Why can't I construct a sentient machine? What is it that separates a human being from a mere mechanism?
Several months ago I considered this very interesting question with a philosophy professor. If you'll bear with my waning memory, I'll summarize the discussion and continue with some of my later realizations.
As usual, I took the devil's advocate role. I maintained that it was possible to construct a human; my "trump card" was the concept of the Star Trek transporter. I assumed that as on the Enterprise it should be possible to pull a person's atoms apart and reassemble them in a remote location. Likewise it should be possible to store that "image" of the person in the transporter and make duplicate people. One could even tweak the image and make "new" people. For that matter, one could make two new people, say, in the middle of a philosophical debate about the impossibility of making new people.
We ended our lunch without converging on any unique conclusion, though I thought I had the better of the discussion.
My argument depended on the possibility of a transporter-type device. But what if it weren't possible? It occurred me that the quantum mechanical Heisenburg uncertainty principle (HUP) would make such a thing impossible in principle. In a future post, I'll consider more fully the relationship between quantum mechanics and holism, but for the present purpose, it will suffice for you to know the HUP says that on a microscopic scale, it is impossible to measure the position and velocity of a particle with infinite precision at the same time. (To be more exact, the HUP says that the product of uncertainty in position and uncertainty in momentum must be more than a very small number known as Plank's constant.)
Pursing the obvious, I turned to The Physics of Star Trek. Chapter five of this book consists of very clear explanations of the myriad difficulties in building a working transporter device. Among these is the HUP that I've just mentioned (pp. 79-81).
You may know the author, Lawrence M. Krauss, from the news. He is a physicist at Case Western who testified before the Ohio State Board of Education to exclude the teaching of any theory but Darwinism in public schools. The irony is that the Darwinian worldview is precisely the sort of materialism that Krauss's discussion of the HUP helps to diffuse.
In the past few weeks, I came across Richard Hassing's very good article "Animals Versus the Laws of Inertia," in which he describes the philosophical assumption implicit in my counter-argument:
[R]eductionism, ...the presupposition that, regardless of technical details, physics has simply shown that parts are always prior to wholes.
Interestingly Hassing's paper contrasts the law of inertia as formulated by Descartes with that of Newton. He finds that Descartes's version requires reductionism, while Newton's is "causally neutral" and perfectly "compatible with irreducibly internal, or holistic causes of motion" because of Newton's addition of his third law (action-reaction).
An holistic (I prefer "integral") view puts the whole before the parts of which it is composed. The parts of, for example, a dog, are only what they are in terms of the whole they compose. Aristotle says, "[parts] cannot exist if separated from the whole; for it is a finger of an animal not in any manner whatsoever, since it is equivocally called 'a finger' if it is dead" (Metaphysics 7.10, 1035b23-25). In other words your finger is not really a finger unless it is a living part of the rest of you. For an organism, the whole is prior to the parts.
In contrast, a machine part is the same whether incorporated into a larger mechanism or not. An automotive fan belt is essentially the same inside the car as on the store shelf. For machines, the parts are prior to the whole.
But (to return to our original topic) what does this have to do with putting together a human being? Why can't one create a person by assembling parts?
All organisms, including human beings, grow from a very small origin (seed, embryo, etc.).** The whole gradually accumulates bits of matter that it incorporates into itself by forming them into its constituent parts. There is some sort of principle within the nascent organism that organizes the matter and must therefore exist (in some sense) before the organism. The perenniel philosophical term for this inner principle that makes a thing what it is is substantial form.
So the whole comes before the parts, not just in our reason but also in time. There is a wholness about humans that no machine possesses. Assembling parts into a "thinking" machine is conceivable, but it would seem that those parts would lack the intrinsic inter-relation to work together in the integrated wholeness of a person.
** The universe also grew from a very small size, though I doubt it could be called an organism, except metaphorically.
Lawrence M. Krauss, The Physics of Star Trek (New York: Basic Books, 1995).
R.F. Hassing, "Animals Versus the Laws of Inertia," Review of Metaphysics 46 (September 1992): 29-61.