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A point particle is not necessarily an approximation for leptons, they could truly be point particles. Rotiro 08:00, 11 April 2006 (UTC)
Is a point mass and point particle the same thing_ If so, these two articles should be merged. —Preceding unsigned comment added by 200.49.213.61 ( talk • contribs) 20:50, 9 August 2006
I wrote a blurb about J.J.Thomson. Ti-30X ( talk) 01:21, 26 June 2009 (UTC)
I added a blurb about the (accurate) history of the point particle. So far a very short history. Ti-30X ( talk) 02:54, 26 June 2009 (UTC)
I am removing the re-improve template stating "This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (May 2009)".
Everything now has the needed in-line citations. Quinn 16:17, 13 July 2009 (UTC)
It seems like the entire section Point particle properties has little to do with point particles. It's just a couple of stubs for electron and quark articles. It doesn't really discuss the "pointness" of electrons or quarks very well. Jpkotta ( talk) 18:35, 28 August 2009 (UTC)
I deleted some nonsense stating that the electron has a radius equal to some small number, with a reference to Lederman's book. Lederman's book does not say that the electron radius is equal to that number; it says that its radius is measured to be smaller than that number. As of 2000, all X-ray scattering experiments have shown that electrons behave as point-like particles with no spatial extent (ref: H. Haken; Hans Christoph Wolf (2000). The physics of atoms and quanta: introduction to experiments and theory (6th ed.). Springer. p. 70. ISBN 3540672745.).
There is a classical radius associated with the electron, which is derived by making the assumption that it is a sphere with all its electrical charge distributed on the surface, and that its rest mass is equal to the electrostatic energy of its charge. This is a theoretical derivation, and is based on classical Newtonian mechanics, which does not adequately describe all the properties of the electron; it has nothing to do with the actual spatial extent of the electron. What this "classical radius" means is that if the electron were a spherical charge, then classical electromagnetism predicts that it would have a radius of this value. In fact, based on which theoretical assumptions are made, one can derive a number of different values, all of which may be said to be the "radius" of the electron in some sense. Any attempt to ascribe such hypothetical "radius" values to an actual, physical radius is misleading at best, and totally nonsensical at worst.— Tetracube ( talk) 21:57, 22 September 2009 (UTC)
The article needs to discuss how a point particle can (indeed must) simultaneously be delocalised over an appreciable volume of space, to conform with Heisenberg's principle, and yet this is not a contradiction with its having a "pointlike" nature – i.e. the notion of "pointness" is a bit more sophisticated than just where the particle is.
Thus, for example, a photon is a point particle. But without contradiction, a photon emitted by an electron transitioning from an excited state to a ground state is typically about 106 or 107 wavelengths long [1] -- ie of the order of a metre or two long. Under special conditions, it may be possible to manufacture with an even more narrowly defined frequency. Spatially, these would be even longer.
The "pointness" of the particle is to do with the Green's functions it can be analysed into, not the physical space it's actually spread over. Jheald ( talk) 14:26, 17 November 2009 (UTC)
I am going to continue this discussion over here. My first understanding of the point particle came from reading the "God Particle:" by Lederman. On page 141 and 142 he discusses electron and refers to it as a point particle. It has the "spooky" QM qualities of lacking radius, but has mass and charge and has spin. If you link to the book on google books and enter "electron" in the search function you will see page 142 as one of the links. Scroll back from 142 to 141 and read forward. Steve Quinn (formerly Ti-30X) ( talk) 02:29, 18 November 2009 (UTC)
My view is that there's (1) "point particle", a concept in classical physics, and there's (2) "point particle", a concept in quantum particle physics, and they're different concepts. The first two paragraphs define (1), the third paragraph defines (2), the second body section elaborate on (2), the third and fourth body paragraphs elaborate on (1), etc. There's no reason for (1) and (2) to be the same article. (2) is already a very nice article, elementary particle. I would propose to merge the quantum half of this article into elementary particle, and keep this article as the classical concept. Of course we would make it clear in the first sentence that "point particle" can also mean "elementary particle", see elementary particle for more information! :-) -- Steve ( talk) 05:21, 18 November 2009 (UTC)
Here's my understanding of some of the areas I think the article should discuss, to treat what is meant by point particle in quantum mechanics. As I have said elsewhere, I'd be happier if this could be taken up by somebody more practiced at thinking about and explaining this stuff than I am (and who knows some good citeable references). But these are (I think) some aspects that the article should examine, not as text to go into the article, but summarising informally:
(Could use more work)
That's what's in my head; but I wonder if I am making a meal of it, or if there is a more obvious way into it. Jheald ( talk) 12:32, 18 November 2009 (UTC)
Here I just rewrote the article, deleting everything about the taxonomy of the various elementary particles. As Djr said, we already have an article on elementary particles, and that's the right place to discuss elementary particles. I put in a new section on quantum mechanics primarily to address the issue of what people mean when they say that an elementary particle has zero size...when the wavepacket can be very spread out (see discussions above). This question is very on-topic in this article IMO, unlike the stuff I deleted about decay rates and color charges and the photon mass and on and on. [Again, very good material, but not on-topic in this article, only in elementary particle, IMO.]
