It is said that objects in free fall passively follows the geodesics of space-time. If space-time is curved at some random place, due to the presence of a nearby gravitationnal field, the object will continue to follow the straight path of the geodesics, which will appear as a curved trajectory for us. This is the official explanation for how does gravity works and it describes very well HOW objects moves in a gravitationnal field. But to my ears, this is an incomplete explanation. It doesn't explain WHY an hypothetical stationnary object would START to move in the first place. I take it like this: if the train moves and the tracks are curved, the train will turn. But if the train is at rest, it takes more than curved tracks to make it moves....