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Dear prof. Nelson,
I agree with your arguments, that no thermally related currents are present in the ferromagnetic domain or in the superconductor in ext. magnetic field at the thermal equilibrium
However thermostatics is formulated so, that a current is rather general propert related to each independent variable.

The initial statement that there are no currents at thermal equilibrium means, that we have no current of any quantity. Thermodynamics is related to the electrical properties as well. I think that this is generally true in the classical systems and not in quantum systems at thermal equilibrium.

And in the systems you mention, there's no net flow of spin (a quantum mechanical process) or magnetic direction.  You're taking net spin to equal a "current flow," which is the wrong way to look at it.  Similarly with superconductors, there's no net flow of current.  You have to look at net flow in a loop of superconductive material.  If you just had an isolated balloon in empty space in thermal equilibrium, heat is being exchanged between different parts of the balloon, but at the same rate.  You're forgetting that this is just equilibrium, not absolute zero.  If you have an object floating in water within a perfectly insulated container, there's still a heat current from the water to the object and the object to the water.  They're just equal and cancel out.  Now I can see where you'd think that a superconducting loop with a current would be different, but you'd be wrong.  The net flow in and out of each piece  of material is equal, and by the zeroth law of thermodynamics that makes all pieces of the system in thermal equilibrium.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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