A huge rock of an essay, but worth the read:
Intriguingly, some involved in the AI project have begun to theorize
about replicating the mind not on digital computers but on some
yet-to-be-invented machines. As Ray Kurzweil wrote in The Singularity is Near:
"Computers
do not have to use only zero and one.... The nature of computing is not
limited to manipulating logical symbols. Something is going on in the
human brain, and there is nothing that prevents these biological
processes from being reverse engineered and replicated in nonbiological
entities."
In principle, Kurzweil is correct: we have
as yet no positive proof that his vision is impossible. But it must be
acknowledged that the project he describes is entirely different from
the original task of strong AI to replicate the mind on a digital computer. When the task shifts from dealing with the stuff of minds and
computers to the stuff of brains and matter—and when the instruments
used to achieve AI are thus altogether different from those of the
digital computer—then all of the work undertaken thus far to make a
computer into a mind will have had no relevance to the task of AI other
than to disprove its own methods. The fact that the mind is a machine
just as much as anything else in the universe is a machine tells us
nothing interesting about the mind. If the strong AI project is to be
redefined as the task of duplicating the mind at a very low level, it
may indeed prove possible—but the result will be something far short of
the original goal of AI.