Well, scientists would argue that general relativity (I.e. gravity the way we understand it now) does predict a lot of things really well. Now, the problem is

Well, scientists would argue that general relativity (I.e. gravity the way we understand it now) does predict a lot of things really well. Now, the problem is that its predictions fall apart at quantum scale and cosmological scale. Dark thingies are just a way to make the equations work at cosmological scale. There's always modified gravity, which takes an alternative approach by changing the equations. That's how they taught me 15 years ago, so give or take:-)