Astronomers discover a strange galaxy without dark matter
wired.com
wired.com
If there is no such thing as dark matter, why doesn't this galaxy behave as the others do? It has the same amount of normal matter as it's neighbours, yet acts totally differently. Dark Matter as a theory has an answer: this galaxy has none. MOND has a much harder time explaining it.
> Now it is such a bizarrely improbable coincidence that anything so mindbogglingly useful could have evolved purely by chance that some thinkers have chosen it to see it as a final and clinching proof of the non-existence of God.
> The argument goes something like this: "I refuse to prove that I exist," says God, "for proof denies faith, and without faith I am nothing."
> "But," says Man, "the Babel fish is a dead giveaway isn't it? It could not have evolved by chance. It proves you exist, and therefore, by your own arguments, you don't. QED."
> "Oh dear," says God, "I hadn't thought of that," and promptly vanishes in a puff of logic.
> "Oh, that was easy," says Man, and for an encore goes on to prove that black is white and gets killed on the next zebra crossing
Modified newtonian dynamics
If so, would it be strange to find a galaxy with less blackhole mass?
Each non-dark matter theory (i.e. MOND, primordial blackholes effort) usually has some pretty large glaring issue that's unsolvable.
I'm all game to refute dark-matter but still waiting for the contender that fits the observations[1].
[0] https://www.youtube.com/watch?v=qy8MdewY_TY
[1] https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
A proponent of MOND could probably declare the existence of some form of dark exotic matter in galaxies that behave "Newtonian".
My point is: As long as a dark matter theory doesn't make predictions that can be experimented upon, we will always have these kind of interpretation games.
Side question: What would actually distribute dark matter throughout the universe in the first place? If it is only affected by gravity and there is much more dark matter than visible matter, shouldn't it be forming a huge invisible ball somewhere?
You need collisions to get things to lose momentum to heat and clump together. Normal matter has collisions via interaction with the electromagnetic field, dark matter doesn't. Neutrinos also don't clump together, but are disqualified as dark matter candidates due to there not being enough of them; something about the relative abundance of different fundamental particles (e.g. electrons and neutrons) being important to get the universe we observer today.
ETA: modified gravity doesn't give anything we can experiment on either; the difference of TeVeS[1] vs GR are not detectable at non-cosmological scales.
[1] https://en.wikipedia.org/wiki/Tensor%E2%80%93vector%E2%80%93...
Your point is well-taken, but I have to be pedantic here (and everyone loves to make this mistake, so don't worry about it). Dark Matter is not a theory,, not like the General Theory of Relativity is a theory. Dark Matter is a hypothesis.
In any case, I think that any modified theory of gravitation has to fight an uphill battle because it seems to be easy to come up with a configuration of dark matter that explains any observation. That's my biggest grievance with DM, btw.: It doesn't make any predictions that could be used to falsify it, at least not in a sense that I could intuitively understand it. Effectively, it appears to act as a completely free parameter, distributed however we need it at the moment.
https://tritonstation.com/2022/01/10/the-curious-case-of-agc...
> Baryonic Tully-Fisher relation showing the ultradiffuse galaxies discussed by Mancera Piña et al. (2019) as gray circles. These are all outliers from the relation; AGC 114905 is highlighted in orange. Placing much meaning in the outliers is a classic case of missing the forest for the trees. The outliers are trees. The Tully-Fisher relation is the forest.
I'm not clear why the distance errors wouldn't average themselves out over the rotation
A failure to estimate accurately any of those metrics seems like the issue with this galaxy, not MOND itself.
For people new to the Tully-Fisher relation, the essence of it is that at galactic scale, gravity is not like v^2/r = GM/r^2.
