> Because once you properly set the initial state of the ball (force=velocity=0, or any other values), then the solution becomes unique and that’s it,

The original tumblr post linked to this wikipedia article: https://en.wikipedia.org/wiki/Picard%E2%80%93Lindel%C3%B6f_t... The initial conditions here are _not_ sufficient to pin to a unique solution.

> anything acting on it would violate other principles of classical mechanics

What other principles of classical mechanics does it violate though? I think that's the point of the exercise. To reflect on part of our mathematical modeling would prevent this.