According to this website, http://www.particleadventure.org/pauli.html "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." 1-What does the "particles in the same quantum state" mean? Does it mean particles for which all four quantum numbers are the same or something else? 2-How does it explain there is chemistry?