It's more like v^2/r ~ sqrt(GM/r^2), so v^4 ~ M
When someone actually detects Dark Matter is when I will give that hypothesis any attention, while MOND is equally unpersuasive. Solving the "missing matter" problem is going to happen, and it's either going to be an adjustment of the data (or more precise or better measurements), or it'll be that we just didn't have the whole picture, and once we do, it's going to be a "duh" moment (which I suspect is going to be that there was never any missing matter, and everything and the kitchen sink thrown in that Dark Matter is invented to explain will be explained without the need for Dark Matter).
But I think this is ultimately a good thing. I'm pretty sure we're on the right path here with several decent explanations to dark matter, like sterile neutrinos or axions. Some candidates are testable today and bright people are working on it right now.
Dark matter feels like one of those things that may suddenly see a path towards being solved within years, but that it might also take much longer time.
Wait what? I was under the impression that more scientists are turning to MOND than ever. I have a hot take prediction that in 5-10 years MOND will be the preferred explanation over LCDM.
Sterile neutrinos were ruled out late last year. Axions were ruled out a decade? ago... Though I guess "revised" axions are still on the table; IIRC last year another huge swath of axion masses were ruled out.
MOND has explained similar galaxies in the past by postulating that there's very little dust.
In other words, MOND explains galaxy dynamics by modifying gravity and postulating the existence of small amounts of conventional matter that are below the detection threshold of our telescopes.
Dark matter theories explain galaxy dynamics by postulating the existence of huge amounts of an exotic matter (alongside some conventional dust) that we can't see and haven't been able to detect in any experiments.
The objective should be to make correct predictions and understand how things actually work not for one side to win the argument.
https://www.sciencedaily.com/releases/2021/12/211220120813.h...
Maybe these disperse galaxies have little to no black holes?
But maybe the stock of primordial black holes started as Dark Matter particles. They then have the problem of explaining why so much of the Dark Matter started out in or close to a black hole. Maybe each Dark Matter particle is so dense it is a black hole all by itself?
You have to be careful talking about what a black hole is made of. Stuff that falls in only has a description before it falls in. After it falls in, it can't be thought of as made out of anything, anymore. So if black holes were part of the initial universe, there is no saying which flavor of matter they represent. After things have settled down, these black holes could proceed to swallow any amount of regular matter, and any amount of "other stuff", if there is any.
The assumption is generally that the "other stuff" has difficulty cooling off enough to be sucked wholesale into black holes, unlike regular matter that is happy to radiate away a big fraction of its energy as photons, leaving the rest able to collapse and form planets and stars, and thence perhaps be gathered into the nearest black hole. Meanwhile, the Dark Matter can mill around a black hole's vicinity indefinitely, maybe swooping close and getting ejected, but otherwise hardly bothered unless it blunders straight in.
Or, maybe there wasn't anything until there was enough room for it to be in. Then you don't need a black hole.
Cosmologists like to toss about "expanding universe" and "inflation" as if they mean something, but they really are like gravity to Newton: a name for a process that can be described, but is otherwise wholly incomprehensible.
My understanding is:
1. there needs to be somewhere to escape to, for the schwarzschild radius to make sense, and there's no "outside" to the universe
2. we don't know how big the universe is or what it looks like; if it's infinite and uniform then there won't be any central point for a singularity
3. as others have mentioned, inflation is a get-out-of-black-hole card
4. the physics of the early universe aren't necessarily the same as physics now
It’s more that we had infinite density. Then space itself spread out.
Oversimplified disclaimer.
[Dr. Mohamed Abdullah] explained that one well-proven technique for determining the total amount of matter in the universe is to compare the observed number and mass of galaxy clusters per unit volume with predictions from numerical simulations. Because present-day galaxy clusters have formed from matter that has collapsed over billions of years under its own gravity, the number of clusters observed at the present time is very sensitive to cosmological conditions and, in particular, the total amount of matter.
That article links to paper, co-authored by Abdullah, Anatoly Klypin, and Gillian Wilson, which concludes that "matter makes up 31.5±1.3% of the total amount of matter and energy in the universe" and "80% of matter is actually dark matter". So 20% of 31.5±1.3% is 6.3±0.26%, which is how much normal matter is in the total amount of matter and energy in the universe.
