Talk:Chirality (physics)

Untitled
Alterations and restructuring are needed to properly represent use and meaning of the word chirality. Please join the multi-disciplinary discussion on Talk:Chirality. --Cigno 22:12, 15 November 2005 (UTC)

Confusion in "Chirality and helicity" paragraph
Please clear up or explain seeming contridiction in the paragraph "Chirality and helicity". This paragraph starts with "The helicity of a particle is right-handed if the direction of its spin is the same as the direction of its motion", which implies the axis of spin is perpendicular to the direction of motion. But then the paragraph says "...a standard clock, with its spin vector defined by the rotation of its hands, tossed with its face directed forwards, has left-handed helicity", which implies the axis of spin along the ( parallel to) direction of motion; this is implied because this illustration says the clock is "tossed with its face directed forwards". — Preceding unsigned comment added by 63.224.64.220 (talk) 22:42, 30 June 2013 (UTC)


 * This needs to be rewritten, or the pictures need to be corrected. Curling my fingers according to the left-handed rule, my thumb will point in the direction of motion of the clock (assuming I understand what was written here), which (I always thought) means the vector points the way my thumb does for left-handed spin. The picture shows the opposite. Is the picture wrong? Is the definition in terms of the clock wrong? (Or am I screwed up?)


 *   Solo Owl   12:42, 31 October 2014 (UTC)


 * The first paragraph of the introduction, IMHO, is one of the worst first paragraphs in all of Wikipedia. The third sentence refers to "symmetry transformation", which has its own section in the article. However "symmetry transformation" is (highly technically) defined in terms of operators, which is highly unhelpful to the layman. In the fourth sentence, the English preposition "by" suggests that the fermions are acting on something somewhere -- I don't think this is what is meant. And what is a Dirac fermion, as opposed to a non-Dirac fermion?


 * It is a good thing for Wikipedia to give technically correct definitions, in terms that specialists will understand. It is at least as important for Wikipedia to give nontechnical explanations for the layman; both should be in the same article, and clearly flagged. (I think that the standard idea of "layman" was someone who has a high-school education, but doesn't really remember his math and science courses.)


 *   Solo Owl   14:11, 31 October 2014 (UTC)

Merge with Helicity
Two reasons.
 * For massless particles, there's no difference between chirality and helicity, except for numerical factor.
 * For massive particles, the two are often confused. Even this article talks about "relative chirality, which depends on the observer’s reference frame", but what it really means is that massive particles have relative helicities. As the article correctly says in the section 2, chirality is given by the operator $$\gamma^5$$. Chirality is Lorentz-invariant, and helicity is not. --Itinerant1 05:27, 4 September 2006 (UTC)


 * If you're an expert on the subject (or have knowledge) by all means please merge. Radagast83 19:58, 28 October 2006 (UTC)

Don't merge with helicity

 * The two quantities are often conflated and, unless expertly done, merging the articles is only likely to encourage this misconception to persist. It may even be worth adding "not to be confused with helicity" or such into the first paragraph of this article, but I don't feel I'm expert enough to draw the appropriate distinction yet.

Chirality Explained Wrong
Chirality is explained wrong. It is not the projection of the spin in the direction of motion. Helicity is in fact the spin projection on the direction of motion (and therefore depends on the reference frame). Chirality is a much more abstract concept, and it does not depend on the frame of reference. For massless particles (and only for those), chirality and helicity are the same. For massive particles they are different - one independent of the frame of reference, the other not. So, for massless particles, a chirality left-handed particle is always helicity left-handed. But for massive particle, a chirality left-handed particle can be helicity right-handed. See for example pion decay, where this effect (and its dependence on the mass of the particle) plays a major role. It is however true, that parity transforms chirality left-handed particles to chirality right-handed ones, as well has helicity left-handed ones to helicity right-handed ones (and vice versa).

