I’ve often wondered if an extension on our laws of gravity wouldn’t be sufficient to explain the discrepancies in mass that we see in galaxies etc. but many Quorians have posted saying that we’ve done experiments that show that DM is more likely- what are those experiments? How do they work?
Your instincts are correct. Dark matter is just a fudge factor. The anti-scientists will not allow for real science to go ahead. Real science would entail going back to the drawing board and systematically re-investigating Gravity for the first time in three centuries. The leadership is treating gravity as a personal secret. They have these physicists jumping through hoops to avoid anyone doing actual science. Its not just dark matter that proves they have gravity wrong. Before that we had the insane doctrine that the largest objects are made out of lifting gases that defied everything we know about the behaviour of these gases and self-compressed, leaving the rocks to amalgamate separately. Only extreme control and abuse could lead to these outcomes.
They have not done the experiments you have suggested. The physics-boy 101 types are belligerent against the suggestion that physicists ought to indulge in due diligence as opposed to propaganda.
It is not so much modified Newtonian gravity that is needed here. “Modified” does not capture it. What is required is a systematic overhaul. But the specific problem of the outer stars rotating at similar velocity can be handled as follows;
Imagine our new formulation has matter less “clumpy” than the heritage formulae suggest. Less clumpy, more tightly held, and far more “forgiving.” (Even before the work is done these tendencies should be apparent).
So big objects really “wish” to orbit and not to collide. But still the Galaxy is not tied together like a cartwheel. Its just that the mechanism is more geared to strong orbits. Since these orbits are developing over billions of years it seems only natural that the velocities will wind up synchronised with that of stars in the adjacent spiral arms.