Uniqueness in nature.................


This discussion of the property of spin leads us to one of the most important principles in quantum physics, the Pauli exclusion principle (formulated by Wolfgang Pauli in 1925), which states that no two identical fermions may occupy the same quantum state simultaneously (although two electrons, for example, may acquire opposite spin in order to differentiate their quantum states). Another way of stating the principle is that no two fermions in a quantum system can have the same values of all four quantum numbers at any given time.