Oddball Galaxy Puts Dark Matter Theory to the Test
scientificamerican.com
scientificamerican.com
Indeed, to say just a given galaxy lacks dark matter is inherently to say that dark matter exists.
It means that some assumption somewhere in the calculation is wrong.
The laws of physics don't form a complete (fully connected) graph. Not every force (edge) affects every particle (vertex). Electrons and photons (obviously) affect each other, electrons and protons do the same (through the electromagnetic field, for example), but photons and neutrinos do not.
Why should we assume that the overall graph has only a single connected component?
The existence of 100% non-interacting particles is by definition non-falsifiable, therefore scientifically irrelevant.
We can’t account for the mass of the universe so we are looking for it.
There are two options either there is mass that we cannot detect through non-gravitational related observations or that we don’t understand gravity on a macro level which also puts relativity at odds.
MOND was pretty much killed last year and it’s now completely off the books so modifying Newtonian gravity to fit in our understanding of the universe won’t work, which leaves dark matter which is again a place holder name for one or more types of matter that are very hard to observe.
It can be wimps or it can be that there are a lot more brown dwarfs, rogue planets, and other bodily objects that we can’t see.
(not that various mond's were ever particularly viable)
> Last Thursdayism (alternately Last Tuesdayism! or Last Wednesdayism) is the idea that the universe was created last Thursday, but with the physical appearance of being billions of years old.
That's exactly what happened with last year's neutron star merger. It was detected as GRB and GW, localized based off of the GW data, and then an observing campaign found a transient at the predicted location in visible light, IR, UV, radio, and X-ray.
https://www.ligo.caltech.edu/page/press-release-gw170817
Gravitational waves are all candidates until they can be confirmed with external sources.
All I can say is that other source clearly describes that the Fermi team announced detection of a gamma ray burst well beforehand, and that the ligo team treated the situation as exceptional due to that announcement.
>"Gravitational waves are all candidates until they can be confirmed with external sources."
My understanding is that there is expected to be no accompanying external evidence for waves generated by inspiraling black holes.
I explained this in a reply that I just posted to your other comment. GCN is basically a mailing list where notices are posted in real-time to coordinate the observation of transient phenomena. If you dig into the citations from the paper you quoted, you'll read that the GW data takes on the order of 5 minutes to process before it can register an event, but it was indeed detected in real-time by their algorithms (gstlal).
There's nothing in the paper you quoted to support the claim that the LIGO team adjusted their analysis based on Fermi's announcment to GCN. 6 minutes isn't "well beforehand" when the GW data takes 30-60 minutes for human vetting (http://iopscience.iop.org/article/10.1088/0004-637X/748/2/13...).
> My understanding is that there is expected to be no accompanying external evidence for waves generated by inspiraling black holes.
Multiple signals is the whole point of multi-messenger astronomy. Each detection was independent, but having evidence in GW, GRB, and optical provides multiple lines of evidence, which is a cornerstone of good science.
"Single-detector gravitational-wave triggers had never been disseminated before in low latency. Given the temporal coincidence with the Fermi-GBM GRB, however, a GCN Circular was issued"
I interpret it as "Because we read the report from Fermi, we treated this data in an exceptional way". In which case their signal to noise ratio is going to be messed up, for the background estimates to be valid they need to treat everything exactly the same every time. Basically, if they want to do this, Fermi needs to be distributing false positive GRB reports so they can incorporate them into the background.
>"Multiple signals is the whole point of multi-messenger astronomy. Each detection was independent, but having evidence in GW, GRB, and optical provides multiple lines of evidence, which is a cornerstone of good science."
Ok, but I'm saying it is my understanding that no one expects to detect any supporting evidence in the case of the black holes. Ie, not that it was missed. There is "nothing to see":
"These momentous black-hole clashes produced gravitational waves that were audible to LIGO-Virgo but there was nothing to see." https://www.nature.com/collections/gghkrvklfb
Because gravitational waves' amplitudes fall off linearly with distance rather than quadratically, because gravitational waves are so weakly interacting that they essentially do not scatter and are not absorbed, and because the environments around binary mergers (and between the binaries and us) can strongly absorb or scatter light (incl. radio and gamma), there should be lots of detections which have obscure, dim, or even undetectable optical (also incl. radio and gamma) signals.
