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I was talking with some physicists from Fermilab last week about dark matter (I'm a physics enthusiast but certainly no physicist) and one thing they were discu

I was talking with some physicists from Fermilab last week about dark matter (I'm a physics enthusiast but certainly no physicist) and one thing they were discussing was how current dark matter experiments are constraining possible dark matter candidates significantly as they get more sensitive without finding any. This has lead to increased interest by physicists in alternative theories, including MOND. This galaxy discovery, though, appears to be strong evidence against MOND or other modified-gravity theories since the dark matter is missing in this case. It provides more evidence for dark matter's existence, even as the strongest candidate, Weakly Interacting Massive Particles (WIMPs) are becoming more constrained by lack of evidence.

cozzyd 9y ago
"Strongest candidate" is a bit strong. Certainly WIMPs are convenient theoretically, but so are e.g. axions.
- rmcpherson 9y ago
  I used "strongest candidate" not as my opinion (I don't know) but that is how physicists see the various possibilities. Certainly WIMP research has received the largest amount of funding in experimental physics as compared to other candidates.
  - cozzyd 9y ago
    (I am a physicist who used to work on a WIMP detector). WIMP funding has certainly gotten the largest share of funding. Part of the reason is probably that we know how to build detectors good enough to reach a swath of parameter space and the relative popularity of supersymmetry. I've heard some people suggest that part of the reason for funding such expensive WIMP experiments is that we know exactly where the limits of the detection technique lie and they are reachable given enough money.
noetic_techy 9y ago
Why am I not surprised. As a engineering-physics major who works in software, I always correct people when they ask me "what do you think dark matter is?" I think the more appropriate question is, and always has been: Does dark matter even exist? Thank you for casting light on MOND. My money has always been on modified gravity. I think we missed a few terms in the equation.
- dwaltrip 9y ago
  The comment that you are responding to says that this weakens the case for MOND.
  - noetic_techy 9y ago
    I saw that, it was more so a response to Fermi lab Physicist are taking MOND more seriously. MOND has its problems also. Its my opinion that there is something about the black hole at the center of these galaxies that's causing discrepancies that we attribute to "dark matter". The fact that this new galaxy is so sparse and distributed and shows no sign of dark matter seems to re-affirm this. I'd be curious to know if it even has a central black hole.
    - rmcpherson 9y ago
      To clarify, no one's taking MOND nearly as seriously as WIMPs in terms of funding for experiments to test it. That said, the lack of evidence has lead to increased interest in alternative theories that could explain the phenomenon. Some of these are alternative dark matter particle candidates though, just not WIMPs.
      - koheripbal 9y ago
        It's a pointless conversation the argue over which unproven theory is taken most seriously. The reality is that we don't know.
      - ravar 9y ago
autokad 9y ago
I dont know much about it, but that may not necessarily be the case. Lets assume dark matter does not exist and the people talking about it believe it does. It could be that the people describing it are only describing it through the lens of what they already believe. As in, I believe there are invisible blobs that keep cars close together. I observe some cars far apart and i say "hey look at all that missing blobs"
- anyfoo 9y ago
  That's missing the point entirely, which is that under theories like MOND, you would not expect to see any galaxies that behave like galaxies with no dark matter, as it posits that dark matter does not exist.
  - autokad 9y ago
    > "you would not expect to see any galaxies that behave like galaxies with no dark matter" you miss my point entirely, your explanation is around an assumption of dark matter. You are not saying this galaxy behaves in such a way that MOND cannot explain, you are saying the galaxy behaves in such a way that based on believing in dark matter, this galaxy moves as if it doesnt have it thus MOND is wrong.
    - rmcpherson 9y ago
      This finding certainly weakens the case for MOND. The authors write that in the conclusion of their paper, as quoted in this article: https://arstechnica.com/science/2018/03/galaxy-seems-to-lack-dark-matter-stumping-astronomers/ https://arstechnica.com/science/2018/03/galaxy-seems-to-lack... MOND can not explain a galaxy without dark matter as it is a proposal for the modification of the laws of gravity at large distances, and can explain the already-observed galaxies that behave as if they have dark matter (or, as MOND posits, the laws of gravity are different than what we have observed on earth.)
    - autokad 9y ago
      @rmcpherson I am not defending MOND or attacking dark matter. I am stating based on what they have said, it doesnt make sense unless they provide some basis on why its problematic for MOND
poelzi 9y ago