I realize that's different than the 4% number given by the other commenter. This is the latest estimate I could find. Maybe the estimated ratio of dark matter has changed with newer measurements, or maybe the other commenter was working from older estimates.
One of the problems with the standard model of the early universe is that whenever an observation -- e.g. mix of light-element isotopes, expansion rate, simulations -- produces a number different from its predictions, its prediction has been easily adjusted to match.
That's how the scientific method works. You come up with a hypothesis, you test it, you adjust it accordingly, and you re-test it. If you can't come up with tests for it, or if your measurements never match the hypothesis, you throw the hypothesis out. That's why string theory and MOND are getting crapped on in this thread.
DES scientists used two methods to measure dark matter. First, they created maps of galaxy positions as tracers, and second, they precisely measured the shapes of 26 million galaxies to directly map the patterns of dark matter over billions of light-years, using a technique called gravitational lensing.
To make these ultraprecise measurements, the DES team developed new ways to detect the tiny lensing distortions of galaxy images, an effect not even visible to the eye, enabling revolutionary advances in understanding these cosmic signals. In the process, they created the largest guide to spotting dark matter in the cosmos ever drawn (see image). The new dark matter map is 10 times the size of the one DES released in 2015 and will eventually be three times larger than it is now.
There's more info here:
https://news.fnal.gov/2021/05/dark-energy-survey-releases-mo...
And here:
https://www.darkenergysurvey.org/
Dust accounting for the missing 80% of matter and made out of normal matter would be visible in these surveys. It would block, reflect, or emit light. But it isn't visible despite bending light around it—and that's the dictionary definition of dark matter.
A black hole enthusiast then needs to figure out why those black holes would form before big bang expansion
However, the evidence against MACHOs is pretty strong. Once we had a theory of what to look for, experiments were designed to detect them. The thing we looked for is microlensing: Focus a telescope at some stars, and watch for a sudden, short jump in brightness. This can be caused by a massive object passing by in front of the objects, gravitationally lensing the light. We performed these studies and the number of microlensing events that we found were not sufficient to explain dark matter. So MACHOs as an explanation for dark matter isn't the answer.
It's a good suggestion though, and like I said it was a leading theory for a while until we were able to test it.
To hunt for these objects two collaborations, the MACHO Collaboration and the EROS-2 Survey, searched for gravitational microlensing (the changing brightness of a distant object due to the interference of a nearby object) caused by possible MACHOs in the Milky Way halo. (Other collaborations have studied this as well, such as MOA, OGLE, and SuperMACHO.) The MACHO Collaboration painstakingly observed and statistically analyzed the skies for such lensing; 11.9 million stars were studied, with only 13-17 possible lensing events detected. In April of 2007, the EROS-2 Survey reported even fewer events, observing a sample of 7 million bright stars with only one lensing candidate found. This low number of possible MACHOs can only account for a very small percentage of the non-luminous mass in our galaxy, revealing that most dark matter cannot be strongly concentrated or exist in the form of baryonic astrophysical objects. Although microlensing surveys rule out baryonic objects like brown dwarfs, black holes, and neutron stars in our galactic halo, can other forms of baryonic matter make up the bulk of dark matter? The answer, surprisingly, is no, and the evidence behind this claim comes from Big Bang Nucleosynthesis (BBN) and the Cosmic Microwave Background (CMB).
That paragraph references "The SuperMACHO Microlensing Survey," "The MACHO project: microlensing results from 5.7 years of large magellanic cloud observations," and "Limits on the MACHO content of the galactic halo from the EROS-2 survey of the magellanic clouds," if you feel like reading a bunch of physics research papers.
