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.
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.
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.
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.
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.
QM∞ includes quantum field theory and the thermodynamic limit of quantum statistical mechanics — theories which, unlike the 'ordinary' quantum theories typically discussed by philosophers, concern infinite systems. The mathematical framework appropriate for the presentation of a theory of ordinary quantum mechanics is essentially unique. For theories of QM∞, this is not so. This prompts interpretive questions—for instance, about what makes a quantum theory the quantum theory it is — this work aims to chronicle. Having introduced a formal apparatus (operator algebra theory) suited to pursue these questions, the book articulates a variety of accounts of the content of quantum theories, accounts responsive to QM∞'s characteristic non-uniqueness. To evaluate these accounts, the book examines QM∞ settings (e.g. spontaneous symmetry breaking, cosmological particle creation, superconductivity) in which that characteristic non-uniqueness seems to matter, with a view toward determining which accounts sustain the uses to which the non-uniqueness is put. This approach not only brings work on the foundations of quantum theories in contact with the foundational investigation of other sorts of physical theories (e.g., thermodynamics, statistical mechanics, solid state physics, general relativity, and cosmology), it also brings the philosophy of physics in contact with other sorts of philosophy of science (e.g., accounts of explanation, reduction, and explanationist defenses of scientific realism). The book concludes that received notions of physical content and physical modality must be revised if they are to apply usefully to particular physical theories.
One of life’s most fundamental revelations is change. Presenting the fascinating view that pattern is the manifestation of change, this unique book explores the science, mathematics, and philosophy of change and the ways in which they have come to inform our understanding of the world. Through discussions on chance and determinism, symmetry and invariance, information and entropy, quantum theory and paradox, the authors trace the history of science and bridge the gaps between mathematical, physical, and philosophical perspectives. Change as a foundational concept is deeply rooted in ancient Chinese thought, and this perspective is integrated into the narrative throughout, providing philosophical counterpoints to customary Western thought. Ultimately, this is a book about ideas. Intended for a wide audience, not so much as a book of answers, but rather an introduction to new ways of viewing the world.