What do you need to establish that spin is conserved?

In summary, there is no classical interpretation of spin, but it is often considered a conserved quantity and a form of angular momentum. However, this is only true in certain situations, as total angular momentum is the true conserved quantity. References, such as Ballentine's "Quantum Mechanics: A Modern Development," provide further explanation and proof of this concept.
  • #1
Old Person
31
10
TL;DR Summary
What do you need to establish that spin is a conserved quantity?
Hi.

Question as in the summary.
Spin has no obvious classical interpretation but it is often a conserved quantity and considered as some sort of angular momentum. What do you need to establish that spin is a conserved quantity? I'm finding references to situations where spin is not a conserved quantity in general but only in some processes. Hence, what is needed to assert conservation?

Any replies or references to existing discussions or proofs would save me time and be appreciated. Thank you for your time.
 
Physics news on Phys.org
  • #2
Old Person said:
Spin has no obvious classical interpretation but it is often a conserved quantity and considered as some sort of angular momentum.
No, spin by itself is not "often" a conserved quantity. Total angular momentum is the conserved quantity. Only in situations where orbital angular momentum is either identically zero or is conserved on its own can spin be considered a conserved quantity by itself.

As for spin being "some sort of" angular momentum, that's much too vague. Spin is whatever part of total angular momentum is not orbital angular momentum. See, for example, Ballentine, Chapter 7.
 
  • Like
Likes topsquark, hutchphd, vanhees71 and 1 other person
  • #3
Thank you. I'll look for that when I get to a library.
Found: "Quantum Mechanics: A Modern Development" by Leslie E. Ballentine.
No great need to reply - I'll assume it's that book unless you say otherwise.
 
  • Like
Likes vanhees71
  • #4
Old Person said:
Found: "Quantum Mechanics: A Modern Development" by Leslie E. Ballentine.
Yes, that's it.
 
  • Like
Likes vanhees71

Similar threads

Replies
1
Views
1K
  • Quantum Physics
Replies
12
Views
2K
Replies
9
Views
4K
Replies
42
Views
5K
Replies
58
Views
563
  • Quantum Physics
Replies
2
Views
2K
Replies
3
Views
2K
Back
Top