Imagine you have two plates which can either be perfectly conducting or perfectly insulating by changing some conditions (like say, cooling an insulator down until it is superconducting). First, have the two plates be superconducting, and bring them close together so the Casimir effect is non-negligible. Extract work from the system by letting the plates come together. Now, turn your plates into insulators by raising the temperature (to make the material non-superconducting), and pull the plates apart (with less resistive force since the plates are no longer perfect conductors). Repeat the process, voila, free energy? This seems to violate conservation of energy, which doesn't make sense to me. Can someone explain to me why this can't be done and why energy IS conserved?