I think everything Jheald said just above would absolutely be a great way to expand/rewrite that quantum-mechanics section. -- Steve ( talk) 10:21, 25 February 2011 (UTC)
What means "exsitence" please? P0M ( talk) 01:57, 20 November 2009 (UTC)
Alright, I gave the article a trim (removed the infobox-like stuff since it was outdated and is best left for the indivual articles on these particles), chopped the see also section which contained stuff completely unrelated to point particles, and prettied up the references (and properly formatted them) so they don't get in the way of editing (they still need to be sorted by either author or by date). Lots still left to be done, but at least that's out of the way. Headbomb { ταλκ κοντριβς – WP Physics} 16:00, 22 November 2009 (UTC)
In section Pointmass:physics, the article references something called a Center of mass circumference. And requires non-overlapping center of mass circumferences for some reason or another. What is a center of mass circumference? the link currently points to center of mass, and circumference, but neither of these give any clarity to what is meant by their use together. Please Help. 134.29.231.11 ( talk) 17:56, 24 February 2011 (UTC)
Shouldn't the other-language versions for this article include the various other-language articles corresponding to http://ru.wikipedia.org/wiki/Материальная точка? It seems bizarre, for instance, that the Italian article "Punto materiale" and the Spanish article "Punto material" (each literally meaning "material point") are connected to this article but not connected with the Russian "Материальная точка", which also means "material point". Furthermore, the Russian term (along with, presumably, the other terms used for the articles connected to it as other-language versions) has the same meaning as "point particle" in physics (cf. Landau and Lifshitz's Course of Theoretical Physics, which begins with the statement "One of the fundamental concepts of mechanics is that of a particle", with the footnote "Sometimes called in Russian a material point.") — Preceding unsigned comment added by Vorziblix ( talk • contribs) 00:22, 4 March 2012 (UTC)
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, spherical objects interacting in 3-dimensional space whose interactions are described by the inverse square law behave in such a way as if all their matter were concentrated in their centers of mass. This statement seems incorrect. For example when two billiard balls collide they stop going toward each other much sooner than if all the mass was at their center points. So the actual distance traveled between the two billiard balls to the point of impact is less than would be traveled by two point particles. GeeBIGS ( talk) 01:46, 10 February 2013 (UTC)
OK, this: "If the distribution of matter in each body is spherically symmetric, then the objects can be treated as point masses without approximation, as shown in the shell theorem. Otherwise, if we want to calculate the attraction between massive bodies, we need to add all the point-point attraction forces vectorially and the net attraction might not be exact inverse square. However, if the separation between the massive bodies is much larger compared to their sizes, then to a good approximation, it is reasonable to treat the masses as point mass while calculating the gravitational force." Seems to me to say that what you are saying is correct UNLESS the two bodies are close enough that they are likely to collide. Does it not say that? 165.212.189.187 ( talk) 13:48, 11 February 2013 (UTC)
I just came upon this article and read the subject claim and I have an issue with it. A macro-sized object whose entire mass were concentrated into a single point is a black hole. A black hole's interactions with other objects are governed by the inverse square law but extended objects don't "behave as [black holes] in their immediate vicinity." I think the problem with the statement is the expansive term "interactions" -- i.e., "whose interactions are described by the inverse square law..." It needs to be more specific as to the interactions that are contemplated and the points in space where they occur. For example, another object that is located within circumference of the object may behave differently than when the object's mass is a black hole. Also, reflected light, which is governed by the inverse square law will behave differently (it won't reflex) when an object's matter is concentrated to a single point. The claim needs to be restated and well sourced. Sparkie82 ( t• c) 19:24, 11 April 2019 (UTC)
This inclusion with image is about the Standard Model of particle physics. It should be removed because it is only peripherally related to the present article ( point particle), which only talks about elementary particles as one area in relation to point particles. It may be here due to a misunderstanding of the term particle physics, which is not the study of point particles, nor of particles in the broad sense; particle physics is also called high-energy physics and is the specific study of elementary particles and composites of them (which often are not point particles at all) -- please read that article (not just its first couple of sentences which may be contributing to the confusion) if unclear. The present article is about the general concept and characteristics of a point particle, which is originally a classical concept and is certainly not specific to subatomic particles or other particles studied using high energy. Including "{ {Standard model|... } }" pulls in the following terms (once expanded):
Which aren't generally related to the concept of a point particle in particular.
