It is interesting, but it feels like there are too many compromises made at the expense of observational data.
The first issue is the reliance on a ~2eV neutrino to compensate. While sterile neutrinos could theoretically be that massive, we have yet to find conclusive evidence of steriles and don’t know the absolute masses or the mass ordering of the neutrinos mass eigenstates we have observed. (I am in neutrinos, so this is the point I am most familiar with.) While the discovery of steriles could occur, my buddy works on a search for eV scale sterile neutrinos and all of his findings have shown that there is no preference for any sterile signal at or around 1-100eV. Normal neutrinos also can’t work: While we don’t know the masses of each neutrino mass eigenstate individually, we know the sum of the neutrino masses, ~0.06-0.1eV, eliminating normal neutrinos from contention as well. This is a core failing, as it relies on the presence of an equally unproven particle as DM, but isn’t as good a fit as DM in many ways, leading into point 2…
It has a hard time fitting to galactic cluster data. The Bullet cluster is one of the best observational proofs of DM, and MOND doean’t offer a good explanation for what we see. It also doesn’t account for gravitational lensing, which is a problem given we can see that quite clearly. Since it is only effective at huge scales and can’t be easily checked in a lab, it needs to at least consistently describe observations before I can consider it over DM, which does an excellent job of describing observation. This leads into my final point…
There isn’t really any way to experimentally verify/refute it. I am an experimentalist, and while not every theory needs to have a labrotory confirmation, it seems like there is no way to falsify MOND. DM experiments have long proposed models that allow for some DM particle interaction mechanism, however infrequent, with barionic matter that would confirm/deny those models. While far from exhaustive, it at least allows for the ruling out of certain models if the expected flux isn’t there. MOND seems opaque to even this sort of experimental checking.
There are other issue too, but I am not well versed in GR, which is where many other tensions exist. Overall, it seems like an interesting math problem, but I can’t take it seriously until it gives us something to test or describes what we see much more accurately.
It is interesting, but it feels like there are too many compromises made at the expense of observational data.
The first issue is the reliance on a ~2eV neutrino to compensate. While sterile neutrinos could theoretically be that massive, we have yet to find conclusive evidence of steriles and don’t know the absolute masses or the mass ordering of the neutrinos mass eigenstates we have observed. (I am in neutrinos, so this is the point I am most familiar with.) While the discovery of steriles could occur, my buddy works on a search for eV scale sterile neutrinos and all of his findings have shown that there is no preference for any sterile signal at or around 1-100eV. Normal neutrinos also can’t work: While we don’t know the masses of each neutrino mass eigenstate individually, we know the sum of the neutrino masses, ~0.06-0.1eV, eliminating normal neutrinos from contention as well. This is a core failing, as it relies on the presence of an equally unproven particle as DM, but isn’t as good a fit as DM in many ways, leading into point 2…
It has a hard time fitting to galactic cluster data. The Bullet cluster is one of the best observational proofs of DM, and MOND doean’t offer a good explanation for what we see. It also doesn’t account for gravitational lensing, which is a problem given we can see that quite clearly. Since it is only effective at huge scales and can’t be easily checked in a lab, it needs to at least consistently describe observations before I can consider it over DM, which does an excellent job of describing observation. This leads into my final point…
There isn’t really any way to experimentally verify/refute it. I am an experimentalist, and while not every theory needs to have a labrotory confirmation, it seems like there is no way to falsify MOND. DM experiments have long proposed models that allow for some DM particle interaction mechanism, however infrequent, with barionic matter that would confirm/deny those models. While far from exhaustive, it at least allows for the ruling out of certain models if the expected flux isn’t there. MOND seems opaque to even this sort of experimental checking.
There are other issue too, but I am not well versed in GR, which is where many other tensions exist. Overall, it seems like an interesting math problem, but I can’t take it seriously until it gives us something to test or describes what we see much more accurately.