
What’s Up with LIGO? - valeg
http://backreaction.blogspot.com/2019/09/whats-up-with-ligo.html
======
stefco_
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.

[0] [https://www.ligo.caltech.edu/page/detection-companion-
papers](https://www.ligo.caltech.edu/page/detection-companion-papers)

~~~
ISL
Hossenfelder is _not_ a crackpot:
[https://scholar.google.com/citations?user=NaQZcyYAAAAJ](https://scholar.google.com/citations?user=NaQZcyYAAAAJ)

~~~
stefco_
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.

~~~
Keysh
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_.

------
ISL
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.

------
tobinfricke
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.

~~~
lidHanteyk
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.

~~~
ncmncm
What "anti-computer bias"?

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.

------
pdonis
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).

~~~
comex
Then why were 9 events for which alerts were sent later “downgraded because
they were identified as likely of terrestrial origin”?

~~~
tobinfricke
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.

------
antognini
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.

~~~
tobinfricke
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.

------
mehrdadn
My jaw just dropped reading this:

> 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.

~~~
tobinfricke
I think this is referring to the figure on the cover of the issue of Science
in which the detection was first reported.

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](https://www.ligo.caltech.edu/page/detection-companion-papers)

------
zyxzevn
Possible false signals in LIGO via the detection of radio-waves.

See: Ultra sensitive detection of radio waves with lasers
[https://www.nbi.ku.dk/english/news/news14/ultra-sensitive-
de...](https://www.nbi.ku.dk/english/news/news14/ultra-sensitive-detection-of-
radio-waves-with-lasers/)

It would be interesting to see how this method of EM-wave detection interferes
with the GW-detection.

~~~
tobinfricke
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.

~~~
zyxzevn
Good reply, but..

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".

~~~
tobinfricke
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.

2\. This point is valid.

------
jl2718
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.

~~~
throwaway2048
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.

------
dlphn___xyz
“The Nobel-Prize winning figure. We don’t know exactly what it shows.”

nice

------
worlov
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.

~~~
worlov
I mean the following:
[https://physicsprivate.blogspot.com/2019/09/manipulation-
of-...](https://physicsprivate.blogspot.com/2019/09/manipulation-of-results-
of-numerical.html)

