MOND takes a hit

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Pinball1970, Nov 11, 2023.

  1. Pinball1970 Registered Senior Member

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    The recent paper from Banik etc al has caused something of a stir.
    Using the Gaia data taken from the orbits of 1000s of wide binaries,the analysis points to MOND being an unlikely candidate.

    Monthly Notices of the Royal Astronomical Society, stad3393, https://doi.org/10.1093/mnras/stad3393
    Published: 3 November 2023

    I posted this on another forum and discussion is taking place there.

    James R will be interested hopefully, Wegs, Exchem, Billion
     
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  3. Pinball1970 Registered Senior Member

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    As an aside if any of you guys have studied MOND that would be great because I do not understand it!
    Sure it is a tweak to Newtonian gravity but what I do not understand is why that should be the case, at bodies at lower acceleration.

    To me that is like saying ok my momentum is mv UNLESS I am travelling below 100 m per sec THEN p=(m+a)v!

    The first papers were in 1983 so I will check out some of the basics so I can follow this conflict more fully!
     
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  5. C C Consular Corps - "the backbone of diplomacy" Valued Senior Member

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    Aside from specific research-related criticism like this, the overarching disdain for MOND derives from it being incompatible with the so-called Standard Model of Cosmology. The philosophical concern that Merritt explores below (scientific realism) is just one part of the momentum and reasons for wanting to hang onto a background consensus like ACDM.

    ΛCDM and MOND: A debate about models or theory?: "... the MOND approach is likewise viewed by some as unjustifiable. General relativity is a foundational pillar in the contemporary understanding of the universe. Abandoning general relativity would require strong reasons. Therefore, most astrophysicists regard the adoption of modified Newtonian dynamics as unjustifiable. Nevertheless, advocates of MOND claim that their models are equivalent, or even superior in some respects to ΛCDM for describing structural dynamics in the universe."


    MOND vs Dark Matter: Cosmology's crisis challenges scientific realism
    https://iai.tv/articles/cosmologys-...ic-realism-david-merritt-auid-2651?_auid=2020

    INTRO: Dark matter has never been detected, yet it is a key part of the dominant theory of cosmology. An alternative theory, MOND, is empirically equivalent and more successful at making predictions. But the fact that it has no place for the existence of dark matter is a problem for scientific realists who see science as building on past theories. MOND would signal a break with our current cosmological model, making a mockery of the idea of scientific progress as gradually getting closer to a true account of reality, argues astrophysicist David Merritt.
    _
     
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  7. exchemist Valued Senior Member

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    Well MOND was worth a shot, but it look as if we are back to dark matter after all, then.
     
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  8. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    I don't buy this as an issue, though. If a line of reasoning either reaches a dead-end, or an alternative line improves upon our understanding - even it negates what we have otherwise understood - then this is surely a good thing, right? Sticking to just one line of reasoning / model becomes dogmatic rather than a matter of science. The "getting closer to a true account of reality" might be achieved by ditching what we thought we knew and embracing the new branch of understanding.
    That said, if the new branch is not, in effect, backward compatible - i.e. is able to explain everything we already can explain with the "old" line - then it is not an improvement, is it. I don't know whether MOND could explain everything or not, but if it could, then I'm not sure the argument Marritt mentions holds scrutiny. But then maybe I'm missing something.

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  9. C C Consular Corps - "the backbone of diplomacy" Valued Senior Member

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    Yah, as stated, it would merely be one of the (minor?) reasons for the conservatism. Merritt is probably exaggerating the influence of scientific realism in the matter.

    From an instrumentalism or some practical standpoint, the community would largely be hanging onto ACDM because of perceived usefulness rather than a correspondence to "ultimate reality". And it possibly being a unifying umbrella for integrating or coordinating what might otherwise be disparate concerns in cosmology.

    Alternatively, a fickle or permissive approach of frequently trading in established scheme for supposedly "equally predictive and explicative" new rogue models and theories would lead to chaos and fragmentation of broad consensus.

    Again, one can frame "what's going on" or serving as a "roadblock" as being a heavy-handed form of scientific realism -- as Merritt perhaps seems to be doing. But I doubt most scientists in the field really care about conceiving it as progress to something immutable and non-revisable.

    And MOND is being given an opportunity (it's not shut out by default). Of course, "dark matter" hasn't been vindicated, either, and that's perhaps where the envy and projecting a privileged, protected status upon the "standard model of cosmology" comes from.

