Valentini [arXiv:0811.0810] has recently defended the de Broglie-Bohm pilot-wave version of quantum theory from the claim that it is essentially Everett theory encumbered with the redundant postulation of point particles. In this note, Valentini's central arguments are questioned.
Abstract The reality of the patterns in the wave-function representing different worlds is not like that of locality and the uncertainty relations, which hold only for the equilibrium distribution. Nor, in the light of the Deutsch–Wallace representation theorem for the Born rule, is the appeal to non-equilibrium probability distributions as the ground for the distinction between pilot-wave theory and many-worlds theory well-motivated. Finally, Valentini's counter-claim, that the latter is motivated by eigenvalue realism, ignores the need to give an account of macroscopic superpositions.
We reply to claims (by Deutsch, Zeh, Brown and Wallace) that the pilot-wave theory of de Broglie and Bohm is really a many-worlds theory with a superfluous configuration appended to one of the worlds. Assuming that pilot-wave theory does contain an ontological pilot wave (a complex-valued field in configuration space), we show that such claims arise from not interpreting pilot-wave theory on its own terms. Specifically, the theory has its own ('subquantum') theory of measurement, and in general describes a 'nonequilibrium' state that violates the Born rule. Furthermore, in realistic models of the classical limit, one does not obtain localised pieces of an ontological pilot wave following alternative macroscopic trajectories: from a de Broglie-Bohm viewpoint, alternative trajectories are merely mathematical and not ontological. Thus, from the perspective of pilot-wave theory itself, many worlds are an illusion. It is further argued that, even leaving pilot-wave theory aside, the theory of many worlds is rooted in the intrinsically unlikely assumption that quantum measurements should be modelled on classical measurements, and is therefore unlikely to be true.
Abstract This chapter replies to claims that the pilot-wave theory of de Broglie and Bohm is really a many-worlds theory with a superfluous configuration appended to one of the worlds. Assuming that pilot-wave theory does contain an ontological pilot wave (a complex-valued field in configuration space), the chapter shows that such claims arise from not interpreting pilot-wave theory on its own terms. Specifically, the theory has its own (‘subquantum’) theory of measurement, and in general describes a ‘non-equilibrium’ state that violates the Born rule. Furthermore, in realistic models of the classical limit, one does not obtain localised pieces of an ontological pilot wave following alternative macroscopic trajectories: from a de Broglie–Bohm viewpoint, alternative trajectories are merely mathematical and not ontological. Thus, from the perspective of pilot-wave theory itself, many worlds is an illusion. It is further argued that, even leaving pilot-wave theory aside, the theory of many worlds is rooted in the intrinsically unlikely assumption that quantum measurements should be modelled on classical measurements, and is therefore unlikely to be true.
In this thesis we study the de Broglie-Bohm pilot-wave interpretation of quantum theory. We consider the domain of non-relativistic quantum theory, relativistic quantum theory and quantum field theory, and in each domain we consider the possibility of formulating a pilot-wave interpretation. For non-relativistic quantum theory a pilot-wave interpretation in terms of particle beables can readily be formulated. But this interpretation can in general not straightforwardly be generalized to relativistic wave equations. The problems which prevent us from devising a pilot-wave interpretation for relativistic wave equations also plague the standard quantum mechanical interpretation, where these problems led to the conception of quantum field theory. Therefore most of our attention is focussed on the construction of a pilot-wave interpretation for quantum field theory. We thereby favour the field beable approach, developed amongst others by Bohm, Hiley, Holland, Kaloyerou and Valentini. Although the field beable approach can be successfully applied to bosonic quantum field theory, it seems not straightforward to do so for fermionic quantum field theory.
Abstract This introductory chapter reviews the main steps in the history of the pilot-wave theory from its inception to the present day, as well as the major philosophical discussions revolving around this theoretical framework. The first part of this essay begins with a discussion of de Broglie’ key ideas leading to the first formulation of the pilot-wave theory in 1924, followed by a detailed analysis of David Bohm’s rediscovery of this framework in 1952 along with the generalizations of his causal interpretation to the Pauli and Dirac theories. Moreover, the second renaissance of the pilot-wave theory is considered. Here I focus on the works of Hiley, Dewdney, Philippidis, Holland and other collaborators of Bohm who provided decisive contributions to the causal interpretation between the late 1970s and the 1980s. This part is concluded taking into account recent developments of the pilot-wave perspective, with particular attention to the approaches of Dürr, Goldstein, Zanghì and Valentini. The second part of the essay discusses in detail some of the main metaphysical debates concerning the ontology of this interpretative framework, as for instance the status of the wave function, the various notions of “particle” employed by various authors, as well as the meaning of quantum operators and contextuality in the de Broglie-Bohm theory. In addition, also the notion of primitive ontology is briefly introduced. Finally, the third part of this introduction illustrates the book chapters, guiding the reader into the various contents of the volume.