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Question regarding the Pauli Exclusion Principle?

  1. Nov 27, 2009 #1
    Okay, I think everyone here knows what the principle states, so I am not even going over that. Is a proton not a fermion with is +1/2 spin? It has an half integral, hence it must be. However, how is this possible for a proton to be fermion when elements like gold have a lot of protons in the nucleus.

    These protons are pushed together by the atomic force, why don't they disappear because they have asymmetrical wave functions, hence they should cancel out?
  2. jcsd
  3. Nov 27, 2009 #2
    The Pauli Exclusion Principle states that no two fermions can have the same quantum state. Quantum state meaning the assortment of quantum numbers that the wave function has in order to describe the system. Sure two protons can have the same total spin, but other things like their spin direction, i.e along the z-axis or the x-axis, or their principal quantum number ,which is their energy state, cannot be the same.

    Anyway, yes protons and neutrons are spin 1/2 fermions that do obey the Pauli Exclusion Principle. Just with different quantum numbers other than total spin.

    I hoped this helped
  4. Nov 27, 2009 #3


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    Easy. They're not in the same place or state.

    If you were to push the nucleons together so they occupied the same space, then the Pauli principle would not lead to them 'disappearing'. (The fact that the wave function 'disappears' means it's an invalid wave function. It's not a solution to the S.E. It doesn't happen.) What happens if they're pushed into the same space is that they're then forced to occupy different (higher) energy states.

    This manifests itself as http://en.wikipedia.org/wiki/Electron_degeneracy_pressure" [Broken]. Which is what keeps neutron stars from collapsing in on themselves.
    Last edited by a moderator: May 4, 2017
  5. Nov 27, 2009 #4
    Okay, I guess you guys answered it, but don't you think your pushing when you say out of all the atoms in the universe, every single proton has a different quantum state?
  6. Nov 27, 2009 #5


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    No, because protons that occupy different positions are not in the same state so the EP does not apply; and the universe is a big place with plenty of space.
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