The reason the model would require near infinite time to run is that its modelling a causal event, it isnt an instance of the same causal event.

When electrical fields oscillate they model a bridge. No amount of activity would ever make them "solid".

All "real" stuff is infinite. This form of infinity is really about saying that our descriptions cannot capture the "full depth" of the world. The world itself has no "depth". Models, rather, are simply partial descriptions of it.

To turn a model into the thing its modelling via increasing its descriptive power quickly introduces infinities: its impossible. To make a model "accurate" in this sense, you must actually just make another example of the target. Ie., build that bridge.

Assume P=NP.

P currently not being NP is exactly the kind of thing someone would build into a simulation to prevent stack overflows.

(I don't believe in simulation because: why would anyone that advanced bother?)

(The demonstration that the lowest possible complexity of comparison-based sorting is O(n log n) comes to mind as a related example.)

https://www.chemistryworld.com/feature/quantum-chemistry-on-...

https://www.technologyreview.com/s/603794/chemists-are-first...

Or if you like something by Feynman:

http://doc.cat-v.org/feynman/simulating-physics/simulating-p...