A Child’s Puzzle Has Helped Unlock the Secrets of Magnetism

To fully understand how the behavior of individual particles leads to the collective phenomenon of ferromagnetism, you would need to keep track of the wave function of every electron in a system as it continually reshapes every other electron’s wave function through their mutual interactions. Their result, called the Nagaoka-Thouless theorem (also Nagaoka’s theorem), relies on an idealized system of electrons on an atomic lattice. “Nagaoka’s theorem is one of the few examples with which you can mathematically prove instances of ferromagnetism,” said Masaki Oshikawa, a physicist at the University of Tokyo.

Source: www.quantamagazine.org