I am currently confused... I read that we don't know yet where does the proton spin come from. But I wonder... 1) Doesn't the proton have effectively 3 quarks of spin 1/2 (I said effectively to leave out the quark-gluon sea within the proton)? In that case, 3 spin 1/2 particles can't be added up to spin 1/2? Where's the problem in that? I also learned they tried to calculate the spin of the interactive gluons within the proton, and it was not enough to give its spin. Now the idea that is being proposed (as I know it'll be tested in CERN LCH-COMPASS experiment) is that the needed spin comes from the angular momentum of the rotating quarks.... Isn't that a weird idea? I mean there is a reason (spacetime) we make the distinguishing between angular momentum and spin...I think that the one can in fact be chosen zero in the rest frame, while the other still exists.... In that case, how could angular momentum produce spin?