BCS theory is a theory that explains superconductivity. It is named after three American physicists, John Bardeen, Leon Cooper, and John Schrieffer. It states that, in a superconductor, electrostatic forces between positive sites on the metal lattice and a conducting electron distort the lattice. A second electron is the affected and, as a result, the current is carried not by individual electrons but by bound pairs of electrons called Cooper pairs. Such a pair is not affected by the lattice and so carries current indefinitely.