Evolution, Explanation, Ethics and Aesthetics, 2016
A closer look at some proposed Gedanken-experiments on BECs promises to shed light on several asp... more A closer look at some proposed Gedanken-experiments on BECs promises to shed light on several aspects of reduction and emergence in physics. These include the relations between classical descriptions and different quantum treatments of macroscopic systems, and the emergence of new properties and even new objects as a result of spontaneous symmetry breaking.
In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity.... more In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity. He calls this a new proof beyond Bell's theorem, arguing elsewhere that it closes the superdeterminism loophole in Bell's theorem. Such strong claims must be backed up by irrefutable arguments. My aim in this post to the workshop "Beyond Bell's theorem" is to refute Gao's "proof" and to show how quantum theory is compatible with relativity theory and so why Gao's "proof" does not take us beyond Bell's theorem
The status of laws of nature has been the locus of a lively debate in recent philosophy. Most par... more The status of laws of nature has been the locus of a lively debate in recent philosophy. Most participants have assumed laws play an important role in science and metaphysics while seeking their objective ground in the natural world, though some skeptics (Giere, van Fraassen, Cartwright) have questioned this assumption. So-called Humeans look to base laws on actual, particular facts such as those specified in David Lewis’s Humean mosaic. Their opponents (including Maudlin) argue that such a basis is neither necessary nor sufficient to support the independent existence of scientific laws. This essentially metaphysical debate has paid scant attention to the details of scientific practice. It has mostly focused on so-called fundamental laws, assumed to take a particular form (such as Maudlin’s FLOTEs). I propose a pragmatist alternative—not as another position in the debate but as an alternative to the debate itself. This pragmatist alternative offers a view that questions the represen...
Alternative views of quantum states are often expressed using the language of representation. For... more Alternative views of quantum states are often expressed using the language of representation. For example, after titling his 2014 review article "Is the quantum state real?", Leifer went on to say "The question of just what type of thing the quantum state, or wavefunction, represents, has been with us since the beginnings of quantum theory." It is important to distinguish three questions here: What is a quantum state? How may a quantum state be represented? What, if anything, does a quantum state represent? I shall defend answers to these questions against alternatives. In brief, a quantum state is an objective relational property of a physical system that describes neither its intrinsic physical properties nor anyone's epistemic state. Since its primary role is to assign Born probabilities to certain physical events involving the system, a quantum state may be represented in quantum theory by any mathematical object that can play this role. If it represents anything, a quantum state represents the objective probabilities it yields in this way. The paper continues like this. Section 2 surveys a variety of equivalent ways a quantum state may be represented in order to serve its function in quantum theory. Section 3 argues that a quantum state is not a physical entity, while section 4 argues that it is not a physical magnitude. In section 5 I argue that a system's quantum state does not represent its intrinsic physical properties or those of three-dimensional space. While few, if any, of these arguments are original or decisive, I take them to motivate consideration of an alternative that can help improve our understanding of quantum theory. So in section 6 I develop a relational account of a quantum state as what I call an extrinsically physical property of a system, brought to you by CORE View metadata, citation and similar papers at core.ac.uk
In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity.... more In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity. He calls this a new proof beyond Bell's theorem, arguing elsewhere that it closes the superdeterminism loophole in Bell's theorem. Such strong claims must be backed up by irrefutable arguments. My aim in this post to the workshop "Beyond Bell's theorem" is to refute Gao's "proof" and to show how quantum theory is compatible with relativity theory and so why Gao's "proof" does not take us beyond Bell's theorem
Realism comes in many varieties, in science and elsewhere. Van Fraassen’s influential formulation... more Realism comes in many varieties, in science and elsewhere. Van Fraassen’s influential formulation took scientific realism to include the view that science aims to give us, in its theories, a literally true story of what the world is like. So understood, a quantum realist takes quantum theory to aim at correctly representing the world: many would add that its success justifies believing this representation is more or less correct. But quantum realism has been understood both more narrowly and more broadly. A pragmatist considers use prior to representation and this has prompted some to dub pragmatist views anti-realist, including the view of quantum theory that the author has been developing recently. But whether a pragmatist view of quantum theory should be labeled anti-realist depends not only on its ingredients but also on how that label should be applied. Pragmatism offers a healthy diet of quantum realism.
