3 ms·

> "Spin" in quantum physics is more of an artistic interpretation of the term. It's similar to how Autism and other disorders have a "spectrum", but aren't divi

by tagrun 10y ago

> "Spin" in quantum physics is more of an artistic interpretation of the term. It's similar to how Autism and other disorders have a "spectrum", but aren't divided into colors. > With wave-particle duality, spin signifies how in-phase one particle's wave part is with the wave part of other particles. What? Is this a joke? (I'm serious, because it's not even wrong) Edit: Since I wrote my reply, the parent was fist deleted, and then edited into a quote from a blog post which tries to explain spin to layman. Well, whatever.

deleted 10y ago
[deleted]
ttctciyf 10y ago
Arrived too late to see the post you're replying to, but isn't it fair to say that an electron's spin, though it corresponds to a notion of angular momentum mathematically, is a little different to everyday ideas of spin? Not least in that spin-half particles like the electron must "rotate" 720 rather than 360 degrees before they get back where they started.
- tagrun 10y ago
  There's an accidental similarity between the groups SO(3) and SU(2), which works for spin. There are other quantum numbers such as flavor SU(3) for there is no mathematical coincidence and such analogies won't work. The differences between SU(2) and SO(3) go beyond just "rotate 720 rather than 360 and you're back where you started". While I understand the urge of expressing new things in terms of what you know, sometimes, analogies aren't helpful and distort reality, and you just need to accept that there can be things in the nature that doesn't correspond to anything in your daily life in the real sense of the word. That being said, the original parent post (which I quoted, so it's actually there) is total nonsense.
  - stephengillie 10y ago
    Could you recommend a good entry point for understanding group theory? It's always been particularly impenetrable, and the wiki page doubly so. Book or video or blog post or even private college course - anything would be appreciated. Is spin the exact same physical phenomena as 'macroscopic' spin, but on a quantum scale? If not, just curious, why use the same word?
    - tagrun 10y ago
      I can recommend Howards Georgi's Lie Algebras in Particle Physics which is a good introduction in the context of particle physics (yes, it covers both Lie algebras and groups). No, it is nothing like the angular momentum of a spinning object. The name is rooted in a historical misconception. It is a form on angular momentum, which caused the misunderstanding. As of today, we still do not have a deeper understanding of spin in quantum mechanics: it's just some intrinsic angular momentum with SU(2) symmetry, and the value of angular momentum is in general different between particles (corresponding to the irreducible representations of SU(2), and the angular momentum is mostly 1/2 or 1 in units of reduced Planck constant except for some exotic/composite particles).

by tagrun 10y ago

deleted 10y ago

[deleted]

ttctciyf 10y ago

Arrived too late to see the post you're replying to, but isn't it fair to say that an electron's spin, though it corresponds to a notion of angular momentum mathematically, is a little different to everyday ideas of spin? Not least in that spin-half particles like the electron must "rotate" 720 rather than 360 degrees before they get back where they started.

tagrun 10y ago
There's an accidental similarity between the groups SO(3) and SU(2), which works for spin. There are other quantum numbers such as flavor SU(3) for there is no mathematical coincidence and such analogies won't work. The differences between SU(2) and SO(3) go beyond just "rotate 720 rather than 360 and you're back where you started". While I understand the urge of expressing new things in terms of what you know, sometimes, analogies aren't helpful and distort reality, and you just need to accept that there can be things in the nature that doesn't correspond to anything in your daily life in the real sense of the word. That being said, the original parent post (which I quoted, so it's actually there) is total nonsense.
- stephengillie 10y ago
  Could you recommend a good entry point for understanding group theory? It's always been particularly impenetrable, and the wiki page doubly so. Book or video or blog post or even private college course - anything would be appreciated. Is spin the exact same physical phenomena as 'macroscopic' spin, but on a quantum scale? If not, just curious, why use the same word?
  - tagrun 10y ago
    I can recommend Howards Georgi's Lie Algebras in Particle Physics which is a good introduction in the context of particle physics (yes, it covers both Lie algebras and groups). No, it is nothing like the angular momentum of a spinning object. The name is rooted in a historical misconception. It is a form on angular momentum, which caused the misunderstanding. As of today, we still do not have a deeper understanding of spin in quantum mechanics: it's just some intrinsic angular momentum with SU(2) symmetry, and the value of angular momentum is in general different between particles (corresponding to the irreducible representations of SU(2), and the angular momentum is mostly 1/2 or 1 in units of reduced Planck constant except for some exotic/composite particles).