Three Plus Anti-symmetric Particles

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Discussion Overview

The discussion centers on the behavior of fermions, particularly how their wavefunctions are anti-symmetric under the exchange of particles when considering three or more indistinguishable particles. The scope includes theoretical aspects of quantum mechanics and the properties of wavefunctions for fermionic systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how the anti-symmetry of fermionic wavefunctions applies when there are three or more particles, wondering if it involves pairs of particles or a more systematic approach.
  • Another participant provides a reference to a source that discusses the wave function for three electrons, noting that the total wavefunction must reverse sign under the exchange of any two particles.
  • A participant expresses confusion regarding the initial question and suggests that it might be better to wait for clarification before proceeding.
  • A later reply clarifies that the wave functions of indistinguishable fermions must be anti-symmetric under the exchange of any pair of particles, detailing the structure of the wavefunction in terms of position and spin components.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the anti-symmetry of wavefunctions for multiple fermions. There is no consensus on the initial question, and some confusion remains about the specifics of the wavefunction behavior.

Contextual Notes

The discussion highlights potential limitations in understanding the implications of anti-symmetry in multi-particle systems, particularly regarding the definitions and assumptions about wavefunctions and particle exchanges.

JohnH
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So I understand that fermions are anti-symmetric under exchange, but in the contexts I've seen this explained they were always talking about two particles, or at least two wavefunctions. I'm curious how this works when there are three or more particles. Is any two given pairs of those 3+ particles anti-symmetric under exchange or is it more systematic? Or is it that there's essentially one wavefunction for all the particles (quanta of energy) in one spin and another wavefunction for all the quanta of energy in the other spin such that it's just those two wavefunctions that are anti-symmetric under exchange?
 
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JohnH said:
So I understand that fermions are anti-symmetric under exchange, but in the contexts I've seen this explained they were always talking about two particles, or at least two wavefunctions. I'm curious how this works when there are three or more particles.
The wave function for three electrons is covered here:

https://galileo.phys.virginia.edu/classes/752.mf1i.spring03/IdenticalParticlesRevisited.htm

The total wavefunction must reverse sign under the exchange of any two particles.
JohnH said:
Is any two given pairs of those 3+ particles anti-symmetric under exchange or is it more systematic? Or is it that there's essentially one wavefunction for all the particles (quanta of energy) in one spin and another wavefunction for all the quanta of energy in the other spin such that it's just those two wavefunctions that are anti-symmetric under exchange?
I can't make any sense of this part of your question.
 
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PeroK said:
I can't make any sense of this part of your question.
Yeah, just trying to answer my own question last minute. Probably better off waiting for an answer. Anyway, thank you for it.
 
The wave functions of indistinguishable fermions must be antisymmetric under exchange of any pair of arguments, ##(\vec{x}_j,\sigma_j##, where ##\vec{x}_j## is the postition and ##\sigma_j## the spin-##z##-component (##\sigma_j\in \{-s,-s+1,\ldots,s-1,s \}##, where ##s## is a half-integer positive number, ##s \in \{1/2,3/2,\ldots \}##), i.e., if ##\psi(t,\vec{x}_1,\sigma_1;\vec{x}_2,\sigma_2;\ldots; \vec{x}_N,\sigma_N)## is an ##N##-particle fermionic wave function, then it's antisymmetric by exchanging any pair ##(\vec{x}_i,\sigma_i)## and ##(\vec{x}_j,\sigma_j)##.
 
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