[AntonioLao]

The outcry of quantum spin for its unintentional misunderstanding is contained in the 1st paragraph of Chapter VIII, Volume 3. 3rd Edition, Course of Theoretical Physics, Quantum Mechanics (Non-relativistic Theory) by L. D. Landau, et al, Pergamon Press, 1958 and quoted:

“In both classical and quantum mechanics, the law of conservation of angular momentum is a consequence of the isotropy of space with respect to a closed system. This already demonstrates the relation between the angular momentum and the symmetry properties under rotation. In quantum mechanics, however, the relation in question is a particularly far-reaching one, and essentially constitutes the basic content of the concept of angular momentum, especially as the classical definition of the angular momentum of a particle as the product of r ´ p has no direct significance in quantum mechanics, owing to the fact that position and momentum cannot be simultaneously measured.”

[TinyTree]

In both classical and quantum mechanics, the law of conservation of angular momentum is a consequence of the isotropy of space with respect to a closed system.

Is conservation of angular momentum an intrinsic property of the system- or a derived property?

If it is a derived property, then it is perhaps not meaningful to consider the limitations of position and momentum precise measurements.

[mkirkpatrick]

Originally Posted by AntonioLao The outcry of quantum spin for its unintentional misunderstanding is contained in the 1st paragraph of Chapter VIII, Volume 3. 3rd Edition, Course of Theoretical Physics, Quantum Mechanics (Non-relativistic Theory) by L. D. Landau, et al, Pergamon Press, 1958 and quoted: “In both classical and quantum mechanics, the law of conservation of angular momentum is a consequence of the isotropy of space with respect to a closed system. This already demonstrates the relation between the angular momentum and the symmetry properties under rotation. In quantum mechanics, however, the relation in question is a particularly far-reaching one, and essentially constitutes the basic content of the concept of angular momentum, especially as the classical definition of the angular momentum of a particle as the product of r ´ p has no direct significance in quantum mechanics, owing to the fact that position and momentum cannot be simultaneously measured.”

What
force could stop a quantum spin?Any Ideas!

kind regards michael.

[AntonioLao]

Originally Posted by mkirkpatrick What force could stop a quantum spin?

From the perspective of theoretical quantum space-time (TQS), orthogonal forces could stop a quantum spin. Actually the existence of these forces give rise to quantum spin.

Originally Posted by TinyTree Is conservation of angular momentum an intrinsic property of the system

It is an intrinsic property of an isotropic closed system. I am changing it to an open system where mass and energy are free to go in and out.

[Guille]

Originally Posted by AntonioLao From the perspective of theoretical quantum space-time (TQS), orthogonal forces could stop a quantum spin. Actually the existence of these forces give rise to quantum spin.

When are primary forces orthogonal? And when are secondary forces orthogonal? If a primary force is orthogonal to a secondary force, what is the physical implication?

[AntonioLao]

Originally Posted by GUILLE When are primary forces orthogonal? And when are secondary forces orthogonal? If a primary force is orthogonal to a secondary force, what is the physical implication?

The vector outer cross products of orthogonal forces are zero. The scalar inner dot products are infinitely large.