One of the most fascinating areas of philosophical study is the study of human consciousness. What is it exactly and where does it come from? The physicalist view is that consciousness is just a product of brain chemistry, but many philosophers are not convinced that consciousness can be reduced to atoms spinning around in the brain.
Physicalism is essentially synonomous with materialism (the view that matter is all there is). It's the view that everything is explicable in terms of physical processes and forces. There's nothing about us, the physicalist maintains, which is non-physical. As such, it's possible that someday computers may possess all the attributes of human beings.
Human consciousness, however, is the fly in the physicalist soup. There is no physicalist explanation of consciousness that has really been successful in persuading philosophers not already inclined toward physicalism.
Consider one aspect of the problem posed to physicalism by consciousness - the problem of sensory experience, or what philosophers refer to as qualia. If human beings are purely physical, like machines, then everything about us should be quantifiable. A complete physical description of us should be a complete description of us. But it's not. The problem was illustrated by Frank Jackson in 1986. Jackson invites us to imagine a student named Mary:
Mary is confined to a black-and-white room, is educated through black-and-white books and through lectures relayed on black-and white television. In this way she learns everything there is to know about the physical nature of the world. She knows all the physical facts about us and our enviroment, in a wide sense of 'physical' which includes everything in completed physics, chemistry, and neurophysiology, and all there is to know about the causal and relational facts consequent upon all this, including, of course, functional roles. If physicalism is true, she knows all there is to know. For to suppose otherwise is to suppose that there is more to know than every physical fact, and that is what physicalism denies.
It seems, however, that Mary does not know all there is to know. For when she is let out of the black-and-white room or given a color television, she will learn what it is like to see something red, say. This is rightly described as learning--she will not say "ho, hum." Hence, physicalism is false.
In other words, Even if Mary knows everything there is to know about the physical world she doesn't know what it is like to see red (or hear noise, or smell fragrance). She can't know it until she has the experience, but this experience cannot be described in physical terms. A complete physical description of the world is not a complete description of the world.
Thus, there must be more to reality than just the physical, and it is doubtful that a computer, or any machine, could ever know what it is like to experience color or enjoy pleasure or suffer pain.
RLC