Frankly, I just reject SPIN, in the sense that it says you get a single result when you measure. Measurement, as amply demonstrated by quantum eraser experiments, is simply entangling two subsystems and then tracing over one of them. For example, given state A = x|0> + y|1> and state B = |0>, we apply the unitary operator ctrl-NOT = |00><00| + |01><01| + |10><11| + |11><10| to both to get ctrl-NOT|AB> = x|00> + y|11>. If A is a photon, B is my brain, and ctrl-NOT is a polarizing beam splitter followed by a complicated reaction involving my retina and a lot of neurons, then it's very hard to disentangle the two systems afterward, and the universe is left in a superposition of |photon-goes-into-my-eye, I-remember-seeing-the-photon> and |photon-goes-the-other-way, I-don't-remember-seeing-the-photon>. All conscious experience after that interaction involves one memory or the other. The real mystery in measurement is why we don't perceive superpositions: why is |00>, |11> the preferred basis instead of |00>+|11>, |00>-|11>? There are papers invoking "the master equation" in relation to preferred bases and decoherence, but I don't understand them yet. -- Mike Stay - metaweta@gmail.com http://math.ucr.edu/~mike http://reperiendi.wordpress.com