Chirality Fixed Up a Bit
The old definition is now (correctly) called helicity. In the new definition, chirality tells us whether a particle transforms in a right or left handed representation of the poincare group. Someone else can feel free to incorporate more detail. Drkarat (talk) 18:20, 3 June 2008 (UTC)


 * This article doesn't really explain what chirality is. (It does say a lot about helicity) Hopefully an expert can expand on the brief comment about left-handed and right-handed representations of the Poincare group. Mathewsyriac (talk) 20:47, 16 May 2010 (UTC)

Absolute and Relative Chirality
I think the material discussing "absolute" vs. "relative" chirality is misleading and should be removed. Chirality is chirality; the terms "absolute chirality" and "relative chirality" are certainly not in common usage and seem to have been invented in this article. If there are no objections, I'll try to clean this up (and also make the definitions of chirality and helicity clearer) when I get the time. Aiwendil42 02:15, 11 July 2007 (UTC)


 * I agree entirely. Rather than this absolute v. relative discussion, a section on chirality vs helicity would clarify things.  I've tried to clean out what I believe to be inaccuracies, though it was in a section about what things "are called" which is always debatable.PhysPhD 23:38, 4 August 2007 (UTC)


 * Though the recent changes were a step in the right direction, I think the above Chirality Explained Wrong criticism has not been adequately addressed. We need a clear definition of chirality that differs from helicity.  Frankly, I don't know how chirality is defined geometrically, only that the Chirality operator is represented on fermions as $$\gamma^5 $$.  Also, how does the Pauli-Lubanski pseudo-vector fit into this?PhysPhD 21:27, 30 August 2007 (UTC)

Chirality is definitely defined wrong in this article. One way to define it is through Lorentz transformation: left and right spinors transform differently under the Lorentz group —Preceding unsigned comment added by 128.141.132.197 (talk) 14:23, 5 November 2007 (UTC)

Simple Summary of Chirality vs Helicity
Helicity is a physical space kind of thing. If the fingers of your right hand curl in the direction of spin, and the thumb of the same hand points in the direction of the velocity (momentum direction), you have right hand helicity. If it works in the same way for your left hand, you have left hand helicity.

In contrast, chirality is related to the charge of the weak force field the particle feels. It is not related to the physical space, per se, but rather to an abstract space (the Dirac spinor space and the associated $$\gamma^5 $$ matrix found therein.)  For example, a chiral left hand election has a weak charge of -1/2; a chiral left hand neutrino, +1/2; and any chiral right hand particle, zero. Thus, only the left hand chirality particles feel the weak force (at least at high energy before symmetry breaking, but that is another story). These chirality based, weak charge interactions have little to do with helicity, EXCEPT a funny thing happens as particle speed approaches that of light. If one follows the math, one sees that helicity then approaches chirality, in effect. For massless particles, as noted above, the speed is that of light, so helicity and chirality are the same.

The use of the terms "left hand chirality" and "right hand chirality" probably has its origin in that phenomenon (i.e., what happens as v --> c), but chirality really doesn't have a kind of physical handedness like helicity. The choice of nomenclature, early on, has led to immense confusion over the years.

To see a simplified chart summary comparing chirality to helicity, and an in depth explanation of how the two become the same thing at the speed of light, go to Pedagogic Aids to Quantum Field Theory and scroll down to near the bottom of the page. I am unaware of any texts showing this material. —Preceding unsigned comment added by Bob108 (talk • contribs) 21:25, 22 October 2007 (UTC) Bob108 21:29, 22 October 2007 (UTC) --Bob108 (talk) 19:51, 11 August 2008 (UTC)Bob108 (talk) 19:53, 12 August 2008 (UTC)
 * You are assuming a fresnel zone interaction in the near field of two particles. In the absence of anything else, ie: a blob of photon infinitely removed from all other blobs of whatever, there is only angular momentum (energy) and linear momentum (energy) (excepting other forms of energy related to the dynamics of time), therefore there is no weak force in the manner that the weak force is defined. (No insult was intended, blob is in no relation to bob, as there is in the dimensional space in which I happen to inhabit). (Fractalhints (talk) 21:14, 29 January 2010 (UTC))

