All articles say that in superconductive state, the materials have exactly zero resistance, but is this the case in real life experiment?, because if this were true, a process without energy dissipation, wouldn't it be contradictory with thermodynamics. Same question with friction for superfluids. Also if either were true could you support it with a scientific article (no Wikipedia if possible).

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    $\begingroup$ The second law says $\dot S\geq 0$. Nothing wrong with the equal sign. $\endgroup$ – Thomas Oct 3 '15 at 1:22
  • $\begingroup$ The equal is when no process happens. $\endgroup$ – user162485 Oct 3 '15 at 3:19
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    $\begingroup$ No, reversible processes, like superfluid flow, have $\dot{S}=0$. Now you can argue that in the real world nothing is ever exactly reversible (the system interacted with a cosmic background photon ..), but there is no limitation in principle. In practice, superconducting currents have been sustained for many years. $\endgroup$ – Thomas Oct 5 '15 at 1:03
  • $\begingroup$ @Thomas The truth is that the entropy indeed grows in a superconductor, with a typical time-scale with value larger than the age of the universe. Unfortunately, this is all what is written in Wikipedia : en.wikipedia.org/wiki/… so the OP will complain. Just one thing though : if user162485 had an eye on wiki's page, (s)he will find references for this standard fact of physics that nothing is eternal ! $\endgroup$ – FraSchelle Oct 5 '15 at 9:44
  • $\begingroup$ @FraSchelle The Wiki entry only says that (i) if the superconductor is type II, and (ii) if there is a large B-field, then there is a new dissipation mechanism (vortex drag). That's fine. This does not change the fact that if you set up a pure superflow in a ring, there is no dissipation mechanism (it cannot decay by quantization of circulation). $\endgroup$ – Thomas Oct 5 '15 at 18:25

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