The pointsman: Maxwell's demon, Victorian free will, and the boundaries of science.

The railway pointsman was the vigilant employee shifting tracks and posting signals to route hurtling trains safely on their way. In a twelve-hour shift in 1880, a pointsman might pull two thousand levers.1 Their daily life was governed by "reliability, service, and coolness."2 The power of the railway pointsman began in his disciplined mind and ended in the placement of his hands on the correct levers. In this, he replicated a critical assumption of Victorian religious and social thought: conscious free-will. As the human body would only act when prodded to do so by the soul, the signalman would move physically only after deliberate decisions.3But the Victorian period also saw tremendous advances in science that made many doubt the truth of the pointsman's power. The march of physics through the conquered territories of mechanics, thermodynamics, and electricity, and biology's beachhead in the nervous system and mind, all seemed to herald the victory of a materialist, mechanical worldview. In this view all phenomena can and should be explained solely with recourse to matter and motion, implying a harsh determinism: the behavior of everything made of atoms, including humans, was strictly determined only by their current physical state. The appropriate railway metaphor here was not the pointsman, but rather the train itself, carried forward by momentum and uncaring for trivialities such as humans in its way. Like the future events of a materialist universe, the path of the train was fixed by the shackles of the track.Whether or not the success of science demanded humans forfeit their intuition of individual volition was a major intellectual crisis of the Victorian period. Both Christian doctrine and simple social responsibility needed humans to be able to control their own actions and accept responsibility for them. But was this tenable in light of daily leaps forward in science? Much hope rested in the metaphor of the pointsman, a tiny figure who through cunning and forethought could master the overwhelming force of physical determinism.One of its chief proponents was the devout Christian physicist James Clerk Maxwell, best known for his epochal work in electromagnetism and statistical mechanics.4 In one letter he invoked it thus:There is action and reaction between body and soul, but it is not of a kind in which energy passes from one to the other,-as . . . when a pointsman shunts a train it is the rails that bear the thrust.5This was in the context of theological problems surrounding the nature of the soul. But note that Maxwell uses nearly identical language here:In this way the temperature of B may be raised and that of A lowered without any expenditure of work, but only by the intelligent action of a mere guiding agent (like a pointsman on a railway with perfectly acting switches who should send the express along one line and the goods along another).6This was in a quite different context, a discussion of the laws of thermodynamics. The pointsman as described here would receive the peculiar name of "Maxwell's demon," a thought experiment that has survived to this day as a tool in statistical mechanics.7 The image of the pointsman was used by Maxwell to solve not just religious difficulties but scientific ones as well.Other work has noted this parallelism but this essay will consider this shared metaphor in detail, particularly in light of Maxwell's religious context and personal religiosity.8 What was the overlap of conceptual space that made this a reasonable project in both religion and science? I will argue both instantiations of the pointsman indicate a deeper concern of Maxwell's: the danger of mistaking observed regularity for a true scientific law. And more generally, the danger of solely materialist explanations in science.The pointsman was a tool by which Maxwell hoped to remind investigators to tread carefully in declaring something to be proven by science. …