[yew]

. . . our ability to perform computation is not a valid argument to that computation, or the inner workings of our mind, being the same as digital computers performing computation.

No one [1] thinks that the human brain is likely to be a digital computer performing arithmetic on fixed-width binary integers and IEEE floating-point numbers. The argument for AI is simply that the mind appears to be a material object and the laws of physics appear to be Turing-equivalent. If that holds, the mind is provably equivalent to a Turing machine (or, less likely, some less powerful class of automaton). Arguing about whether in fact that does hold, as Penrose does, can be justified (though I personally think Penrose lost the plot years ago). Arguing about whether your preferred model for categorizing abstract ideas renders the argument inconceivable, with no reference to experimental results or formalisms, can not.

[1] Feel free to add your preferred qualifiers here. The existence of people who believe tobacco companies are run by lizard-people has no bearing on whether cigarettes cause lung cancer.

[wwweston]

> The argument for AI is simply that the mind appears to be a material object and the laws of physics appear to be Turing-equivalent.

This line of argument does achieve the goal of making it trivially true under the definitions given that the brain is a computer, but it seems to me it robs the assertion of insight -- e.g., the brain is computer because everything is a computer, including the nearest rock, since it's also a physics-governed system.

[dragonwriter]

> This line of argument does achieve the goal of making it trivially true under the definitions given that the brain is a computer, but it seems to me it robs the assertion of insight

I think, rather, it reveals the fundamental lack of clarity of the contrary position.

> e.g., the brain is computer because everything is a computer, including the nearest rock, since it's also a physics-governed system.

Right. But no one is questioning the ability to build a computer that simulates the behavior of a rock; or most other physics-governed systems. The AI-is-impossible position boils down to the argument that the mind is not like all other physics governed systems, though it tends to waffle and hedge and bob and weave around that point rather than coming right out with it. Pointing to Turing equivalence and the apparent computability of natural phenomena forces the AI-is-impossible-because-the-mind-is-not-the-kind-of-thing-a-computer-can-simulate argument to come straight out and either (1) reject the universal computability of physical systems, or (2) reject the mind as a physical system.

It still, of course, leaves plenty of room for the proposition that AI is possible but really quite hard.

[coldtea]

>But no one is questioning the ability to build a computer that simulates the behavior of a rock; or most other physics-governed systems.

Actually it sounds especially difficult.

A crude approximation (simulation) at best.

Nothing like a full rock, with its full interactions with its full environment (that might need simulating the whole universe), and with oversimplifying most of its properties (molecular interactions, heat dynamics, etc).

Now make it a "wet rock" and we're even further away (and I wont even dare ask for mold on it or anything, much less living micro-organisms)...

[wwweston]

> But no one is questioning the ability to build a computer that simulates the behavior of a rock; or most other physics-governed systems.

I'm willing to make that challenge: a complete simulation of rock sounds like a formidable problem to me, one I'm not at all certain is within state of the art.

Particularly if (as we're generally imagining when we're talking about simulating brains) we're asking the simulation to be able to stand in for its analog as part of a process-chain connected to a non-simulated situation.

[yew]

It certainly spectacularly fails to provide any advice on the practical problem of engineering AI [1]. The same is true of many non-constructive mathematical proofs, though - and I can't say I find such proofs any less insightful for that.

[1] Though, at least in my opinion, the cognitive science and AI research people have made great progress here - by studying real brains and the formalisms underlying computation.

[justinpaulson]

I think there are far too many assumptions about how the body works and the laws of physics (both of which we are far away from completely understanding) to say that the mind is equivalent to a Turing machine.