Superconductivity's Smorgasbord of Insights: A Movable Feast: Physicists have applied the theory of superconductivity directly to nuclear matter, liquid helium, and ultracold atomic gases. Historically, insights from superconductivity convinced theorists of the importance of symmetries and the ways in which a physical system can muddle or “break” them. The concept of “spontaneous symmetry breaking” now undergirds theory in many fields, especially particle physics. “It was not a way that people were thinking, certainly not in elementary particle physics,” says Gordon Baym, a theorist at the University of Illinois, Urbana-Champaign. Superconductivity, he says, “changed the way people thought in different fields..."
The BCS model was more than a one-trick pony. Bardeen, Cooper, and Schrieffer had based it on just two assumptions: that the particles are fermions and that they attract each other. So “it was obvious to all of us” that the theory would apply to other particles interacting through different forces, Cooper says.
First came applications to atomic nuclei. In the summer of 1957, before the BCS theory was published, Pines visited the University of Copenhagen. There he, Aage Bohr (Niels Bohr's son), and Ben Mottelson found they could explain long-standing puzzles, such as why nuclei with an even number of protons and even number of neutrons are particularly tightly bound. The protons and neutrons, also fermions, independently pair.