrelation frequency. In other words, how often do signals with signature X appear, in each detector? If it's frequent then the likelihood of a by chance cross correlation is higher.
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.11...
Well, there is still the chance that similar terrestrial events might happen at the same time near each detector. Especially while we only have 2 or 3 active LIGO detectors.
I don't know how closely "fingerprinted" each event is to rule out such coincidences. It might be purely theoretical.
Then again there is still the theoretical chance that an event will occur at an equidistant point from the LIGO stations and produce a signal of the same signature at all places at the same time.
Probably absurdly unlikely, even as a conscious prankster attack.
(Sorry for being so difficult...)
Such a coincidence would have to produce the same specific signal in each detector. That's highly unlikely.
> there is still the theoretical chance that an event will occur at an equidistant point from the LIGO stations and produce a signal of the same signature at all places at the same time.
You're misunderstanding the relative time criterion. It is not that the signals are seen at the same time in all the detectors. It is that the signals are seen at just the right different times at the detectors that would be expected from an outside signal that travels at the speed of light through the Earth, hitting the different detectors at different times as it passes through. An event that really is seen at the same time in all the detectors would obviously be of terrestrial origin and would not be reported as a detection of an outside signal. Even events that are at different times, but the wrong different times for a light speed signal coming from outside, would not be reported as a detection.
To be fair, electromagnetic (i.e. radio) waves do travel at the speed of light through the Earth, though almost none can significantly penetrate the Earth itself, except extremely low frequencies. Electromagnetic interference should be quite easy to measure and look for correlations though; if scientists did their homework (likely), it has been ruled out.
But indeed I'm not an expert by any means on magma properties, perhaps someone else can chime in. If magma is conductive then even less radiation goes through.
Keep in mind at extremely low frequencies the whole Earth is in mid-field or near-field of emissions, so it doesn't behave attenuated like light rays.
Yes, but they won't jiggle the test masses in LIGO, so they won't produce a signal.
Every false alarm should be investigated to see what produces such frequent apparent events. They need to distinguish better real events from ersatz events, independently of simultaneous reports elsewhere or optical confirmations.
No, it records interference patterns at a detector which are produced by jiggling of the test masses. There are no other means of producing those interference patterns--certainly not by low frequency EM radiation happening to pass through the apparatus, which was what the post I was responding to was talking about.
The question is what makes the test masses jiggle. A gravitational wave is one possibility, but certainly not the only one. Seismic disturbances, a truck driving by the facility, someone banging on the wall of the vacuum chamber, etc.
The electrical signals you are talking about come from the interference detector. It is possible that there could be electrical noise elsewhere in the circuit, but that's something the experimenters already allow for and take great precautions to minimize, just as the test masses are isolated to minimize any source of jiggling of them other than gravitational waves.
> They need to distinguish better real events from ersatz events
What do you think they could do better?
They already have plenty of these. Comparison of signal arrival times at multiple detectors is not even close to being the only criterion they use. It's just an important one that is not mentioned in Hossenfelder's article.
My understanding is that the LIGO team generally assumes that the orbits are perfectly circular before merger. This is normally quite a good assumption because gravitational waves will circularize the orbit, so if the orbit began with any modest eccentricity the eccentricity right before zero would be nearly zero.
The interesting thing is that if the original system was not a two-body system but was a three-body system, then the influence of the third body could have driven the inner two to extremely high eccentricities (say, 0.999). Although gravitational waves would still reduce the eccentricity, there could plausibly still be a residual eccentricity of ~0.1 at merger. It's not clear to me how signals like that would match with the pre-calculated templates.
Back when I was in the field (four years ago now) there was just starting to be a pretty good awareness in astronomy about the importance of three-body systems for various astronomical events, but I had the sense that that awareness hadn't yet spread to the LIGO community.
> 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.
In the provided link:
> Brown, part of the LIGO collaboration at the time, explains this as an attempt to provide a visual aid. “It was hand-tuned for pedagogical purposes.” He says he regrets that the figure wasn’t labelled to point this out.
I think you will find that any ambiguities are resolved in one of the thirteen peer-reviewed publications on the detection available here:
https://www.ligo.caltech.edu/page/detection-companion-papers
See: Ultra sensitive detection of radio waves with lasers https://www.nbi.ku.dk/english/news/news14/ultra-sensitive-de...
It would be interesting to see how this method of EM-wave detection interferes with the GW-detection.
1. At the LIGO observatories there are numerous auxiliary sensors, including radio receivers, that are used as "vetoes" for candidate gravitational wave events.
2. For binary black hole or neutron star inspirals, the gravitational wave waveforms are well-modeled using numerical general relativity. The fact that the observed detection matches the prediction so well lends additional credibility to the detection.
Regarding #2, we are of course hoping to detect something unexpected, with an unknown waveform. In those cases we'll rely on the veto channels to ensure that we have not detected contamination from a radio event.
Regarding 1: In the article, they describe an antenna that is MORE sensitive than the normal antennas. So you may not be able to detect the low frequency radio-waves without a similar sensitive apparatus.
Regarding 2: There is the problem that Electric signals can have high similarities with the "Chirps" that LIGO is looking for. For example: even in space, you can find all kinds of "chirps" caused by solar plasma. google "noises from space".
2. This point is valid.
Accepting their points as valid and not disputing them just leads to the perception there are two equally valid opinions about the topic, when one of them is fringe and makes bad arguments. We do ourselves no favors by that sort of attitude being common and accepted.
nice