Jeffrey Barrett

Wittgenstein used the notion of a language game to illustrate how language is interwoven with action. Here we consider how successful linguistic discourse of the sort he described might emerge in the context of a self-assembling evolutionary game. More specifically, we consider how discourse and coordinated action might self-assemble in the context of two generalized signaling games. The first game shows how prospective language users might learn to initiate meaningful discourse. The second shows how more subtle varieties of discourse might co-emerge with a meaningful language.

Everett (1957a, b, 1973) relative-state formulation of quantum mechanics has often been taken to involve a metaphysical commitment to the existence of many splitting worlds each containing physical copies of observers and the objects they observe. While there was earlier talk of splitting worlds in connection with Everett, this is largely due to DeWitt’s (Phys Today 23:30–35, 1970) popular presentation of the theory. While the thought of splitting worlds or parallel universes has captured the popular imagination, Everett himself favored the language of elements, branches, or relative states in describing his theory. The result is that there is no mention of splitting worlds or parallel universes in any of Everett’s published work. Everett, however, did write of splitting observers and was willing to adopt the language of many worlds in conversation with people who were themselves using such language. While there is evidence that Everett was not entirely comfortable with talk of many worlds, it does not seem to have mattered much to him what language one used to describe pure wave mechanics. This was in part a result of Everett’s empirical understanding of the cognitive status of his theory.

The present paper shows how one might model Everettian quantum mechanics using hyperfinitely many worlds. A hyperfinite model allows one to consider idealized measurements of observables with continuous-valued spectra where different outcomes are associated with possibly infinitesimal probabilities. One can also prove hyperfinite formulations of Everett’s limiting relative-frequency and randomness properties, theorems he considered central to his formulation of quantum mechanics. Finally, this model provides an intuitive framework in which to consider no-collapse formulations of quantum mechanics more generally.

Recent experimental evidence suggests that human subjects use a win–stay/lose–shift with inertia learning dynamics (WSLSwI) to establish signalling conventions in the context of Lewis signalling games. Here we consider the virtues and vices of this low-rationality dynamics. Most saliently, WSLSwI is much faster than simple reinforcement learning in establishing conventions. It is also more reliable in producing optimal signalling systems. And it exhibits a high degree of the stability characteristic of a reinforcement dynamics. We consider how increasing inertia may increase speed in finding optimal conventions under this dynamics, the virtues of cognitive diversity, and how the dynamics meshes with high-order rationality. In brief, WSLSwI is extremely well suited to establishing conventions. That human subjects use it for this purpose is a remarkable adaptation.

Empirical inquiry involves the coevolution of predictive theory and descriptive language. Here we consider how one might model this coevolution using the tools of evolutionary game theory. We will see how subsequently evolved languages might exhibit semantic drift, invention, and discard. These evolutionary models also illustrate how subsequently evolved languages might be incommensurable yet nevertheless provide faithful descriptions of nature. Finally, we will consider how a model for the coevolution of predictive theory and descriptive language accounts for endogenous epistemic norms.

Here we use generalized signaling games to model how one’s beliefs might coevolve with the language one uses to characterize those beliefs. We will start by considering how one might individuate pragmatic notions of truth and how such notions might coevolve with a descriptive language. We will then consider how agents might evolve a language that allows them to characterize their beliefs and degrees of belief. Finally, we will consider evolutionary conditions under which a principle of indifference that assigns equal prior probability to each possibility that one can describe in one’s evolved language might in fact be successful.

This article considers how a generalized signalling game may self-assemble as the saliences of the agents evolve by reinforcement on those sources of information that in fact lead to successful action. On the present account, generalized signalling games self-assemble even as the agents co-evolve meaningful representations and successful dispositions for using those representations. We will see how reinforcement on successful information sources also provides a mechanism whereby simpler games might compose to form more complex games. Along the way, I consider how an old game might be appropriated to a new context by reinforcement on successful associations between old and new saliences.

We consider how human subjects establish signaling conventions in the context of Lewis-Skyrms signaling games. These experiments involve games where there are precisely the right number of signal types to represent the states of nature, games where there are more signal types than states, and games where there are fewer signal types than states. The aim is to determine the conditions under which subjects are able to establish signaling conventions in such games and to identify a learning dynamics that approximates how they succeed when they do. Our results suggest that human agents tend to use a win-stay/lose-shift with inertia dynamics to establish conventions in such games. We briefly consider the virtues and vices of this low-rationality dynamics.

We are concerned here with how structural properties of language may come to reflect features of the world in which it evolves. As a concrete example, we will consider how a simple term language might evolve to support the principle of indifference over state descriptions in that language. The point is not that one is justified in applying the principle of indifference to state descriptions in natural language. Instead, it is that one should expect a language that has evolved in the context of facilitating successful action to reflect probabilistic features of the world in which it evolved.

We consider how an epistemic network might self-assemble from the ritualization of the individual decisions of simple heterogeneous agents. In such evolved social networks, inquirers may be significantly more successful than they could be investigating nature on their own. The evolved network may also dramatically lower the epistemic risk faced by even the most talented inquirers. We consider networks that self-assemble in the context of both perfect and imperfect communication and compare the behaviour of inquirers in each. This provides a step in bringing together two new and developing research programs, the theory of self-assembling games and the theory of network epistemology.