For black holes to be visible due to Hawking radiation against the cosmic microwave background, they would have to be pretty small, about 0.8% of the mass of Earth or about the mass of the Moon (https://arxiv.org/abs/astro-ph/9911309). I don't think anyone's found such a small black hole anywhere, yet. If they did, it would be a pretty big discovery since such a small black hole would have to be primordial.
As an aside, "dense" doesn't really make sense in the context of a black hole, which has infinite density.
They are just some not very well known bodies that may challenge all of our assumptions, or may fall in line with our theories once we get to know more about them. What is well, the best you can expect from new observations.
And if you expect a difference on particle genesis at the beginning of the Universe, it would be a major kind of anisotropy that is against much more than just the cosmology theories.
Why is it so hard to accept that we may have no good theory for explaining a galaxy without dark matter?
It doesn't have to behave like visible matter to behave in a specified manner. It's defined by interacting with gravity and not electromagnetism.
A theory compatible with all conceivable evidence is meaningless.
But maybe you didn't mean to say what you said.
Are you sure that any theory which allows for different things happening in different locations is inherently and unavoidably meaningless? Or is there something else that bothers you?
I would like to understand why people such as yourself viscerally dismiss "dark matter" as if it were inconsistent with all science and rational thinking. Can you describe what's obviously special about it compared to all of the other things we can't see and take for granted?
I assume we all accept the idea of matter that is invisible because it is cold and doesn't emit light...there's nothing particularly weird about asteroids and planets adrift far from stars that are "dark" due to lack of light, right?
And electromagnetic radiation that we can't see is everyday stuff right? Like radio waves, and ultraviolet, and infrared, and x-rays? There's nothing weird about feeling the heat from something and not seeing the rays that carry it, correct?
Everybody knows that nuclear radiation can kill you while being completely invisible, right? Gamma rays and neutrons don't look like anything.
It's not weird that gases are invisible, like air. We all accept that air is around us and without contaminants is transparent.
Gravity itself is invisible, and we take for granted that it exists. Gravitational wave detectors correlate sometimes with visual events, meaning the invisible gravitational waves have definitely traveled over unimaginable distances, passing through everything in the way without being affected.
Neutrino detectors are old hat at this point. Neutrinos are incredibly unlikely to interact with what they pass through, so the detectors have gigantic amounts of material underground with detectors to see mindbogglingly rare flashes when a neutrino hits something. I think neutrinos may still be a candidate for dark matter.
Sound is normally invisible, even though it is the motion of atoms around us which are real.
Heat is invisible within a normal range. If a frying pan is 350 degrees it doesn't look different from 250 degrees.
Electricity in a wire is invisible. Magnetic fields are invisible.
Even lasers made of light itself are invisible if you look from the side and there's no dust in the air.
Are any of these besides "dark matter" unbelievable?
Dark matter is a plug. We observe the mass of galaxies and based on our understanding of gravity the galaxies should fly apart. The most parsimonious explanation is that there is a large amount of matter we don’t/can’t observe.
We don’t observe it and we don’t interact with it. While it’s the best explanation we currently have, it rankles to have to admit that the majority of the universe is made of something literally unobservable to us except through gravitational effects.
In the case of dark matter, this would most convincingly take the form of a multimodal observation. Predict that X particle is DM. It then has interaction Y that isn't gravitational. Then Y, which we were not looking for yet, is found.
That’s how we observe it. We just don’t know what it is built from.
(On the other hand, does it really have to be built from anything? Like, can’t it be some sort of an “intrinsic” distortion of spacetime that, naturally, has an effect on the “normal” matter in the only way it can do so?)
I see what you did here.
What does "observe" mean to you? It's a sticky philosophical question, but I think that consistency in definitions is essential.
Perhaps dark matter is just a victim of its own success. If it were just referred to as non-baryonic matter of a currently unknown construction instead of a catchy name like dark matter, perhaps few people would care.
The more variation we see, the more likely that we're missing something
What it is is the question posed by its name but its existence is generally agreed upon. Many apologies to any "English is my second language, please have mercy on my internal parser" for that last sentence.