DavRosen (
talk) 14:29, 20 January 2017 (UTC) (edited)
DavRosen (
talk)
14:42, 20 January 2017 (UTC)
At one point in the article the wave packet is delocalized, but as a superposition of quantum states (what else?) it seems to be localized. I'm confused. 2A02:A463:2848:1:C0FF:DBE0:6E0F:DBD6 ( talk) 14:09, 4 September 2023 (UTC)
This is just the volume of a sphere with the Bohr radius, which is arbitrary at best. The atomic orbital itself extends up to infinity. Thus inside the Bohr radius you will find the electron with a probability of x < 1. 128.176.10.74 ( talk) 11:03, 26 June 2024 (UTC)
This is the
talk page for discussing improvements to the
Point particle article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
This
level-5 vital article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||||||
|
A point particle is not necessarily an approximation for leptons, they could truly be point particles. Rotiro 08:00, 11 April 2006 (UTC)
Is a point mass and point particle the same thing_ If so, these two articles should be merged. —Preceding unsigned comment added by 200.49.213.61 ( talk • contribs) 20:50, 9 August 2006
I wrote a blurb about J.J.Thomson. Ti-30X ( talk) 01:21, 26 June 2009 (UTC)
I added a blurb about the (accurate) history of the point particle. So far a very short history. Ti-30X ( talk) 02:54, 26 June 2009 (UTC)
I am removing the re-improve template stating "This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (May 2009)".
Everything now has the needed in-line citations. Quinn 16:17, 13 July 2009 (UTC)
It seems like the entire section Point particle properties has little to do with point particles. It's just a couple of stubs for electron and quark articles. It doesn't really discuss the "pointness" of electrons or quarks very well. Jpkotta ( talk) 18:35, 28 August 2009 (UTC)
I deleted some nonsense stating that the electron has a radius equal to some small number, with a reference to Lederman's book. Lederman's book does not say that the electron radius is equal to that number; it says that its radius is measured to be smaller than that number. As of 2000, all X-ray scattering experiments have shown that electrons behave as point-like particles with no spatial extent (ref: H. Haken; Hans Christoph Wolf (2000). The physics of atoms and quanta: introduction to experiments and theory (6th ed.). Springer. p. 70. ISBN 3540672745.).
There is a classical radius associated with the electron, which is derived by making the assumption that it is a sphere with all its electrical charge distributed on the surface, and that its rest mass is equal to the electrostatic energy of its charge. This is a theoretical derivation, and is based on classical Newtonian mechanics, which does not adequately describe all the properties of the electron; it has nothing to do with the actual spatial extent of the electron. What this "classical radius" means is that if the electron were a spherical charge, then classical electromagnetism predicts that it would have a radius of this value. In fact, based on which theoretical assumptions are made, one can derive a number of different values, all of which may be said to be the "radius" of the electron in some sense. Any attempt to ascribe such hypothetical "radius" values to an actual, physical radius is misleading at best, and totally nonsensical at worst.— Tetracube ( talk) 21:57, 22 September 2009 (UTC)
The article needs to discuss how a point particle can (indeed must) simultaneously be delocalised over an appreciable volume of space, to conform with Heisenberg's principle, and yet this is not a contradiction with its having a "pointlike" nature – i.e. the notion of "pointness" is a bit more sophisticated than just where the particle is.
