General Term: Classical Thermodynamics

Classical Thermodynamics

A branch of physics developed in the nineteenth century that deals with the study of heat, and thus with the collision and interaction of particles in large, near-equilibrium systems.

In the 19th century, thermodynamics, the study of heat transformation and exchange, was concerned with closed systems (i.e., systems which do not exchange matter or energy with their environment). In such systems although the total amount of energy E is always conserved (the “first” law, DE=0), the amount of available energy inevitably decreases to zero (the “second” law); equivalently, the entropy S of the system, defined as the amount of unusable energy, increases to a maximum: DS>=0. During the 20th century, the field was broadened to include open systems (i.e., systems which exchanged matter and/or energy with their environment). These first included non-linear systems in which effects on the system were highly amplified, and then non-linear systems far from equilibrium in which spontaneous fluctuations were even more fully amplified. Such systems demonstrated the surprising phenomena of ‘order out of chaos’, to use Ilya Prigogine’s famous phrase: they could spontaneously move to greater forms of organization, driven always by the internal production and dissipation of entropy (i.e., ‘dissipative systems’), and though, of course, the total entropy of the open system plus its environment obeyed the second law. Two final points: 1) Whether ‘entropy’ applies to the universe as a ‘closed’ system is subject to intense debate. 2) Although most physicists reduce thermodynamics to dynamics, thus explaining (away) time’s (thermodynamic) arrow, Prigogine and others insist it should be the converse. In any case, non-linear, non-equilibrium thermodynamics points to at least one form of novelty and apparent openness in nature, although it still comes (pace Prigogine) under the rubric of deterministic classical dynamics, and, like chaos theory, rendering its portrait of novelty in terms of epistemic ignorance.