J.S. Bell's work has convinced many that correlations in violation of CHSH inequalities show ... more J.S. Bell's work has convinced many that correlations in violation of CHSH inequalities show that the world itself is non-local, and that there is an apparently essential conflict between any sharp formulation of quantum theory and relativity. Against this consensus, this paper argues that there is no conflict between quantum theory and relativity. Quantum theory itself helps us explain such (otherwise) puzzling correlations in a way that contradicts neither Bell's intuitive locality principle nor his local causality condition. The argument depends on understanding quantum theory along pragmatist lines, and on a more general view of how that theory helps us explain. Quantum theory is compatible with Bell's intuitive locality principle and with his local causality condition not because it conforms to them, but because they are simply inapplicable to quantum theory, as so understood.
Three recent arguments seek to show that the universal applicability of unitary quantum theory is... more Three recent arguments seek to show that the universal applicability of unitary quantum theory is inconsistent with the assumption that a well-conducted measurement always has a definite physical outcome. In this paper I restate and analyze these arguments. The import of the first two is diminished by their dependence on assumptions about the outcomes of counterfactual measurements. But the third argument establishes its intended conclusion. Even if every well-conducted quantum measurement we ever make will have a definite physical outcome, this argument should make us reconsider the objectivity of that outcome.
Jerusalem Studies in Philosophy and History of Science
Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces... more Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces a serious measurement problem, whose solution requires a new theory or at least a novel interpretation of standard quantum mechanics. Itamar Pitowsky did not. Instead, he argued in a major paper (Pitowsky, Quantum mechanics as a theory of probability. In: Demopoulos W, Pitowsky I (eds) Physical theory and its interpretation. Springer, Dordrecht, pp 213-240, 2006) that quantum mechanics offers a new theory of probability. In these and other respects his views paralleled those of QBists (quantum Bayesians): but their views on the objectivity of measurement outcomes diverged radically. Indeed, Itamar's view of quantum probability depended on his subtle treatment of the objectivity of outcomes as events whose collective structure underlay this new theory of probability. I've always been puzzled by the thesis that quantum mechanics requires a new theory of probability, as distinct from new ways of calculating probabilities that play the same role as other probabilities in physics and daily life. In this paper I will try to articulate the sources of my puzzlement. I'd like to be able to think of this paper as a dialog between Itamar and me on the nature and application of quantum probabilities. Sadly, that cannot be: by taking his part in the dialog I will inevitably impose my own distant, clouded perspective on his profound and carefully crafted thoughts.
Quantum theory is a fundamental part of contemporary science. But some recent arguments have been... more Quantum theory is a fundamental part of contemporary science. But some recent arguments have been taken to show that if this theory is universally applicable then the outcome of a quantum measurement is not an objective fact. They motivate the more general reappraisal of the notions of fact and objectivity that I offer here. I argue that if quantum theory is universally applicable the facts about the physical world include a fact about each quantum measurement outcome. The physical facts may lack an ideal kind of objectivity but their more modest objectivity is all that science needs.
