Understanding the Pauli Exclusion Principle

In summary, the Pauli Exclusion Principle is a fundamental concept in quantum mechanics that states that no two identical particles can occupy the same quantum state simultaneously. This principle plays a crucial role in explaining the behavior of electrons in atoms and the periodic table, and has significant implications in understanding the properties of matter at the atomic and subatomic level. It is a cornerstone of our understanding of the structure and behavior of matter in the quantum realm.
  • #1
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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  • #2
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.
 
  • #3
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?
 
  • #4
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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  • #5
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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  • #6
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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  • #7
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.
 
  • #8
The advantage of making these mistakes here is that someone usually notices and I can correct them.
The disadvantage is that, well, somebody noticed :(
 

FAQ: Understanding the Pauli Exclusion Principle

What is the Pauli Exclusion Principle?

The Pauli Exclusion Principle is a fundamental principle in quantum mechanics that states that no two identical fermions (particles with half-integer spin) can occupy the same quantum state simultaneously.

Why is the Pauli Exclusion Principle important?

The Pauli Exclusion Principle is important because it helps explain the behavior of electrons in atoms and molecules, as well as the properties of matter at a microscopic level. It also plays a crucial role in determining the electronic structure of atoms and the periodic table.

How does the Pauli Exclusion Principle relate to electron configuration?

The Pauli Exclusion Principle dictates that each electron in an atom must have a unique set of quantum numbers, including its energy level, orbital, and spin. This leads to the arrangement of electrons in distinct energy levels and orbitals, known as electron configuration.

What happens when the Pauli Exclusion Principle is violated?

If the Pauli Exclusion Principle is violated, it would lead to the destabilization of atoms and molecules, as well as the breakdown of the periodic table. This would fundamentally change our understanding of the behavior and properties of matter.

Can the Pauli Exclusion Principle be applied to particles other than electrons?

Yes, the Pauli Exclusion Principle can be applied to all fermions, including protons, neutrons, and all other subatomic particles with half-integer spin. It is a fundamental principle that applies to all matter at a microscopic level.

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