From: Zardoz ® 03/11/2001 8:29:44 Subject: re: QUANTUM MECHANICS FAQ post id: 482678 Exactly what does the word spin mean in quantum terms? It is nothing like a ball spinning? http://www.colorado.edu/physics/2000/elements_as_atoms/spin.html SPIN From: Terry Frankcombe (Avatar) Briefly, spin is a property that particles have. "Quantum mechanically", as you put it , spin is no different to charge in nature. It is simply a property that a particle has, that causes it to interact with its environment in certain ways. In the case of spin, it causes particles to interact with magnetic fields in certain ways. The nature of that interaction looks the same as if the particle were two seperate particles rotating around a central point. That is, it looks like angular momentum. This is alluded to by the term "spin" or more correctly "spin angular momentum", though no-one suggests (at least not these days!) that the electron is really a little ball spinning about. As for why I say that introducing a factor of 2 would be inconsistent, you need to understand a bit of QM theory. In a nutshell the half integer values come out as eigenvalues of the spin operator. Just because the eigenvalues of some of the other QM operators come out as integers is no reason to go messing with the spin operator! From: James R (Avatar) The 1/2 integral and integral thing in spin quantum numbers is a historical accident more than anything else. It is a result of the magnitude of Planck's constant. It would be quite possible to measure angular momentum in different scaled units and define integral odd and even spin instead of half integral and integral spin. In fact, I think it could simplify a lot of things if it was done that way. I had that idea a few years ago, but haven't got around to working on the details yet. I'm sure there's a paper or two in it.