Understanding the Pauli Exclusion Principle

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Discussion Overview

The discussion revolves around the Pauli Exclusion Principle (PEP) and its implications in quantum mechanics, particularly focusing on the behavior of fermions and their interactions. Participants explore theoretical aspects, conceptual clarifications, and the mathematical underpinnings of the principle.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how fermions interact, suggesting that fermion x might send out bosons to inform fermion y to move aside.
  • Another participant argues that fermions do not need to "know" to move, as no two fermions can occupy the same quantum state, likening it to cars in separate lanes on a motorway.
  • There is a discussion about the concept of combined fields and how particles exchange quantum numbers, with one participant seeking clarification on what constitutes a combined field.
  • Participants discuss the electromagnetic interactions between electrons and the role of photons in these interactions, suggesting that these exchanges inform the particles of each other's spin.
  • One participant emphasizes that the PEP should be understood mathematically and is a manifestation of symmetry rather than relying on intuitive analogies.
  • Another participant critiques a linked source by a fringe scientist, questioning the necessity of referencing it and suggesting that the explanation should be more grounded in established physics.
  • There are references to alternative sources for understanding the PEP, with some participants expressing frustration over the quality of examples provided.

Areas of Agreement / Disagreement

Participants express differing views on the nature of fermion interactions and the explanations surrounding the Pauli Exclusion Principle. There is no consensus on the best way to conceptualize or mathematically approach the principle, and some participants challenge the credibility of external sources referenced in the discussion.

Contextual Notes

Limitations in understanding arise from the complexity of quantum fields and the nature of indistinguishable particles. The discussion highlights the need for mathematical rigor in grasping the implications of the PEP, while also revealing varying levels of familiarity with the topic among participants.

susskind99
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When a fermion x approaches another fermion y does x send out bosons to y which tell it to get out of the way? In short, how does y know to get out of the way of x?
 
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It doesn't have to know - there is no other way to go.
In principle, no two fermions in the Universe have exactly the same total quantum state.
It's as if each car has it's own lane on the motorway - sometimes the motorway lanes are close together and sometimes they are far apart.

Usually the effect is too small to bother with so we don't.
The size of the effect is related to the combined fields though... in that sense you do have exchange particles letting everyone know they are fermions or bosons by measuring each others spin. I get a bit of a cringe at the picture of particles firing stuff at each other - how do they know where to aim? It's more that there is a probability, that a package of "quantum numbers" will be exchanged, that varies with distance.
 
Simon Bridge said:
The size of the effect is related to the combined fields though... in that sense you do have exchange particles letting everyone know they are fermions or bosons by measuring each others spin.

Could you please expand a bit on that sentence. What is a combined field?

It's more that there is a probability, that a package of "quantum numbers" will be exchanged
So they exchange a package of quantum numbers by exchanging bosons right?
 
What is a combined field?
Where do the "potential wells" in introductory QM come from?

So they exchange a package of quantum numbers by exchanging bosons right?
two electrons - for eg. have an electromagnetic field associated with each.
They can interact electromagnetically - in the particle model - by exchanging photons.
This means they know each other's spin etc.
Mathematically, the result is a bunch of numbers representing their state gets moved around.
But don't think that some particles float around and at some time exchange a boson, and then suddenly realize they are fermions and thus, politely, shift to different quantum states. I suppose you could imagine that the boson exchange shoves them into different states? But I don't think that accounts for the statistics.

PEP is not something that you can understand well by intuition about other things.
You should do the math. It's best treated as a manifestation of a symmetry. i.e. fermions know to have separate states for much the same reason your reflection knows to invert left and right.
 
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Simon Bridge said:
See:
http://drmyronevans.wordpress.com/2...xclusion-principle-from-the-fermion-equation/

Myron Evans is a well known fringe scientist (politely speaking) who among other things claims/supports that "The very foundations of the CERN theory have collapsed and this is an irrefutable fact. I have pointed this out to the British Prime Minister." (see note 223 on the blog you linked, 2012/07/05/, - I do not want to link to it again). Also his claim that his derivation "is a major advance over quantum field theory" is pretty absurd.

Is there a deeper necessity to link to his stuff?Regarding the initial question: What is the OP's level of physics knowledge? If it is deep, the easiest thing is to do the math. As an explanation on a more handwaving level, one should keep in mind that for fermions are excitations of their corresponding fields. So two identical fermions are not really completely independent entities. An excitation of two indistinguishable particles is therefore way more complicated than two single distinguishable particles. In a somewhat simplifying picture, the symmetry properties of these fields influence how the probability amplitudes for processes leading to several excitations ending up in the same indistinguishable state behave. For bosonic fields probability amplitudes leading to high excitations of single states interfere constructively (giving rise to faeatures like bosonic final state stimulation or stimulated emission), while these amplitudes interfere destructively for fermions, which gives rise to stuff like the exclusion principle.
 
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Cthugha said:
Myron Evans is a well known fringe scientist (politely speaking) who among other things claims/supports that "The very foundations of the CERN theory have collapsed and this is an irrefutable fact. I have pointed this out to the British Prime Minister." (see note 223 on the blog you linked, 2012/07/05/, - I do not want to link to it again). Also his claim that his derivation "is a major advance over quantum field theory" is pretty absurd.

Is there a deeper necessity to link to his stuff?
Good grief - that's what you get for just reading the abstract. Need a better example.

Stuff like:
http://scienceblogs.com/builtonfacts/2009/05/22/why-the-exclusion-principle/
http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Connection_to_quantum_state_symmetry
... but I was trying for a step-by-step without having to do it myself.
 
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Simon Bridge said:
Good grief - that's what you get for just reading the abstract. Need a better example.

Oh yes, he is good with words...I immediately remembered that blog because I fell for his tricks once, too.
 
The advantage of making these mistakes here is that someone usually notices and I can correct them.
The disadvantage is that, well, somebody noticed :(
 

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