Talk:Fermion

message: So a grain of sand prevents another grain of sand from occupying the same location.
Unless it's cold enough to form a bose einstein condensate!
BECs are formed out of bosons! Hence "bose." However, fermions can form condensates -- but they are condensates in momentum space only, not physical space. (i.e., the condensate has lots of fermions with the same momentum, but they are not all in the same place), so the Pauli ex. principle is not violated.
:Can you explain this or point to a reference? As far as I'm aware, there's no difference in this respect between position space and momentum space -- antisymmetry in both cases requires the wavefunction to vanish at equal position/equal momentum. Fpahl 06:15, 8 Oct 2004 (UTC)
thread_title:  bose einstein condensate 

message: The Pauli exclusion principle doesn't always work, according to my quantum textbook. See my discussion in talk:Pauli exclusion principle. -- Tim Starling
:The result of that discussion was that the textbook meant not that it doesn't always work, but that in some circumstances it's a safe approximation to ignore it in calculations. Tim agreed, so I guess the comment above is just a leftover. Fpahl 06:15, 8 Oct 2004 (UTC)
thread_title:  Pauli exclusion principle 

message: We have all noticed that spin is described as being a multiple of hbar/2. I thought that it would be better to set this value to a constant giving, 
hdot = hbar/2 = 5.2728584118222738157569629987­554e-35 J.s 
But now the equations for spin did not work with hdot, so I had to correct them. 
Here are the corrected equations, 
|sv| = sqrt(s(s + 2)) * hdot 
and 
Sz = ms.hdot 
where, 
sv is the quantized spin vector,
|sv| is the norm of the spin vector,
s is the spin quantum number, which can be any non negative integer,
Sz is the spin z projection,
ms is the secondary spin quantum number, ranging from -s to +s in steps of two integers 
For spin 1 particles this gives: 
|sv| = sqrt(3).hdot and Sz = -hdot, +hdot 
For spin 2 particles this gives: 
|sv| = sqrt(8).hdot and Sz = -hdot, 0, +hdot 
Now that the spin equations have been corrected, the definitions for fermions and bosons are incorrect, and must be redefined as follows. 
Fermions are particles that that have an odd integer spin.
Bosons are particles that have an even integer spin.
Would these redefinitions have any other effects on the Standard Model? Can these redefinitions explain any currently unexplained phenomena? Are there any experiments that could confirm or refute these claims?
I would like eveyone to have a good think about this, and give me your objections to it, or even data to support it.
: The change you're proposing is a trivial renormalization; physicists are perfectly happy with the convention as it stands, tho mathematicians studying lie groups tend to use a normalization with steps of two. -- Xerxes 17:47, 2005 Jun 8 (UTC)
**Actually, the above explanation is no different than the Standard Model except in notation.  In spin-statistics theorem, the only difference is the word "net" where fermions have a "net" energy rotation spin and bosons are particles where the "net" energy rotation cancels in the composite matter structures.  The notation of the Standard Model was developed through the evolution of theory.  Bosons were discovered first so assigned integer values beginning with 1 as is the common mathematical convention.  Had fermions been discovered first, then fermions would have been denoted 1 and no doubt, bosons, would have taken even numbers to show that the net spin effect cancels.  Scientific and mathematical notation often simply follows the legacy of the evolving discoveries i.e. s,p,d for azimuthal quantum numbers makes no real sense except it is legacy notation.--Voyajer 19:56, 21 December 2005 (UTC)
thread_title:  Fermions with odd integer spin 

message: We need some help defining just what a bosonic field is, and what a fermionic field is.  Please see the discussion pages for Bosonic field and Fermionic field.  Thanks. RK 19:56, 21 May 2006 (UTC)
thread_title:  Bosonic field and Fermionic field articles 

message: I am an ignorant of physics, so I do not understand these two sentences in the article, which look contradictory to me:
"[fermions] are sometimes said to be the constituents of matter."
"All observed elementary particles are either fermions or bosons."
The first sentence seems to exclude bosons, and it is stated the same in other articles in Wikipedia ("quark", for example). Will anybody be so kind to explain?
Thanks 200.55.118.233 23:42, 31 August 2006 (UTC)
replies: text: The statement that "fermions are usually associated with matter, whereas bosons are generally force carrier particles", which, following the discussion presented in this section, appears to have been present in the article since at least 2007 (!), cannot reasonably be said to be theoretically correct in current form.  As the recent poster mentions, the deuteron -- as well as any meson, electronic cooper-pair, hydrogen molecule, helium-4 atom, or water molecule, among many, many, 'many' others falling clearly under any intuitive concept of the theoretically ill-defined term "matter" -- is also a bosonic system.  There are two possible "fixes" for the issue; the first, which surely better represents the author's original intentions but is in my opinion the worse fix, would be to add the qualifier "elementary" in front of "fermions" and "bosons", making clear that the author is not referring to composite particular systems.  However, since the proton and the neutron, which are 'not' elementary particles (as the article correctly indicates), are given in the article as "key building blocks of matter", further confusion may ensue.  The better fix, in my opinion, would be to remove the statement entirely (as well as the similar associated statement from the Boson article), as "matter" in any case is not a term that has a robust theoretical definition in the Standard Model.  I suppose some combination of the two, perhaps adding both the "elementary" qualifier and some disclaimer emphasising that "matter" is not a theoretically robust term in particle physics, might even be best in an article aimed generally at the layperson.  At any rate, given the unfortunate behaviour of many Wikipedia science-section editors, I won't attempt to make any change myself, but since lay visitors have presumably been confused by the unfortunate wording in the article for some five years now, I suspect it would serve the article well to finally address the issue.70.113.16.249 (talk) 06:23, 15 October 2012 (UTC)
thread_title:  Elementary particles?? 

message: The article has the following paragraph:
All observed elementary particles are either fermions or bosons. A composite particle (made up of more fundamental particles) may either be a fermion or a boson, depending only on the number of fermions it contains:
* Composite particles containing an even number of fermions are bosons, such as a meson, or the nucleus of a carbon-12 atom.
* Composite particles containing odd number of fermions are fermions, such as a baryon, or the nucleus of a carbon-13 atom.
I could not understand how an even number of fermions are bosons, while all elementary particles are either fermions or bosons. Also I could not understand how the fermions have only odd number of fermions. It doesn't make sense.
I guess it could be poor choice of words. Otherwise please explain further about how these particles behave. —The preceding unsigned comment was added by Tenri (talk • contribs) 04:10, 10 March 2007 (UTC)
thread_title:  Confusing paragraph 

message: Please comment of the new table of elementary particles at Wikipedia:Graphic_Lab/Images_to_improve#String Theory. Thanks. Dhatfield (talk) 22:51, 28 June 2008 (UTC)
thread_title:  New image 

message: Don't you think it is necesary for non physicist to know some fundamental experimental facts to explain why it is postulated the existence of fermions? Paranoidhuman (talk) 00:44, 18 August 2008 (UTC)
thread_title:  Experimental fact 

message: Chirality (physics) says there are some left-handed fermions (the ones that feel the weak nuclear force) implying there are right-handed ones that don't.  Should this article on fermions mention chirality or refer somewhere ?  Weak interaction has a table of left-handed fermions (and implies their antiparticles are right-handed and feel the weak interaction). Standard_Model seems to say W and Z behave differently regarding L/R-handedness. Are there any right-handed fermions (as opposed to antifermions) ? - Rod57 (talk) 17:57 26 November 2012 (UTC)
:Yes, there are plenty of right handed fermions - except for the neutrino, which only feels the weak force.-- cheers, Michael C. Price talk 20:43, 26 November 2012 (UTC)
thread_title:  Right-handed fermions 

message: When the text says a Dirac (massive) fermion can be treated as a "combination" of two Weyl (massless) fermions, the word combination must mean something other than a composite particle, which if it were made of two fermions would be a boson.  I suspect it means superposition.  If so it would be good say  superoposition and for some knowledgeable person to add, or point to, a simple explanation of how a superposition of two massless particles can have mass.CharlesHBennett (talk) 13:54, 15 May 2013 (UTC)
thread_title:  Elementary fermions 

message: Wikipedia has articles on Dirac fermions and Majorana fermions but nothing at all on Weyl fermions beyond the parenthetical "massless" in this article and a mysterious link to Spinors whose only mention of any kind of fermion is in the phrase "electrons and other fermions".  The article on Fermionic fields refers to Weyl spinors without however saying what they are.  Moreover Wikipedia lists 38 topics named after Hermann Weyl with no mention of Weyl fermions.  Yet a web search for "Weyl fermion" turns up 9,740 results.  Why this omission?  --Vaughan Pratt (talk) 17:53, 9 October 2013 (UTC)
thread_title:  Nothing in Wikipedia on Weyl fermions? 

message: At the moment the first sentence of the article says "In particle physics, a fermion [...] is any particle characterized by Fermi–Dirac statistics and [...]". I'd like to ask a question about definitions here, as I'm fairly sure that this sentence is wrong and misleading.
As far as I understand, when people say "Fermi Dirac statistics" they have in mind a result from statistical thermodynamics of non-interacting fermions in thermal equilibrium. This very specific and idealized result is associated with the Fermi occupation number \scriptstyle N_i = [1 + \exp(\tfrac{E_i-\mu}{kT})]^{-1}. If this is the intended meaning of Fermi-Dirac statistics, then I'd like to point out that typically, fermions do not obey Fermi Dirac statistics: fermions that we can get into equilibrium generally have significant interactions (e.g. electrons); fermions with weak interactions are usually not in equilibrium (e.g. neutrinos). Fermi Dirac statistics are often a good approximation for electrons in metals / semiconductors, but by no means are they exact and violations are often found.
On the other hand, if "Fermi Dirac statistics" is intended to refer to the general quantum mechanical principles of Pauli exclusion / exchange antisymmetry / etc., then indeed all fermions follow Fermi Dirac statistics. However, if that is so, then the article Fermi–Dirac statistics needs to be massively reworked for this more general meaning.
The question is, which is the generally recognized meaning of "Fermi Dirac statistics"? Nanite (talk) 18:30, 30 January 2014 (UTC)
thread_title:  All fermions obey Fermi Dirac statistics - true or false? (definition question) 

message: Substituted at 15:05, 29 April 2016 (UTC)
thread_title: Assessment comment

message: What is the difference between a spin-1/2 and spin 3/2 and spin 5/2 fermion, and are there any known fermions with 3/2 or 5/2 or higher? I just redirected Spin 3/2 and Spin 5/2 here because Spin (physics)#Higher spins only has math which is meaningless to most readers. -- Beland (talk) 07:44, 11 September 2021 (UTC)
thread_title:  Spin 3/2 and 5/2