I'm a LIGO Ph.D. student and this is a crackpot hit piece. I won't go through everything, but let me address this point:
> 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.
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.
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?)
She may not be a crackpot within her field of expertise, but she is writing confidently without doing background research. I stand by my characterization of this piece as being of crackpot quality, and while I trust that she is perfectly capable in her own field, I think her willingness to write such a slapdash post—a post that will be read and trusted by very many given her large platform—indicates a pretty cavalier approach to physics writing in general. As someone with a reasonably large platform, I think she has a responsibility to do more research before writing a piece like this; I can immediately tell that she didn’t talk to any one of the hundreds of people who could have addressed many of her points. Instead, she cites hearsay that has been addressed in detail. I don’t consider that to be good faith writing; it’s lazy and she doesn’t deserve praise for it, regardless of the quality of her other work.
As an indicator of the slapdash quality: she calls into question the neutron-star merger by saying, "Furthermore, the interpretation of this signal as a neutron-star merger has also been criticized."
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.
I think a lot of people that you could dismiss with terms like "crackpot" are more accurately described as "gradually slipping into writing clickbait for economic reasons".
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...
On the subject of glitches: There is an entire branch of the LIGO Scientific Collaboration dedicated to "Detector Characterization". The article implicitly, and incorrectly in my opinion, casts doubt upon the excellent work of a great many smart and dedicated people.
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.
I did my PhD working on LIGO, but haven't been involved in the project for about five years. To me this article sounds like a crackpot hit-piece akin to the 9-11 deniers claiming that jet fuel can't melt steel.
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.
Yeah, Sabine's sounding not-so-solid these days. Her recent videos are also a little, well, crackpotted. It's frustrating -- she has a point with her criticisms of string theory, and it's only with the relatively recent rise of "swampland" thinking that the crazier stuff is getting correctly marked as such, but her anti-computer bias is getting to be a bit too much.
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.
> 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.
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.)
Every paragraph of this blog post consists of FUD that has been debunked elsewhere. The blog post repeats all of these various sources of doubt without including the follow-up that has been done bolstering support for the LIGO results. It seems like the purpose of the blog post is to sow doubt in the LIGO results, which is not warranted.
> 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:
> 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.
> "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.
> 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.
The GW170817 neutron star merger (that LIGO detected, and was confirmed by telescopes) is such a blatant contradiction of the articles claims, this entire article is garbage.
Every time I travel to New York, though I am not American and lost nobody in the attack, I take a morning to visit the site and mourn. The atrocity committed against the whole of humanity that day was stunning, and I still haven’t come to terms with it (personally).
>> With the still lacking independent confirmation that LIGO sees events of astrophysical origin
> 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.
I took that sentence to mean "independent" as in having some confirmation other than the gravitational wave signal. That's provided by the optical observations of GW170817 which confirm independently that the event is real.
> 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.
There is a lot more data than simply that figure on Wikipedia. For example, you may download all of the raw gravitational wave strain data and re-analyze it yourself if you felt so inclined. The LIGO community has done an amazing job with the "open science center" that releases both the timeseries data and tools useful in processing it.
The chance of a spurious signal from the direction, distance and magnitude GW170817 lining up with telescope observations by random chance is absolutely astronomically tiny.
let's say a "telescope observation" has to be on the order of a supernova explosion to be observable. There are about 30 supernova explosions per second in the observable universe. To date about 10,000 supernovas have been observed using EM spectra, on average that's about one observed major astronomical event every other day.
GRB170817A isn't a supernova though, so the SNe rate is irrelevant. First estimate of kilonova rates I found online is one per day per Gpc, and with your absurd extrapolation to the entire observable universe you get one per hour in one of the 40 000 degrees^2 of the entire sky.
Why do you think I'm assuming the type of the most well studied optical transient we've had this century? This is a source that was observed by something like a hundred different teams.
I'm ruling out a SN origin on the basis of the (at least) dozen of direct observations that show it isn't.
One factor that this article does not take into account is the signal correlation between detectors. LIGO only counts signals as a detection of an event if the same signal appears in multiple detectors with the appropriate time delays (indicating light speed travel time in a particular direction through the Earth). The same signal in multiple detectors rules out detector errors, and the relative timing rules out terrestrial origin: no signal of terrestrial origin will travel at anywhere close to the speed of light through the Earth (earthquake waves travel orders of magnitude slower).
