> which necessarily won't be able to simulate the entire universe nor anything at a high level of fidelity and so requires constant tricks to convince the inhabitants things are real"
No tricks. Simulating the minds is the entire point. Simulating physics isn't the interesting part of these kinds of simulations.
> I absolutely do not understand how you can just simulate minds without an environment
Each simulated mind contains a set of beliefs about the local environment. The intersection of the belief-sets of the people in close physical proximity dictates the local reality. If some belief-sets conflict, choose the set that has more believers.
Global consistency can be assured if all beliefs that survive a conflict satisfy certain conditions.
> I suppose I will have to read the book because the noise argument you are presenting seems bizarre to me.
You don't need to simulate the LHC, you only need to simulate what outputs the scientists believe the LHC should produce, ie. they expect results consistent with the statistical models of quantum mechanics. Introduce some random errors here and there as a demonstration of human fallibility (like the FTL neutrinos mistake a few years back due to a loose cable).
> No I don't think so. The number of possible "simulated objects" is infinite
The number at any given time is not. Every simulated object will have logical properties associated with it, particularly at its interface. Satisfy the logical properties of the interface, and a simulated mind wouldn't know the difference.
> Not convinced on this point either, but anyway this would conflict with reality considering a great many people already believe with certainty that they are living in a simulation.
They may believe it but they can never prove it, and so they're not actually seeing through the simulation.