Space

When an object moves in a straight line through space the properties of space determine where it moves.  Somehow the object interacts with space.  Space tells it which way is straight, and what distance is. 

Gravity changes the properties or information stored in space by creating a gravitational field in space.  Objects which would have moved in a straight line start moving in the direction of objects that are near them.  The more massive the object the more it alters the properties of the space that is near it.  The nearer the space the stronger the gravitational vector.