# Spin change of Fermions and quantum energy spectrum

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• claymine
This is just about the creation of particles.In summary, the conversation discusses the concept of boson and fermion excitations and the rules surrounding them in QM. It is mentioned that while boson excitations can happen one at a time, fermion excitations always occur in pairs due to the restriction of changing the total angular momentum of the system by a half-integer value. The conversation also touches on the topic of spin flips in fermions, which can occur individually without any restrictions.
claymine
Okay i was reading abrikosov's book and he said since in QM spin only changes by integer values boson excitiation happens one at a time and fermion ALWAYS appears or disappears in pairs. but isn't change from a spin up to spin down 1/2 to -1/2? or i had the wrong convention which |1/2| shouldve been the story?

Thank you

I guess, what's meant is that in the creation of particles a spin-1/2 fermion can only be created in pairs, because otherwise you'd change the total angular momentum of the system by a half-integer value, which however is impossible due to the angular-momentum algebra (i.e., the su(2)-Lie algebra).

Of course there's nothing that prevents the spin flip from 1/2 to -1/2 of a single spin-1/2 fermion.

claymine

## 1. What is spin change in fermions?

Spin change in fermions refers to the change in the intrinsic angular momentum (spin) of a particle that belongs to the class of fermions, which includes protons, neutrons, and electrons. This change can occur due to interactions with other particles or external fields.

## 2. How is spin change related to the quantum energy spectrum?

The spin of a particle is one of the quantum numbers that determines its energy level in the quantum energy spectrum. The energy levels of fermions are quantized, meaning they can only have certain discrete values, and the spin of the particle is one of the factors that contributes to this quantization.

## 3. What is the significance of spin change in fermions?

The spin of fermions plays a crucial role in determining their properties and behavior. Spin change can affect the stability of particles, their interactions with other particles, and even their role in fundamental physical processes such as magnetism.

## 4. Is spin change of fermions observable?

Spin change itself is not directly observable, but its effects can be observed through various experimental techniques. For example, changes in the spin of electrons can be detected through their magnetic properties, while changes in the spin of nucleons (protons and neutrons) can be observed through nuclear reactions.

## 5. How is spin change of fermions studied in quantum mechanics?

In quantum mechanics, the spin of fermions is described by the spin quantum number, which is one of the quantum numbers used to characterize the state of a particle. The behavior of spin change in fermions is studied through mathematical models and experimental observations, which have led to a deeper understanding of the fundamental nature of matter.

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