Ben and Eliezer: Any reply puts me in great danger of violating the spirit of Eliezer’s rule that non-realists hold their fire! (I say the spirit and not the letter, since I’m not actually a non-realist myself, just an equal-opportunity kibitzer.)
OK, quickly. Sure, an interesting question for subjectivists is how to deal with pure states, but an interesting question for realists is how to deal with mixed states! The issue is that you can’t just say a density matrix ρ represents a statistical ensemble over “true states of the world” and be done with it, since then you have to make a completely arbitrary, physically-unmotivated choice for whether those true states lie in the {0,1} basis, the {+,-} basis, etc. In an interpretations of QM seminar at Berkeley, we spent pretty much the entire semester arguing about this and nothing else! Yes, it got tiresome, and no, I wasn’t even suggesting that Eliezer bring in mixed states before people understood the fundamentals. I was just alluding to it as a key thing to get to eventually, that’s all.
Ben and Eliezer: Any reply puts me in great danger of violating the spirit of Eliezer’s rule that non-realists hold their fire! (I say the spirit and not the letter, since I’m not actually a non-realist myself, just an equal-opportunity kibitzer.)
OK, quickly. Sure, an interesting question for subjectivists is how to deal with pure states, but an interesting question for realists is how to deal with mixed states! The issue is that you can’t just say a density matrix ρ represents a statistical ensemble over “true states of the world” and be done with it, since then you have to make a completely arbitrary, physically-unmotivated choice for whether those true states lie in the {0,1} basis, the {+,-} basis, etc. In an interpretations of QM seminar at Berkeley, we spent pretty much the entire semester arguing about this and nothing else! Yes, it got tiresome, and no, I wasn’t even suggesting that Eliezer bring in mixed states before people understood the fundamentals. I was just alluding to it as a key thing to get to eventually, that’s all.