Wave Particle Interpretation

Oct 2017
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For fundamental particles, spin is a quantum number and actually has nothing to do with spinning objects. The name comes from early theories that were later replaced.
 
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There are a lot of things in physics that have the same name as "every-day" things
but are in actuallity very different.
Even terms like particle and wave (which we might feel we know)
have a very different interpretation in QM than they do at the beach.
 
Apr 2015
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Somerset, England
For fundamental particles, spin is a quantum number and actually has nothing to do with spinning objects. The name comes from early theories that were later replaced.
Indeed so.
However this spin quantum number allows calculation of dipole moments, angular momentum and so on, whcih are classical properties exhibited by those same particles (in conjunction with fundamnetal constants such as the charge on the electron - a fundamental particle.).

This is how ESR (electron spin resonance) spectroscopy works.
 
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Oct 2017
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Indeed so.
However this spin quantum number allows calculation of dipole moments, angular momentum and so on, whcih are classical properties exhibited by those same particles (in conjunction with fundamnetal constants such as the charge on the electron - a fundamental particle.).

This is how ESR (electron spin resonance) spectroscopy works.
Interesting...

TL;DR: It seems that it's still nope. Also, QM is really weird.


However...

I think there's a lot of naming confusion in QM because of the history behind the move towards QM from classical physics, but I see where you're coming from and it's really interesting to consider each case and see how those might relate to the classical phenomena. I did some surface level digging to try and find some information.

- Electric dipole moment:
I think the smallest candidates for "classical" electric dipole moments are hadrons (like protons and pions), which have size and shape, so that's fine.
What about electrons? I noticed there's a wikipedia page on electron electric dipole moments (!) After some reading, it seems to be a measurement effect because some of the possible Feynman diagrams that describe the possible sets of measured states involve virtual quarks, so it's a really weird indirect effect that can result in an incredibly weak measured dipole moment. There's some heavy QM there that I don't understand, but I've encountered indirect stuff like this before (e.g. photon-photon interactions caused by photon shadowing) so it seems plausible to me at least that something like that can happen.

That's still pretty remarkable!

- Angular momentum:
Yes... all particles, as well as fundamental particles, have sets of possible measurable angular momentum quantum numbers, J, based on their spin angular momentum, L and their intrinsic spin, S. There's also the isospin quantum number, which is related to angular momentum. After some digging I came across the following:

What is spin?

American Journal of Physics 54, 500 (1986); https://doi.org/10.1119/1.14580
Hans C. Ohanian

Unfortunately it's behind a paywall, but the abstract seems to suggest that size and shape are not required even for angular momentum at the particle level. It's really interesting though and I do wonder if QM has more surprises up its sleeve when it comes to classical concepts at very small spatial scales.
 
Apr 2015
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Who said anything about electrical dipole moments?

NMR machines have become commonplace in hospitals these days.
This is proton or carbon13 or similar resonance.

But a similar technique can also be played with electrons, albeit at different frequencies.
This is much weaker than NMR, but still solidly managable with modern (? I studied the beginnings of this in 1968) equipment.
Just recently I was helping an Msc pharmacy student because the triplet states of many organic molecules (ie the electrons in them) are useful in chemical analysis.
You will find some theory in books like

Physical Chemistry by Atkins

Spectroscopy by Whiffen

I can find plenty more if you are interested, but we seem to have a couple of onging larger subjects already at the moment.

There is the postgrad question about activity coefficients and Debye Huckle theory in the Chemistry section,
and I don't know how much effort to put into the current rude troll and SR.

:)
 
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@ benit:
Mass Point Dynamics ignore specific structure of objects. What they emphasize is math game. That's good enough. At least math seems to have strict logic...
If basic particles have no shape / size, how does our concept of shape / size in macroscopic scale come from? Mass point is just something abstract.
.................................
From history long long ago, people are always exploring trueth in two directions:
1, Outward, into the sky, and they got stars, galaxies, etc...
2, Inward, into the matter, and they got molecules, atoms, etc...
 

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Apr 2015
1,238
359
Somerset, England
Mass Point Dynamics ignore specific structure of objects. What they emphasize is math game. That's good enough. At least math seems to have strict logic...
If basic particles have no shape / size, how does our concept of shape / size in macroscopic scale come from? Mass point is just something abstract.
This is true but what is the relevance?
 
Oct 2017
676
348
Glasgow
@ benit:
Mass Point Dynamics ignore specific structure of objects. What they emphasize is math game. That's good enough. At least math seems to have strict logic...
If basic particles have no shape / size, how does our concept of shape / size in macroscopic scale come from? Mass point is just something abstract.
Yes, there's the maths behind QM, but there's also experiments...

Having more than one fundamental particle in a particular system allows distances between those particles to be determined (at least to some finite accuracy based on the measurement apparatus and the system under study; QM complicates everything). If two or more quantum particles remain in close proximity for a long time to form some kind of stable (but not necessarily static) system, it's meaningful to talk about the combined whole as a entity with a shape and size (amongst others...). This is true for protons because they are formed from three quarks which are bound together by the strong nuclear force.
 
Oct 2017
676
348
Glasgow
Who said anything about electrical dipole moments?
Okay... yes. I should probably have just talked about general dipole moments.

NMR machines have become commonplace in hospitals these days.
This is proton or carbon13 or similar resonance.

But a similar technique can also be played with electrons, albeit at different frequencies.
This is much weaker than NMR, but still solidly managable with modern (? I studied the beginnings of this in 1968) equipment.
Just recently I was helping an Msc pharmacy student because the triplet states of many organic molecules (ie the electrons in them) are useful in chemical analysis.
You will find some theory in books like

Physical Chemistry by Atkins

Spectroscopy by Whiffen

I can find plenty more if you are interested, but we seem to have a couple of onging larger subjects already at the moment.
Yes. I've studied a little bit of physical chemistry and spectroscopy at university.

Just to be clear, I'm only saying that size and shape are not particularly meaningful discussions for fundamental particles (leptons and individual quarks). Everything else which has them as constituents (hadrons, nuclei, atoms, molecules, etc.) is fine. I always found the nuclear radius really interesting as a concept nuclei because they are a bit diffuse, like clouds.

There is the postgrad question about activity coefficients and Debye Huckle theory in the Chemistry section,
and I don't know how much effort to put into the current rude troll and SR.

:)
No problem. I'm in the same boat. I have a lot to study at work and I don't have as much time or energy as I like (at the moment at least...) to revise my old university stuff or start my own research projects.