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Nonetheless, historical comments about what the classical thermodynamic term, entropy, is and is not about are in order.

We recall that Richard Feynman, in his well-known 1962 class notes, Lectures on Physics, said that the subject of thermodynamics is the study of relationships among the heat, energetic and organizational properties of materials, without knowing their internal structure. Historically, the relational formalisms of equilibrium thermodynamics emerged before our knowledge of the internal structure of matter. For examples, the pressure in an insulated container of gas is due to molecular bombardment of the container walls, which increases with heat or compression of its volume. Compression of its volume increases its temperature and expansion of its volume leads to cooling. Note that these relationships hold without specifying the constituents and the specifics of a particular gas or solid.

In his lectures, Feynman’s intuitively accessible examples of reversible thermodynamic properties are reminiscent of his on camera performance at the Senatorial hearings about the Challenger disaster. Recall that he dropped an O-ring in a glass of iced water demonstrating cold-induced rigidification of the rubber ring, which he postulated to be the cause of the fuel leak and resulting explosion. In his Lectures, he said that if one holds a rubber band between ones lips as a crude thermometer, stretching a rubber band heats up the lips and relaxing it cools them. Working the same system in reverse, and equilibrium thermodynamic systems are classically reversible, we find that heating a rubber band makes it contract. These changes involve complicated alterations in the internal arrangements of the polymeric strands of rubber, their structural properties, the details of which, for the purpose of global thermodynamic characterization, need not be known. The relationships between physical state, energy and temperature in this material were predictable from thermodynamic laws even without specific knowledge of the complex internal structure and physical dynamics of rubber.

Thermodynamic theory, which makes deep conceptual connections between quantitatively measurable primitives such as heat, hotness and work and the invisible in the form of derived ideas such as energy and entropy, yielded an

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