i think i didn't ask the question right. my question is, is it possible to define acceleration with only one object in the universe? lets suppose that object is an atom.
the reason for my question is, if it'd be possible to define acceleration with only one object, i would understand that acceleration is not relative. if it cannot be defined without two objects, it must be relative, right?
of course i understand if we have two objects, such as the pendulum and earth, there would be acceleration. even in an universe with two objects, if we move the objects away from each other, we must have motion, and as their relative motion goes from 0 to x velocity, we would have acceleration. but what if we don't have two objects?
-shami