Ae Sha, Protto Mechanics

i want to ask you about this concept of cost. Ou say you can't have a property called velocity. Only a pair of things can have this property. A single object cannot. And i a sort of mental game i like to play is to imagine, like a particle in an empty universe. Can it have a velocity? Well, it has no meaning to have a velocity. If you are the only thing in the universe, right?