•  175
    The Quantum Revolution in Philosophy
    Analysis 80 (2): 381-388. 2020.
    Richard Healey’s The Quantum Revolution in Philosophy is a terrific book, and yet I disagree with nearly all its main substantive conclusions.1 1 The purpose of this review is to say why the book is well worth your time if you have any interest in the interpretation of quantum theory or in the general philosophy of science, and yet why in the end I think Healey’s ambitious project fails to achieve its full goals.
  •  57
    Interpreting the quantum mechanics of cosmology
    In A. Ijjas & B. Loewer (eds.), Philosophy of Cosmology: an Introduction, Oxford University Press. forthcoming.
    Quantum theory plays an increasingly significant role in contemporary early-universe cosmology, most notably in the inflationary origins of the fluctuation spectrum of the microwave background radiation. I consider the two main strategies for interpreting standard quantum mechanics in the light of cosmology. I argue that the conceptual difficulties of the approaches based around an irreducible role for measurement - already very severe - become intolerable in a cosmological context, whereas the …Read more
  •  67
    `Quantum theory' is not a single physical theory but a framework in which many different concrete theories fit. As such, a solution to the quantum measurement problem ought to provide a recipe to interpret each such concrete theory, in a mutually consistent way. But with the exception of the Everett interpretation, the mainextant solutions either try to make sense of the abstract framework as if it were concrete, or else interpret one particular quantum theory under the fiction that it is fundam…Read more
  •  47
    I argue that wavefunction realism --- the view that quantum mechanics reveals the fundamental ontology of the world to be a field on a high-dimensional spacetime, must be rejected as relying on artefacts of too-simple versions of quantum mechanics, and not conceptually well-motivated even were those too-simple versions exactly correct. I end with some brief comments on the role of spacetime in any satisfactory account of the metaphysics of extant quantum theories.
  •  25
    In discussions of the foundations of statistical mechanics, it is widely held that the Gibbsian and Boltzmannian approaches are incompatible but empirically equivalent; the Gibbsian approach may be calculationally preferable but only the Boltzmannian approach is conceptually satisfactory. I argue against both assumptions. Gibbsian statistical mechanics is applicable to a wide variety of problems and systems, such as the calculation of transport coefficients and the statistical mechanics and ther…Read more
  •  28
    Spontaneous symmetry breaking in quantum systems, such as ferromagnets, is normally described as degeneracy of the ground state; however, it is well established that this degeneracy only occurs in spatially infinite systems, and even better established that ferromagnets are not spatially infinite. I review this well-known paradox, and consider a popular solution where the symmetry is explicitly broken by some external field which goes to zero in the infinite-volume limit; although this is formal…Read more
  •  21
    I distinguish between two versions of the black hole information-loss paradox. The first arises from apparent failure of unitarity on the spacetime of a completely evaporating black hole, which appears to be non-globally-hyperbolic; this is the most commonly discussed version of the paradox in the foundational and semipopular literature, and the case for calling it `paradoxical' is less than compelling. But the second arises from a clash between a fully-statistical-mechanical interpretation of b…Read more
  •  18
    Decoherence and Ontology, or: How I Learned To Stop Worrying And Love FAPP
    In Simon Saunders, Jonathan Barrett, Adrian Kent & David Wallace (eds.), Many Worlds? Everett, Quantum Theory, and Reality, Oxford University Press. 2010.
    I make the case that the Universe according to unitary quantum theory has a branching structure, and so can literally be regarded as a "many-worlds" theory. These worlds are not part of the _fundamental_ ontology of quantum theory - instead, they are to be understood as structures, or patterns, emergent from the underlying theory, through the dynamical process of decoherence. That they are structures in this sense does not mean that they are in any way unreal: indeed, pretty much all higher-leve…Read more
  •  48
    The case for black hole thermodynamics part I: Phenomenological thermodynamics
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 64 52-67. 2018.
