Of all the machines that have changed our lives, perhaps the most influential is the computer, the quintessential child of the industrial revolution. It is mass produced and easily available. It combines brilliant scientific insight with a product that improves the real world. The speed of its growth is astounding. Its refinement and improvement rides the very edge of scientific achievement. Computers can generate realistic images of dinosaurs on the run, defeat human chess champions, and serve as humble hubs linking anybody in the world with the World Wide Web. Truly impressive.

But can it think? If a machine can think for itself on some level, perhaps even learn from and improve upon its performance through experience, it can be a far more useful tool. Just about everyone agrees this is a desirable thing, but how to get there is a whole other question.

One camp in the artificial intelligence field sees the human brain as a computer that can be copied to produce an artificial mind. Others argue that human behavior defies the strictures of a computer program. At the heart of this discussion lies the truly slippery question facing those who would fashion artificial intelligence: What does it mean to think? And its corollary: Does thinking constitute consciousness?

In the attempt to get computers to behave in a somewhat thinking/conscious manner, scientists have had to study human beings in a whole new light. It turns out that much of what we take for granted in the world -- that a dropped apple will fall to the ground or that rain makes things wet -- constitutes an invisible set of assumptions that form a backdrop to all human interactions with the world. Thus, before an intelligent robot maid can vacuum the floor, a mass of facts about the 3-D world -- the amount of pressure needed to remove dirt from a carpet; the difference between an ink stain and a black-and-white design, etc. -- must be coded and downloaded.

Human beings learn by integrating their sensory experiences of the world into patterns. We do it naturally, automatically, incorporating and cross-referencing thoughts, conversation and interactions with the world at large. A single interaction with an apple or a snowstorm or a car that won't start brings us reams of new information about the world -- processed without conscious effort and seamlessly integrated with what we already know to create a better, broader understanding.

Neural networks, designed to promote and create AI, approach the experience-learning-new information-integration problem by modeling the biology of the human nervous system. These vastly simplified networks show promise, but the computing cycles necessary to power them make complicated neural nets run slowly.

The speed breakthrough that foreshadows the jump to true AI may hinge in the switch from silicon memory to molecular memory (as made clear by Mark A. Reed and James M. Tour in "Computing with Molecules"). Combine that with the ability of molecules to function as switches and other products of nanotechnology, and the accompanying increase in processing power could set the stage for AI's grand show: the intelligent robot.

The dream of a mobile, autonomous, sentient, non-biological creation has been with us for about a century. Some predict the robot will be a conscious entity, capable of feelings, emotions, and insights. Some cast the robot as a task-specific machine, thoughtful perhaps, but empty of human considerations and subtleties.

Robots, and certain other limited forms of artificial intelligence, have made their mark in the world already, from super-computers to robotic factories. The questions and challenges that face the latest generation of researchers in this field, explored here in detail, make it clear that we are well on the way to thinking machines becoming an important player in the details of everyday life.

The Turing test for consciousness shaped the early efforts in the artificial intelligence field. Can a machine convince a human being that it, the machine, is human? Perhaps the test is flawed and should be discarded, say authors Ford and Hayes. The greatest value of artificial intelligence may lie not in imitating human thinking but in extending it into new realms.