Thus, for example, a photon is a point particle. But without contradiction, a photon emitted by an electron transitioning from an excited state to a ground state is typically about 106 or 107 wavelengths long [1] -- ie of the order of a metre or two long. Under special conditions, it may be possible to manufacture with an even more narrowly defined frequency. Spatially, these would be even longer.
The "pointness" of the particle is to do with the Green's functions it can be analysed into, not the physical space it's actually spread over. Jheald ( talk) 14:26, 17 November 2009 (UTC)
I am going to continue this discussion over here. My first understanding of the point particle came from reading the "God Particle:" by Lederman. On page 141 and 142 he discusses electron and refers to it as a point particle. It has the "spooky" QM qualities of lacking radius, but has mass and charge and has spin. If you link to the book on google books and enter "electron" in the search function you will see page 142 as one of the links. Scroll back from 142 to 141 and read forward. Steve Quinn (formerly Ti-30X) ( talk) 02:29, 18 November 2009 (UTC)
My view is that there's (1) "point particle", a concept in classical physics, and there's (2) "point particle", a concept in quantum particle physics, and they're different concepts. The first two paragraphs define (1), the third paragraph defines (2), the second body section elaborate on (2), the third and fourth body paragraphs elaborate on (1), etc. There's no reason for (1) and (2) to be the same article. (2) is already a very nice article, elementary particle. I would propose to merge the quantum half of this article into elementary particle, and keep this article as the classical concept. Of course we would make it clear in the first sentence that "point particle" can also mean "elementary particle", see elementary particle for more information! :-) -- Steve ( talk) 05:21, 18 November 2009 (UTC)
Here's my understanding of some of the areas I think the article should discuss, to treat what is meant by point particle in quantum mechanics. As I have said elsewhere, I'd be happier if this could be taken up by somebody more practiced at thinking about and explaining this stuff than I am (and who knows some good citeable references). But these are (I think) some aspects that the article should examine, not as text to go into the article, but summarising informally:
(Could use more work)
That's what's in my head; but I wonder if I am making a meal of it, or if there is a more obvious way into it. Jheald ( talk) 12:32, 18 November 2009 (UTC)
Here I just rewrote the article, deleting everything about the taxonomy of the various elementary particles. As Djr said, we already have an article on elementary particles, and that's the right place to discuss elementary particles. I put in a new section on quantum mechanics primarily to address the issue of what people mean when they say that an elementary particle has zero size...when the wavepacket can be very spread out (see discussions above). This question is very on-topic in this article IMO, unlike the stuff I deleted about decay rates and color charges and the photon mass and on and on. [Again, very good material, but not on-topic in this article, only in elementary particle, IMO.]
I think everything Jheald said just above would absolutely be a great way to expand/rewrite that quantum-mechanics section. -- Steve ( talk) 10:21, 25 February 2011 (UTC)
What means "exsitence" please? P0M ( talk) 01:57, 20 November 2009 (UTC)
Alright, I gave the article a trim (removed the infobox-like stuff since it was outdated and is best left for the indivual articles on these particles), chopped the see also section which contained stuff completely unrelated to point particles, and prettied up the references (and properly formatted them) so they don't get in the way of editing (they still need to be sorted by either author or by date). Lots still left to be done, but at least that's out of the way. Headbomb { ταλκ κοντριβς – WP Physics} 16:00, 22 November 2009 (UTC)
In section Pointmass:physics, the article references something called a Center of mass circumference. And requires non-overlapping center of mass circumferences for some reason or another. What is a center of mass circumference? the link currently points to center of mass, and circumference, but neither of these give any clarity to what is meant by their use together. Please Help. 134.29.231.11 ( talk) 17:56, 24 February 2011 (UTC)
Shouldn't the other-language versions for this article include the various other-language articles corresponding to http://ru.wikipedia.org/wiki/Материальная точка? It seems bizarre, for instance, that the Italian article "Punto materiale" and the Spanish article "Punto material" (each literally meaning "material point") are connected to this article but not connected with the Russian "Материальная точка", which also means "material point". Furthermore, the Russian term (along with, presumably, the other terms used for the articles connected to it as other-language versions) has the same meaning as "point particle" in physics (cf. Landau and Lifshitz's Course of Theoretical Physics, which begins with the statement "One of the fundamental concepts of mechanics is that of a particle", with the footnote "Sometimes called in Russian a material point.") — Preceding unsigned comment added by Vorziblix ( talk • contribs) 00:22, 4 March 2012 (UTC)
An image used in this article,
File:Modeling.pdf, has been nominated for speedy deletion at
Wikimedia Commons for the following reason: Copyright violations
Don't panic; deletions can take a little longer at Commons than they do on Wikipedia. This gives you an opportunity to contest the deletion (although please review Commons guidelines before doing so). The best way to contest this form of deletion is by posting on the image talk page.
