On Squires' many-views interpretation of quantum theory

Bradley Monton

Dualistic interpretations attempt to solve the measurement problem of quantum mechanics by postulating the existence of non-physical minds, and by giving a suitable dynamical equation for how these minds evolve. I consider the relative merits of three extant dualistic interpretations (Albert and Loewer’s single-mind and many-minds interpretations, and Squires’ interpretation), and I defend Squires’ interpretation as preferable to the Albert/Loewer interpretations. I also argue that, for all three of these interpretations, the minds evolve independently of the physical universe, and hence render the physical universe otiose; the interpretations are better viewed as supporting not dualism, but mental monism.

Alfred Lands

Alfred Landé

Cini

Where is the problem? by J.M. Levy-Leblond Experiment and quantum measurement theory by A. Zeilinger A consistent interpretation of quantum mechanics. The measurement process in the individual interpretation of quantum mechanics by H. Primas Principle of stationarity in the action functional and the theory of measurement by R. Fukuda Quantum (statistical) mechanics, measurement and information by R. Balian State vector collapse as a classical statistical effect of measurement by M. Cini and M. Serva Consecutive quantum measurements by A. Peres No-collapse versions of quantum mechanics by Y. Ben-Dov An attempt to understand the many-worlds interpretation of quantum theory by E.J. Squires Uncertainty and measurement by P.T. Landsberg Author Index

Ralph Schiller

David Papineau

An increasingly popular interpretation of quantum mechanics holds that in any genuinely chancy situation, all possible outcomes occur.1 For example, if the spin of a typical electron is measured in a given direction, then both 'up' and 'down' results will be registered. (True, 'up' and 'down' won't occur within the same 'branch of reality', for that would be inconsistent. Rather, the idea is that reality comes to contain two elements, with 'up' registered relative to one, and 'down' registered relative to the other.) This kind of 'many worlds' or 'many minds' interpretation of quantum mechanics has advantages and disadvantages. The main advantage is that it avoids any 'collapse of the wave function' and so avoids the measurement problem, mysterious non-local interactions, and the like. The most obvious disadvantage is that its burgeoning world of duplicate histories seems repugnant to common sense. Some commentators think that there is another disadvantage. They argue that this interpretation undermines itself by destroying any notion of objective probability. Quantum mechanics is, if anything, a theory which specifies the objective probabilities of certain results. But in what sense is there an objective probability for 'up' and 'down' in a spin measurement, if both results always happen? (Albert [1]; Albert and Loewer [3], [4]; Healey [5]; Squires [9]; Stein [8].) This looks like a good objection. But I shall show in this note that it is not. The proposed interpretation does leave objective probability as a rather mysterious notion. But it is no more mysterious on the proposed interpretation than on the conventional view of the world. This is not the place to go into details about the 'many minds'2 interpretation of quantum mechanics, but one point may help readers. If both the 'up' and 'down' results occur, why do we experience only one?