This is clearly unsatisfactory. If quantum mechanics applies to everything, then it must apply to a physicist’s measurement apparatus, and to physicists themselves. On the other hand, if quantum mechanics does not apply to everything, then we need to know where to draw the boundary of its area of validity. Does it only apply to systems that are not too large? Does it apply if a measurement is made by some automatic apparatus, and no human reads the result?

Page 88: There seems to be a widespread impression that decoherence solves all obstacles to the class of interpretations of quantum mechanics which take seriously the dynamical assumptions of quantum mechanics as applied to everything, including measurement. My own opinion is that these interpretations, like the Copenhagen interpretation, remain unsatisfactory. ...

Statements of this sort about probabilities are predictions about how the state vectors evolve in time during measurements, so if measurement is really described by quantum mechanics, then we ought to be able to derive such formulas by applying the time-dependent Schrodinger equation to the case of repeated measurement. This not just a matter of intellectual tidiness, of wanting to reduce the postulates of physical theory to the minimum number needed. If the Born rule cannot be derived from the time-dependent Schrodinger equation, then something else is needed, something outside the scope of quantum mechanics, and the many worlds interpretation thus shares the inadequacies of the Copenhagen interpretation.16

Page 95: There is nothing absurd or inconsistent about the decoherent histories approach in particular, or about the general idea that the state vector serves only as a predictor of probabilities, not as a complete description of a physical system. Nevertheless, it would be disappointing if we had to give up the “realist” goal of finding complete descriptions of physical systems, and of using this description to derive the Born rule, rather than just assuming it. We can live with the fact that the state of a physical system is given by a vector in Hilbert space rather than by numerical values of the positions and momenta of all the particles in the system, but it is hard to live with no description of physical states at all, only an algorithm for calculating probabilities. My own conclusion (not universally shared) is that today there is no interpretation of quantum mechanics that does not have serious flaws, and that we ought to take seriously the possibility of finding some more satisfactory other theory, to which quantum mechanics is merely a good approximation.

Page 336: There is a troubling weirdness about quantum mechanics. Perhaps its weirdest feature is entanglement, the need to describe even systems that extend over macroscopic distances in ways that are inconsistent with classical ideas.

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