Jeffrey Barrett

In order for Bayesian inquiry to count as objective, one might argue that it must lead to a consensus among those who use it and share evidence, but presumably this is not enough. It has been proposed that one should also require that the consensus be reached from very different initial opinions by conditioning only on basic experimental evidence, evidence free from subjective, social, or psychological influence. I will argue here, however, that this notion of objectivity in Bayesian inquiry is too narrow.

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.

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.

Insofar as empirical inquiry involves the coevolution of descriptive language and theoretical commitments, a satisfactory model of empirical knowledge should describe the coordinated evolution of both language and theory. But since we do not know what conceptual resources we might need to express our future theories or to provide our best future faithful descriptions of the world, we do not now know even what the space of future descriptive options might be. One strategy for addressing this shifting-resource problem is to track the predictive and linguistic dispositions of inquirers rather than to track their theories and conceptual resources directly. Sender-predictor games, a variant of Skyrms–Lewis sender-receiver games, provide very simple models for the coordinated coevolution of predictive and linguistic dispositions. Such models explain how it is possible for predictive and descriptive dispositions of inquirers to coevolve, term-wise incommensurable, but nevertheless descriptively faithful languages, to sequentially evolve, and a sort of underdetermination to occur where inquirers might satisfy their descriptive and predictive aims by revising their linguistic dispositions, their theoretical dispositions, or both. Such models also provide an elementary characterization of what it might mean for descriptions of the world to be faithful and hence for empirical inquiry to be successful. In doing so they provide a relatively weak, but perfectly clear, endogenous account of epistemic norms.

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.

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.

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.

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.

A situated observer is an observer as modeled within the world characterized by one’s physical theory. A physical theory arguably only makes empirical predictions if it makes predictions for the records of a situated observer. In this spirit, one has a satisfactory solution to the measurement problem only if one has a formulation of quantum mechanics that makes the right empirical predictions for the records of a situated observer. Bohmian mechanics addresses the measurement problem by explaining what measurement records are, how a situated observer might produce them, and why a situated observer should expect the standard quantum predictions. The notion of an effective wave function is crucial in understanding how the theory makes empirical predictions.

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.

Accuracy in the philosophical theory of rationality demands that we recognize particular beliefs as arising within the context of larger units, the cultural or conceptual schemes, patterns, or practices, involvement in which itself provides standards and grounds for their rational evaluation. At the same time, though, a satisfactory account of rationality cannot hold the standards, values, or commitments of one particular culture, practice, or conceptual scheme, even one’s own, immune from rational criticism. In order to accurately and responsibly picture the shape of our commitments and the dynamics of their revision over time, in other words, the theory of rationality must reconcile the immanence of reason to particular cultural and conceptual units with its transcendence of them. This raises a deep and far-ranging problem of perspective. In his perspicuous presentation of it, Hilary Putnam put the problem this way: There are two points that must be balanced, both points that have been made by philosophers of many different kinds: (1) talk of what is ‘right’ and ‘wrong’ in any area only makes sense against the background of an inherited tradition; but (2) traditions themselves can be criticized … On the one hand, there is no notion of reasonableness at all without cultures, practices, procedures; on the other hand, the cultures, practices, procedures we inherit are not an algorithm to be slavishly followed. As Mill said, commenting on his own inductive logic, there is no rule book which will not lead to terrible results ‘if supposed to be conjoined with universal idiocy.’ Reason is, in this sense, both immanent (not to be found outside of concrete language games and institutions) and transcendent (a regulative idea that we use to criticize the conduct of all activities and institutions). (p. 431). As Putnam argues, it is difficult to find a standpoint of theory from which the contrasting claims of immanence and transcendence can be reconciled..

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.