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The Pauli Exclusion Principle

We can use these quantum particle properties to categorize the particles we find.

At one time, physicists thought that no two particles in the same quantum state could exist in the same place at the same time. This is called the Pauli Exclusion Principle, and it explains why there is chemistry.

But it has been since discovered that a certain group of particles do not obey this principle. Particles that do obey the Pauli Exclusion Principle are called fermions, and those that do not are called bosons.

Imagine there is a large family of identical fermion siblings spending the night at the Fermion Motel, and there is another large family of identical boson siblings spending the night at the Boson Inn. Fermions behave like squabbling siblings, and not only refuse to share a room but also insist on rooms as far as possible from each other. On the other hand, boson siblings prefer to share the same room. (Since fermions rent more rooms than bosons, motel owners prefer doing business with fermions. Some motels even refuse to rent rooms to bosons!)