We consider how cue-reading, sensory-manipulation, and signaling games may initially evolve from ritualized decisions and how more complex games may evolve from simpler games by polymerization, template transfer, and modular composition. Modular composition is a process that combines simpler games into more complex games. Template transfer, a process by which a game is appropriated to a context other than the one in which it initially evolved, is one mechanism for modular composition. And polymerization is a particularly salient example of modular composition where simpler games evolve to form more complex chains. We also consider how the evolution of new capacities by modular composition may be more efficient than evolving those capacities from basic decisions.

Everett wanted a formulation of quantum mechanics that (i) took the linear dynamics to be a complete and accurate description of the time-evolution of all physical systems and (ii) logically entailed the same subjective appearances predicted by the standard formulation of quantum mechanics. While most everyone would agree with this description of Everett’s project, there is little agreement on exactly how his relative-state formulation was supposed to work. In this paper, I consider two very different readings of Everett: the bare reading and the splitting-worlds reading. What distinguishes these is their interpretation of the wave function and how one accounts for the experiences of observers. The difficulty in interpreting Everett, however, is illustrated by the fact that neither reading is entirely compatible with his own description of his project.

There is good reason to suppose that our best physical theories, quantum mechanics and special relativity, are false if taken together and literally. If they are in fact false, then how should they count as providing knowledge of the physical world? One might imagine that, while strictly false, our best physical theories are nevertheless in some sense probably approximately true. This paper presents a notion of local probable approximate truth in terms of descriptive nesting relations between current and subsequent theories. This notion helps explain how false physical theories might nevertheless provide physical knowledge of a variety that is particularly salient to diachronic empirical inquiry.

Jeffrey Barrett presents the most comprehensive study yet of a problem that has puzzled physicists and philosophers since the 1930s. The standard theory of quantum mechanics is in one sense the most successful physical theory ever, predicting the behaviour of the basic constituents of all physical things; no other theory has ever made such accurate empirical predictions. However, if one tries to understand the theory as providing a complete and accurate framework for the description of the behaviour of all physical interactions, it becomes evident that the theory is ambiguous, or even logically inconsistent. The most notable attempt to formulate the theory so as to deal with this problem, the quantum measurement problem, was initiated by Hugh Everett III in the 1950s. Barrett gives a careful and challenging examination and evaluation of the work of Everett and those who have followed him. His informal approach, minimizing technicality, will make the book accessible and illuminating for philosophers and physicists alike. Anyone interested in the interpretation of quantum mechanics should read it.

Because of the measurement problem, the standard theory of quantum mechanics is at best incomplete and at worst logically inconsistent. Everett suggested that the measurement problem could be resolved by taking the linear dynamics to be a complete and accurate description of the time-evolution of every physical system. The purpose of this dissertation is to see what happens when one takes Everett's proposal seriously. This dissertation includes a discussion of the standard theory of quantum mechanics and its origins, the measurement problem, Everett's relative-state formulation, the many-worlds interpretation, Albert's bare theory and its suggestive properties, and Albert and Loewer's single-mind and many-minds theories. I will show how one might construct a theory that exploits the bare theory's suggestive properties without encountering its empirical problems.

This paper is concerned with the possibility and nature of relativistic hidden-variable formulations of quantum mechanics. Both ad hoc teleological constructions of spacetime maps and frame-dependent constructions of spacetime maps are considered. While frame-dependent constructions are clearly preferable, they provide neither mechanical nor causal explanations for local quantum events. Rather, the hiddenvariable dynamics used in such constructions is just a rule that helps to characterize the set of all possible spacetime maps. But while having neither mechanical nor causal explanations of the values of quantummechanical measurement records is a significant cost, it may simply prove too much to ask for such explanations in relativistic quantum mechanics.

C. S. Peirce's psychological analysis of belief, doubt, and inquiry provides insights into the nature of scientific knowledge. These in turn can be used to construct an account of scientific knowledge where the notions of belief, truth, rational justification, and inquiry are determined by the relationships that must hold between these notions. I will describe this account of scientific knowledge and some of the problems it faces. I will also describe the close relationship between pragmatic and naturalized accounts of scientific knowledge.

Because of the conceptual difficulties it faces, quantum mechanics provides a salient example of how alternative metaphysical commitments may clarify our understanding of a physical theory and the explanations it provides. Here we will consider how postulating alternative quantum worlds in the context of Hugh Everett III’s pure wave mechanics may serve to explain determinate measurement records and the standard quantum statistics. We will focus on the properties of such worlds, then briefly consider other metaphysical options available for interpreting pure wave mechanics. These reflections will serve to illustrate both the nature and the limits of naturalized metaphysics.

A resolution of the quantum measurement problem would require one to explain how it is that we end up with determinate records at the end of our measurements. Metaphysical commitments typically do real work in such an explanation. Indeed, one should not be satisfied with one's metaphysical commitments unless one can provide some account of determinate measurement records. I will explain some of the problems in getting determinate records in relativistic quantum field theory and pay particular attention to the relationship between the measurement problem and a generalized version of Malament's theorem.