Distinguishing among the similar inspiral chirps for similar binary masses where the composition of the masses differ is an area of active research. The strong equivalence principle drives the GW similarity, but whereas binary NSes's surfaces can contact, BH surfaces (if they exist) are deep inside their horizons, so (ignoring any matter in the neighbourhood, such as colliding accretion disks) all we get from binary BH mergers is the ringdown as the hair from the lumpy merging horizon falls off leaving a much more symmetrical horizon. A mixed binary can shred the NS, leaving behind a brilliant structure.
For binary NS mergers the GW events are brief compared to optical events (and the non-gravtiational radiation can interact with (relatively) nearby gas and dust as light echos and the like, so the results of those emissions can be studied for longer). It is much more likely that a GW detection will spur a search by non-gravitational observatories than the reverse. In any case, everything is carefully timestamped, and the records can be compared well after that, including by people who aren't experimentalists. :D
Sure, and the extra info is appreciated, but here is what I was responding to:
>"Gravitational waves are all candidates until they can be confirmed with external sources."
I believe this is false. They expect to detect many gravitational waves that will never be "confirmed with external sources". Namely, those triggered by black holes, and for the reasons you mention.
I'm not sure if that's what @dogma1138 meant, but I'm pretty sure that's how the past GW detections have been confirmed.
If you back up a sentence, it says:
> A GCN Notice was issued at 13:08:16 UTC.
If you extend your quote a few words:
> a GCN Circular was issued at 13:21:42 UTC
Note the 13 minute gap between the Notice and the Circular. The Notice was based on LIGO's own detection (which, again, was not rejected as noise by their algorithms as you have claimed). The Circular was issued based on the temporal coincidence with Fermi's detection.
The difference between a Notice and a Circular is explained on GCN's website:
> The GCN system distributes:
> * Locations of GRBs and other Transients (the Notices) detected by spacecraft (most in real-time while the burst is still bursting and others are that delayed due to telemetry down-link delays).
> * Reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other particle observers.
> In which case their signal to noise ratio is going to be messed up.
The LIGO detection was triggered by an algorithm (gstlal) that constantly evaluates the SNR of the data coming off the detector. The Fermi detection had nothing to do with that. You're trying very hard to make a boogieman out of nothing.
> Ok, but I'm saying it is my understanding that no one expects to detect any supporting evidence in the case of the black holes. Ie, not that it was missed. There is "nothing to see".
This wasn't a black hole merger. It was a neutron star merger, which is expected to produce counterparts.
I'm talking about the sentence where it seems to say they treated the data from a certain time interval exceptionally, ie in a way not addressed by the "background" measurements. This whole post (while containing otherwise interesting/useful info) is about other sentences and totally ignores the one I asked about.
>"The LIGO detection was triggered by an algorithm (gstlal) that constantly evaluates the SNR of the data coming off the detector. The Fermi detection had nothing to do with that. You're trying very hard to make a boogieman out of nothing."
The sentence I quoted seems to suggest otherwise. I don't know the details of all the ways bias can sneak into the results over there, but I know in general it's not hard, at all.
Anyway, its easy to test. Have Fermi, etc send them some fake positive "notices" and see if they detect more gw's than usual during those times. It'd be an even better test if no one at LIGO was in on it at all. Is this something you could agree with in principle? I mean I have no idea what practical difficulties may be involved.
> "This wasn't a black hole merger. It was a neutron star merger, which is expected to produce counterparts."
Yes, I have no confusion about that. This was a case where we could expect verification. If it were another black hole merger my understanding is we would not expect it possible for other type of measurement to verify it.
> I'm talking about the sentence where...
