You say, ". . . the Church Thesis, which I would paraphrase as saying that
there are no physical processes more computationally powerful than a Turing
machine, or in other words that the universe could in principle be simulated
on a TM. I wouldn't be surprised if most people who believe that minds can
be simulated on TMs also believe that everything can be simulated on a TM."
I'm out of my depth here, but this doesn't make sense to me. My
understanding is that the Turing Machine is a hypothetical device. If one
could be built that operated at faster-than-light or infinite speed, maybe
it could, in principle, simulate the universe. However, this isn't
possible. Does this mean that the Church Thesis, hence computationalism,
is, in reality, false?