Darwin's Dangerous Idea - Evolution and the Meaning of Life

446 THE EMPEROR'S NEW MIND, AND OTHER FABLES
Lucas (1970) yearned to drag quantum physics into this arena, but he thought
that the indeterminacy gaps of quantum physics would permit a Cartesian
spirit to intercede, twiddling the neurons, in effect, to get some extra mindpower
out of the brain, a doctrine that has also been energetically defended
by Sir John Eccles, the Nobel-laureate neurophysiologist who has
scandalized his colleagues for years with his unabashed dualism (Eccles
1953, Popper and Eccles 1977). This is not the time and place for me to
review the reasons for dismissing this dualism—the times and places are
Dennett 1991a, 1993d—since Penrose shuns dualism as vigorously as
anybody else in the materialist camp. What is refreshing about his attack on
AI, in fact, is his insistence that he hopes to replace it with something that
would still be a physical science of the mind, not some unexplorable mystery
that takes place in the never-never-land of dualism.
Without abandoning the physical sphere, we might get some strange new
powers out of subatomic particles, according to recent speculations about
"quantum computers" (Deutsch 1985). Such a quantum computer would take
advantage (it is claimed) of the "superposition of eigenstates" prior to the
"collapse of the wave packet" in order to check out Vast (yes, Vast) search
spaces in ordinary amounts of time. By being a sort of supermassively parallel
computer, it could do Vastly many things "at once," and this could render
feasible whole classes of algorithms that otherwise were unfeasible—such as
the algorithm for perfect chess. This is not what Penrose is seeking, however,
for such computers, even if they are possible, would still be Turing machines,
and hence capable of computing only the officially computable functions—
the algorithms (Penrose 1989, p. 402 ). They would hence fall under the
limitations discovered by Godel. Penrose is holding out for a phenomenon
that is truly noncomputable, not just impractical to compute.
Present-day physics (including present-day quantum physics) is all computable,
Penrose acknowledges, but he thinks that we might have to revolutionize
physics, incorporating an explicitly noncomputable theory of
"quantum gravity." Why does he think such a theory (which neither he nor
anyone else has yet formulated ) would have to be noncomputable? Because
otherwise AI is possible, and he thinks he has already shown, via his argument
from Godel's Theorem, that AI is not possible. That's all. Penrose
candidly admits that none of his reasons for believing in the noncomputability
of quantum-gravity theory are drawn from quantum physics itself; the
only reason he has for thinking that a theory of quantum gravity would be
noncomputable is that otherwise AI would be possible after all. In other
words, Penrose has a hunch that someday we're going to find a skyhook. This
is the hunch of a brilliant scientist, but he himself admits that it is only a
hunch.
In a review of the physicist Steven Weinberg's recent book, Dreams of a
The Phantom Quantum-Gravity Computer 447
Final Theory (Weinberg, you will recall from chapter 3, gave two cheers for
reductionism), Penrose mused as follows:
In my view, if there is to be a Final Theory, it could only be a scheme of
a very different nature. Rather than being a physical theory in the ordinary
sense, it would have to be something more like a principle—a mathematical
principle whose implementation might itself involve nonmechanical
subtlety (and perhaps even creativity). [Penrose 1993, p. 82.]
So it is not surprising that Penrose has expressed grave skepticism about
Darwinism. And the grounds he gives are familiar: he can't imagine how
"natural selection of algorithms" could do all that good work:
[T]here are serious difficulties with the picture whereby algorithms are
supposed to improve themselves in this way. It would certainly not work
for normal Turing machine specifications, since a 'mutation' would almost
certainly render the machine totally useless instead of altering it only
slightly. [Penrose 1990, p. 654.]
Most mutations, Penrose sees, are either invisible to selection or fatal; only a
very few improve things. That is true, but it is just as true of the evolutionary
processes that produced the mandibles of crabs as it is of those that produced
the mental states of mathematicians. Penrose's conviction that there are these
"serious difficulties" is undercut, as Poe's conviction was, by the brute
historical fact that genetic algorithms and their kin are daily Overcoming
these fearsome odds and improving themselves by, well, leaps and bounds
(on the geological time scale).
If our brains were equipped with algorithms, Penrose argues, natural
selection would have to have designed those algorithms, but:
The 'robust' specifications are the ideas that underlie the algorithms. But
ideas are things that, as far as we know, need conscious minds for their
manifestations. [Penrose 1989, p. 415]
In other words, the designing process would have to appreciate, somehow,
the rationale of those algorithms it was designing, and doesn't that take a
conscious mind? Could there be reasons recognized without some conscious
mind's recognizing them? Yes, says Darwin, there could be. Natural
selection is the blind watchmaker, the unconscious watchmaker, but still a
discoverer of forced moves and other Good Tricks. This is not as inconceivable
as many have taken it to be.
To my way of thinking, there is still something mysterious about evolution,
with its apparent 'groping' towards some future purpose. Things at least