A detail about the history of thermodynamics:
"Thermodynamics", starting with Carnot and Clausius, was pretty-well fleshed out during the 19th century, and named "the queen of the physical sciences", predicting the relationship between temperature and mechanical energy.
"Statistical mechanics", starting with Boltzman and Maxwell, used random molecular motion to explain the observations of thermodynamics, including a microscopic understanding of "entropy" that had already been found macroscopically in thermodynamics.
After Planck, "quantum statistical mechanics" discussed how quantum descriptions of molecules and atoms affected the macroscopic observables.
In all of this evolution, the theories were accepted based on experimental verification, while earlier theories were rejected due to new experimental evidence.