I follow the BSM-SG model, which also has no dark matter to explain galaxy rotations. Disclaimer: I choose my models after reduction of assumptions and stricter logic is better (Solomonoff Induction). Secondly, I understood when studying physics, that there seems something wrong, but could not put my finger on it. So, naturally it made the most sense for me, to first check all the assumptions currently used and drop those that could easily be seen differently. In fact, the BSM-SG model assumes so less, that I actually accepted it after a year of heavy studying and thinking - the first model ever for me. It however has some "dark matter" called filaments which are the residue of the galactic crystallization egg so to say. Read some paper last year that found them, but of course, they thought it's dark matter. It is actually black black - absolutely no photon emissions even when heated to millions of degrees. In the BSM-SG model galaxies crystallize, it does not have a big bang theory. The galactic redshift has a very different explanation. The filaments are only located around the super massive black hole in every well formed galaxy (not globular clusters). They are the hardest and densest hard matter in the universe. Everything we know is super soft compared to this stuff. Our hole star system is maybe a cubic centimeter of this stuff. If you take all the fragments of the fillaments and put them together they build a perfect hollow sphere that fits perfectly around the black hole. Another really wired property: if you take a cube of it and cut it in half, the mass of both parts will be more then the mass of the original cube. Sounds paradoxical at first, but once you understand how Newtonian mass is derived and that it is basically an surface property it makes sense. If you separate ordinary matter, you don't increase to surface of atomic structures towards the vacuum. You get relativistic changes due the microcurviture, but the surface stays the same. This stuff you can cut and increase the surface until the particle is smaller then the CL node distance ~10^-20 m at which point it will loos its Newtonian mass and only the intrinsic mass will manifest. Same effect as some Neutrinos have. But year, I'm a nut job who does not believe in what most think is true, but to be honest, I don't care. It works so wonderfully and if you can interpret papers from this models perspective, I have not found a single paper that even shakes on it's fundamentals. Some days ago a paper was posted here in which they found "magic angles" in graphene which was doted. I predicted 2 years ago that there will be some angle influence between the graphene layers. To predict something more, you know, because I'm nuts: most of the grapheme we use is quite unordered. There are 2 possibilities in which the carbon atom can be positioned. To get a really good conductor the atoms need to be properly aligned together with the alignment of the 2 layers. The standard perspective on the atomic nucleus is totally oversimplified and this is something quite some scientists found trough different ways. The BSM-SG model was the first model where the periodic table stared to make sense for me, together with all the isotopes.
nonbel 9y ago
>"This galaxy discovery, though, appears to be strong evidence against MOND or other modified-gravity theories since the dark matter is missing in this case." What makes you say this?
- sulam 9y ago
  The article sketches the explanation — if dark matter doesn’t actually exist and is simply an observational side effect, all galaxies should demonstrate that effect. That this galaxy doesn’t strengthens the case for dark matter being separable from regular (visible) matter.
  - nonbel 9y ago
    See my post here: https://news.ycombinator.com/item?id=16702599 https://news.ycombinator.com/item?id=16702599 From what I understand of MOND, the less attraction to visible mass (as you would expect from a "ultra diffuse" galaxy like this), the smaller the effect should be. So MOND predicts the effect should be relatively small for this galaxy. Further, in the paper that the OP references they do a calculation and get odds of something around 1/20 that a galaxy like this will exist if MOND is correct. The interesting part is that for some reason they interpret that as ruling out MOND, while meanwhile saying "no one has any idea how this thing can exist if the dark matter theory is right". I would think "no idea how it can exist" should correspond to odds less than 1/20.
    - sulam 9y ago
      This galaxy is down in the 1 in 100_000 parts, not 1 in 20 fwiw. I am not going to debate MOND, I am just explaining the reasoning.
      - nonbel 9y ago
        I drew the blue vertical line at 20 km/s: https://image.ibb.co/m38AH7/galaxy.png https://image.ibb.co/m38AH7/galaxy.png Are you claiming this is cutting off 1e-5 of the area of that Gaussian curve they fit? It looks very close to 1/20 to me. I don't care about .05, just to get an order of magnitude and compare it to the "this is an unbelievable result" quotes.
yiyus 9y ago
I do not think this is an argument in favor or against the existence of dark matter. I think it is a very surprising result either way. Only thing we know is that this galaxy is a very special fluke. It will surely be difficult to explain by non-dark-matter theories, but I do not think dark matter advocates are going to have any easier to explain why this galaxy (and, as far as we know, only this galaxy) doesn't have any dark matter. It will be exciting to see what explanations both camps come up with.
- simias 9y ago
  I'm no physicist or astronomer but as far as I can tell I don't think what you said makes complete sense. While it's true that it remains to be explained why a certain galaxy doesn't have the same amount of DM as the others at a glance it doesn't seem particularly implausible that such dramatic variation could theoretically happen depending on what DM truly is and how it ends up in galaxies in the first place. On the other hand you'd expect a modification to the theories of physics themselves like MOND would apply to all objects in the universe in the same way, if you find a galaxy where the model breaks down then the model is not good enough. That would be like finding a galaxy far away where gravity itself works differently, that'd be wild. So as far as I can tell it does seem to discredit something like MOND more than DM because you expect physical laws to be universal while it's plausible that DM could not be distributed equally everywhere.

