Simple Lie groups – in a sense, the basic atoms of symmetry – come in several infinite series. There is also a list of five “exceptional" ones, of which E8 is the largest and, to many mathematicians and physicists, the most beautiful. For physics, E8 has mainly attracted the interest of string theorists, but now it has turned up in laboratory studies of quantum magnetism.
Radu Coldea of the University of Oxford and colleagues applied a strong magnetic field to a supercooled crystal of cobalt niobate, which behaves like a quasi one-dimensional Ising ferromagnet. Despite the simplicity of the system, it exhibits a quantum phase transition that is predicted to have excitations corresponding to an emergent E8 symmetry. The two lowest-lying “meson" states turn out to have a mass ratio of the golden mean (about 1.618), just as predicted from the E8 theory.