    I give a fairly systematic and thorough presentation of the case for regarding black holes as thermodynamic systems in the fullest sense, aimed at students and non-specialists and not presuming advanced knowledge of quantum gravity. I pay particular attention to the availability in classical black hole thermodynamics of a well-defined notion of adiabatic intervention; the power of the membrane paradigm to make black hole thermodynamics precise and to extend it to local-equilibrium contexts; the …Read more
  •  89
    Quantum mechanics, and classical mechanics, are framework theories that incorporate many different concrete theories which in general cannot be arranged in a neat hierarchy, but discussion of ‘the ontology of quantum mechanics’ tends to proceed as if quantum mechanics were a single concrete theory, specifically the physics of nonrelativistically moving point particles interacting by long-range forces. I survey the problems this causes and make some suggestions for how a more physically realistic…Read more
  •  66
    Fundamental and Emergent Geometry in Newtonian Physics
    British Journal for the Philosophy of Science 71 (1): 1-32. 2020.
    Using as a starting point recent and apparently incompatible conclusions by Saunders and Knox, I revisit the question of the correct spacetime setting for Newtonian physics. I argue that understood correctly, these two versions of Newtonian physics make the same claims both about the background geometry required to define the theory, and about the inertial structure of the theory. In doing so I illustrate and explore in detail the view—espoused by Knox, and also by Brown —that inertial structure…Read more
  •  10
    The working assumption amongst most philosophers of QFT appears to be that algebraic QFT, and not the "Lagrangian" QFT of the working physicist, is the proper object of philosophical and foundational study. I argue that this assumption is unmotivated, and fails to take into account important features of the post-1960s development of Lagrangian QFT. From a modern perspective the two forms of QFT are better seen as rival research programs than as variant formulations of one theory; furthermore, th…Read more
  •  43
    I provide a self-contained introduction to the problem of the arrow of time in physics, concentrating on the irreversibility of dynamical processes as described in statistical mechanics.
  •  110
    Diachronic Rationality and Prediction-Based Games
    Proceedings of the Aristotelian Society 110 (3pt3): 243-266. 2010.
    I explore the debate about causal versus evidential decision theory, and its recent developments in the work of Andy Egan, through the method of some simple games based on agents' predictions of each other's actions. My main focus is on the requirement for rational agents to act in a way which is consistent over time and its implications for such games and their more realistic cousins
  •  132
    Protecting cognitive science from quantum theory
    Behavioral and Brain Sciences 27 (5): 636-637. 2004.
    The relation between micro-objects and macro-objects advocated by Kim is even more problematic than Ross & Spurrett (R&S) argue, for reasons rooted in physics. R&S's own ontological proposals are much more satisfactory from a physicist's viewpoint but may still be problematic. A satisfactory theory of macroscopic ontology must be as independent as possible of the details of microscopic physics.
  •  57
    I investigate the consequences for semantics, and in particular for the semantics of tense, if time is assumed to have a branching structure not out of metaphysical necessity (to solve some philosophical problem) but just as a contingent physical fact, as is suggested by a currently-popular approach to the interpretation of quantum mechanics.
  •  373
    Gravity, Entropy, and Cosmology: in Search of Clarity
    British Journal for the Philosophy of Science 61 (3): 513-540. 2010.
    I discuss the statistical mechanics of gravitating systems and in particular its cosmological implications, and argue that many conventional views on this subject in the foundations of statistical mechanics embody significant confusion; I attempt to provide a clearer and more accurate account. In particular, I observe that (i) the role of gravity in entropy calculations must be distinguished from the entropy of gravity, that (ii) although gravitational collapse is entropy-increasing, this is not…Read more
  •  120
    Who's afraid of coordinate systems? An essay on representation of spacetime structure
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 67 125-136. 2019.
    Coordinate-based approaches to physical theories remain standard in mainstream physics but are largely eschewed in foundational discussion in favour of coordinate-free differential-geometric approaches. I defend the conceptual and mathematical legitimacy of the coordinate-based approach for foundational work. In doing so, I provide an account of the Kleinian conception of geometry as a theory of invariance under symmetry groups; I argue that this conception continues to play a very substantial r…Read more
  •  37
    I argue that the metaphysical import of the Aharonov-Bohm effect has been overstated: correctly understood, it does not require either rejection of gauge invariance or any novel form of nonlocality. The conclusion that it does require one or the other follows from a failure to keep track, in the analysis, of the complex scalar field to which the magnetic vector potential is coupled. Once this is recognised, the way is clear to a local account of the ontology of electrodynamics ; I sketch a possi…Read more
  •  49
    The Everett interpretation of quantum mechanics - better known as the Many-Worlds Theory - has had a rather uneven reception. Mainstream philosophers have scarcely heard of it, save as science fiction. In philosophy of physics it is well known but has historically been fairly widely rejected. Among physicists, it is taken very seriously indeed, arguably tied for first place in popularity with more traditional operationalist views of quantum mechanics. In this article, I provide a fairly short an…Read more
  •  585
    Time-dependent symmetries: the link between gauge symmetries and indeterminism
    In Katherine Brading & Elena Castellani (eds.), Symmetries in Physics: Philosophical Reflections, Cambridge University Press. pp. 163--173. 2002.