Certain properties of galaxies implies that there is more matter in them than is observed directly. The extra stuff could be clotted cream but then I would personally be able to detect it from billions of light years away. We can only really say that gravity is a thing that we think works like ... this (cue pretty piccies from some Holywood films and Hubble etc). Gravity is an emergent property of matter according to Mr Einstein.
Take a large collection of matter, say of the order of 100,000 light years across, like our Milky Way or Andromeda, which is spinning and has a measurable distribution of matter. You can predict how it ought to behave. For example it ought to spin at x or be distributed as y etc. However, measurements show that it doesn't. So you take the observed parameters and run your models and equations backwards to get the actual matter that would be involved.
It turns out that over four fifths of stuff is currently unobservable, which is a bit embarrassing.
A galaxy without Dark Matter is one that doesn't have stuff that we don't even know what it is that it lacks or something. Assuming that stuff is reasonably homogeneously distributed across the universe, this is a very odd ratio of observable to non observable stuff indeed.
Hope that clears that up 8)
I understand we looked at distribution of mass i galaxies and have inferred that for them to keep a stable shape, they need to be spinning at a certain rate which requires more mass than is observed and hence dark matter.
Do we know that galaxies are actually spinning in a steady state and are not actually in the process of flying apart? We've been photographing galaxies for only a hundred years or so at high quality. Would we have detected that they're spinning in a steady stare within this period if time?
So you’d have to fit another massive coincidence which is that the stars flying apart are also at the same time changing their emission spectrums to not look like they are.
The Milky Way (the Romans originally named it that - when you get a decent view of it with no light pollution, it does look like a milky road) is roughly 100,000 light years across. Andromeda is about 2.5 million LY away and so any light from it that we see is getting on a bit. Andromeda is counted as part of the "local group" so considered close to us. Really far away stuff is billions of light years away.
That new satellite that's all over the news - James Webb - is something else. Hubble was seriously impressive, even with its "squint" (technical hitch that needed correcting shortly after its launch). Hubble has delivered some of the most stunning science and imagery possible and JW will go much, much further.
Just you wait until James Webb starts delivering results. It will be awesome, and I don't use words like that lightly.
Now, you mention "matter ... sparse enough ... massive". I think you have answered your own question. The matter in question may be sparse but if there is enough of it, then it will become "massive" and hence detectible.
Not sure what a "cold electron" is - it sounds unlikely.
Dark Matter is postulated and not a "thing" per se. A lot of good science does seem to imply that 4/5ths of matter is unseen.
The key thing I am trying to get across is that our human need to slap a name on something is not appropriate here but we do it anyway.
The cool kids with massive budgets and impressive machines in space cannot yet tell you and I what the stuff is but for now we will call it "dark matter". It might sound a bit mad for people more used to dealing with certainties like Civil Engineering (lol - Britannia Bridge in London - resonance). I'm a Civ Eng grad.
That's quite a long way of saying "no"!
Also, more hidden (somehow) baryonic matter would change our current theories surrounding Big Bang nucleosynthesis in ways that aren't supported by other observations, like the percentages of (visible) matter like helium and lithium.
Astronomers define/describe dark matter as matter that seems to interact with normal matter gravitationally but in no other way. But we can "see" this gravitational interaction in a number of ways and so we know a reasonable amount about dark matter, especially, through the motion of normal matter we know approximately where it is and isn't.
I have no idea whether this is a true representation of how things are, or some kind of artifact.
It hasn’t been detected, so not much until we know what it is or if it even exists.
Galaxies would attract each other and "pool" to the same 3d space. This one would have an associated galaxy with less mass or at a greater distance. For the opposite case (galaxy present there, but not here), it would mean that we should see areas in our space with more gravitational lensing than is warranted by the local matter.
I made a simulator (dumb 4d cartesian stuff) back then, and have been waiting for someone to find gravitational lensing out in the middle of nowhere, so I could see if it matches the expected shape.
