 On the standard collapse formulation of quantum mechanics, somehow during the measurement interaction the state would collapse to either the first term of this expression (with probability equal to \(a\) squared) or to the second term of this expression (with probability equal to \(b\) squared). In the former case, \(J\) ends up with the determinate measurement record “spin up”, and in the later case \(J\) ends up with the determinate measurement record “spin down”. But on Everett’s proposal no collapse occurs. Rather, the post-measurement state is simply this entangled superposition of \(J\) recording the result “spin up” and \(S\) being \(x\)-spin up and \(J\) recording “spin down” and \(S\) being \(x\)-spin down. Call this state \(\boldsymbol{E}\). 