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Australasian Journal of Philosophy

David Lewis and Schrödinger's Cat

David Papineau

Published Mar 1, 2004• 17 citations
Publisher

Abstract

In 'How Many Lives Has Schrödinger's Cat?' David Lewis argues that the Everettian no-collapse interpretation of quantum mechanics is in a tangle when it comes to probabilities. This paper aims to show that the difficulties that Lewis raises are insubstantial. The Everettian metaphysics contains a coherent account of probability. Indeed it accounts for probability rather better than orthodox metaphysics does.

DOI
10.1080/713659793

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David Lewis and Schro dinger’s Cat

David Papineau

Abstract In ‘How Many Lives Has Schro dinger’s Cat?’ David Lewis argues that the Everettian no-collapse interpretation of quantum mechanics is in a tangle when it comes to probabilities. This paper aims to show that the difficulties that Lewis raises are insubstantial. The Everettian metaphysics contains a coherent account of probability. Indeed it accounts for probability rather better than orthodox metaphysics does. On 27 June 2001, not four months before his untimely death, David Lewis delivered the third Jack Smart Lecture at the Australian National University. His title was ‘How Many Lives has Schro dinger’s Cat?’ > and he spoke on a topic which is absent from his published writings, the interpretation of quantum mechanics. More specifically, he discussed the ‘no-collapse’ interpretation of quantum mechanics pioneered by Hugh Everett III [1957]. Lewis allowed that this interpretation offers initial theoretical attractions, but also argued that it suffers from irremediable flaws. If you have heard of Everett because of his association with the ‘many-worlds’ interpretation of quantum mechanics popularised by Bryce Dewitt [1970; 1973], you might suppose that there is some affinity between the no-collapse interpretation and Lewis’s philosophical realism about possible worlds. But this would be a mistake. While Everett’s interpretation does add extra ‘branches’ to the reality recognized by common sense, these additions fall far short of Lewis’s multiplication of worlds. For a start, the extra ‘branches’ that Everett adds to reality all lie within the actual world that evolves from the actual initial conditions in line with the actual laws of physics-these branches by no means include all possibilities. Moreover, Everett’s branches are best conceived, not as sundering’s of the whole universe, but rather as entities that spread out causally at finite speeds, ‘like ripples on a pond’, as Lewis puts it. For example, in the Schro dinger’s Cat experiment, firstthe photon branches into a deflected and undeflected version when it passes through the half-silvered mirror; thenthe detector branches into a triggered and untriggered state when it interacts with the photon; thenthe poison bottle branches into a smashed bottle and an unsmashed bottle under the influence of the detector; and so on, culminating in the cat branching into a live and dead cat, and the human observer branching into a self who sees a live cat and a self who sees a dead cat. >

•Sep 2, 2004•0 citations

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Recent work on probability in the Everett interpretation of quantum mechanics yields a decision-theoretic derivation of David Lewis’ Principal Principle, and hence a general metaphysical theory of probability; part 1 is a discussion of this remarkable result. I defend the claim that the ‘subjective uncertainty’ principle is required for the derivation to succeed, arguing that it amounts to a theoretical identification of chance. In part 2, I generalize this account, and suggest that the Everett interpretation, in combination with a plausible view of natural laws, has the potential to provide a reductive theory of metaphysical modality. I defend the resulting naturalistic modal realism, and outline some of its implications for other parts of metaphysics.

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The ins and outs of Schrodinger's cat box: a response to Papineau

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The so-called many-worlds or many-minds interpretations of quantum mechancis, derived from the work of Hugh Everett III (1957), continue to have a very mixed reception among the well-informed, partly because of the theories' weirdness. Peter Lewis (2000) has argued that an important class of these interpretations have the extraordinary implication that a subject confronted by apparently life-threatening situations involving quantum measurement should be fully confident of having future experience. David Papineau (2003) has attempted to block Lewis's argument and I shall argue that the attempt fails.

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This article sits at a point of intersection between the philosophy of physics and the metaphysics of modality. There are clear similarities between Everettian quantum mechanics and various modal metaphysical theories, but there have hitherto been few attempts at exploring how the two topics relate. In this article, I build on a series of recent papers by Wilson ([2011], [2012], [2013]), who argues that Everettian quantum mechanics’ connections with traditional modal metaphysics are vital in defending it against objections. I show that Wilson’s preferred version of Everettian quantum mechanics has two problems. First, it is unable to account for the contingency of various intuitively contingent modal claims. Second, it fails to yield intuitive truth values on modal claims about the number of branches in a given Everettian multiverse. Since modal claims about branch number are instrumental in decision-theoretic solutions to Everettian quantum mechanics’ problem(s) with probability, this second problem has wider dialectical implications. I suggest amendments to the underlying metaphysics that overcome these problems. The result is a more robust version of Everettian quantum mechanics.