I would post links to my cool geocities page containing the source/graphic I made in QBasic, but it's been dead for a couple decades now. Maybe I can find my palm pilot that has ranting notes about it.
edit: Why downvote. I'm fully aware it was just a dumb idea from high school. I really enjoyed physics at the time, and really enjoyed making simulations. I'm don't honestly believe this is how the universe works.
- modified gravity (MOND), which accurately models the centripetal acceleration of stars in hundreds of galaxies, models acceleration as sqrt(GM/R^2 * cH/(2pi))
- cH/(2pi) = c^2 / (2pi * 13.8 bly), which looks like some super extreme v^2/r centripetal acceleration
- like something moving at c, from a point 2pi * 13.8 bly away = 87 bly away
- maybe if ones goes straight for 87 bly, one ends up at the "same point" in abstract space
- maybe the universe has the shape of a hypersphere. maybe the radius of the hypersphere is 13.8 bly.
Webb also took years and years to launch in the first place, what's the timeline like with two?
The reason "dark matter" has persisted in the public consciousness is that TV cosmologists keep pumping it, and academics currently in charge built their careers on it and don't want to lose their funding.
The galaxy in question, AGC 114905, is described as lacking dark matter _because_ its rotational characteristics are readily explained by its baryonic matter content alone. MOND, therefore (and your entire argument), does not apply. You may have mistaken this for a regular galaxy with "missing" matter that also happens to lack dark matter, which would then suggest the need for an alternate explanation.
EDIT: The abstract also says, among other things: "We also find that the rotation curve of AGC 114905 deviates strongly from the predictions of Modified Newtonian dynamics."
[0]: https://academic.oup.com/mnras/advance-article/doi/10.1093/m...
McGaugh says the same here https://www.scientificamerican.com/article/dark-matter-may-b....
When we are discussing not-settled facts, there's better ways to frame our discussion.
For instance: "I believe, that CDM is an antiquated theory and MOND is a better explanation, because _______. I've had discussions with ______ and in particular ______"
It's less effort than your opening flame, it's less abrasive, and it opens productive discourse. Your opening statement is more like that of a political partisan than someone seeking discussion.
Therefore, learning from their experience, the one thing that works is accurately calling the status quo's invisible blobs of noninteracting kludge as what it is.
From there, a good question is "How do we model it?". And sqrt(GM/R^2 * cH/(2pi)) works really well.
By the way, cH/(2pi) = c^2 / (2pi * 13.8 bly), which looks like centripetal acceleration.
I'm also struggling to find what MOND has to say about all the astrophysics observed that LCDM people try to model to get their Tully-Fisher to work. If MOND is true, why would all these astrophysical feedback effects (such as supernovae) not matter for Tully-Fisher?
- galaxy clusters
- lensing
- Bullet Cluster, El Gordo
all have answers in the work of modified gravity (MOND) cosmologists. Stacy McGaugh does a really good job going through each one.
The essential thing, and I mean really essential, is that modified gravity (MOND) uses fewer free parameters than cold dark matter (CDM), by a long shot.
[1] https://twitter.com/dudedarkmatter/status/109452639162072268... [2] https://twitter.com/DudeDarkmatter/status/109452792999493222...
certainly, these are still open questions in cosmology
Meanwhile it's good to restate the obvious.
Modified gravity (MOND), where acceleration at galactic scales isn't just GM/R^2 but modeled as sqrt(GM/R^2 * cH/(2pi)), works for 100s of galaxies, and is more precise than cold dark matter (CDM).
Modified gravity only has one free parameter. cH/(2pi) = c^2 / 87 bly.
Perhaps the "dark matter" of a galaxy is the rest of the galaxies of the universe.
The only MOND formulations that actually work are ones that simply reduce cold dark matter from 80% of the universe to 30% of the universe. MOND has all -- literally all, as in 100% of them -- the free parameters of lCDM plus the parameters for MOND.
