I wasn't proposing that a computer running our universe is based on electronic circuits; rather, I was proposing that computation itself is all that's needed to

I wasn't proposing that a computer running our universe is based on electronic circuits; rather, I was proposing that computation itself is all that's needed to simulate our universe. Since an 'outside' universe doesn't need to bear any relation to our 'inside' universe, it can be vastly simpler. Maybe it's a rule 110 cellular automaton; maybe it's a 2,3 turing machine; maybe its an iota evaluator; it could even be just some abstract computational essence, distinct from implementation. That's enough to run a simulation. Now, the question is 'why simulate the universe when you could just simulate a brain'? This is basically the Boltzmann Brain argument. In terms of bits (see Kolmogorov complexity) the universe is simpler to describe (physics + initial conditions) than a whole brain (neurons, synapses, hormones, etc.). Basically, the universe can unfold from a tiny core (the big bang), whereas a single brain can't (it could unfold from a fertilised egg, but that's already huge, and requires all kinds of matter and physics to work which the big bang would have used anyway). In that case, a random program running on an 'outside' computer is much more likely to be a universe than a brain. By the anthropic principle, we could ask if our universe is the simplest which can support life, in terms of the number of bits required to encode the laws of physics as a program.