Abstract

In 1866 J.C. Maxwell thought he had discovered a Maxwellian demon—though not under that description, of course [1]. He thought that the temperature of a gas under gravity would vary inversely with the height of the column. From this he saw that it would then be possible to obtain energy for work from a cooling gas, a clear violation of Thompson’s statement of the second law of thermodynamics. This upsetting conclusion made him worry that “there remains as far as I can see a collision between Dynamics and thermodynamics.” Later, he derived the Maxwell-Boltzmann distribution law that made the temperature the same throughout the column. However, he continued to think about the relationship between dynamics and thermodynamics, and in 1867, he sent Tait a note with a puzzle for him to ponder. The puzzle was his famous “neat-fingered being” who could make a hot system hotter and a cold system colder without any work being done. Thompson in 1874 christened this being a “demon”; Maxwell unsuccessfully tried to rename it “valve.” However named, the demon’s point was to “show that the second law of thermodynamics has only a statistical validity.” Since that time a large physics literature has arisen that asks a question similar to that asked in theology, namely, does the devil exist? Beginning with Popper, philosophers examining the literature on Maxwell’s demon are typically surprised—even horrified [2,3,4,5,6,7]. As a philosopher speaking at a physics conference exactly 100 yrs after Popper’s birth, I want to explain why this is so. The organizers of this conference instructed me to offend everyone, believers and non-believers in demons. Thus my talk, apart from an agnostic middle section, contains a section offending those who believe they have exorcized the demon and a section offending those who summon demons. Throughout the central idea will be to clearly distinguish the various second laws and the various demons..