Related Experiment Video
Updated: Jun 14, 2026

Thermocapillary Convection Space Experiment on the SJ-10 Recoverable Satellite
Published on: March 11, 2020
Dependence of the fluctuation-dissipation temperature on the choice of observable
Kirsten Martens1, Eric Bertin, Michel Droz
1Department of Theoretical Physics, University of Geneva, CH-1211 Geneva 4, Switzerland.
Abstract:
On general grounds, a nonequilibrium temperature can be consistently defined from generalized fluctuation-dissipation relations only if it is independent of the observable considered. We argue that the dependence on the choice of observable generically occurs when the phase-space probability distribution is nonuniform on constant energy shells. We relate quantitatively this observable dependence to a fundamental characteristics of nonequilibrium systems, namely, the Shannon entropy difference with respect to the equilibrium state with the same energy. This relation is illustrated on a mean-field model in contact with two heat baths at different temperatures.
Related Concept Videos
Atomic Spectroscopy: Effects of Temperature
At thermal equilibrium, the relative populations of excited and ground state atoms can be estimated using the Maxwell–Boltzmann distribution. For example, an increase in temperature from...
Entropy
Entropy
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
Consider an infinitesimal step in the expansion, which...
Entropy and the Second Law of Thermodynamics
Entropy and the Second Law of Thermodynamics
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
Second Law of Thermodynamics

