Abstract These essays in natural philosophy were all written from a pragmatist point of view developed over the past 15 years. They show what work pragmatism can do in science as well as philosophy. Many essays express a view of quantum theory developed using ideas of contemporary pragmatist philosophers: other essays apply these more widely to science and metaphysics. Quantum models are used not to represent physical systems but to offer good advice on how to represent them. The role of a quantum state is not to describe a system but to yield objective probabilities for alternative outcomes of events involving it. A situated agent could use these probabilities to decide what to do, and one can use them to explain phenomena. They are probabilities for physical events including measurements: pragmatist inferentialism helps one to say what these are, and when they have outcomes, thereby resolving the quantum measurement problem. One can use quantum theory locally to explain non-localized correlations, and why quantum field theory poses no ontological problem. Despite its unrivaled success, quantum theory offers no scientific image of the physical world on which a naturalist could construct a metaphysics. There are structural reasons why the rest of physical theory cannot be reduced to quantum theory. This pragmatist view of quantum theory is not instrumentalist. One essay explains why it should count as realist. Other essays defend pragmatist views of scientific laws and explanations as well as causation, truth, and objectivity.
Abstract These essays in natural philosophy were all written from a pragmatist point of view developed over the past 15 years. They show what work pragmatism can do in science as well as philosophy. Many essays express a view of quantum theory developed using ideas of contemporary pragmatist philosophers: other essays apply these more widely to science and metaphysics. Quantum models are used not to represent physical systems but to offer good advice on how to represent them. The role of a quantum state is not to describe a system but to yield objective probabilities for alternative outcomes of events involving it. A situated agent could use these probabilities to decide what to do, and one can use them to explain phenomena. They are probabilities for physical events including measurements: pragmatist inferentialism helps one to say what these are, and when they have outcomes, thereby resolving the quantum measurement problem. One can use quantum theory locally to explain non-localized correlations, and why quantum field theory poses no ontological problem. Despite its unrivaled success, quantum theory offers no scientific image of the physical world on which a naturalist could construct a metaphysics. There are structural reasons why the rest of physical theory cannot be reduced to quantum theory. This pragmatist view of quantum theory is not instrumentalist. One essay explains why it should count as realist. Other essays defend pragmatist views of scientific laws and explanations as well as causation, truth, and objectivity.
Abstract The introduction explains the origin and development of the views expressed in these essays. Fruitful interaction with physicists applying quantum theory provided the kernel for the author’s growing interest in contemporary pragmatism, initially as a source of ideas that could solve conceptual problems blocking an understanding of quantum theory. These pragmatist ideas were later applied to more general issues in the philosophy of science and metaphysics. After briefly sketching the pragmatist view of quantum theory defended in the essays, the introduction explains the implications—for the place of quantum theory in science, for metaphysics, and for the philosophy of science and specifically for the issue of scientific realism. New results in the foundations of physics prompted revision of the original view of the objectivity of quantum event outcomes. Some later essays show how elaborating a pragmatist view of the function of truth helped to acknowledge that the outcome of a quantum measurement is a relative fact that remains objective in the sense that matters for science: others take a neo-pragmatist view of causation, explanation, and laws in science. All these later essays illustrate the neo-pragmatist moral that by focusing on the intellectual function of a concept, one can satisfy a demand for understanding that might otherwise provoke a fruitless metaphysical quest.
Quantum theory launched a revolution in twentieth-century physics. But we have yet to appreciate the revolution’s significance for philosophy. Most studies of the conceptual foundations of quantum theory first try to interpret the theory—to say how the world could possibly be the way the theory says it is. But, though fundamental, quantum theory is enormously successful without describing the world in its own terms. When properly applied, models of quantum theory offer good advice on the significance and credibility of claims about the world expressed in other terms. This first of several philosophical lessons of the quantum revolution dissolves the quantum measurement problem. Pragmatist treatments of probability and causation show how quantum theory may be used to explain the non-localized correlations that have been thought to involve ‘spooky’ instantaneous action at a distance. Given environmental decoherence, a pragmatist inferentialist approach to content shows when talk of quantum probabilities is licensed, resolves any residual worries about whether a quantum measurement has a determinate outcome, and solves a dilemma about the ontology of a quantum field theory. This approach to meaning and reference also reveals the nature and limits of objective description in the light of quantum theory. While these pragmatist approaches to probability, causation, explanation, and content may be independently motivated by philosophical argument, their successful application here illustrates their practical importance in helping philosophers come to terms with the quantum revolution.
