The quantum stability of a superconductor ensures that electrons can carry current perfectly, without losing energy. There are 2 ingredients to this physics: 1. Electrons pair into "composite bosons"; 2. The bosonic pairs all fall into the same lowest energy wavefunction (called Bose condensation.) Since bosons don't obey the Pauli exclusion principle, they can all occupy the same wavefunction macroscopically -- that's right, you might get 10^23 bosons in the same wavefunction. Once they're there, they're very hard to disturb (that's quantum stability), and in this phase of matter, electrons can carry current without energy loss. We show a video of a magnet levitating over a superconductor (called the Meissner effect), available at www.fys.uio.no/super/levitationLecture Audio

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