# When is the spin of an electron changing?

An electron can have a half spin up or down. The up spin can become a down spin to lose his weak charge. But when are electrons changing their spin?

• Do you want an awnser in the context of high-energy physics ? In condensed matter, electron spins can be flipped by interacting with magnetic impurities, as it is described in the Kondo model Feb 11 '16 at 13:11
• I'm not sure I understand your comment, but a spin up becomes a spin down and vice-versa. Feb 17 '16 at 8:13
• This question is either too simple or lacks details. The usual answer would be: the projection of the spin changes when there are interactions that change the spin (magnetic interactions, spin-orbit, exchange, high energy interactions...) Jun 27 at 10:16
• What do you believe a spin flip has to do with weak charge transfer? Jun 27 at 18:41

If initially you had the spin projection in a certin (eigen)state and then you apply a spin-dependent interaction, the spin wave function becomes a superposition of up and down eigenstates. Measurements will find the up-state with a probability $$P_{\text{up}}$$ and the down-state with the probability $$P_{\text{down}}=1-P_{\text{up}}$$, the mean value being between up and down.