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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.
The Pauli exclusion principle doesn't always work, according to my quantum textbook. See my discussion in talk:Pauli exclusion principle. -- Tim Starling
PEP works all the time for all the massive fermions in a bound state (I haven't heard about massless half-integer spin particles, as neutrinos are considered in Standard Model of Elementary Particle, to form a bound state). serbanut —Preceding signed but undated comment was added at 07:39, 15 September 2007 (UTC)
In the first line it is stated, and in the definition it is repeated, that fermions obey Fermi-Dirac statistics by definition. What is meant here is perhaps Fermi-Dirac statistics which to my knowledge codes for anticommutation relations for second quantized operators, thus antisymmetric wavefunctions. This is something different from the momentum distribution referred to by Fermi-Dirac statistics / distribution of many free fermions. I propose to change fermi-dirac into fermi in the two indicated places because it spreads confusion to those not familiar with the subject.
The subtlety is purely semantic, because clearly interacting electrons aren't in general described by fermi-dirac statistics. For instance, the fermi-liquid isn't merely described by a stepfunction in momentum space at zero temperature. —Preceding unsigned comment added by Danielabel ( talk • contribs) 14:39, 16 September 2009 (UTC)
I'm wondering whether the article's definition of fermions as particles requiring antisymmetric states is the best approach. According to the spin-statistics theorem, this is equivalent with having half-integer spin. But if a particle were found to violate that theorem, say a particle with integer spin and antisymmetric wavefunction (I'm aware that it's not clear how this could be and it would probably require a major change in quantum field theory), would we say "we found a fermion whose spin isn't half-integer", or would we say "we found a boson whose state isn't symmetric"? I think the latter, which would imply that the definition of a fermion is a particle with half-integer spin. This is also how Eric Weisstein's World of Physics defines it. (The same applies, obviously, to bosons; I added a link to this discussion on their talk page.) Fpahl 06:15, 8 Oct 2004 (UTC)
The Particle Data Group controls these definitions. Here are the definitions from Particle Data Group: Fermion: Any particle that has odd-half-integer (1/2, 3/2, ...) intrinsic angular momentum (spin), measured in units of h-bar. All particles are either fermions or bosons. Fermions obey a rule called the Pauli Exclusion Principle, which states that no two fermions can exist in the same state at the same time. Many of the properties of ordinary matter arise because of this rule. Electrons, protons, and neutrons are all fermions, as are all the fundamental matter particles, both quarks and leptons. Boson: A particle that has integer intrinsic angular momentum (spin) measured in units of h-bar (spin =0, 1, 2, ...). All particles are either fermions or bosons. The particles associated with all the fundamental interactions (forces) and composite particles with even numbers of fermion constituents (quarks) are bosons.
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.
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)
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) Nahuel
There are two groups of particles in elementary particle physics:
1. elementary particles described by non-interacting fields;
2. interaction carriers describing the interacting fields.
The first category contains fermions, and the second contains bosons. For example, electrons, muons, taons, neutrinos, quarks are fermions (spin one half) and they are considered elementary particles, and photons, Z0, W+/-, gluons are interaction carriers and they are bosons. serbanut —Preceding signed but undated comment was added at 07:48, 15 September 2007 (UTC)
This is the dilemma of Wikipedia: that reasonable questions about clarity and accuracy can persist for years without being resolved. This is an encyclopedia and the "non-expert" can be expected to be the "primary customer", not a particle physicist. I find the following ambiguity in 2012: in the introduction there is the statement: " Fermions are usually associated with matter, whereas bosons are generally force carrier particles; although in the current state of particle physics the distinction between the two concepts is unclear." I think that the distinction is much more clear than than the reader is led to believe. Moreover, the deuteron (spin =1), which is a boson, is as much a particle of matter as the proton (spin=1/2), a fermion. So the statement that "bosons are generally force carrier particles can hardly be correct. I suspect that the author meant to say that force carrier particles are generally (always?) bosons. In other words, this appears to me to be lax English (I hope!). In any case, a clarification by a knowledgable expert is over due: you can help save Wikipedia from scientific perdition. Tachyon 13:09, 8 October 2012 (UTC) — Preceding unsigned comment added by Janopus ( talk • contribs)
The paragraph begining "Of course..." is not helpfull to the uninitiated (I speak as someone visiting the page without a prior background in the subject matter). If there is a more appropriate topic on why "determining the fermionic or bosonic behavior of a composite particle (or system) is only seen at large (compared to size of the system) distance", perhaps there should be a link to it.
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:
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).
I think the wording is confusing--fermion simply describes any particle with half integer spin so it can describe both elementary as well as composite particles. Primary fermions are quark and leptons. 3 quarks together is a baryon which is a composite fermion (because it has half spin). 2 quarks together makes a meson (having integer spin). I will edit the text to try to clarify. Can someone please double check and see if it makes sense? Thanks Tensegrity 23:45, 2 April 2007 (UTC) Ah, thank you for correcting my brain fart re: the atomic weight/nbr of nucleons. :) Tensegrity 18:10, 4 April 2007 (UTC)
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)
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)
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)
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)
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)
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 . 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)
The comment(s) below were originally left at Talk:Fermion/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
I gave the article the start rating as it is very short, but still bigger than a stub. The importance rating was set to high as fermions are very important within the field of particle physics! Snailwalker | talk 00:51, 15 October 2006 (UTC) |
Last edited at 00:51, 15 October 2006 (UTC). Substituted at 15:05, 29 April 2016 (UTC)
The first sentence "In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin: spin 1/2, spin 3/2, etc" bears a warning that reads "contradicts material at the article 'Spin-1/2'." I personally don't see where the contradiction is. It if refers to the fact than the Spin-1/2 article reads "All known fermions, (…) have a spin of ½," there is actually no contradiction.
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)