Yes it is mass but they are having trouble with putting a theory together that handles many of the anomalies that are found in space planets with glithces in their orbit that can not be answer by one theory so another is formed and some other anomaly causes problems with that. There are approximately 10 different theories of gravity that address on issue but not them all.
not at all, in physics often scientists make simplified models, these modles are there to make it easier to understand and predict, For example people thought that the earth was at the centre of the universe, then scientists observed and realized the earth was not at the centre but going around the sun in a circular orbit, then the model (sun-center/earth and other planets in a circle around it) got refined and instead of circular orbits the orbits where defined as elyptical because they beter defined what was being observed.
You talk about gravity, but look at the two equations I posted F = GMm/RČ and F=mg
usually in school you use 10m/s
2 and you say F=10m for something on earth. But that 10 comes from GM/R
2 and so if the person is in a ravine or at the top of Everest g should be slightly different. But 10 is close enough for most calculations you will do.
This is the same thing people create different models hoping to make the concept easier to understand "think of the uUniverse as a big bed, a planet on it is like a bowling ball, you put it on the bed and it makes a V because of the weight of the ball on the bed, then you put a marble, if it is far enough, there is no effect but put it in the dent caused by the BB it then "gravitates" twords the BB.
That is a model to explain it. Also the issue is not gravity (or any of the other forces) but that many physicists assume that all of them (be it gravity, electromagnetisme, quantum physics.....) are related and that one should be able to come to a simple model that explains them all, from the sub atomic to the planetary forces.
