Good questions.<p>It could be a force - if someone finds a theory that describes all the observational data. They haven&#x27;t.<p>The reason to insist geometry is that general relativity manages to predict extremely accurately the result of all gravitational experiments&#x2F;observations as of 2015. In science, prediction comes before explanation, meaning if you have to accept whatever explanation the best predictive theory offers and not vice versa.<p>Well, its has been explained - you just haven&#x27;t gone through the right books. There are two answers, which I will simplify. One, the Big Bang threw everything all over the place and now masses are moving so as to reach the state of minimum energy. Two, there are 3 other forces in the universe which can cause masses to move. For example you can use electromagnetic forces during the combustion of rocket fuel to send a satellite in space. The satellite then moves in orbit because of the geometry of spacetime. Same when stars explode - this involves all three forces.