Exactly what James says. This is a rebuttal of Bostrom. If we wish to debate whether we are being simulated in some universe that in no way resembles ours, then my argument is much simpler. It’s not impossible but it is unknowable and cannot be proved nor disproved. It makes no difference to anything whatever and has no evidence in support of it other than it apparently seeming plausible to people such as yourself. I believe this plausibility comes from the existence of lifelike simulations in our world, and that Bostrom, tempted to wonder if we mightn’t ourselves be in one, attempted to justify this possibility through a logical argument. That argument is faulty. Therefore we are back to square one, which is wondering about what realities we might be nested inside of. This reminds me of an argument I made way back when studying philosophy. It asks how we know we are not dreaming if, when dreaming, we believe ourselves awake. The answer is that we remember the characteristics of dreams: illogical sequences, lack of coherence and so on, and these features tell us we are not dreaming now. Now the counter argument, analogous to your argument that the simulating world’s physics need not resemble ours at all, is that we are in a dream so can’t accurately recall the characteristics of dreams. And this is can’t be disproved, but is also self contradictory, since then we have shifted the definition of a dream not to be what we call a dream, but to be something else that is unknowable and about which we cannot argue or reason. So believe we are in a dream or a simulation by all means. Do not claim however that there is any rational reason for that belief.