cozzyd 9y ago

"Strongest candidate" is a bit strong. Certainly WIMPs are convenient theoretically, but so are e.g. axions.

rmcpherson 9y ago
I used "strongest candidate" not as my opinion (I don't know) but that is how physicists see the various possibilities. Certainly WIMP research has received the largest amount of funding in experimental physics as compared to other candidates.
- cozzyd 9y ago
  (I am a physicist who used to work on a WIMP detector). WIMP funding has certainly gotten the largest share of funding. Part of the reason is probably that we know how to build detectors good enough to reach a swath of parameter space and the relative popularity of supersymmetry. I've heard some people suggest that part of the reason for funding such expensive WIMP experiments is that we know exactly where the limits of the detection technique lie and they are reachable given enough money.

noetic_techy 9y ago

Why am I not surprised. As a engineering-physics major who works in software, I always correct people when they ask me "what do you think dark matter is?" I think the more appropriate question is, and always has been: Does dark matter even exist? Thank you for casting light on MOND. My money has always been on modified gravity. I think we missed a few terms in the equation.

dwaltrip 9y ago
The comment that you are responding to says that this weakens the case for MOND.
- noetic_techy 9y ago
  I saw that, it was more so a response to Fermi lab Physicist are taking MOND more seriously. MOND has its problems also. Its my opinion that there is something about the black hole at the center of these galaxies that's causing discrepancies that we attribute to "dark matter". The fact that this new galaxy is so sparse and distributed and shows no sign of dark matter seems to re-affirm this. I'd be curious to know if it even has a central black hole.
  - rmcpherson 9y ago
    To clarify, no one's taking MOND nearly as seriously as WIMPs in terms of funding for experiments to test it. That said, the lack of evidence has lead to increased interest in alternative theories that could explain the phenomenon. Some of these are alternative dark matter particle candidates though, just not WIMPs.
    - koheripbal 9y ago
      It's a pointless conversation the argue over which unproven theory is taken most seriously. The reality is that we don't know.
    - ravar 9y ago

autokad 9y ago

I dont know much about it, but that may not necessarily be the case. Lets assume dark matter does not exist and the people talking about it believe it does. It could be that the people describing it are only describing it through the lens of what they already believe. As in, I believe there are invisible blobs that keep cars close together. I observe some cars far apart and i say "hey look at all that missing blobs"

anyfoo 9y ago
That's missing the point entirely, which is that under theories like MOND, you would not expect to see any galaxies that behave like galaxies with no dark matter, as it posits that dark matter does not exist.
- autokad 9y ago
  > "you would not expect to see any galaxies that behave like galaxies with no dark matter" you miss my point entirely, your explanation is around an assumption of dark matter. You are not saying this galaxy behaves in such a way that MOND cannot explain, you are saying the galaxy behaves in such a way that based on believing in dark matter, this galaxy moves as if it doesnt have it thus MOND is wrong.
  - rmcpherson 9y ago
    This finding certainly weakens the case for MOND. The authors write that in the conclusion of their paper, as quoted in this article: https://arstechnica.com/science/2018/03/galaxy-seems-to-lack-dark-matter-stumping-astronomers/ https://arstechnica.com/science/2018/03/galaxy-seems-to-lack... MOND can not explain a galaxy without dark matter as it is a proposal for the modification of the laws of gravity at large distances, and can explain the already-observed galaxies that behave as if they have dark matter (or, as MOND posits, the laws of gravity are different than what we have observed on earth.)
  - autokad 9y ago
    @rmcpherson I am not defending MOND or attacking dark matter. I am stating based on what they have said, it doesnt make sense unless they provide some basis on why its problematic for MOND

