Published online by Cambridge University Press: 28 February 2022
In a recent article Itamar Pitowsky (1991) has analyzed some measurement possibilities presented by an entangled state of three spin ½ particles. From that analysis he has concluded that the valid predictions of results of possible future measurements, made by observers who actually carry out mutually space-like separated measurements, can be incompatible with one another in the sense that their conjunction contradicts the quantum theory. From this result Pitowsky infers the inherently observer specific, or relative, character of quantum predictions as opposed to the results of actual observations or measurements, which, he claims, are covariant; i.e. (I take it) compatibly translatable from one observer to another.
I wish to thank Jeremy Butterfield, Robert Cifton and Constantin Pagonis for extensive discussion which led to considerable clarification of an earlier draft of this paper.