The quantum theory of decoherence plays an important role in a pragmatist interpretation of quant... more The quantum theory of decoherence plays an important role in a pragmatist interpretation of quantum theory. It governs the descriptive content of claims about values of physical magnitudes and offers advice on when to use quantum probabilities as a guide to their truth. The content of a claim is to be understood in terms of its role in inferences. This promises a better treatment of meaning than that offered by Bohr. Quantum theory models physical systems with no mention of measurement: it is decoherence, not measurement, that licenses application of Born’s probability rule. So quantum theory also offers advice on its own application. I show how this works in a simple model of decoherence, and then in applications to both laboratory experiments and natural systems. Applications to quantum field theory and the measurement problem will be discussed elsewhere. PACS 03.65.Yz, 03.65.Ta, 01.70.+w
A quantum state represents neither properties of a physical system nor anyone's knowledge of ... more A quantum state represents neither properties of a physical system nor anyone's knowledge of its properties. The important question is not what quantum states represent but how they are used as informational bridges. Knowing about some physical situations (its backing conditions), an agent may assign a quantum state to form expectations about other possible physical situations (its advice conditions). Quantum states are objective: only expectations based on correct state assignments are generally reliable. If a quantum state represents anything, it is the objective probabilistic relations between its backing conditions and its advice conditions. This paper offers an account of quantum states and their function as informational bridges, in quantum teleportation and elsewhere.
The British Journal for the Philosophy of Science, 2021
Measurement outcomes provide data for a physical theory. Unless they are objective they support n... more Measurement outcomes provide data for a physical theory. Unless they are objective they support no objective scientific knowledge. So the outcome of a quantum measurement must be an objective physical fact. But recent arguments purport to show that if quantum theory is universally applicable then there is no such fact. This calls for a reappraisal of the notions of fact and objectivity. If quantum theory is universally applicable the facts about the physical world include a fact about each quantum measurement outcome. These physical facts lack an ideal kind of objectivity but their more modest objectivity is all that science needs.
Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces... more Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces a serious measurement problem, whose solution requires a new theory or at least a novel interpretation of standard quantum mechanics. Itamar Pitowsky did not. Instead, he argued in a major paper (Pitowsky, Quantum mechanics as a theory of probability. In: Demopoulos W, Pitowsky I (eds) Physical theory and its interpretation. Springer, Dordrecht, pp 213–240, 2006) that quantum mechanics offers a new theory of probability. In these and other respects his views paralleled those of QBists (quantum Bayesians): but their views on the objectivity of measurement outcomes diverged radically. Indeed, Itamar’s view of quantum probability depended on his subtle treatment of the objectivity of outcomes as events whose collective structure underlay this new theory of probability. I’ve always been puzzled by the thesis that quantum mechanics requires a new theory of probability, as distinct from new w...
This paper argues that there is no conflict between quantum theory and relativity, and that quant... more This paper argues that there is no conflict between quantum theory and relativity, and that quantum theory itself helps us explain (otherwise) puzzling “non-local” correlations in a way that contradicts neither Bell’s intuitive locality principle nor his local causality condition. The argument depends on understanding quantum theory along pragmatist lines I have outlined elsewhere, and on a more general view of how that theory helps us explain. The key counterfactuals that hold in such cases manifest epistemic rather than causal connections between distant events. Quantum theory exploits the possibility of private informational links between an agent and events (s)he neither observes nor brings about, in ways that are strikingly independent of the spatiotemporal relations between them. This possibility has interesting implications for theories of chance in a relativistic world.
This paper aims to show how adoption of a pragmatist interpretation permits a satisfactory resolu... more This paper aims to show how adoption of a pragmatist interpretation permits a satisfactory resolution of the quantum measurement problem. The classic measurement problem dissolves once one recognizes that it is not the function of the quantum state to describe or represent the behavior of a quantum system. The residual problem of when, and to what, to apply the Born Rule may then be resolved by judicious appeal to decoherence. This can give sense to talk of measurements of photons and other particles even though quantum field theory does not describe particles.
