David Lee, Douglas Osheroff — then a doctoral student — and Robert Richardson, at Cornell University, discover in 1972, while studying a completely different phenomenon related to nuclear magnetism, an unexpected anomaly in the behavior of liquid helium-3 at extremely low temperatures, just two thousandths of a degree above absolute zero. After careful analysis, they identify that they are observing helium-3's transition to a superfluid state — flowing with no viscosity whatsoever — a phenomenon much subtler and harder to achieve than the superfluidity of helium-4 discovered and theoretically explained by Landau decades earlier. The fundamental difference lies in the fact that helium-3 atoms are fermions — particles that, per the Pauli exclusion principle, cannot easily occupy the same quantum state — unlike helium-4 atoms, which are bosons and can condense collectively much more readily. To achieve superfluidity, helium-3 atoms must pair up with each other analogously to the Cooper pairs of BCS superconductivity theory, forming an extraordinarily complex collective quantum state with multiple distinct phases depending on the spin orientation of the pairs. The discovery considerably expands the theoretical understanding of macroscopic quantum states of matter and establishes deep connections with the physics of superconductors and, later, with theoretical models of neutron-star physics.