Hi pf. From what I have read, when measured, a particles spin can only be in one direction. So either 100% spinning up or 100% spinning down and not in between. So, you can't have a spin that is in between (tilted) - it must be one or the other. But I recently learnt that when we place a particle in an external magnetic field it precesses like a spinning top. Surely this contradicts what I originally said because if it is precessing then surely it has a component of its spin which is not in the up-down plane? Could someone please clarify, thanks. Also, please could someone clarify if quantum mechanics is as spectacular and weird as it sounds. I have been briefly taught about things like entanglement, tunneling etc which sound fascinating but from reading on other forums some people suggest that there is nothing amazing about them and these quantum aspects are nothing more than mathematical correlations. For instance check this physics forum out (http://physics.stackexchange.com/questions/15282/quantum-entanglement-faster-than-speed-of-light) which argues that if quantum mechanics sounds great and strange then it has been explained wrong? Is that right?