Turing-complete universe

If the universe is one giant computation, anything can be written as code, so is there any theoretical limit to the model-as-engineer approach? Could a model with enough code know-how simulate the universe? (Physical Church–Turing thesis, unproven.) Even if true, it only removes the expressivity ceiling. Two walls remain: compute (computable isn't tractable) and information (code is only as good as what the writer knows about laws and starting conditions; chaos means you have to measure, not reason). That's where experience/RL comes back in.

Deutsch link: the physical-computation side is the Church–Turing–Deutsch principle (1985). His 'universal explainer' idea (Beginning of Infinity) is the knowledge side: a general mind can in principle create any explanation, gained through conjecture and criticism. Maps onto the model writing code (conjecture) then testing it against reality (criticism).