Abstract
Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations.
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Ortiz de Zárate, J.M., Sengers, J.V. On the Physical Origin of Long-Ranged Fluctuations in Fluids in Thermal Nonequilibrium States. Journal of Statistical Physics 115, 1341–1359 (2004). https://doi.org/10.1023/B:JOSS.0000028062.57459.52
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DOI: https://doi.org/10.1023/B:JOSS.0000028062.57459.52