This article got me thinking. I had 2 observations:-

1) Maths is a description of a phenomenon or process (and it may be an attempt to describe the real world, or just an idea in maths). Maths can be exchanged between different mathematicians who can investigate the behaviour of the mathematical system. This is NOT the same as sharing and investigating the real physical system. There is no way of knowing if the simulation is deficient until it "fails" - i.e. diverges from reality. Of course, it is *possible* that we are "experiencing" what we perceive as reality, inside a simulation run by some higher-level mathematician, who might pull the plug on it one day when he's seen enough. This is essentially an appeal to God.

2) The information content of the Universe is finite. To *replicate* the whole Universe as a simulation, inside the Universe, would take at least as much information again, using up every particle in the Universe to BE the simulation. Ergo, the Universe can only be simulated OUTSIDE of the existing Universe. This is essentially an act of creation and is, again, an appeal to God.

I don't know what the answer is, but it looks like it is unknowable to us as inhabitants of this Universe (be it a real on, or a simulation)

(Read "Wang's carpets" for some ideas about how a simulation may appear real, to the entities that evolve inside it...)