11 ms·

Worth noting: For a very long time MOND has been predicting earlier galaxies than LCDM.

JetSetWilly 4y ago
This is not unusual. There's many predictions made by MOND ahead of the fact that are borne out by reality. But don't worry - dark matter will be "retrofitted" so that it fits the facts and everybody will suffer collective memory loss again. Edit: see for example table 1 on page 12 here: https://arxiv.org/pdf/2110.06936.pdf https://arxiv.org/pdf/2110.06936.pdf from a review of prior expectations by both MOND and dark matter vs how they turned out against reality for a large variety of astrophysical scenarios.
- varjag 4y ago
  But MOND itself is a "retrofit" to make it agree with the data, isn't it? It's in the name.
  - rcme 4y ago
    Every theory is a retrofit. A useful theory is also predictive.
    - rqtwteye 4y ago
      MOND is not compatible with some observations. It and dark will probably be tweaked until both agree with observations. At that point they will be the same.
      - throwawaymaths 4y ago
        That's a false equivalence. MOND has made several predictions before they were observed (external field effect, linear Tully fisher relationship, early galaxies). I think LCDM's made fewer if any predictions.
    - varjag 4y ago
      MOND has its share of failed predictions. It also still requires a certain amount of DM to work. This is fine for work in progress that all frontier science is but the issue is far from settled.
- thereddaikon 4y ago
  Dark matter is the umbrella term for the observed discrepancies. MOND is one possible possible explanation for DM. The paper you linked doesn't compare MOND to DM, because that doesn't make any sense. It compares MOND to ΛCDM which is a competing explanation.
- sebzim4500 4y ago
  Am I understanding that paper correctly that their suggested solution to explain the Bullet Cluster using MOND is too introduce an additional kind of matter which can not be detected on earth and doesn't interact with light (namely sterile neutrinos)? Is this satire?
  - aeneasmackenzie 4y ago
    "dark matter but not as much" is still an improvement if you replace it with something better. If MOND predicted these observations and LCDM didn't it's reasonable to say that it is better.
    - sebzim4500 4y ago
      Yeah that's fair. I guess it could also explain why DM has been so hard to pin down, if both MOND and DM are true then there might be DM candidates that have been unfairly ruled out. I do think it significantly hurts the (more philosophical) argument that MOND is simpler or has fewer parameters than DM though.
      - throwawaymaths 4y ago
        So the ongoing problem with LCDM is that the parameter space for allowable particles keeps getting pushed back. We keep falsifying classes of potential particles that could be WIMPs. MOND+ some standard model-adjacent particle (like say right handed neutrinos), if we can have a phenomenological estimate of how much of them should exist, would at least be credible on account of having a constrainable set of parameters, whereas the density of WIMPs in normal LCDM has no constraint besides the same measure that we have to infer its existence (gravitation)
puffoflogic 4y ago
Yeah, but is it even worth saying that when the response will inevitably be "so what?" by the entrenched anti-MOND orthodoxy?
rqtwteye 4y ago
As far as I know , MOND is not compatible with some observations. So dark matter and MOND have to be tweaked to agree with what we see.
- 6nf 4y ago
  MOND is not compatible with all observations but neither is dark matter. A lot of scientists think MOND is a better explanation than a new particle that we've not yet observed. Have a look at Sabine Hossenfelder's work for some of those arguments.
  - rsj_hn 4y ago
    Which researchers (as opposed to pop-sci pundits) think MOND is a better explanation than Dark matter? That is a very, very fringe alt-science view that so far exists in various pop-sci blogs and informal youtube discussions, rather than in mainstream conferences, journals, and research centers. I'm not saying it's bad to speculate or write whimsical blog articles about these topics, there's lots of room for creative speculation, but MOND does not respect Lorentz invariance which is basically a deal breaker for virtually all serious researchers. Fewer things have more robust empirical support than Lorentz invariance, so discarding it forces you to say that your violation is always just over the horizon of what is testable (and this horizon keeps getting pushed back). That's generally a discrediting feature of any theory and a huge red flag. Much better to say "you don't know" than to postulate something which requires such massive fine tuning to always be just beyond the horizon of what is testable, but close enough to that horizon to have explanatory power for observed phenomena. https://phys.org/news/2017-11-evidence-violation-lorentz-invariance.html https://phys.org/news/2017-11-evidence-violation-lorentz-inv... https://asfriedman.physics.ucsd.edu/Papers/Friedman+2020a.pdf https://asfriedman.physics.ucsd.edu/Papers/Friedman+2020a.pd...
    - throwawaymaths 4y ago
      He's passed, but jacob bekenstein?

This is not unusual. There's many predictions made by MOND ahead of the fact that are borne out by reality. But don't worry - dark matter will be "retrofitted" so that it fits the facts and everybody will suffer collective memory loss again. Edit: see for example table 1 on page 12 here: https://arxiv.org/pdf/2110.06936.pdf https://arxiv.org/pdf/2110.06936.pdf from a review of prior expectations by both MOND and dark matter vs how they turned out against reality for a large variety of astrophysical scenarios.

varjag 4y ago
But MOND itself is a "retrofit" to make it agree with the data, isn't it? It's in the name.
- rcme 4y ago
  Every theory is a retrofit. A useful theory is also predictive.
  - rqtwteye 4y ago
    MOND is not compatible with some observations. It and dark will probably be tweaked until both agree with observations. At that point they will be the same.
    - throwawaymaths 4y ago
      That's a false equivalence. MOND has made several predictions before they were observed (external field effect, linear Tully fisher relationship, early galaxies). I think LCDM's made fewer if any predictions.
  - varjag 4y ago
    MOND has its share of failed predictions. It also still requires a certain amount of DM to work. This is fine for work in progress that all frontier science is but the issue is far from settled.
thereddaikon 4y ago
Dark matter is the umbrella term for the observed discrepancies. MOND is one possible possible explanation for DM. The paper you linked doesn't compare MOND to DM, because that doesn't make any sense. It compares MOND to ΛCDM which is a competing explanation.
sebzim4500 4y ago
Am I understanding that paper correctly that their suggested solution to explain the Bullet Cluster using MOND is too introduce an additional kind of matter which can not be detected on earth and doesn't interact with light (namely sterile neutrinos)? Is this satire?
- aeneasmackenzie 4y ago
  "dark matter but not as much" is still an improvement if you replace it with something better. If MOND predicted these observations and LCDM didn't it's reasonable to say that it is better.
  - sebzim4500 4y ago
    Yeah that's fair. I guess it could also explain why DM has been so hard to pin down, if both MOND and DM are true then there might be DM candidates that have been unfairly ruled out. I do think it significantly hurts the (more philosophical) argument that MOND is simpler or has fewer parameters than DM though.
    - throwawaymaths 4y ago
      So the ongoing problem with LCDM is that the parameter space for allowable particles keeps getting pushed back. We keep falsifying classes of potential particles that could be WIMPs. MOND+ some standard model-adjacent particle (like say right handed neutrinos), if we can have a phenomenological estimate of how much of them should exist, would at least be credible on account of having a constrainable set of parameters, whereas the density of WIMPs in normal LCDM has no constraint besides the same measure that we have to infer its existence (gravitation)

puffoflogic 4y ago

Yeah, but is it even worth saying that when the response will inevitably be "so what?" by the entrenched anti-MOND orthodoxy?

rqtwteye 4y ago

As far as I know , MOND is not compatible with some observations. So dark matter and MOND have to be tweaked to agree with what we see.

6nf 4y ago
MOND is not compatible with all observations but neither is dark matter. A lot of scientists think MOND is a better explanation than a new particle that we've not yet observed. Have a look at Sabine Hossenfelder's work for some of those arguments.
- rsj_hn 4y ago
  Which researchers (as opposed to pop-sci pundits) think MOND is a better explanation than Dark matter? That is a very, very fringe alt-science view that so far exists in various pop-sci blogs and informal youtube discussions, rather than in mainstream conferences, journals, and research centers. I'm not saying it's bad to speculate or write whimsical blog articles about these topics, there's lots of room for creative speculation, but MOND does not respect Lorentz invariance which is basically a deal breaker for virtually all serious researchers. Fewer things have more robust empirical support than Lorentz invariance, so discarding it forces you to say that your violation is always just over the horizon of what is testable (and this horizon keeps getting pushed back). That's generally a discrediting feature of any theory and a huge red flag. Much better to say "you don't know" than to postulate something which requires such massive fine tuning to always be just beyond the horizon of what is testable, but close enough to that horizon to have explanatory power for observed phenomena. https://phys.org/news/2017-11-evidence-violation-lorentz-invariance.html https://phys.org/news/2017-11-evidence-violation-lorentz-inv... https://asfriedman.physics.ucsd.edu/Papers/Friedman+2020a.pdf https://asfriedman.physics.ucsd.edu/Papers/Friedman+2020a.pd...
  - throwawaymaths 4y ago
    He's passed, but jacob bekenstein?