That is why I have doubts about their scalability. There are fundamental physics reasons we were able to scale digital computers and were unable to do the same to analog ones.
That's certainly true. But - the fastest possible machine to compute the sound of a guitar string reverberating in a concert hall is a guitar in a concert hall. The world itself does a tremendous amount of compute - the question is whether it is useful compute. I don't think this has been explored nearly enough.
Nonlin ar partial differential equations through a large continuum are expensive. Even if you can scale this particular example, it doesn't refute the point, the universe does a tremendous amount of compute that we don't know how to exploit.
I think it is totally possible for the computing to take non-zero time, but we observe it in zero-time as our consciousness only steps forward only with each iteration of computing the world state. So we observe zero time reality computations.