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Last I understood (I am not an expert) MOND and related theories fails to explain certain observed phenomena, and goes against other experimentally verified law

Last I understood (I am not an expert) MOND and related theories fails to explain certain observed phenomena, and goes against other experimentally verified laws/phenomena. PBS Spacetime covers this topic in several videos, a good one being [1]. Matt (the host, an astrophysicist), describes what MOND (and other alternative theories, like relativistic-MOND) needs to do but haven't done yet: 1. Give the right answer in more than one special case. MOND may describe a few situations accurately, but it does not describe all situations where we have evidence for dark matter. Only some. 2. Consistent with other known laws and theories that are experimentally verified. According to Matt and others, MOND is not consistent with existing laws such as conservation of energy or angular momentum. 3. Make testable predictions beyond what it was tuned for. Am I missing out on some extraordinary development in MOND and/or MOND-like theories that occurred recently? [1] https://www.youtube.com/watch?v=0sTBZ2G4vow https://www.youtube.com/watch?v=0sTBZ2G4vow

jvanderbot 4y ago
The article is not about MOND, it is about the falsification of Dark Matter. They do advocate MOND, but the main takeaway is right up front: > The current cosmological model only works by postulating the existence of dark matter – a substance that has never been detected, but that is supposed to constitute approximately 25% of all the universe. But a simple test suggests that dark matter does not in fact exist. If it did, we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particles, but we detect no such slow-down. A host of other observational tests support the conclusion: dark matter is not there.
- canjobear 4y ago
  So if DM is falsified and MOND is unworkable, what should scientists do? Just admit that they have no idea what's going on, but it looks a lot like missing mass? Oh wait, that's the definition of dark matter.
  - StanislavPetrov 4y ago
    >Just admit that they have no idea what's going on, but it looks a lot like missing mass? The way I see things, the much more prevalent attitude is, "we have a good idea of what's going on, we just haven't been able to confirm our confident assessments with objective data". Very few, if any, prominent people in the field admit, "we don't have any idea what's going on, it is all baseless conjecture that might pan out if 75% of the universe is made of some invisible stuff that we haven't been able to detect in 4 decades despite our best efforts". I'd like to see a paradigm shift from, "we have a good understanding of how things work, now we just need to detect the invisible particles that make all of our formulas work" to "we have really have no idea what is happening, but here is some wild speculation that is the best we can come up with". A lot of the "dark matter" debate reminds me of the Alzheimers/amyloid situation. Groupthink develops among the establishment in the field, based on very little (if any) objective proof, which ends up discouraging and marginalizing those who pursue other theories.
  - naasking 4y ago
    > Oh wait, that's the definition of dark matter. No, actually calling it missing mass is dark matter. MOND would be another explanation, and there's no reason to conclude it's unworkable.
    - albertopv 4y ago
      MOND still need dark matter, it seems https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Responses_and_criticism https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
      - naasking 4y ago
        That's not what you can infer from the data. Some observations fit well with MOND, some with dark matter. See: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm
- ziddoap 4y ago
  >They do advocate MOND Which is why I'm asking about MOND, which I just explained in my comment is falsified from the start (violation of existing established physics).
  - TremendousJudge 4y ago
    I don't think MOND proponents say the theory is complete, just that alternative gravitation theories is the direction that should be taken for research instead of funding futile dark matter detection projects.