Helicity.
Change spin to angular momentum and motion of trajectory to be linear momentum (energy considerations). Angular momentum in the plane perpendicular to the direction of motion of linear momentum does not contain vectors in the direction of motion, all others do. That would provide you with the left and right handed orientation when your viewpoint is into the direction of motion. For all other orientations, with a viewpoint into the direction of motion, there are two vectors of angular momentum that contribute to linear momentum, one forwards, one backwards. In those particular cases you cannot use a single instantaneous point but must use both points (Alice or möbius strip orientation). There is absolutely no reason for the ideal that angular momentum must allways be in the plane perpendicular to the direction of linear momentum (not even when v-->c for linear momentum). —Preceding unsigned comment added by Fractalhints (talk • contribs) 20:31, 29 January 2010 (UTC)

Wraparound Universe Makes Helical Gravitons Behave Like Dark Energy
If a graviton is imagined to be analagous to an Archimedes screw, then a hypothetical wraparound universe will create an effect where the circularly travelled helical gravitons (if they exist) appear to behave like anti-gravitons i.e. making objects move away from an observer, although the gravitons are still attracting the object, just in the opposite direction from which they were emitted. No-one else has made this connection as far as I'm aware a.k.a dark energy. The same principle can also be applied to the notion of electrical current in a closed loop or circuit. The concept is introduced in the FQXi essay competition 'Is Reality Digital or Analog' by Alan Lowey. — Preceding unsigned comment added by 195.59.118.105 (talk) 12:17, 27 June 2011 (UTC)

Questionable paragraph
"Only left-handed fermions interact with the weak interaction. In most circumstances, two left-handed fermions interact more strongly than right-handed or opposite-handed fermions implying that the universe has a preference for left-handed chirality," - the first sentence contradicts the second - either it's "all" or "most"... furthermore the fact that right is the opposite of left is somewhat obvious (and in this context the phrasing kinda reads like "left-handed, right-handed or opposite-handed"...)

92.230.146.4 (talk) 07:44, 29 December 2012 (UTC)

Merger proposal
The articles Left-right symmetry and Chiral symmetry are technical, lacking in context and references, and cover the same topic. I propose they be merged into Chirality (physics). RockMagnetist(talk) 22:41, 17 August 2015 (UTC)


 * Sounds good, Left–right symmetry and chiral symmetry as sections in Chirality (physics) since the latter seems to be the most general. Chirality (physics) is fairly short, so could use some expansion which puts the other two articles to use. M&and;Ŝc2ħεИτlk 22:57, 17 August 2015 (UTC)


 * Good idea. Some effort might be warranted early on to uniformize the notation and conventions. Cuzkatzimhut (talk) 23:54, 17 August 2015 (UTC)

I have added Chiral symmetry breaking to the list. RockMagnetist(talk) 16:47, 19 August 2015 (UTC)


 * What about Mirror symmetry and P-symmetry? Maybe I'm wrong, but aren't these essentially the same thing as Chiral symmetry?  If so, can there just be one article, with all the distinct terminologies, with redirects?  I think there is probably enough material for an article, not just a subsection.  — Preceding unsigned comment added by 70.247.174.3 (talk) 18:32, 12 September 2015 (UTC)

I think you may be wrong. They are different, although they touch on the subject, tangentially. Mission creep might prove to be the undoing of the proposal. Cuzkatzimhut (talk) 18:45, 12 September 2015 (UTC)

There is consensus for my original proposal, so I'll do the merge. It will start as a crude full-content paste, after which we can clean it up. RockMagnetist(talk) 19:12, 12 September 2015 (UTC)


 * A resounding "thanks" from the community. Much better. Can take its time, now, to uniformize notation, level, and style. Cuzkatzimhut (talk) 20:12, 12 September 2015 (UTC)

Assessment comment
Substituted at 11:33, 29 April 2016 (UTC)

This article is puzzling
Chirality is explained as something to do with a mirror, which involves the fact that we see a reflection with two eyes, which appear to switch our own image left/right (the mirror shows us as others see us). But why would an ordinary mirror deserve an article about physics? And what, exactly, is chirality, the subject of the article? I don't see a good definition. I see a diagram, but it doesn't make any sense: two spheres and an arrow. Are electrons chiral? Are photons chiral? Does this have to do with L and D isomers? How can an elementary particle be chiral when it is isotropic? Why are some WP articles so obscure that one gives up trying to make sense of them? David Spector (talk) 23:02, 29 July 2023 (UTC)