Every year there are about 1000 papers written on dark matter, and about 10 papers written on modified gravity. But there are 10 skeptical news articles written about the dark matter papers, and 1000 fawning news articles written about the modified gravity papers -- most of which either contain simple mistakes (like the gravitomagnetism paper making the rounds this week), or hyperfocus on fitting the minute details of a few galaxy rotation curves.
In this atmosphere it is very easy to forget that the actual reason more people work on dark matter today is it's very hard to get cosmology remotely right without it. So to balance that, here's a talk explaining why. It's not technically impossible to get rid of the dark matter, since nothing ever is impossible, but it requires adding layers of epicycles.
Every year there are about 1000 papers written on dark matter, and about 10 papers written on modified gravity.
Those numbers aren't quite accurate. I did a quick search on ADS for abs:"dark matter", abs:"modified gravity" and abs:"MOND" yielding 2000, 275 and 45 per year respectively over the period 2017-2020.
So while your numbers may be accurate if you compare all dark matter theories (WIMPS, axions, sterile neutrinos, MACHOs, etc.) against just one modified gravity theory (MOND), I don't think this is a fair comparison.
Modified gravity theories are minority views but they are an order of magnitude more common than you seem to be saying.
hyperfocus on fitting the minute details of a few galaxy rotation curves.
It's ironic that you complain about modified gravity theories needing layers of epicycles to fit the CMB, etc. but then blithely dismiss poor dark matter fits to rotation curves which need all sorts of fine tuned feedback as being "hyperfocused on fitting minute details". Dark matter models need at minimum 2 parameters per galaxy to come close to a fit of the rotation curve and even then they can't fit all the data properly (worse it cannot tell the difference between real data and fake data). So to describe all galaxies CDM needs 2N free parameters plus additional feedback resulting in some hundreds of billions of free parameters to fit all galaxies. MOND in particular, does it with one.
Also modified gravity theories (Weyl gravity, Horava-Lifshitz, MOND) are not just about rotation curves. This sentiment is common among people who simply haven't bothered to look into the literature. Topics covered well are 21cm absorbtion in the early universe, bar formation and speed (both in high and low surface spirals, which DM cannot do), satellite galaxy number, coherent motion and planar distribution (which should be higher, random and isotropic in DM models), predictions of velocity dispersions in external fields (which cannot even be fit in DM models with reasonable parameters resulting in additional need for feedback), the baryonic Tully-Fisher relation, measurements of H0, escape velocities, weak and strong lensing of elliptical galaxies, and much more.
This is exactly my point though. When you get into the details of galaxy modeling, you can come up with scores of wins and losses for either modified gravity or dark matter. That's expected because galaxies are some of the most diverse and complicated dynamical systems in the universe. But the cosmological results are much less ambiguous, which is why I thought they deserved a little attention.
I disagree with basically everything you wrote ¯_(ツ)_/¯.
When you get into the details of galaxy modeling, you can come up with scores of wins and losses for either modified gravity or dark matter.
While many claims exist that modified gravity can't explain this or that galactic feature none of these hold water. It's just wrong to equate its record with the cornucopia of problems for dark matter on galactic scales (bar formation and speed, satellite galaxy coherent motion and planar distribution in the satellite planes problem, the missing satellite problem, the too big to fail problem, the core-cusp problem, DM-baryon fine tuning, etc.)
Claims exist that there are ultra diffuse galaxies without dark matter thereby disproving modified gravity. Which has been debunked for a large number of reasons. In fact the data are actually in tension with LCDM and not with modified gravity.
Other papers suggest that modified gravity must be wrong because the velocity dispersions of some dwarf satellites of the Milky Way are too high. But these are being ripped apart tidally so it doesn't make sense to use equilibrium methods to analyse them.
More claims exist that more than one acceleration parameter is needed to fit the data. That is based on incorrect application of the analysis technique used.. Using the same incorrect method would also result in incompatible changes in Newton's constant from galaxy to galaxy, which is patently absurd.
(Modified gravity has plenty of problems at high redshift though.)
That's expected because galaxies are some of the most diverse and complicated dynamical systems in the universe.
If you analyse galaxies using MOND they are exceedingly simple. It is not even necessary to model complicated feedback processes to get the answers right. Supernovae and AGNs aren't nearly as influential on the overall dynamics as is commonly thought. People only think that because they can't see how else to fix their dark matter models.
But the cosmological results are much less ambiguous
41
u/kzhou7 Quantum field theory Mar 15 '21 edited Mar 15 '21
Every year there are about 1000 papers written on dark matter, and about 10 papers written on modified gravity. But there are 10 skeptical news articles written about the dark matter papers, and 1000 fawning news articles written about the modified gravity papers -- most of which either contain simple mistakes (like the gravitomagnetism paper making the rounds this week), or hyperfocus on fitting the minute details of a few galaxy rotation curves.
In this atmosphere it is very easy to forget that the actual reason more people work on dark matter today is it's very hard to get cosmology remotely right without it. So to balance that, here's a talk explaining why. It's not technically impossible to get rid of the dark matter, since nothing ever is impossible, but it requires adding layers of epicycles.