    - ziddoap 4y ago
      >alternative gravitation theories is the direction that should be taken for research instead of Why instead of? Dark matter is, so far, the best model we have. Seems sensible to continue research in that direction. >futile dark matter detection projects. Why are they futile?
      - jvanderbot 4y ago
        In the context of this article, evaluating the no-dark-matter future is probably in scope. In general, that statement would require defense.
- eloff 4y ago
  They are advocating MOND by omission. If you say dark matter isn't there you now need a theory that can explain all the observations that do support dark matter. MOND seems to be the only semi reasonable alternative.
  - StanislavPetrov 4y ago
    It's perfectly reasonable to say, "your theory is full of holes and isn't based on anything objective that can be measured or proved" without coming up with an alternative theory. You can (and should in my opinion) point out things that are baseless conjecture whether or not you have a better idea. "I don't know" is something a lot of us would be better off saying more often.
    - eloff 4y ago
      I agree, it's fine to point out holes in a theory without an alternative explanation. However, it does still leave the problem of how else do you explain all the dark matter observations. So one must be careful not to give to much weight to those kinds of criticisms, as finding one hole in something that explains ten observations doesn't give much confidence in saying the whole theory is wrong (just an example.) Dark matter still seems a much better explanation than MOND to date, even if I personally feel it looks like a hack.
- hannasanarion 4y ago
  The article tries to conclusively throw out good and predictive science based on a single rare edge case test that well-educated people believe to be explainable within the same paradigm. If you're going to claim that dark matter doesn't exist, you need to have a way to explain all of the cases that are known to show that dark matter does exist. Cases like the Bullet Cluster, where a collision left all of the visisble matter in one region, and all of the gravitational matter in another. How can this possibly happen if there is no such thing as invisible gravitational matter? How can there be galaxies like AGC 114905 that don't have any dark matter, if there is no such thing as dark matter for galaxies to have or not?
  - ncmncm 4y ago
    No, you don't need to explain anything. DM falsehood does not depend on any other known thing being correct. It particularly does not depend on MOND being correct. The honest fallback position is not "this other thing is better", it is, "We do not know. We had hoped we did, but were wrong." Then, start entertaining hypotheses that encompass all observations, without prejudice, not just favored ones.
    - deleted 4y ago
      [deleted]
- eterevsky 4y ago
  The article writes upfront: "The implications of this are nothing short of a revision of Einstein’s theory of gravitation."
naasking 4y ago
> 1. Give the right answer in more than one special case. MOND may describe a few situations accurately, but it does not describe all situations where we have evidence for dark matter. Only some. DM also fails numerous observations, like the one described in this article, external field effects, and more. It failed numerous previous observations as well until more parameters were added to DM theories to account for actual observations. > 3. Make testable predictions beyond what it was tuned for. This is backwards. DM has been tuned to match certain predictions, where MOND's predictions are free of parameters and yet fit observations. That's actually strong evidence in favour of MOND. See my other comments here for a reference to a paper that reviews the evidence for/against both.
- ziddoap 4y ago
  Take it up with the astrophysicists who gave this criteria, not me. Unless you are also an astrophysicist, I'll stick with trusting their judgement over yours. You can also watch the video I provided for a more nuanced explanation.
  - naasking 4y ago
    Here's your nuanced review by astrophysicists: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm

jvanderbot 4y ago

The article is not about MOND, it is about the falsification of Dark Matter. They do advocate MOND, but the main takeaway is right up front: > The current cosmological model only works by postulating the existence of dark matter – a substance that has never been detected, but that is supposed to constitute approximately 25% of all the universe. But a simple test suggests that dark matter does not in fact exist. If it did, we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particles, but we detect no such slow-down. A host of other observational tests support the conclusion: dark matter is not there.

canjobear 4y ago
So if DM is falsified and MOND is unworkable, what should scientists do? Just admit that they have no idea what's going on, but it looks a lot like missing mass? Oh wait, that's the definition of dark matter.
- StanislavPetrov 4y ago
  >Just admit that they have no idea what's going on, but it looks a lot like missing mass? The way I see things, the much more prevalent attitude is, "we have a good idea of what's going on, we just haven't been able to confirm our confident assessments with objective data". Very few, if any, prominent people in the field admit, "we don't have any idea what's going on, it is all baseless conjecture that might pan out if 75% of the universe is made of some invisible stuff that we haven't been able to detect in 4 decades despite our best efforts". I'd like to see a paradigm shift from, "we have a good understanding of how things work, now we just need to detect the invisible particles that make all of our formulas work" to "we have really have no idea what is happening, but here is some wild speculation that is the best we can come up with". A lot of the "dark matter" debate reminds me of the Alzheimers/amyloid situation. Groupthink develops among the establishment in the field, based on very little (if any) objective proof, which ends up discouraging and marginalizing those who pursue other theories.
- naasking 4y ago
  > Oh wait, that's the definition of dark matter. No, actually calling it missing mass is dark matter. MOND would be another explanation, and there's no reason to conclude it's unworkable.
  - albertopv 4y ago
    MOND still need dark matter, it seems https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Responses_and_criticism https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
    - naasking 4y ago
      That's not what you can infer from the data. Some observations fit well with MOND, some with dark matter. See: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm
ziddoap 4y ago
>They do advocate MOND Which is why I'm asking about MOND, which I just explained in my comment is falsified from the start (violation of existing established physics).
- TremendousJudge 4y ago
  I don't think MOND proponents say the theory is complete, just that alternative gravitation theories is the direction that should be taken for research instead of funding futile dark matter detection projects.
  - ziddoap 4y ago
    >alternative gravitation theories is the direction that should be taken for research instead of Why instead of? Dark matter is, so far, the best model we have. Seems sensible to continue research in that direction. >futile dark matter detection projects. Why are they futile?
    - jvanderbot 4y ago
      In the context of this article, evaluating the no-dark-matter future is probably in scope. In general, that statement would require defense.
eloff 4y ago
They are advocating MOND by omission. If you say dark matter isn't there you now need a theory that can explain all the observations that do support dark matter. MOND seems to be the only semi reasonable alternative.
- StanislavPetrov 4y ago
  It's perfectly reasonable to say, "your theory is full of holes and isn't based on anything objective that can be measured or proved" without coming up with an alternative theory. You can (and should in my opinion) point out things that are baseless conjecture whether or not you have a better idea. "I don't know" is something a lot of us would be better off saying more often.
  - eloff 4y ago
    I agree, it's fine to point out holes in a theory without an alternative explanation. However, it does still leave the problem of how else do you explain all the dark matter observations. So one must be careful not to give to much weight to those kinds of criticisms, as finding one hole in something that explains ten observations doesn't give much confidence in saying the whole theory is wrong (just an example.) Dark matter still seems a much better explanation than MOND to date, even if I personally feel it looks like a hack.
hannasanarion 4y ago
The article tries to conclusively throw out good and predictive science based on a single rare edge case test that well-educated people believe to be explainable within the same paradigm. If you're going to claim that dark matter doesn't exist, you need to have a way to explain all of the cases that are known to show that dark matter does exist. Cases like the Bullet Cluster, where a collision left all of the visisble matter in one region, and all of the gravitational matter in another. How can this possibly happen if there is no such thing as invisible gravitational matter? How can there be galaxies like AGC 114905 that don't have any dark matter, if there is no such thing as dark matter for galaxies to have or not?
- ncmncm 4y ago
  No, you don't need to explain anything. DM falsehood does not depend on any other known thing being correct. It particularly does not depend on MOND being correct. The honest fallback position is not "this other thing is better", it is, "We do not know. We had hoped we did, but were wrong." Then, start entertaining hypotheses that encompass all observations, without prejudice, not just favored ones.
  - deleted 4y ago
    [deleted]
eterevsky 4y ago
The article writes upfront: "The implications of this are nothing short of a revision of Einstein’s theory of gravitation."

naasking 4y ago

> 1. Give the right answer in more than one special case. MOND may describe a few situations accurately, but it does not describe all situations where we have evidence for dark matter. Only some. DM also fails numerous observations, like the one described in this article, external field effects, and more. It failed numerous previous observations as well until more parameters were added to DM theories to account for actual observations. > 3. Make testable predictions beyond what it was tuned for. This is backwards. DM has been tuned to match certain predictions, where MOND's predictions are free of parameters and yet fit observations. That's actually strong evidence in favour of MOND. See my other comments here for a reference to a paper that reviews the evidence for/against both.

ziddoap 4y ago
Take it up with the astrophysicists who gave this criteria, not me. Unless you are also an astrophysicist, I'll stick with trusting their judgement over yours. You can also watch the video I provided for a more nuanced explanation.
- naasking 4y ago
  Here's your nuanced review by astrophysicists: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm