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Such papers only prove that the simplest formula proposed for MOND may be too simple. While it matches well many experimental facts, there also other experimen

Such papers only prove that the simplest formula proposed for MOND may be too simple. While it matches well many experimental facts, there also other experimental facts that appear to contradict it. There is an essential difference between a MOND-like theory and a dark matter based theory. For a MOND-like theory one has to choose some mathematical relationship that determines the gravitational forces, given the observed distribution of matter in the Universe. Then one must compute the expected movements and compare them with the observed movements, to verify or falsify the postulated mathematical model. On the other hand, any theory based on dark matter does not have any predictive power or any usefulness. Because the observed movements of the bodies in the Universe cannot be explained by the conventional mathematical model, one adds arbitrarily dark matter wherever it is necessary to remove the discrepancies in the observed movements. When one is free to add dark matter, then all mathematical models for gravitation become equivalent and none can be used to predict what we observe. Unless an alternative method for observing dark matter would be discovered, using it is just an euphemism for avoiding to recognize that the current model of gravitation is not accurate enough.

pfdietz 3y ago
But you're just demonstrating the annoying aspect of MOND: it's not one theory, so it fails that first requirement of being science, that it be falsifiable. We see this all the time when MOND is tested. It ends up failing, but then the proponents say "oh, well, it's not that MOND we're talking about". It's like some sort of pseudoscientific cockroach that keeps escaping after you crush it with a shoe.
- jcranmer 3y ago
  ... so just like supersymmetry and string theory?
  - pfdietz 3y ago
    Yes, just like that.
- adrian_b 3y ago
  Any specific variant of MOND, with definite formulae for the gravitational quantities, is falsifiable. (Though it may not be very easy to verify or falsify it, because besides the hypothetical "dark matter" there also exists true dark matter, i.e. interstellar gas and dust clouds.) Any theory based on dark matter is not falsifiable, regardless what model is used for gravitation, because for now there is no constraint on the distribution of the dark matter. The only way for the theory of dark matter to become a scientific theory is to discover an alternative way to determine where the dark matter is located, besides placing it wherever necessary to remove the discrepancies between the observations of the movements of the celestial bodies and the predictions of the current model of gravitation.
- nicktelford 3y ago
  Isn't this essentially the same problem with Dark Matter though? They keep looking for it, not finding it and proclaiming "well, it must be somewhere else!". I always got the impression that when Dark Matter was initially labelled as such, it was just a name for the discrepancy between theoretical models and observations; and that the name itself seems to have driven this idea that it's the observations that are wrong and not the models. Personally, when discussing Dark Matter vs. MOND, I think neither should be treated as a concrete "theory", but simply a different perspective on where the problem lies. "Dark Matter" is the idea that our observations are incomplete, and MOND is the idea that our theoretical models are wrong. Hopefully this conundrum is resolved within my lifetime, because I'd love to know what the answer is. It would be absolutely wild if they're both right i.e. that our observations are incomplete and our models are wrong.
  - mr_mitm 3y ago
    > that our observations are incomplete and our models are wrong. I'd say that's a given regardless of the DM mystery. It's consensus that QM and GR are incompatible and that we need a new theory out of which both of these come out as a special case. String theory was considered a hopeful contender for that for a while. And that we haven't observed everything to a satisfying degree yet should be obvious. > Isn't this essentially the same problem with Dark Matter though? They keep looking for it, not finding it and proclaiming "well, it must be somewhere else!". No (unless you mean "where" in parameter space), we have a pretty good idea where it is thanks to gravitational lensing surveys. We don't what it is.
    - nicktelford 3y ago
      Yes, I meant in "parameter space" :-)

pfdietz 3y ago

But you're just demonstrating the annoying aspect of MOND: it's not one theory, so it fails that first requirement of being science, that it be falsifiable. We see this all the time when MOND is tested. It ends up failing, but then the proponents say "oh, well, it's not that MOND we're talking about". It's like some sort of pseudoscientific cockroach that keeps escaping after you crush it with a shoe.

jcranmer 3y ago
... so just like supersymmetry and string theory?
- pfdietz 3y ago
  Yes, just like that.
adrian_b 3y ago
Any specific variant of MOND, with definite formulae for the gravitational quantities, is falsifiable. (Though it may not be very easy to verify or falsify it, because besides the hypothetical "dark matter" there also exists true dark matter, i.e. interstellar gas and dust clouds.) Any theory based on dark matter is not falsifiable, regardless what model is used for gravitation, because for now there is no constraint on the distribution of the dark matter. The only way for the theory of dark matter to become a scientific theory is to discover an alternative way to determine where the dark matter is located, besides placing it wherever necessary to remove the discrepancies between the observations of the movements of the celestial bodies and the predictions of the current model of gravitation.
nicktelford 3y ago
Isn't this essentially the same problem with Dark Matter though? They keep looking for it, not finding it and proclaiming "well, it must be somewhere else!". I always got the impression that when Dark Matter was initially labelled as such, it was just a name for the discrepancy between theoretical models and observations; and that the name itself seems to have driven this idea that it's the observations that are wrong and not the models. Personally, when discussing Dark Matter vs. MOND, I think neither should be treated as a concrete "theory", but simply a different perspective on where the problem lies. "Dark Matter" is the idea that our observations are incomplete, and MOND is the idea that our theoretical models are wrong. Hopefully this conundrum is resolved within my lifetime, because I'd love to know what the answer is. It would be absolutely wild if they're both right i.e. that our observations are incomplete and our models are wrong.
- mr_mitm 3y ago
  > that our observations are incomplete and our models are wrong. I'd say that's a given regardless of the DM mystery. It's consensus that QM and GR are incompatible and that we need a new theory out of which both of these come out as a special case. String theory was considered a hopeful contender for that for a while. And that we haven't observed everything to a satisfying degree yet should be obvious. > Isn't this essentially the same problem with Dark Matter though? They keep looking for it, not finding it and proclaiming "well, it must be somewhere else!". No (unless you mean "where" in parameter space), we have a pretty good idea where it is thanks to gravitational lensing surveys. We don't what it is.
  - nicktelford 3y ago
    Yes, I meant in "parameter space" :-)