I’m not sure if you quoted the right portion of my message - but I don’t think the halting problem plays any part in this scenario. It’s perfectly possible to simulate a computer running a program with an unknown halting state - there’s no real need to know if or when a nested program will halt to simulate it anyways. The arbitrary future state you want to determine may just have it in a non-halted state. The simulation itself is likely non-halting.

I want to clarify that I say “simulation”, but I don’t mean it in the sense it’s usually used at all - I think our universe is as real as real gets. I think of it like this xkcd. If you accept that the universe can in principle be simulated (Such that you, as an inhabitant of the universe, would notice no difference), then why not accept that it can be so simulated with rocks? And if you can accept that your entire existence and subjective experience is determined by rock placement in a desert - then why require the rocks at all? To me, the fact that the universe is mathematically consistent is then enough for it to exist - at least as far as it and its inhabitants are concerned.

I will admit that non-determinism from quantum randomness makes this all a bit hairier / fuzzier, but I don’t think it invalidates the whole thing at all.