Quantum entanglement is widely believed to be a feature of physical reality with undoubted (thoug... more Quantum entanglement is widely believed to be a feature of physical reality with undoubted (though debated) metaphysical implications. But Schrödinger introduced entanglement as a theoretical relation between representatives of the quantum states of two systems. Entanglement represents a physical relation only if quantum states are elements of physical reality. So arguments for metaphysical holism or nonseparability from entanglement rest on a questionable view of quantum theory. Assignment of entangled quantum states predicts experimentally con…rmed violation of Bell inequalities. Can one use these experimental results to argue directly for metaphysical conclusions? No. Quantum theory itself gives us our best explanation of violations of Bell inequalities, with no superluminal causal in ‡uences and no metaphysical holism or nonseparability-but only if quantum states are understood as objective and relational, though prescriptive rather than ontic. Correct quantum state assignments are backed by true physical magnitude claims: but backing is not grounding. Quantum theory supports no general metaphysical holism or nonseparability; though a claim about a compound physical system may be signi…cant and true while similar claims about its components are neither. Entanglement may well have have few, if any, …rst-order metaphysical implications. But the quantum theory of entanglement has much to teach the metaphysician about the roles of chance, causation, modality and explanation in the epistemic and practical concerns of a physically situated agent.
Durante su larga y extraordinariamente productiva carrera, Hilary Putnam flirteó de vez en cuando... more Durante su larga y extraordinariamente productiva carrera, Hilary Putnam flirteó de vez en cuando con el pragmatism. Pero su realismo científico aportó un punto fijo para sus intentos de interpretar la teoría cuántica. Recientemente he defendido que los tratamientos pragmatistas de la representación, la explicación y la probabilidad son claves para comprender cómo usamos la teoría cuántica con tanto éxito y, así, como debería ser interpretada. Para Putnam, el realismo científico es en sí mismo una hipótesis científica que explica el éxito de la ciencia. Si estoy en lo correcto, el éxito de la teoría cuántica debilita esta clase de realismo científico mientras que apoya un pragmatismo rival. El realismo científico permanece inmune a la refutación empírica si se ve no como una hipótesis científica sino como un ideal regulativo. Pero una pers- pectiva pragmatista de la teoría cuántica plantea un desafío a una cierta clase de realismo metafísico.
Evolution, Explanation, Ethics and Aesthetics, 2016
A closer look at some proposed Gedanken-experiments on BECs promises to shed light on several asp... more A closer look at some proposed Gedanken-experiments on BECs promises to shed light on several aspects of reduction and emergence in physics. These include the relations between classical descriptions and different quantum treatments of macroscopic systems, and the emergence of new properties and even new objects as a result of spontaneous symmetry breaking.
In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity.... more In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity. He calls this a new proof beyond Bell's theorem, arguing elsewhere that it closes the superdeterminism loophole in Bell's theorem. Such strong claims must be backed up by irrefutable arguments. My aim in this post to the workshop "Beyond Bell's theorem" is to refute Gao's "proof" and to show how quantum theory is compatible with relativity theory and so why Gao's "proof" does not take us beyond Bell's theorem
The status of laws of nature has been the locus of a lively debate in recent philosophy. Most par... more The status of laws of nature has been the locus of a lively debate in recent philosophy. Most participants have assumed laws play an important role in science and metaphysics while seeking their objective ground in the natural world, though some skeptics (Giere, van Fraassen, Cartwright) have questioned this assumption. So-called Humeans look to base laws on actual, particular facts such as those specified in David Lewis’s Humean mosaic. Their opponents (including Maudlin) argue that such a basis is neither necessary nor sufficient to support the independent existence of scientific laws. This essentially metaphysical debate has paid scant attention to the details of scientific practice. It has mostly focused on so-called fundamental laws, assumed to take a particular form (such as Maudlin’s FLOTEs). I propose a pragmatist alternative—not as another position in the debate but as an alternative to the debate itself. This pragmatist alternative offers a view that questions the represen...
