I think you're only aware of a narrow definition of "supposed to", you're saying the same thing I am.
Edit: to expand a bit. My point is exactly that - if the universe is deterministic. This only applies up to the limit of precision that it can use to calculate its own physics laws but otherwise it should be deterministic. And within a deterministic system all objects are supposed to do certain things, according to the laws that govern them. There's no ulterior moral "supposed to" in the way I'm using the word, which I think is valid usage but I'm not native.