The inertia replaces the friction
The inertia replaces the friction
In the classical world of normal metals, conductivity is a measure of loss. When an alternating current is applied, the electrons are whipped back and forth by the electric field, constantly crashing into the vibrating atoms of the lattice. This scattering creates friction. The energy of the wave is bled away as heat, and the metal resists the flow.
When the metal crosses the critical temperature and becomes a superconductor, the Mattis-Bardeen theory reveals a fundamental mathematical rotation. The conductivity ceases to be a real number and becomes imaginary.
The Cooper pairs no longer crash into the lattice. The friction drops to zero. But the electrons still have mass, and because they are now moving as a perfectly frictionless, phase-coherent fluid, that mass becomes the dominant force in the circuit.
When the microwave field tries to reverse their direction, the Cooper pairs resist not with friction, but with sheer mechanical inertia. They want to keep moving. This kinetic inductance stores the energy of the wave in the physical momentum of the electrons themselves, turning the metal from a resistor that destroys the signal into a perfect, frictionless spring that simply catches the wave and throws it back.