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refuse to go to my mother’s house any more than a rock could refuse to fall at nine point eight meters per second squared. Looking at life from this perspective, it seems pretty pointless.
    Of course it isn’t the job of physicists to find meaning in human existence, but still, it’s a little rough to have to come out and say, “We’ve got this theory that explains everything, and oh, by the way, it means that life is pointless.” Classical physics got around this problem by essentially ignoring it, taking its cue from Rene Descartes, who divided nature into a mental part and a physical part. The mental part contains our thoughts, ideas and sensations, whereas the physical part is defined as those aspects of nature that can be described by assigning mathematical properties to space-time points. This is the classic Cartesian notion of dualism .
    Isaac Newton built on Descartes ’ notion and the observations of Galileo, Kepler, and Brahe to create the foundation of classical physics. Later thinkers like LaPlace refined Newton’s ideas, but the framework built on his ideas is still referred to as “Newtonian.” According to the Newtonian framework, the entire physical universe, from the largest objects to the smallest ones, is bound by the principle of physical determinism, which is the notion that a complete description of the values of all physically described variables at any one time fully determines the values of the physically described variables at any later time. In other words, if you knew the location and trajectory of every particle in the universe, you could (theoretically) predict the entire future of the universe and reconstruct the entire past.
    But Descartes and Newton were careful to say that these principles applied only to the physical part of the universe; not the mental part. Since the workings of the human mind were far beyond the understanding of science at the time of Newton (and still are, for the most part), this was a sensible way to divide things up. As a bonus, leaving mental reality out of classical physics allowed them to preserve the notion of free will: because minds are not part of the physical universe, they don’t necessarily have to follow the laws of physics. I get the impression from my research that physicists have historically been ambivalent about this limitation of their realm: on one hand, they were relieved not to have to deal with nebulous ideas like human freedom, but on the other hand, they resented the fact that there were areas of reality that science couldn’t penetrate. They reacted by marginalizing the mental (and spiritual) parts of reality as much as possible. Religion and spiritualism were derided; there was little tolerance for the idea that there were avenues to truth outside of empirical observation. The Wikipedia entry on Newton notes that the father of classical physics didn’t seem to have a problem with the existence of an unobservable reality: Newton was a mystic who wrote more on biblical hermeneutics and the occult than he did on science or mathematics.
    Anyway, the point is that although classical physics seems at first glance to be hostile to the notion of free will, it has a built-in escape hatch: classical physics has little to say about minds, so minds aren ’t constrained by the ironclad process of cause and effect. Still, as the sciences of neurology and psychology advanced, it became clear that a lot of human behavior could be explained in terms of cause and effect: as a matter of brain chemistry or, more broadly, biological determinism or conditioning. The physical sciences were gradually encroaching on the territory of the mind, and although there was little danger of the idea of free will disappearing completely, more and more constraints were being put on it. Darwin rocked traditional morality and ethics with the idea that human beings could best be understood not as creatures created in the image of God but as animals who had – purely