Nope. It doesn't work that way. You don't get to cherry-pick sentences and demand that they be explained out of context. You need to understand what "low-latency" means and why the GCN exists in order to understand the meaning of those sentences. You can't choose to ignore that.
> they treated the data from a certain time interval exceptionally
Huh? There's only the data from the time of the detection. What other time interval would they be analyzing?
> The sentence I quoted seems to suggest otherwise.
Only if you fill in gaps in your understanding with your own bias and ignore facts that contradict your theory. The text is pretty clear to me. LIGO and Fermi made two independent observations. Both were issued as GCN Notices. Then, 13 minutes after the second notice, because they had two independent observations that were consistent with a neutron star merger, they decided to disseminate this information to observatories for follow-up observations in optical.
> I don't know the details of all the ways bias can sneak into the results
The detection was triggered by software. You can't choose to ignore that.
> Anyway, its easy to test. Have Fermi, etc send them some...
I have a better idea. If you want to accuse the scientists of intellectual dishonesty, why don't you provide some evidence? @raattgift pointed out to you that all the observations and communications are timestamped. I've given you links to the software used to analyze the data. Go ahead and audit it yourself if you think something's amiss. Your inability to understand the content of a paper is not evidence. It just means you don't understand the paper.
If you have any concerns about the validity of the GW data analysis, keep in mind that they predicted the location (including distance---so three dimensions, not just two, which severely cuts down the volume for potential matches) based on the GW data. Follow-up observations (again, this is the purpose of GCN Circulars) found a transient at the predicted location in visible light, IR, UV, radio, and X-ray, consistent with a neutron star merger.
I think the scientists have met their burden of proof. If you want to call shenanigans, the burden of proof is on you now.
I'm done with this conversation. You can have the last word if you wish. I won't be replying to any more comments.
In one detector, which (afaict from the sentence you think im cherry picking) is usually discarded or something, but these were exceptional circumstances...
Look maybe I'm just unclear on what happened here, but to me it sounds like they have humans in the loop making decisions and its not automated. If that is the case, its a recipe for disaster when it comes to comparing a signal to the background.
You are saying that you know there are no humans making decisions in the loop? Is that correct?
> Approximately 6 minutes later, a gravitational-wave candidate (later designated GW170817) was registered in low latency (Cannon et al. 2012; Messick et al. 2017).
"Registered in low latency" means that it was detected by their data analysis algorithms, which directly contradicts your conclusion that "they found data their algorithms had previously rejected as noise." If you doubt me, you can follow the citations from that paper. Cannon et al. 2012 resolves to http://iopscience.iop.org/article/10.1088/0004-637X/748/2/13..., which discusses the data processing and latencies involved (~5 minutes to trigger a detection and ~30 minutes for human vetting), which is consistent with the timeline you quoted. They even published the source code:
> We have implemented a prototype of the low-latency filtering stage using an open-source signal processing environment called GStreamer. ... We have extended the GStreamer framework by developing a library called gstlal that provides elements for GW data analysis.
gstlal's home page is https://wiki.ligo.org/DASWG/GstLAL
The part you quoted mentions a few notices that were circulated through GCN. That's basically a mailing list to coordinate observation of transient phenomena. It's home page is https://gcn.gsfc.nasa.gov/. The circulars discussing the GW are here: https://gcn.gsfc.nasa.gov/other/G298048.gcn3. From the first post in the circulars:
> The online CBC pipeline (gstlal) has made a preliminary identification of a GW candidate associated with the time of Fermi GBM trigger.
gstlal is the library we met earlier in Canon et al. 2012. "Online" means it was processing the data in real-time.
Your claim that the data was rejected by their algorithms as noise isn't supported by the paper you're quoting or the original sources.
There is evidence of the supersolid dark matter every time a double-slit experiment is performed, as it is the supersolid dark matter that waves.
Supersolid dark matter ripples when galaxy clusters collide and waves in a double-slit experiment, relating general relativity and quantum mechanics.