Alternative views of quantum states are often expressed using the language of representation. For... more Alternative views of quantum states are often expressed using the language of representation. For example, after titling his 2014 review article "Is the quantum state real?", Leifer went on to say "The question of just what type of thing the quantum state, or wavefunction, represents, has been with us since the beginnings of quantum theory." It is important to distinguish three questions here: What is a quantum state? How may a quantum state be represented? What, if anything, does a quantum state represent? I shall defend answers to these questions against alternatives. In brief, a quantum state is an objective relational property of a physical system that describes neither its intrinsic physical properties nor anyone's epistemic state. Since its primary role is to assign Born probabilities to certain physical events involving the system, a quantum state may be represented in quantum theory by any mathematical object that can play this role. If it represents anything, a quantum state represents the objective probabilities it yields in this way. The paper continues like this. Section 2 surveys a variety of equivalent ways a quantum state may be represented in order to serve its function in quantum theory. Section 3 argues that a quantum state is not a physical entity, while section 4 argues that it is not a physical magnitude. In section 5 I argue that a system's quantum state does not represent its intrinsic physical properties or those of three-dimensional space. While few, if any, of these arguments are original or decisive, I take them to motivate consideration of an alternative that can help improve our understanding of quantum theory. So in section 6 I develop a relational account of a quantum state as what I call an extrinsically physical property of a system, brought to you by CORE View metadata, citation and similar papers at core.ac.uk
In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity.... more In a recent archive post Shan Gao has argued that quantum theory is incompatible with relativity. He calls this a new proof beyond Bell's theorem, arguing elsewhere that it closes the superdeterminism loophole in Bell's theorem. Such strong claims must be backed up by irrefutable arguments. My aim in this post to the workshop "Beyond Bell's theorem" is to refute Gao's "proof" and to show how quantum theory is compatible with relativity theory and so why Gao's "proof" does not take us beyond Bell's theorem
Realism comes in many varieties, in science and elsewhere. Van Fraassen’s influential formulation... more Realism comes in many varieties, in science and elsewhere. Van Fraassen’s influential formulation took scientific realism to include the view that science aims to give us, in its theories, a literally true story of what the world is like. So understood, a quantum realist takes quantum theory to aim at correctly representing the world: many would add that its success justifies believing this representation is more or less correct. But quantum realism has been understood both more narrowly and more broadly. A pragmatist considers use prior to representation and this has prompted some to dub pragmatist views anti-realist, including the view of quantum theory that the author has been developing recently. But whether a pragmatist view of quantum theory should be labeled anti-realist depends not only on its ingredients but also on how that label should be applied. Pragmatism offers a healthy diet of quantum realism.
J.S. Bell's work has convinced many that correlations in violation of CHSH inequalities show ... more J.S. Bell's work has convinced many that correlations in violation of CHSH inequalities show that the world itself is non-local, and that there is an apparently essential conflict between any sharp formulation of quantum theory and relativity. Against this consensus, this paper argues that there is no conflict between quantum theory and relativity. Quantum theory itself helps us explain such (otherwise) puzzling correlations in a way that contradicts neither Bell's intuitive locality principle nor his local causality condition. The argument depends on understanding quantum theory along pragmatist lines, and on a more general view of how that theory helps us explain. Quantum theory is compatible with Bell's intuitive locality principle and with his local causality condition not because it conforms to them, but because they are simply inapplicable to quantum theory, as so understood.
Three recent arguments seek to show that the universal applicability of unitary quantum theory is... more Three recent arguments seek to show that the universal applicability of unitary quantum theory is inconsistent with the assumption that a well-conducted measurement always has a definite physical outcome. In this paper I restate and analyze these arguments. The import of the first two is diminished by their dependence on assumptions about the outcomes of counterfactual measurements. But the third argument establishes its intended conclusion. Even if every well-conducted quantum measurement we ever make will have a definite physical outcome, this argument should make us reconsider the objectivity of that outcome.
Jerusalem Studies in Philosophy and History of Science
Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces... more Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces a serious measurement problem, whose solution requires a new theory or at least a novel interpretation of standard quantum mechanics. Itamar Pitowsky did not. Instead, he argued in a major paper (Pitowsky, Quantum mechanics as a theory of probability. In: Demopoulos W, Pitowsky I (eds) Physical theory and its interpretation. Springer, Dordrecht, pp 213-240, 2006) that quantum mechanics offers a new theory of probability. In these and other respects his views paralleled those of QBists (quantum Bayesians): but their views on the objectivity of measurement outcomes diverged radically. Indeed, Itamar's view of quantum probability depended on his subtle treatment of the objectivity of outcomes as events whose collective structure underlay this new theory of probability. I've always been puzzled by the thesis that quantum mechanics requires a new theory of probability, as distinct from new ways of calculating probabilities that play the same role as other probabilities in physics and daily life. In this paper I will try to articulate the sources of my puzzlement. I'd like to be able to think of this paper as a dialog between Itamar and me on the nature and application of quantum probabilities. Sadly, that cannot be: by taking his part in the dialog I will inevitably impose my own distant, clouded perspective on his profound and carefully crafted thoughts.
Quantum theory is a fundamental part of contemporary science. But some recent arguments have been... more Quantum theory is a fundamental part of contemporary science. But some recent arguments have been taken to show that if this theory is universally applicable then the outcome of a quantum measurement is not an objective fact. They motivate the more general reappraisal of the notions of fact and objectivity that I offer here. I argue that if quantum theory is universally applicable the facts about the physical world include a fact about each quantum measurement outcome. The physical facts may lack an ideal kind of objectivity but their more modest objectivity is all that science needs.
The quantum theory of decoherence plays an important role in a pragmatist interpretation of quant... more The quantum theory of decoherence plays an important role in a pragmatist interpretation of quantum theory. It governs the descriptive content of claims about values of physical magnitudes and offers advice on when to use quantum probabilities as a guide to their truth. The content of a claim is to be understood in terms of its role in inferences. This promises a better treatment of meaning than that offered by Bohr. Quantum theory models physical systems with no mention of measurement: it is decoherence, not measurement, that licenses application of Born’s probability rule. So quantum theory also offers advice on its own application. I show how this works in a simple model of decoherence, and then in applications to both laboratory experiments and natural systems. Applications to quantum field theory and the measurement problem will be discussed elsewhere. PACS 03.65.Yz, 03.65.Ta, 01.70.+w
A quantum state represents neither properties of a physical system nor anyone's knowledge of ... more A quantum state represents neither properties of a physical system nor anyone's knowledge of its properties. The important question is not what quantum states represent but how they are used as informational bridges. Knowing about some physical situations (its backing conditions), an agent may assign a quantum state to form expectations about other possible physical situations (its advice conditions). Quantum states are objective: only expectations based on correct state assignments are generally reliable. If a quantum state represents anything, it is the objective probabilistic relations between its backing conditions and its advice conditions. This paper offers an account of quantum states and their function as informational bridges, in quantum teleportation and elsewhere.
The British Journal for the Philosophy of Science, 2021
Measurement outcomes provide data for a physical theory. Unless they are objective they support n... more Measurement outcomes provide data for a physical theory. Unless they are objective they support no objective scientific knowledge. So the outcome of a quantum measurement must be an objective physical fact. But recent arguments purport to show that if quantum theory is universally applicable then there is no such fact. This calls for a reappraisal of the notions of fact and objectivity. If quantum theory is universally applicable the facts about the physical world include a fact about each quantum measurement outcome. These physical facts lack an ideal kind of objectivity but their more modest objectivity is all that science needs.
Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces... more Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces a serious measurement problem, whose solution requires a new theory or at least a novel interpretation of standard quantum mechanics. Itamar Pitowsky did not. Instead, he argued in a major paper (Pitowsky, Quantum mechanics as a theory of probability. In: Demopoulos W, Pitowsky I (eds) Physical theory and its interpretation. Springer, Dordrecht, pp 213–240, 2006) that quantum mechanics offers a new theory of probability. In these and other respects his views paralleled those of QBists (quantum Bayesians): but their views on the objectivity of measurement outcomes diverged radically. Indeed, Itamar’s view of quantum probability depended on his subtle treatment of the objectivity of outcomes as events whose collective structure underlay this new theory of probability. I’ve always been puzzled by the thesis that quantum mechanics requires a new theory of probability, as distinct from new w...
