I was reading a physics article (related to the recent discovery of a particle that could be the Higgs boson) and the article was discussing electron spin and how spin can only be either up or down. I've always found this confusing – I know the directions 'up' and 'down' can be seen as arbitrary as they are relativistic in space. So, unless spin orients itself depending on the nearest gravity source, spin in this context must mean something different than in ordinary English.
I'm also confused by the claim in the article that you can have right or left spin as a result of a spin measurement:
Suppose you do measure an electron as spin up, and then try to measure the left-right spin. Common sense would tell you that that number would be zero, since you know that the electron is spin up, not left or right, but I warned you about common sense before. It turns out that a) half the time you'll measure the electron to be left and the other half you'll get right, and b) whether it's left or right is completely random.
I probably would understand what is meant by up/down spin if I knew how the spin of a particle is actually measured (I think i could handle a detailed and precise explanation, but a crude explanation will suffice if it gives insight as to 1. why spin is up or down and 2. why it can come off as left and right when measured).
Is up down just a name given by physicists to two different types of spins? Or does it have something to do with the actual directions?