I like MOND. It's elegant. It's intuitive. It's simple. You get to put your name at the end of the sequence Aristotle, Copernicus, Kepler, Newton, Einstein. When I first started reading about dark matter in the '90s I thought MOND was the obvious solution. (MACHO was still a leading theory at the time, they were still analyzing the data from the microlensing surveys) lCDM is messy and existentially unsatisfying. We don't know what what it is, and if it has the properties we think it has, we could not conceivably ever know what it is. But regardless of the fact that MOND is nicer than lCDM, lCDM explains all of our observations, but MOND only explains some of them, and depending on which formulation of MOND you subscribe to, is falsified by the the bullet cluster, or by galaxies whose rotation curves show a lack of dark matter, or by the LIGO/VIRGO observations that show gravity moves at the speed of light.
MOND reminds me of the meme of Homer Simpson where he's standing there looking fairly fit and then the camera turns around him and he's just got all his fat and loose skin pinned and tied up on his back. It looks great on the face of it but once you really, really start digging into the details it doesn't work anymore. lCDM wears all of its warts on its face.
What kinds of relativistic effects have been postulated for explaining our observations?
Something about dark matter which always struck me was that I have not seen explanations which incorporate the very limited perspective we have on galaxies -- being singular beings on a tiny rock very far away -- and how the light follows geodesics which may be significantly different from straight lines in the non-relativistic view. If these galaxies are large enough to lens light from elsewhere, doesn't it follow that this should be happening in places of high mass/energy density like the interior of galaxies, too? In other words, are the edges of the galaxies really where we think they are?
Is there any "whirlpool" effect that gravitational waves may have that would sweep or twist these geodesics as the galaxy rotates?
It hit me one day that the galactic rotation curves had me thinking about it backwards. That had led me to think a galaxy has dark matter in it while more likely the dark matter has a galaxy in it.
This is a very strange thing to declare definitely can't be happening, in a universe where subatomic particle interactions do not have definite results or even particularly comprehensible abstract models of how they work to human minds.
Especially when the alternative is "gravity has some minimum force over distance which is exactly small enough we can't detect it on Earth".
I'm aware the jury is out on it.
Please, furnish us with YOUR credentials that allow you to have such unique insights into this field.
Otherwise, you just sound like a crank. I don't know if you're right or wrong, but your unsourced certainty is definitely setting off my bullshit meter.
Asking questions is fine, but making a claim like "dark matter is not a real thing" with certainty is premature and does not predispose others to taking you seriously.
It's not really any of my business, but in your shoes I would be making sure to disclaim these statements regarding MOND as secondhand opinion rather than presenting them as established scientific fact.
- It's a debate, not a settled fact.
- When your opening salvo describes the other side as "stupid and ludicrous" you should not be surprised that some people respond with hostility in kind.
- Having studied something somewhat intensely for 20 weeks doesn't put your personal opinion on the subject on a higher standing than people who have studied this at a high academic level for a lifetime. You're free to make arguments, but not to proclaim absolute truths.
- For the particular article we're discussing: A galaxy that seems to have no rotational speed anomaly is a blow for both CDM & MOND theories, but it would seem to be a bigger blow for MOND (e.g. CDM anomaly could just be a weird distribution of dark matter).
- I already was not surprised by the HackerNews crowd responding with hostility.
- I am pointing the HackerNews crowd to people who have studied this at a high level for a lifetime. Moti Milgrom. Stacy McGaugh. Pavel Kroupa.
- This article is actually a blow to bad journalism. This article is also an opportunity to call out that what "cold dark matter" is, is actually bad machine learning, where academics forcefit a new blob of invisible, noninteracting matter for every galaxy, which gives cold dark matter (CDM) no predictive power. Contrast with modified gravity (MOND), which models acceleration as sqrt(GM/R^2 * cH/(2pi)), which has predictive power.
