[David Bailey]

Paul C. Anagnostopoulos has suggested that I start a new thread to consider the gedanken experiment of simulating a brain (or whole body) on a computer. Unfortunately this will involve some repetition of ideas already presented, but please bear with me.

We normally suppose that any physical system can, in principle, be simulated on a sufficiently powerful computer. This statement is more or less equivalent to stating that we know the relevant laws of physics for the system in question. The simulation of quantum phenomena will also require the use of a random number generator, but computers come equipped with good deterministic pseudo-random number generators.

Of course, if we simulate a stellar explosion or an electronic circuit, we obviously don't expect the computer program to be completely equivalent to the original thing - just to provide a good numerical approximation to its behaviour.

Now consider a human brain (possibly including the rest of the body). Suppose we simulate that in a gedanken experiment - say for a period of 30 mins. We somehow take a snapshot of the system at the start of the period - converted to numbers - and then allow the simulation to proceed on the computer.

Q1. Is the computer program consciously aware in the same way as the original brain? If the answer to this is no, what is the essential difference, and can it be rectified?

A lot of materialists will answer yes to Q1 because they consider that a brain's behaviour is only defined operationally.

Perhaps the body in question is suffering internally generated pain, so those who answer yes to Q1 should presumably worry that the simulation may also be suffering pain.

Q2. If the program is run again with the same inputs, does it suffer all over again, or are the two simulations somehow equivalent?


Now consider this. Given the combination input/program/output, what you have is a rather quirky theorem. Like any other theorem, this is true for all time (assuming the semantics of the programming language are not wilfully altered!). So we have a situation in which this emotional program has actually become a theorem - something like:

{assorted bodily inputs}=>P=>{output to glands, etc}


Now, it seems reasonable to me to ask just exactly when (and how often) does this program feel all these emotions of pain?

Q3. Is it every time the program is run, or every time someone proves this theorem, or maybe these experiences are completely de-localised over space-time, as with any other theorem?

My point is that computer is really just a very specialised theorem prover. It repeats a transformation from input to output that is already completely defined once the program has been defined. It is merely a tool for reproducing that transformation. Looked at in that light, does it really make sense to credit the system with emotions, or qualia of any sort?

Note that the above argument is extremely general - it works for any theory of consciousness, provided it is possible in principle to perform the simulation. Of course, if the brain acts as a filter then the simulation step might well not be possible - analogous to trying to simulate the behaviour of a TV set without including the incoming electromagnetic radiation.

Comments please

David