The universe has no shortage of bizarre materials. Superfluids are liquids that can flow straight up walls, Bose-Einstein condensates are gasses that will vibrate eternally, and neutron stars are essentially city-sized subatomic particles.
Physicists have now developed a mathematical theory that describes how collective quantum mechanical weirdness leads to the strange properties of these materials. While previous work has focused on each individual system, the new theory unites the behavior for many materials, including magnets, superfluids, and neutron star matter.
“It’s like shooting many, many birds with one stone,” said particle physicist Hitoshi Murayama of UC Berkeley, co-author of a paper on the work that appeared in Physical Review Letters June 15. Murayama and his graduate student, Haruki Watanabe, showed that the behavior of these materials hinges on a phenomenon known as spontaneous symmetry breaking. Symmetry breaking happens when a group of particles that once had no preferred alignment or direction suddenly does, creating a collective behavior.
One of the best-known occurrences of symmetry breaking happens when certain metals — such as iron — cool down and form a magnet. Each atom in the metal contains an electron that forms a microscopic magnetic field. When the metal is hot, the atoms have their individual magnets pointing willy-nilly in random directions. But as they cool down, the atoms start to point their magnets in the same direction as their neighbors. If enough of the atomic magnetic fields align, their collective action will be strong enough to attract and repel other magnetic materials.