You -opened- with hostility.
> - I am pointing the HackerNews crowd to people who have studied this at a high level for a lifetime. Moti Milgrom. Stacy McGaugh. Pavel Kroupa.
And ignoring the other side, presenting it as settled.
Read your opening statement. It is not conducive to discourse. It just flames CDM without advancing any argument of its own.
It doesn't matter the topic: if I think, say, global warming critics elsewhere have been jerks, I still don't improve things if I talk in roaring hyperbole and dismissiveness in statements about it here. I won't get listened to, and I won't improve the quality of discourse.
From the first two site guidelines for comments:
> Be kind. Don't be snarky. Have curious conversation; don't cross-examine. Please don't fulminate. Please don't sneer, including at the rest of the community.
> Comments should get more thoughtful and substantive, not less, as a topic gets more divisive.
Continuing on to:
> Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.
So this is an excuse to be rude to different random strangers here, because they might (or might not) share some views with the people acting in the way you don't like?
I'm really patiently trying to explain this to you. "These other people were rude first" is never a good argument. It's even worse when the "other people" aren't here or a party to the discussion.
But the poster in question opened with a salvo just denigrating all the other options without any information in defense of his view. This shouldn't be lauded. It opens no interesting line of discourse.
I never said he repeated himself. I just said his opening gambit in the conversation was a salvo that merely denigrated the other options without any information in defense of his view.
This tends to not invite productive discourse.
Anyone paying attention to experts knows that none of them, including the ones you cite (McGaugh et al), speak with the certainty that you do. All of them readily admit that there are problems with both leading theories. So when you “explain” to everyone why their stupid ideas are stupid, it comes off as cheerleading born out of either naïveté or intellectual dishonesty, and harms your credibility. “MOND is obviously incomplete and I despair of making it into a proper theory. LCDM has no realistic chance of explaining MOND’s many predictive successes. Right now, we’re hosed.” - Stacy McGaugh
It’s a bit funny that you then go on to talk down on “the HN Crowd” downthread - the most common complaint I usually hear about “the HN Crowd” is best summed up as “it’s full of people who think a computer science degree makes them an expert in everything.”
I did the math; still just one in seven billion.
Building websites and collating data isn’t that novel these days. It’s not like you alone collected it or defined any of the first principles.
Welcome to being a normie.
Doesn't really matter how many data points(galaxies) MOND can accurately predict, if it can't predict all parts of the dataset, what is the point? (I'm not saying CDM is better, it can't predict all data points either, but it seems to be better at explaining a wide range of things once you step outside galactic rotation rates).
> In their work, Fraternali and his colleagues tested a leading contender among dark matter alternatives, called MOND, for Modified Newtonian Dynamics, which involves tweaking Isaac Newton’s law of gravity. First proposed by Israeli physicist Mordehai Milgrom in the 1980s, MOND hypothesizes that standard gravitational physics, which accurately explains the motions of objects with high gravitational accelerations, like planets in our solar system, might not apply the same way to slowly orbiting stars at the edge of a galaxy’s disc. So the discrepancy between the expected velocities of the stars in galaxies and how fast they appear to be moving may not indicate missing mass, but rather a math error, if the MOND gravitational law is right. But while the MOND model fares well with more normal galaxies, it too couldn’t explain the rotation of Fraternali’s team’s fluffy galaxy. It fared just as poorly as dark matter models do.
Maybe try reading before calling others stupid
"lost" is what I would say the people pumping it are.
EDIT: Nvm, parent answered similar question here https://news.ycombinator.com/item?id=29914380
Following links it appears that proponents of MOND believe that running the calculations will show that MOND predicts this.
Despite popular belief physicists are actually quite clever and have evaluated theories such as this.
cold dark matter (CDM) is a superimposed amorphous blob of invisible non-interacting matter, hence its inability to model the kinks in the real rotation curve
modified gravity (MOND) models the kinks in the rotation curve