    Mathematically, gauge theories are extraordinarily rich --- so rich, in fact, that it can become all too easy to lose track of the connections between results, and become lost in a mass of beautiful theorems and properties: indeterminism, constraints, Noether identities, local and global symmetries, and so on. One purpose of this short article is to provide some sort of a guide through the mathematics, to the conceptual core of what is actually going on. Its focus is on the Lagrangian, variatio…Read more
  •  26
    I contrast two possible attitudes towards a given branch of physics: as inferential, and as dynamical. I contrast these attitudes in classical statistical mechanics, in quantum mechanics, and in quantum statistical mechanics; in this last case, I argue that the quantum-mechanical and statistical-mechanical aspects of the question become inseparable. Along the way various foundational issues in statistical and quantum physics are illuminated.
  •  237
    Everettian rationality: defending Deutsch's approach to probability in the Everett interpretation
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 34 (3): 415-439. 2003.
    An analysis is made of Deutsch's recent claim to have derived the Born rule from decision-theoretic assumptions. It is argued that Deutsch's proof must be understood in the explicit context of the Everett interpretation, and that in this context, it essentially succeeds. Some comments are made about the criticism of Deutsch's proof by Barnum, Caves, Finkelstein, Fuchs, and Schack; it is argued that the flaw which they point out in the proof does not apply if the Everett interpretation is assumed…Read more
  •  34
    The quantitative content of statistical mechanics
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 52 (Part B): 285-293. 2015.
  •  215
    A formal proof of the born rule from decision-theoretic assumptions [aka: How to Prove the Born Rule]
    In Simon Saunders, Jon Barrett, Adrian Kent & David Wallace (eds.), Many Worlds?: Everett, Quantum Theory & Reality, Oxford University Press. 2009.
    I develop the decision-theoretic approach to quantum probability, originally proposed by David Deutsch, into a mathematically rigorous proof of the Born rule in (Everett-interpreted) quantum mechanics. I sketch the argument informally, then prove it formally, and lastly consider a number of proposed ``counter-examples'' to show exactly which premises of the argument they violate. (This is a preliminary version of a chapter to appear --- under the title ``How to prove the Born Rule'' --- in Saund…Read more
  •  249
    Quantum probability from subjective likelihood: Improving on Deutsch's proof of the probability rule
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 38 (2): 311-332. 2007.
    I present a proof of the quantum probability rule from decision-theoretic assumptions, in the context of the Everett interpretation. The basic ideas behind the proof are those presented in Deutsch's recent proof of the probability rule, but the proof is simpler and proceeds from weaker decision-theoretic assumptions. This makes it easier to discuss the conceptual ideas involved in the proof, and to show that they are defensible.
  •  54
    More problems for Newtonian cosmology
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 57 35-40. 2017.
    I point out a radical indeterminism in potential-based formulations of Newtonian gravity once we drop the condition that the potential vanishes at infinity. This indeterminism, which is well known in theoretical cosmology but has received little attention in foundational discussions, can be removed only by specifying boundary conditions at all instants of time, which undermines the theory's claim to be fully cosmological, i.e., to apply to the Universe as a whole. A recent alternative formulatio…Read more
  • How to prove the Born rule
    In Simon Saunders, Jonathan Barrett, Adrian Kent & David Wallace (eds.), Many Worlds?: Everett, Quantum Theory & Reality, Oxford University Press. 2010.
  •  71
    What is Orthodox Quantum Mechanics?
    In Alberto Cordero (ed.), Philosophers Look at Quantum Mechanics, Springer Verlag. 2019.
    What is called ``orthodox'' quantum mechanics, as presented in standard foundational discussions, relies on two substantive assumptions --- the projection postulate and the eigenvalue-eigenvector link --- that do not in fact play any part in practical applications of quantum mechanics. I argue for this conclusion on a number of grounds, but primarily on the grounds that the projection postulate fails correctly to account for repeated, continuous and unsharp measurements and that the eigenvalue-e…Read more