Hi, I'm a little confused by the selection rules for atomic transitions. In pretty much any standard QM text, they derive the fact that an electron can't transition in an atom unless [itex]\Delta\ell=\pm1[/itex], i.e. unless the orbital angular momentum changes by one unit. Then the books go on to say that this can be interpreted as a consequence of the fact that the photon carries one unit of spin. This seems strange to me, since the Schrodinger equation doesn't predict spin, and as far as I can tell, spin is not even put in by hand in these calculations. How do the transition rules somehow predict that the angular momentum must change by one unit when the whole formalism doesn't incorporate spin angular momentum? It seems like someone working out this effect without any knowledge of spin would have to come up with some other interpretation. Thanks!