Published online by Cambridge University Press: 01 April 2022
If we take the state function of quantum mechanics to describe belief states, arguments by Stairs and Friedman-Putnam show that the projection postulate may be justified as a kind of minimal change. But if the state function takes on a physical interpretation, it provides no more than what I call a fortuitous approximation of physical measurement processes, that is, an unsystematic form of approximation which should not be taken to correspond to some one univocal “measurement process” in nature. This fact suggests that the projection postulate does not provide a proper locus for interpretive investigation. Readers will also find section 3's analysis of fortuitous approximations of independent interest and presented without the perils of quantum mechanics.
Much of this research was supported by NSF grant #SES-8108175. My thinking has been guided at a great many points by the work of Geoffrey Hellman, Michael Friedman, Jeffrey Bub, Allen Stairs, and Arthur Fine. Two anonymous referees insisted on more careful treatment at a number of crucial junctures, thereby greatly strengthening the paper.