I'm never quite sure what this is meant to mean. Is it comparing to other simulations like computer games or physical simulations where you could change a seed or a data structure and have it manifest in reality? What is expected from a simulation to differ from reality? What does it even mean to make this distinction when we are observing inside the process we are trying to distinguish between real and simulated?
I prefer Greg Egan's interpretation in Permutation City, where simulations can become self-bootstrapping and that simulations need no "simulator" at all. No one's loaded universe.exe in some higher-lever reality, it runs itself.
That still won't stop me from attempting rowhammer attacks.
It could even be a very simple system, as long as it produces complex behavior.
As I put it, the older understanding of the universe working in mechanical ways does not imply the universe is actually a machine nor that it was built by someone or for some purpose similar to the way we build machines. Likewise, the newer understanding of the universe working in computational ways does not imply the universe is actually running on some computer nor that its code was written by someone or for some purpose similar to the way we run simulations.
Metaphysically, I'm strongly opinionated on this now after many years of research on this topic. -see this video from a group of philosophers and idealism-minded thinkers - (also it is way more plausible to me than simulation theory)
Also: Church encodings for integers and bootstrapping number systems from the empty set. https://en.m.wikipedia.org/wiki/Church_encoding And Lisp, of course; where the book Gödel, Escher, Bach shows's up how to build a number system from empty lists:
So they actually realised it.
https://en.wikipedia.org/wiki/Hofstadter%27s_butterfly#:~:te...
This is exactly the point I was making, so I agree. :)