### Abstract

In our derivation of the second law of thermodynamics from the relation of adiabatic accessibility of equilibrium states, we stressed the importance of being able to scale a system's size without changing its intrinsic properties. This leaves open the question of defining the entropy of macroscopic, but unscalable systems, such as gravitating bodies or systems where surface effects are important. We show here how the problem can be overcome, in principle, with the aid of an 'entropymeter'. An entropymeter can also be used to determine entropy functions for non-equilibrium states and mesoscopic systems.

Original language | English (US) |
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Article number | 20140192 |

Journal | Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences |

Volume | 470 |

Issue number | 2167 |

DOIs | |

State | Published - Jul 8 2014 |

### All Science Journal Classification (ASJC) codes

- Mathematics(all)
- Engineering(all)
- Physics and Astronomy(all)

### Keywords

- Entropy meters
- Non-extensive systems
- Second law of thermodynamics

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## Cite this

Lieb, E. H., & Yngvason, J. (2014). Entropy meters and the entropy of non-extensive systems.

*Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences*,*470*(2167), [20140192]. https://doi.org/10.1098/rspa.2014.0192