Applications of quantum mechanics have led to many successful predictions and explanations of puzzling phenomena, and we now apply quantum mechanics to gain, process, and communicate information in novel ways. We can understand quantum mechanics by understanding how we have applied it. We should not seek agreement on the nature of the world it represents, because this theory does not itself represent the physical world (though its applications do help us to represent it better). When applied to a quantum state, quantum mechanics yields probabiities for physical events: both state and probability are objective--not because they represent elements of phyiscal reality, but because each exerts norrmative authority over the beliefs of anyone who accepts quantum mechanics and applies it relative to a physical situation they may (but need not) occupy. These events may be described by statements that are meaningful in an appropriate environmental context, and quantum mechanics can help one to say when that is. Measurement creates an appropriate context, so here the Born rule indirectly yields probabilities of measurement outcomes. The quantum state of a system does not "collapse" on measurement: a new state must be assigned relative to a physical situation in which information about the outcome is accessible. Understood this way, there is no measurement problem, and violations of Bell inequalities does not demonstrate "spooky" non-local action. Quantum field theories have no physical ontology of their own: a quantum field is a mathematical object in a model whose application helps us to improve and extend our descriptions of the world in other terms. We cannot realise the scenario of Wigner's friend and its recent extensions: but the data that provide overwhelming evidence for quantum mechanics are objective in the same sense as the relative measurement outcomes described in those scenarios.
Applications of quantum mechanics have led to many successful predictions and explanations of puzzling phenomena, and we now apply quantum mechanics to gain, process, and communicate information in novel ways. We can understand quantum mechanics by understanding how we have applied it. We should not seek agreement on the nature of the world it represents, because this theory does not itself represent the physical world (though its applications do help us to represent it better). When applied to a quantum state, quantum mechanics yields probabilities for physical events: both state and probability are objective—not because they represent elements of physical reality, but because each exerts normative authority over the beliefs of anyone who accepts quantum mechanics and applies it relative to a physical situation they may (but need not) occupy. These events may be described by statements (about values of magnitudes) that are meaningful in an appropriate environmental context, and quantum mechanics can help one to say when that is. Measurement creates an appropriate context, so here the Born rule indirectly yields probabilities of measurement outcomes. The quantum state of a system does not “collapse” on measurement: a new state must be assigned relative to a physical situation in which information about the outcome is accessible. Understood this way, there is no measurement problem, and violation of Bell inequalities does not demonstrate “spooky” non-local action. Quantum field theories have no physical ontology of their own: a quantum field is a mathematical object in a model whose application helps to improve and extend our descriptions of the world in other terms. We cannot realise the scenario of Wigner’s friend and its recent extensions: but the data that provide overwhelming evidence for quantum mechanics are objective in the same sense as the relative measurement outcomes described in those scenarios.
Pragmatism is not a doctrine but an approach to conceptual problems. It regards concepts as intellectual tools we create and use for particular purposes, improving them in the light of experience. Neopragmatism provides an approach to conceptual problems wherever these arise as humans manifest their naturally explicable capacity to deploy concepts in thought as well as in language and in science as well as in philosophy. It rejects any attempt to solve these problems by appeal to something in unconceptualized reality for a concept to represent or a linguistic item to refer to or be made true by. Focusing on concepts’ symbolic expression, the neopragmatist asks what function is served by talk of various kinds―of freedom, morals, mathematics, causes, modality, probabilities, truth, reference, and representation. Starting with what we have learnt from science about our situation in the world, a neopragmatist asks how talking that way helps us to solve general problems we face as situated agents. She sees good answers as dissolving conceptual problems that stem from the assumption that the function of this talk is simply to represent reality. There are many ways in which neopragmatism helps one to dissolve problems we face in understanding quantum theory. It shows how we apply models of a theory non-representationally. It reveals the significance of talk of probability and laws of nature without indulging in metaphysics. It explains the non-representational roles of quantum states and how inference, not reference, makes claims about the results of measurements meaningful. It makes sense of relative truth as an extension of a deflationary approach to truth and uses this to dissolve some novel quantum paradoxes. Finally, it shows that quantum theory is objective, although it offers no “view from nowhere”.
I take a pragmatist perspective on quantum theory. This is not a view of the world described by quantum theory. In this view quantum theory itself does not describe the physical world, nor our observatons, experiences or opinions of it. Instead, the theory offers reliable advice on when to expect an event of one kind or another, and on how strongly to expect each possible outcome of that event. The actual outcome is a perspectival fact: a fact relative to a physical context of assessment. Measurement outcomes and quantum states are both perspectival. By noticing that each must be relativized to an appropriate physical context one can resolve the measurement problem and the problem of nonlocal action. But if the outcome of a quantum measurement is not an absolute fact, then why shoud the statistics of such outcomes give us any objective reason to accept quantum theory? One can describe extensions of the scenario of Wigner's friend in which a statement expressing the outcome of a quantum measurement would be true relative to one such context but not relative to another. However, physical conditions in our world prevent us from realizing such scenarios. Since the outcome of every actual quantum measurement is certified at what is essentially a single context of assessment, the outcome relative to that context is an objective fact in the only sense that matters for science. We should accept quantum theory because the statistics these outcomes display are just those it leads us to expect.