> the relative timing rules out terrestrial origin: no signal of terrestrial origin will travel at anywhere close to the speed of light through the Earth
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.
> I don't know how closely "fingerprinted" each event is to rule out such coincidences.
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.
Moreover, it is through these time delays, and knowledge of the angular "antenna pattern" of the detectors, that it is possible to localize the sky position of a gravitational wave source.
> no signal of terrestrial origin will travel at anywhere close to the speed of light through the Earth (earthquake waves travel orders of magnitude slower)
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.
> 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
Yes, but they won't jiggle the test masses in LIGO, so they won't produce a signal.
LIGO does not record jiggling test masses. It records electrical signals that can be generated by jiggling test masses, and also by other means.
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.
> LIGO does not record jiggling test masses. It records electrical signals that can be generated by jiggling test masses, and also by other means.
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
They need to discover better ways to reject apparent events without relying on the other detectors. The frequency of apparent real events needs to approach that of actual events, for corroboration from other detectors to mean anything.
> They need to discover better ways to reject apparent events without relying on the other detectors.
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.
Is the index of refraction of the Earth at low radio frequencies really 1? I'd expect it to be higher, and so there to be some slowdown for radio waves.
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.
Even an infinitely conductive sphere does not screen the quasi-static near field very well. Although the delay is probably going to be weird, greater than direct visibility. Atmospheric EM events indeed are what comes to mind.
> The same signal in multiple detectors rules out detector errors
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.
Figure 4 in the original detection paper shows a histogram of this false alarm rate (SNR versus detection frequency) and the detection as a significant outlier:
It is always possible for a random signal to appear by coincidence in several detectors simultaneously. LIGO also gathers data from a huge number of "auxiliary channels" that monitor the local environment (seismometers, microphones, radio receivers, etc). Possible detections are heavily scrutinized by ensuring that the detectors were operating normally during the time of detection, and no local disturbances are seen in the auxiliary channels.
Because looking at the signal correlation is not the only test that is applied. But it is a significant test that was not discussed in Hossenfelder's article.
Because analyzing them takes time, and they want to inform telescopes as soon as possible so optical/EM data can be captured while the event (possibly) occurs.
A false positive is a lot better than a false negative here.
This is just a bit of idle speculation on my part as a former astronomer, but I wonder the extent to which the LIGO pipeline allows for non-zero eccentricities in the orbit. Because the signal-to-noise ratio is so low the pipeline has to find events by matching the observed data with precomputed templates. Thus in some sense you need to already know what you're looking for in order to find it.
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.
Matched filters are indeed necessary to get the most sensitivity. However, in addition to the matched filter searches, LIGO performs "waveform agnostic" searches that will find a signal regardless of its waveform. However, these searches are necessarily less sensitive than the matched-filter searches. No unmodeled events have yet been detected.
> 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.
Radio signals could definitely interfere with LIGO, and show up with consistent time delays corresponding to some sky position. There are two defenses against this:
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".
1. I took a look at the attached article. The device they describe is an optomechanical setup specifically engineered to be very sensitive to radio waves. LIGO, by contrast, is engineered to be sensitive to gravitational waves and not radio waves.
It’s a little bit ridiculous to hear that scientists are now so often acting as politicians and clergy, as in, defending their ideas as ‘proven’. A scientific theory is tautologically impossible to prove. It can only be disproven, and scientists should be trying to disprove theories rather than advocating for them.
There is nothing wrong with defending valid science against discredited, unsubstantiated, repeatedly debunked crap.
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.
Disproving requires discarding non-sensical counterarguments though. You don’t find a strong counterexemplar by believing every bad thing anyone says about the exemplar.
In the end, LIGO's fraud will hurt the credibility of physical science. This comparison with edited and cut templates is already a dirty trick. There is not much left of the results of relativistic computer simulations. The rest is a snippet (so-called "chirp"). You can never recover the original oscillation from this. Here the evidence chain is broken. The filtered out signal matches the prepared template, but the prepared template itself does not match the relativistic computer simulation.
> 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