Approaches to the Study of Thermodynamics

The macroscopic approach is empirical (that is, depend on experiment) and uses the continuum model for matter. It deals with noticeable properties, and either generalizes the “laws” from experiments or defines them as axioms. The previous approach is explained as “inductive” or “operational-inductive”, and uses the idea of “operational” definitions. Such approach develops the laws as inductive generalizations or inferences from observation and experiments. It starts by defining fundamental quantities in terms of how they are measured. The operational definition removes the circularities which accompany other kinds of definitions, and was first introduced by P. W. Bridgeman. It then charges the outcomes of experience and conducts experiments among such quantities and generalizes the laws from the outcomes. The laws are then employed deductively to appear at new conclusions.  

In the axiomatic or “axiomatic-deductive” approach, some required terms are defined, and the numerous laws are defined as axioms or first principles. The axioms are justified by the inability of anybody to disprove them, and the enduring content of the subject is inferred from the axioms.

Therefore the macroscopic approaches are differentiated by:

• Whether the laws are defined at the outset as axioms or whether the laws are arrived at inductively as generalizations from interpretation; and by  

• The type of definitions employed for terms.

The microscopic approach is hypothetical and uses the molecular model for matter. It applies statistical analysis to the supposed molecular model, and computes outcomes that are then deduced in terms of the macroscopic properties and laws. There are three primary microscopic approaches as follows:

• Kinetic theory and statistical mechanics,
• Quantum mechanics, and
• Information theory.

All of them suppose that matter is made of discrete particles. Kinetic theory is the oldest microscopic approach; it does not take into account the quantized nature of energy and position of particles, and therefore has limited usefulness. The quantum mechanics utilizes the findings of quantum theory and probability theory to specify the most probable state as the macroscopically examined one. Information theory necessarily does similar thing though postulates that the examined macroscopic state of the system.