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I thought the problem with modifying gravity was that there was no one modification you could make to explain observations. It's plausible that 1000s of differ

I thought the problem with modifying gravity was that there was no one modification you could make to explain observations. It's plausible that 1000s of different galaxies spin differently because they each have different amount of mass of dark matter in them. But it's not really possible to explain 1000s of different data points without 1000s of different gravity equations. If there were some rule (eg on large scales gravity is actually an exponential) then someone would have found it and we would have a candidate for a new law. But they haven't... Is that wrong?

naasking 4y ago
> It's plausible that 1000s of different galaxies spin differently because they each have different amount of mass of dark matter in them. You also need a plausible explanation why all of these galaxies have such different distributions even though they have similar visible mass. If DM is only supposed to interact gravitationally then there should be a tight correspondence with little deviation, but there are galaxies entirely free of DM and distributions that differ across visible mass. There are also observations that don't even match DM (external field effects, tidal effects, and more). There's clearly a lot more to the story.