So for what I understand, when a star collapses, the electrons do not like to overlap their quantum states because of the pauli exlusion principle. Is this different from an E&M force? If so, then why isn't it a fundamental interaction? All forces are made of a combination of the 4 fundamental interactions( excluding gravity if you count GR). If I try to squeeze two electrons together, I would have to push it with the E&M force. They would in turn push back with the EM force as well. But as I amp up the force, the electrons should eventually push back with the electron degeneracy pressure. But that would then be a force out of the fundamental that is pushing back at me.