poelzi 9y ago

I follow the BSM-SG model, which also has no dark matter to explain galaxy rotations. Disclaimer: I choose my models after reduction of assumptions and stricter logic is better (Solomonoff Induction). Secondly, I understood when studying physics, that there seems something wrong, but could not put my finger on it. So, naturally it made the most sense for me, to first check all the assumptions currently used and drop those that could easily be seen differently. In fact, the BSM-SG model assumes so less, that I actually accepted it after a year of heavy studying and thinking - the first model ever for me. It however has some "dark matter" called filaments which are the residue of the galactic crystallization egg so to say. Read some paper last year that found them, but of course, they thought it's dark matter. It is actually black black - absolutely no photon emissions even when heated to millions of degrees. In the BSM-SG model galaxies crystallize, it does not have a big bang theory. The galactic redshift has a very different explanation. The filaments are only located around the super massive black hole in every well formed galaxy (not globular clusters). They are the hardest and densest hard matter in the universe. Everything we know is super soft compared to this stuff. Our hole star system is maybe a cubic centimeter of this stuff. If you take all the fragments of the fillaments and put them together they build a perfect hollow sphere that fits perfectly around the black hole. Another really wired property: if you take a cube of it and cut it in half, the mass of both parts will be more then the mass of the original cube. Sounds paradoxical at first, but once you understand how Newtonian mass is derived and that it is basically an surface property it makes sense. If you separate ordinary matter, you don't increase to surface of atomic structures towards the vacuum. You get relativistic changes due the microcurviture, but the surface stays the same. This stuff you can cut and increase the surface until the particle is smaller then the CL node distance ~10^-20 m at which point it will loos its Newtonian mass and only the intrinsic mass will manifest. Same effect as some Neutrinos have. But year, I'm a nut job who does not believe in what most think is true, but to be honest, I don't care. It works so wonderfully and if you can interpret papers from this models perspective, I have not found a single paper that even shakes on it's fundamentals. Some days ago a paper was posted here in which they found "magic angles" in graphene which was doted. I predicted 2 years ago that there will be some angle influence between the graphene layers. To predict something more, you know, because I'm nuts: most of the grapheme we use is quite unordered. There are 2 possibilities in which the carbon atom can be positioned. To get a really good conductor the atoms need to be properly aligned together with the alignment of the 2 layers. The standard perspective on the atomic nucleus is totally oversimplified and this is something quite some scientists found trough different ways. The BSM-SG model was the first model where the periodic table stared to make sense for me, together with all the isotopes.

nonbel 9y ago

>"This galaxy discovery, though, appears to be strong evidence against MOND or other modified-gravity theories since the dark matter is missing in this case." What makes you say this?

sulam 9y ago
The article sketches the explanation — if dark matter doesn’t actually exist and is simply an observational side effect, all galaxies should demonstrate that effect. That this galaxy doesn’t strengthens the case for dark matter being separable from regular (visible) matter.
- nonbel 9y ago
  See my post here: https://news.ycombinator.com/item?id=16702599 https://news.ycombinator.com/item?id=16702599 From what I understand of MOND, the less attraction to visible mass (as you would expect from a "ultra diffuse" galaxy like this), the smaller the effect should be. So MOND predicts the effect should be relatively small for this galaxy. Further, in the paper that the OP references they do a calculation and get odds of something around 1/20 that a galaxy like this will exist if MOND is correct. The interesting part is that for some reason they interpret that as ruling out MOND, while meanwhile saying "no one has any idea how this thing can exist if the dark matter theory is right". I would think "no idea how it can exist" should correspond to odds less than 1/20.
  - sulam 9y ago
    This galaxy is down in the 1 in 100_000 parts, not 1 in 20 fwiw. I am not going to debate MOND, I am just explaining the reasoning.
    - nonbel 9y ago
      I drew the blue vertical line at 20 km/s: https://image.ibb.co/m38AH7/galaxy.png https://image.ibb.co/m38AH7/galaxy.png Are you claiming this is cutting off 1e-5 of the area of that Gaussian curve they fit? It looks very close to 1/20 to me. I don't care about .05, just to get an order of magnitude and compare it to the "this is an unbelievable result" quotes.

yiyus 9y ago

I do not think this is an argument in favor or against the existence of dark matter. I think it is a very surprising result either way. Only thing we know is that this galaxy is a very special fluke. It will surely be difficult to explain by non-dark-matter theories, but I do not think dark matter advocates are going to have any easier to explain why this galaxy (and, as far as we know, only this galaxy) doesn't have any dark matter. It will be exciting to see what explanations both camps come up with.

simias 9y ago
I'm no physicist or astronomer but as far as I can tell I don't think what you said makes complete sense. While it's true that it remains to be explained why a certain galaxy doesn't have the same amount of DM as the others at a glance it doesn't seem particularly implausible that such dramatic variation could theoretically happen depending on what DM truly is and how it ends up in galaxies in the first place. On the other hand you'd expect a modification to the theories of physics themselves like MOND would apply to all objects in the universe in the same way, if you find a galaxy where the model breaks down then the model is not good enough. That would be like finding a galaxy far away where gravity itself works differently, that'd be wild. So as far as I can tell it does seem to discredit something like MOND more than DM because you expect physical laws to be universal while it's plausible that DM could not be distributed equally everywhere.