Question about the Pauli exclusion principle.

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Discussion Overview

The discussion revolves around the Pauli exclusion principle and its implications for the states of electrons, particularly in relation to their spin states. Participants explore the nature of these states, the concept of linear combinations, and the restrictions imposed by the principle on the occupancy of quantum states by fermions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that while two electrons can occupy two spin states, the idea of forming an infinite number of states through linear combinations of these states leads to confusion regarding occupancy.
  • One participant explains that the Pauli exclusion principle requires the wavefunction to be antisymmetric, which results in the wavefunction for three particles vanishing.
  • Another participant asserts that there is only one allowed two-particle state, which consists of one electron in the spin-up state and the other in the spin-down state.
  • Some participants question whether linear combinations of spin functions can be made, suggesting that ultimately there are only two possible spin states for an electron.
  • Others clarify that while there are only two basis states for electron spin, an infinite number of other states can be created through linear combinations of these two states.

Areas of Agreement / Disagreement

Participants express differing views on the implications of linear combinations of spin states and the nature of the states allowed under the Pauli exclusion principle. No consensus is reached regarding the conclusions about the occupancy of states and the validity of linear combinations.

Contextual Notes

The discussion highlights limitations in understanding the relationship between single-particle states and multi-particle states, as well as the implications of antisymmetry in wavefunctions. There are unresolved questions regarding the nature of spin states and their combinations.

alemsalem
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Suppose there are only two states, and that only two electrons could fit in them (spin states for example), but wouldn't these two states form a basis and so generate an infinite number of states that are linear combinations of these two, so three electrons could be in three different states.

Obviously that's wrong, but why? do they have to be in orthogonal states?
 
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The Pauli exclusion principle arises from the requirement that the wavefunction of the system be antisymmetric under the exchange of fermionic degrees of freedom. Now you may try to write down the wavefunction with three particles, but you'll find that the antisymmetry property causes such a wavefunction to vanish.
 
alemsalem said:
Suppose there are only two states, and that only two electrons could fit in them (spin states for example), but wouldn't these two states form a basis and so generate an infinite number of states that are linear combinations of these two, so three electrons could be in three different states.

Obviously that's wrong, but why? do they have to be in orthogonal states?


I think there is some confusion here. There are two states, yes, so in principle, you can form an infinite number of states through linear combinations, but those are one particle states.

For a two particle state, the only one allowed is the state where one particle is spin up and the other is spin down. There is only one state for for the combined system.

I hope that helps.
 
Should i forward a conclusion that linear combination of the spin functions of the electron cannot be done: that means ultimately there are only 2 possible spin states for an electron ! Anyone can further comment this ?
 
gerrardz said:
Should i forward a conclusion that linear combination of the spin functions of the electron cannot be done: that means ultimately there are only 2 possible spin states for an electron ! Anyone can further comment this ?

There are only two possible BASIS states for the spin states for an electron since they are spin 1/2. However, there an infinite number of spin states for an electron because you can make any number of other states by performing a linear combination of these 2 states.

I hope I got your question correct.
 

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