Testing the Minimum System Entropy and the Quantum of Entropy

Experimental and theoretical results about entropy limits for macroscopic and single-particle systems are reviewed. All experiments confirm the minimum system entropy S > kln2. We clarify in which cases it is possible to speak about a minimum system entropy kln2 and in which cases about a quantum of entropy. Conceptual tensions with the third law of thermodynamics, with the additivity of entropy, with statistical calculations, and with entropy production are resolved. Black hole entropy is surveyed. Claims for smaller system entropy values are shown to contradict the requirement of observability, which, as possibly argued for the first time here, also implies the minimum system entropy kln2. The uncertainty relations involving the Boltzmann constant and the possibility of deriving thermodynamics from the existence of minimum system entropy enable one to speak about a general principle that is valid across nature.

Automated summary

This paper reviews the experimental and theoretical results on the entropy limits for macroscopic and single-particle systems. All experiments confirm the minimum system entropy of S > kln2. The paper clarifies the cases where it is possible to discuss the minimum system entropy kln2 and the cases where the quantum of entropy can be discussed. It resolves conceptual tensions with the third law of thermodynamics, the additivity of entropy, statistical calculations, and entropy production. The paper also surveys black hole entropy. Claims for smaller system entropy values are shown to contradict the requirement of observability, and it is argued for the first time that this also implies the minimum system entropy kln2. The uncertainty relations involving the Boltzmann constant and the derivation of thermodynamics from the existence of minimum system entropy enable the discussion of a general principle valid across nature.