To take part in any discussion, or to review a more detailed deletion rationale please visit the relevant image page (File:Modeling.pdf) This is Bot placed notification, another user has nominated/tagged the image -- CommonsNotificationBot ( talk) 12:00, 13 May 2012 (UTC) |
, spherical objects interacting in 3-dimensional space whose interactions are described by the inverse square law behave in such a way as if all their matter were concentrated in their centers of mass. This statement seems incorrect. For example when two billiard balls collide they stop going toward each other much sooner than if all the mass was at their center points. So the actual distance traveled between the two billiard balls to the point of impact is less than would be traveled by two point particles. GeeBIGS ( talk) 01:46, 10 February 2013 (UTC)
OK, this: "If the distribution of matter in each body is spherically symmetric, then the objects can be treated as point masses without approximation, as shown in the shell theorem. Otherwise, if we want to calculate the attraction between massive bodies, we need to add all the point-point attraction forces vectorially and the net attraction might not be exact inverse square. However, if the separation between the massive bodies is much larger compared to their sizes, then to a good approximation, it is reasonable to treat the masses as point mass while calculating the gravitational force." Seems to me to say that what you are saying is correct UNLESS the two bodies are close enough that they are likely to collide. Does it not say that? 165.212.189.187 ( talk) 13:48, 11 February 2013 (UTC)
I just came upon this article and read the subject claim and I have an issue with it. A macro-sized object whose entire mass were concentrated into a single point is a black hole. A black hole's interactions with other objects are governed by the inverse square law but extended objects don't "behave as [black holes] in their immediate vicinity." I think the problem with the statement is the expansive term "interactions" -- i.e., "whose interactions are described by the inverse square law..." It needs to be more specific as to the interactions that are contemplated and the points in space where they occur. For example, another object that is located within circumference of the object may behave differently than when the object's mass is a black hole. Also, reflected light, which is governed by the inverse square law will behave differently (it won't reflex) when an object's matter is concentrated to a single point. The claim needs to be restated and well sourced. Sparkie82 ( t• c) 19:24, 11 April 2019 (UTC)
This inclusion with image is about the Standard Model of particle physics. It should be removed because it is only peripherally related to the present article ( point particle), which only talks about elementary particles as one area in relation to point particles. It may be here due to a misunderstanding of the term particle physics, which is not the study of point particles, nor of particles in the broad sense; particle physics is also called high-energy physics and is the specific study of elementary particles and composites of them (which often are not point particles at all) -- please read that article (not just its first couple of sentences which may be contributing to the confusion) if unclear. The present article is about the general concept and characteristics of a point particle, which is originally a classical concept and is certainly not specific to subatomic particles or other particles studied using high energy. Including "{ {Standard model|... } }" pulls in the following terms (once expanded):
Which aren't generally related to the concept of a point particle in particular.
DavRosen (
talk) 14:29, 20 January 2017 (UTC) (edited)
DavRosen (
talk)
14:42, 20 January 2017 (UTC)
At one point in the article the wave packet is delocalized, but as a superposition of quantum states (what else?) it seems to be localized. I'm confused. 2A02:A463:2848:1:C0FF:DBE0:6E0F:DBD6 ( talk) 14:09, 4 September 2023 (UTC)
This is just the volume of a sphere with the Bohr radius, which is arbitrary at best. The atomic orbital itself extends up to infinity. Thus inside the Bohr radius you will find the electron with a probability of x < 1. 128.176.10.74 ( talk) 11:03, 26 June 2024 (UTC)