Talk:Angular momentum

message: I checked the reference. This is its abstract:
"The angular momentum of light plays an important role in many areas, from optical trapping to quantum information. In the usual three-dimensional setting, the angular momentum quantum numbers of the photon are integers, in units of the Planck constant ħ. We show that, in reduced dimensions, photons can have a half-integer total angular momentum. We identify a new form of total angular momentum, carried by beams of light, comprising an unequal mixture of spin and orbital contributions. We demonstrate the half-integer quantization of this total angular momentum using noise measurements. We conclude that for light, as is known for electrons, reduced dimensionality allows new forms of quantization."
This is a very specific thing to a very specialized case: reduced dimensions. Yet the [wikipedia] article doesn't allude to that, and is speaking instead in the context of spin-orbit interactions. That makes it misleading. It is not mentioned in the article and does not apply to the situation given. I suggest it be deleted. Betaneptune (talk) 00:27, 2 May 2019 (UTC)
thread_title:  Re "Electrons and photons need not have integer-based values for total angular momentum, but can also have fractional values.[29]" 

message: By the way, is it right to start the quantitative treatment from “”? To me, it is a thoughtless replication of  “”, but the analogy is flawed. While we can explain what the mass is without referring to the momentum directly—and mass is a scalar, after all—it’s impossible to define the moment of inertia without defining the rotational momentum first (either explicitly, or via e.g. torque).
Moreover, we don’t live in the 19th century. Modern physics knows that such things as a particle with spin or a p-orbital rotate without any angular velocity. The same for fields, even such classical field theories as electrodynamics. Incnis Mrsi (talk) 05:17, 13 May 2019 (UTC)
replies: text: No, the moment of inertia is defined without reference to angular momentum, it is strictly a function of the relative positions of the particles, or the density distribution. I agree with your point about quantum fields and particles, and  is not the way to transition to the QM theory, and moment of inertia is, I guess, not as simple.PAR (talk) 05:54, 13 May 2019 (UTC)
replies: text:  “Strictly a function of the relative positions of the particles” makes sense for a “strictly” rigid body only. Incnis Mrsi (talk) 06:06, 13 May 2019 (UTC)
replies: text:  I agree. PAR (talk) 10:27, 13 May 2019 (UTC)
replies: text:  But the scope of the angular momentum is immensely broader, even in Newtonian physics (think celestial mechanics). Indeed the rigid example is an important example, whereas the article—including the photo at the top— currently suggests that it’s the main domain where this notion may be applied. Incnis Mrsi (talk) 12:09, 13 May 2019 (UTC)
replies: text: Again I agree. As such, the article concentrates on introductory concepts, but does not do the full development.PAR (talk) 19:46, 13 May 2019 (UTC)
thread_title:  Should ''I'''''ω''' stand before '''r''' × '''p'''? 

message: I revised the wording of the last paragraph of the introduction and this has been reverted almost immediately as being a 'bad' edit so I will explain my changes.
Firstly, angular momentum is a physical quantity, and so calling it an 'operator' is slightly iffy - an operator is used to represent it in the mathematical formalism of quantum mechanics. That doesn't mean that angular momentum is literally an operator, which is purely a mathematical concept. i.e. it is convenient for us humans to use operator formalism to explain angular momentum, that doesn't mean that any physical measurement will tell us that angular momentum is an operator. Again, the introduction then goes on to talk about eigenvalues - saying that angular momentum is quantized is enough, an eigenvalue reference conjures up associations with linear algebra again which is mathematical rather than physical. It then went on to say 'one projection (one component)' - we don't need two words for one thing in the introduction, especially with brackets. It then commits the same offence in saying 'a particle (i.e. an excitation of a quantum field) - again too much information. It then says 'for technical reasons' particles still possess angular momentum. What are these technical reasons exactly? It is simply an observation that particles possess spin, there is no technicality to it.
The person who revised my introduction complained that I 'pushed' that 'quantum = fundamental', this being problematical. What I did was replace the phrase 'in quantum mechanics' with 'at a more fundamental level'. Again, it's silly to say 'in quantum mechanics blah blah blah', just as it's silly to say 'in classical mechanics, a spring stretches'. The primary thing we are dealing with here is nature, not mathematical representations of things. Quantum Mechanics is a formalism used to represent phenomena that are actually observed, so we should talk primarily of the phenomena, without overly stressing the mathematical theory, especially in the introduction.
I did make an error however of perhaps implying that all particles are spin-1 by talking of three components of angular momentum at a quantum level. I have removed that now.
As such, I have reverted to my previous edit.
Oward98 (talk) 08:55, 7 July 2019 (UTC)
replies: text: You replaced properly sourced content with unsourced content. And see also wp:edit warring and wp:BRD. - DVdm (talk) 08:59, 7 July 2019 (UTC)

text: may disagree on such details as whether the angular momentum “is” an operator, but pushing  and dismissing criticism of that text is a no-go. Incnis Mrsi (talk) 09:57, 7 July 2019 (UTC)
replies: text:  Good edit, this. - DVdm (talk) 10:20, 7 July 2019 (UTC)
thread_title:  Revision of last paragraph of Introduction 

message: Edit: FALSE ALARM. I hadn't noticed that page angular velocity already exists, given that rotational velocity redirected to rotational speed instead. I fixed the redirect to point to angular velocity with a for hatnote at rotational speed. 
See Talk:Rotational_speed#Proposed_move_of_redirect_for_angular_velocity_to_angular_momentum
— MaxEnt 21:49, 22 April 2020 (UTC)
replies: text: On the way by, I also changed a creaky redirect from angular force to centripetal force (yikes!) to point instead to torque so now I feel at least partially redeemed. — MaxEnt 22:27, 22 April 2020 (UTC)
thread_title:  Proposed move of redirect for angular velocity to angular momentum 

message: * Chris Lee: Atoms spin backward while flying along a surface — 23 September 2019 
Thought experiment: if I take two parallel metal plates—both circular of the same diameter—and between these I mount six spinning tops on jeweled bearings in a hexagon pattern, and then I rotate the plate apparatus around it's geometric center, the tops themselves should exhibit gyroscopic stability. 
But what if the tops themselves are actual atoms? Do the individual atoms remain gyro-stable and as such their electronic and nuclear mass contributing nothing much to the angular inertia for the object in question? 
I thought this must be a dumb question, but Chris Lee above shows it maybe isn't as dumb as I thought. — MaxEnt 22:16, 22 April 2020 (UTC)
replies: text: Here we can only discuss the article, not the subject—see wp:Talk page guidelines. You can ask questins at our wp:Reference desk/Science. - DVdm (talk) 06:33, 23 April 2020 (UTC)

text: By the way, user , please sign all your talk page messages with four tildes (~~~~), not three (~~~). With four tildes your user talk page shows as a link in your signature — see Help:Using talk pages. Thanks. DVdm (talk) 06:39, 23 April 2020 (UTC)
thread_title:  Gyroscopic refusniks 

message: On Commons, there are now two talk page remarks (one is my own) concerning deficiencies of this animated illustration. — MaxEnt 17:31, 12 June 2021 (UTC)
thread_title:  Substandard animation