    David Merritt: The attitude of the modern scientific realist is, apparently, “That was then, this is now.” Since they maintain that fundamental changes to our ‘mature’ theories are no longer to be expected, scientific realists have little use for a methodology that encourages bold theorizing. They are motivated instead to favor methodologies that never take theories very far beyond their current (presumed nearly correct) forms.

    [...] It is easy to see how a methodology like abduction or inference to the best explanation fits hand-in-glove with scientific realism, which posits that major changes to accepted theories are no longer to be expected.

    [...] All of this smacks of putting the cart before the horse, epistemologically speaking. Fortunately, it is quite possible to be a realist—in the sense of accepting the existence of a mind-independent, objective reality—without signing on to the additional ism’s that are currently lumped together under the rubric of ‘scientific realism’.
    _
     
  10. TheVat Registered Member

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    In their analysis, levels of confidence with sigma up in the teens. If sigma there means what it does in other fields, that's quite high confidence in Newtonian dynamics versus MOND. Damn. I was sort of rooting for MOND, given that it would upset the apple carts of dark matter and GR. As others note, science doesn't benefit from an entitled perspective that it's always inching towards a truer depiction of reality. And it would be amusing (though not to many with long careers chasing dark matter) if dark matter were to become the new phlogiston.
     
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  11. TheVat Registered Member

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    I tried to make sense of a MOND article a few years ago, and though I fell short it seemed that understanding the EFE, external field effect, would get you some ways towards the goal. At that time, there was some evidence for EFE presented which, again, was above my pay grade.
     
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  12. Pinball1970 Registered Senior Member

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    Banik, the lead author published in favour of MOND previously which is plus for this paper in terms of lack of bias.
    The question mark will be the quality of the data, this was the criticism levelled at the first paper. Lots of data points, 30,000 but in terms of absolute distance, velocity, inclination and eccentricity was more murky.
    This paper claims to have clipped that back, the more murky data points.
    Anyway something is going on in galaxies that cannot be explained by GR and no DM candidate particle has been found at the LHC since it was switched on in 2008.
    Let's see if Chae's team come back with anything defending their analysis.

    There is lot going on now with JWST, HST, Gaia (these two studies) and now Euclid. The race will be on now to solve these questions.

    How do galaxies hold together? Where is all that extra mass?

    Early galaxies with large mass and structure not predicted by LambdaCDM
     
  13. Pinball1970 Registered Senior Member

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    Science has always worked like this.
    It would be nice to have a theory and demonstrate it there and then in different ways to show it's validity.
    Some areas of science you can do that to an extent but if you look at the history of physics, you will see theories go in and out of favour or are just left as speculation until the technology comes along to assist.
    Einstein was rather lucky, GR had a positive result in 1919 and again in the early twenties using eclipses to demonstrate the strength of his theory which was published only a couple of years before.
    GR took a few twists and turns after that but even his patch up job still proves important today.
    Higgs another example, did he think he had cracked it in 1964? It took nearly 50 years to find the Higgs boson. All that time with zero direct evidence of its existence but without it the SM would have need a major rework.
    Dirac didn't believe his equation, predicting the positron, he thought it was a mathematical quirk with no actual physical significance, three years later the positron is discovered.

    The positron was not needed to explain anything in the 20s but the neutrino came to be.
    The Higgs was needed to explain the SM but pentaquarks discovered recently were not.
    We need DM and dark energy because the universe is doing things that it oughtn't!

    MOND put forward 40 years ago has taken it's biggest hit so far. The data will only get stronger with all the kit that is out there right now so the theorists need to get going!
     
  14. exchemist Valued Senior Member

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    12,370
    Yes I agree. It seems to me it is no part of "scientific realism" to assert that current theories are so good that they can never be overturned. That is just hubristic.

    Scientific realism, surely, is a weaker formulation, to the effect that theories of science approximate something objectively real in nature. As such, we may expect that, on the whole, our theories more and more closely approximate that reality over time. But that is not to say that there cannot ever be wrong turnings along the way.
     
  15. Pinball1970 Registered Senior Member

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    844
    Yes and science recovered.
    Phlogiston, aether, faster light neutrinos, Lamarckism, steady state..

    MOND? DM? Jury out!
     

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