This paper argues that there is no conflict between quantum theory and relativity, and that quant... more This paper argues that there is no conflict between quantum theory and relativity, and that quantum theory itself helps us explain (otherwise) puzzling “non-local” correlations in a way that contradicts neither Bell’s intuitive locality principle nor his local causality condition. The argument depends on understanding quantum theory along pragmatist lines I have outlined elsewhere, and on a more general view of how that theory helps us explain. The key counterfactuals that hold in such cases manifest epistemic rather than causal connections between distant events. Quantum theory exploits the possibility of private informational links between an agent and events (s)he neither observes nor brings about, in ways that are strikingly independent of the spatiotemporal relations between them. This possibility has interesting implications for theories of chance in a relativistic world.
This paper aims to show how adoption of a pragmatist interpretation permits a satisfactory resolu... more This paper aims to show how adoption of a pragmatist interpretation permits a satisfactory resolution of the quantum measurement problem. The classic measurement problem dissolves once one recognizes that it is not the function of the quantum state to describe or represent the behavior of a quantum system. The residual problem of when, and to what, to apply the Born Rule may then be resolved by judicious appeal to decoherence. This can give sense to talk of measurements of photons and other particles even though quantum field theory does not describe particles.
Quantum entanglement is widely believed to be a feature of physical reality with undoubted (thoug... more Quantum entanglement is widely believed to be a feature of physical reality with undoubted (though debated) metaphysical implications. But Schrödinger introduced entanglement as a theoretical relation between representatives of the quantum states of two systems. Entanglement represents a physical relation only if quantum states are elements of physical reality. So arguments for metaphysical holism or nonseparability from entanglement rest on a questionable view of quantum theory. Assignment of entangled quantum states predicts experimentally con…rmed violation of Bell inequalities. Can one use these experimental results to argue directly for metaphysical conclusions? No. Quantum theory itself gives us our best explanation of violations of Bell inequalities, with no superluminal causal in ‡uences and no metaphysical holism or nonseparability-but only if quantum states are understood as objective and relational, though prescriptive rather than ontic. Correct quantum state assignments are backed by true physical magnitude claims: but backing is not grounding. Quantum theory supports no general metaphysical holism or nonseparability; though a claim about a compound physical system may be signi…cant and true while similar claims about its components are neither. Entanglement may well have have few, if any, …rst-order metaphysical implications. But the quantum theory of entanglement has much to teach the metaphysician about the roles of chance, causation, modality and explanation in the epistemic and practical concerns of a physically situated agent.
Durante su larga y extraordinariamente productiva carrera, Hilary Putnam flirteó de vez en cuando... more Durante su larga y extraordinariamente productiva carrera, Hilary Putnam flirteó de vez en cuando con el pragmatism. Pero su realismo científico aportó un punto fijo para sus intentos de interpretar la teoría cuántica. Recientemente he defendido que los tratamientos pragmatistas de la representación, la explicación y la probabilidad son claves para comprender cómo usamos la teoría cuántica con tanto éxito y, así, como debería ser interpretada. Para Putnam, el realismo científico es en sí mismo una hipótesis científica que explica el éxito de la ciencia. Si estoy en lo correcto, el éxito de la teoría cuántica debilita esta clase de realismo científico mientras que apoya un pragmatismo rival. El realismo científico permanece inmune a la refutación empírica si se ve no como una hipótesis científica sino como un ideal regulativo. Pero una pers- pectiva pragmatista de la teoría cuántica plantea un desafío a una cierta clase de realismo metafísico.
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