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Non-computability.

Name: Anonymous 2010-03-04 21:21

According to Roger Penrose, humans can perform non-computable feats, such as dealing with Gödel questions. He uses this as a foundation to claim that the human mind cannot be expressed in terms of classical processes, and as such must be party to the only other (known) game in town: Quantum Mechanics.

Now, I haven't had the patience to sit through all of his arguments yet, though I slowly make progress. My understanding is that a large part of his stance is that an algorithm cannot usefully deal with a Gödel question, or equivalently, with the halting problem, while a human can.

My objection to this is that such problems always demand a certain quality of response when asked of UTMs: failing to respond forever is not acceptable as correct, nor is providing any response other than one that yields a truth when taken in combination with the question. This much is fine, however, when it is time for the human to answer, he is permitted the liberty of rejecting the question on the grounds that it is inherently unanswerable.

Obviously I am interested in artificial intelligence, and also find his assertion to be simply a self-serving one with a contrived philosophical backdrop for foundation. If anyone knows of, or can think of, a more sophisticated argument than the one above (or expose my flaws in my assessment of it) I would like to hear it.

Apologies for bringing up a largely philosophical question, my only excuse is that I cannot trust any other board with the question.

Name: Anonymous 2010-03-11 18:50

>>82
But Turing Machines do not have finite tape.  Having an "infinite tape" means that any size program of any complexity can be emulated on it.  You can argue that it isn't possible to write a program that has an infinite number of states, which makes more sense.  So, let us assume a situation where the program does not enter a state more than twice.

Instead of a program, a thread performs some task but enters a situation where it needs to perform more tasks before it can proceed.  It creates and runs a recursive thread on what is left over and has to wait for that new thread to "join."  We shall assume that this is the top level.  Our Turing Machine will prove whether this top level original thread ever finishes.  So now you're in a situation where the Turing Machine has to simulate itself.

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