Quantum theory involves a novel, indirect use of models to further the aims of fundamental science. It is revolutionary because of the way it improves our use and understanding of representations of the universe we could offer without it. The so-called semantic approach takes a scientific theory to supply a collection of models to be used to represent phenomena: but models of quantum theory are applied more indirectly to provide good advice on the significance and credibility of claims about physical things whose existence is assumable here. Inferentialism takes these claims to derive their content through inferential links to others. They are objective, as are the probabilities they are assigned, and some are objectively true.
Quantum theory involves a novel, indirect use of models to further the aims of fundamental science. It is revolutionary because of the way it improves our use and understanding of representations of the universe we could offer without it. The so-called semantic approach takes a scientific theory to supply a collection of models to be used to represent phenomena: but models of quantum theory are applied more indirectly to provide good advice on the significance and credibility of claims about physical things whose existence is assumable here. Inferentialism takes these claims to derive their content through inferential links to others. They are objective, as are the probabilities they are assigned, and some are objectively true.
Abstract Models in quantum theory have non-representational uses through which content accrues to claims involved in their application. A promising approach to understanding how is provided not by a referential semantics but by inferentialist pragmatism. In use, a quantum model is applied to physical systems, but not to represent them or their behavior. It is used to issue probabilistic claims about phenomena involving these systems by the Born Rule. Instances of the Born Rule, statements assigning quantum states, and claims about the values of magnitudes all derive their content through their inferential relations, to one another and to other claims.
This overview introduces the book’s aim of showing how quantum theory marks a radical break from previous scientific theorizing: We are warranted in accepting the fundamental status within contemporary physics of a theory that posits no new physical entities or magnitudes of its own. By contrast with existing interpretations that attempt to say how the world could possibly be the way quantum theory says it is, a pragmatist takes understanding quantum theory to be a matter of knowing how it is applied, and how the theory’s various elements function in these applications. So Part I of the book offers a simple, self-contained presentation of quantum theory, emphasizing applications; while Part II says why the quantum revolution matters for philosophy. Coming to terms with the quantum revolution involves adopting views of scientific theorizing, probability, causation, explanation, objectivity, meaning, and fundamentality that philosophers should have arrived at without its prompting.
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.
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 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.
The world science describes tends to have a very strange look. We can’t see atoms or force fields, nor are they imaginable within visualizable categories, so neither can we even imagine what the world must be like according to recent physical theories. That tension, between what science depicts as reality and how things appear to us, though it is more striking now, has been with us since modern science began. It can be addressed, and perhaps alleviated by inquiring into how science represents nature. In general, representation is selective, theselection is of what is relevant to the purpose at hand, and success may even require distortion. From this point of view, the constraint on science, that it must ‘save the phenomena’, takes on a new form. The question to be faced is howthe perspectival character of the appearances (that is, contents of measurement outcomes) can be related to the hidden structure that the sciences postulate. In the competing interpretations of quantum mechanics we can see how certaintraditional ideals and constraints are left behind. Specifically, Carlo Rovelli’s Relational Quantum Mechanics offers a probative example of the freedom of scientific representation.