The British Journal for the Philosophy of Science•Jun 27, 2018•8 citations
In 'How Many Lives Has Schrödinger's Cat?' David Lewis argues that the Everettian no-collapse interpretation of quantum mechanics is in a tangle when it comes to probabilities. This paper aims to show that the difficulties that Lewis raises are insubstantial. The Everettian metaphysics contains a coherent account of probability. Indeed it accounts for probability rather better than orthodox metaphysics does.
Abstract In ‘How Many Lives Has Schro dinger’s Cat?’ David Lewis argues that the Everettian no-collapse interpretation of quantum mechanics is in a tangle when it comes to probabilities. This paper aims to show that the difficulties that Lewis raises are insubstantial. The Everettian metaphysics contains a coherent account of probability. Indeed it accounts for probability rather better than orthodox metaphysics does. On 27 June 2001, not four months before his untimely death, David Lewis delivered the third Jack Smart Lecture at the Australian National University. His title was ‘How Many Lives has Schro dinger’s Cat?’ > and he spoke on a topic which is absent from his published writings, the interpretation of quantum mechanics. More specifically, he discussed the ‘no-collapse’ interpretation of quantum mechanics pioneered by Hugh Everett III [1957]. Lewis allowed that this interpretation offers initial theoretical attractions, but also argued that it suffers from irremediable flaws. If you have heard of Everett because of his association with the ‘many-worlds’ interpretation of quantum mechanics popularised by Bryce Dewitt [1970; 1973], you might suppose that there is some affinity between the no-collapse interpretation and Lewis’s philosophical realism about possible worlds. But this would be a mistake. While Everett’s interpretation does add extra ‘branches’ to the reality recognized by common sense, these additions fall far short of Lewis’s multiplication of worlds. For a start, the extra ‘branches’ that Everett adds to reality all lie within the actual world that evolves from the actual initial conditions in line with the actual laws of physics-these branches by no means include all possibilities. Moreover, Everett’s branches are best conceived, not as sundering’s of the whole universe, but rather as entities that spread out causally at finite speeds, ‘like ripples on a pond’, as Lewis puts it. For example, in the Schro dinger’s Cat experiment, firstthe photon branches into a deflected and undeflected version when it passes through the half-silvered mirror; thenthe detector branches into a triggered and untriggered state when it interacts with the photon; thenthe poison bottle branches into a smashed bottle and an unsmashed bottle under the influence of the detector; and so on, culminating in the cat branching into a live and dead cat, and the human observer branching into a self who sees a live cat and a self who sees a dead cat. >
Recent work on probability in the Everett interpretation of quantum mechanics yields a decision-theoretic derivation of David Lewis’ Principal Principle, and hence a general metaphysical theory of probability; part 1 is a discussion of this remarkable result. I defend the claim that the ‘subjective uncertainty’ principle is required for the derivation to succeed, arguing that it amounts to a theoretical identification of chance. In part 2, I generalize this account, and suggest that the Everett interpretation, in combination with a plausible view of natural laws, has the potential to provide a reductive theory of metaphysical modality. I defend the resulting naturalistic modal realism, and outline some of its implications for other parts of metaphysics.
The so-called many-worlds or many-minds interpretations of quantum mechancis, derived from the work of Hugh Everett III (1957), continue to have a very mixed reception among the well-informed, partly because of the theories' weirdness. Peter Lewis (2000) has argued that an important class of these interpretations have the extraordinary implication that a subject confronted by apparently life-threatening situations involving quantum measurement should be fully confident of having future experience. David Papineau (2003) has attempted to block Lewis's argument and I shall argue that the attempt fails.
Abstract Recently several philosophers including Huw Price, Peter Lewis, and David Lewis have argued that on one interpretation of quantum theory (genus Indeterminacy, species No Collapse) death is an illusion.1 Taking Schroedinger’s unhappy cat as the standard example, this interpretation tells us that it is as if the whole universe splits into two copies in one of which the cat survives and in the other there is a corpse. Fission into a living organism on the one hand and a corpse on the other is, most of us agree, a way of surviving.2 So we arrive at the first premise, namely that organisms survive situations like that of SchrÖdinger’s cat.
This article sits at a point of intersection between the philosophy of physics and the metaphysics of modality. There are clear similarities between Everettian quantum mechanics and various modal metaphysical theories, but there have hitherto been few attempts at exploring how the two topics relate. In this article, I build on a series of recent papers by Wilson ([2011], [2012], [2013]), who argues that Everettian quantum mechanics’ connections with traditional modal metaphysics are vital in defending it against objections. I show that Wilson’s preferred version of Everettian quantum mechanics has two problems. First, it is unable to account for the contingency of various intuitively contingent modal claims. Second, it fails to yield intuitive truth values on modal claims about the number of branches in a given Everettian multiverse. Since modal claims about branch number are instrumental in decision-theoretic solutions to Everettian quantum mechanics’ problem(s) with probability, this second problem has wider dialectical implications. I suggest amendments to the underlying metaphysics that overcome these problems. The result is a more robust version of Everettian quantum mechanics.