Even though most of it is empty space, those spaces are excluded from being occupied by the Pauli Exclusion Principle which does not allow multiple identical fermions (particles with half-integer spin) to occupy the same quantum state within a quantum system.
Even though most of it is empty space, those spaces are excluded from being occupied by the Pauli Exclusion Principle which does not allow multiple identical fermions (particles with half-integer spin) to occupy the same quantum state within a quantum system.
Translation: This is gonna hurt.