# I Electron Degeneracy Pressure not Fundamental?

1. Jan 4, 2017

### FallenApple

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.

2. Jan 4, 2017

### Staff: Mentor

Yes.

Because it doesn't work the same way fundamental interactions like the E&M force work. Those interactions work via gauge bosons--for example, the E&M force gauge boson is the photon. The Pauli exclusion principle doesn't; it's just a property of the overall wave function of a system containing multiple electrons.

Then by this definition the Pauli exclusion principle is not a "force". But that's a matter of words, not physics. You could also say that a "force" is "anything that can push back" (which we could make more precise by saying something like "anything that can produce pressure"), in which case it is no longer true that "all forces are made of a combination of the 4 fundamental interactions", since the Pauli exclusion principle isn't yet it can still produce pressure. Either choice of words is fine, you just have to be aware of the actual physics behind the words.

3. Jan 5, 2017

4. Jan 5, 2017

### zonde

So called electron degeneracy pressure results from Pauli exclusion principle which states that no two fermions (electrons) can occupy the same quantum state. The same quantum state is not quite the same thing as the same place in ordinary space. Quantum state describes probability density of finding electron at different places within potential. You can't push probability density into some place, instead you can modify probability density by modifying potential well or figuratively speaking you can "drag" electrons into different configuration by modifying potential. So the force you would be exerting would go into modifying potential (squeezing together ions) and not in squeezing together electrons.