[vidarh]

Steam engines and gears are a specific physical manifestation of computation. Computation does not have a single, specific physical manifestation - it can, and has, been done with organic matter, electronics, gears, pipes of water, light.

Per the Church-Turing thesis these can all compute the same set of functions, and unless you can demonstrate that brains and only brains can evoke unknown physics that allows brains to compute a set of functions that can not be computed by other means, the most logical assumption is that it holds, including for brains.

Especially given how much we measure brains without seeing any signs of unusual physics.

[soist]

I think I understand. So what you're saying is that every function that can be implemented with computers must be computable. Your claim is that the brain is actually a computable function, can you tell me which one it is using your favorite version of a Turing complete instruction set? Or maybe I misunderstood and what you're saying is that the brain is not the function but what it does is compute a specific function called your mind in some unknown instruction set?

[vidarh]

I'm saying that per the physical Church-Turing thesis, any function that is computable by ordinary physical means are Turing computable, and we have no evidence that even hints at the physical Church-Turing thesis not holding.

For it not to hold, there would need to be something unique about the physics of a brain that allows it to compute a class of functions which are inherently impossible to compute by other means. That'd imply entirely new/unknown physics that we're somehow not seeing any hints of.

> Your claim is that the brain is actually a computable function, can you tell me which one it is using your favorite version of a Turing complete instruction set?

No, my claim is that absent evidence of unknown physics or another way of disproving the physical Church-Turing thesis, the rational assumption is that the brain follows the same laws of physics as everything else, and so is limited to computation that is equivalent in power to Turing computable functions, just like everything else we know of.

For the brain not to be a computer would imply "magic" - not just that we don't know how the brain works, but for the brain to work in ways inconsistent with all known physics, and inconsistent in ways impossible to simulate with Turing computable functions. No sign of any such unknown physics happening in the brain has ever been recorded.

[soist]

The Church-Turing thesis is a meta-mathematical statement and it neither has a proof nor disproof. In any case, this discussion has run its course.