As far as I understand it, the modern statement of Onsager reciprocity is that the linear-response transport coefficient matrix, when transposed, is equal to that of the time-reversed system (reversed external magnetic field, reversed internal magnetic order, reversed Coriolis forces, and so on). Many consider this to be the fourth law of thermodynamics.

Clifford Truesdell however famously complained of "Onsagerism", which appears to mean the (unjustified) faith in Onsager reciprocity despite what he regarded as shaky foundations: reliance on kinetic theory, and so on. And yet, the foundations of Onsager do not seem so shaky to me: 1) the fluctuation-dissipation theorem and 2) the mathematical fact that fluctuation correlations in a time-reversed system should be, well, time-reversed. Quite general and elegant, really. Might even be worth a Nobel prize.

So, my question: **are there real counterexamples to Onsager?** I have seen many proposed counterexamples where I thought "OK, you just failed to time-reverse your system properly." (and indeed perhaps the difficulty of proper time-reversal indicates an Onsagerism pitfall). But... is the reciprocity fundamentally flawed?

This post imported from StackExchange Physics at 2016-04-13 09:05 (UTC), posted by SE-user Nanite