According to the usual way of applying determinism in physics:- If we know all the intitial conditions of a closed system at time t0, we can fully specify the the system at a time t1>t0. This seems natural and obvious within classical physics, but is it really true? I have never heard of a formal theory about this. It just seems to have come about empirically without theoretical support and passed along to the next generations without formal argument. Are there some sources of formal theory/argument I don't know about (theory/argument sans the philosophical trappings of wordplay, or course) ?