•  30
    This paper investigates the formation and propagation of wavefunction `branches' through the process of entanglement with the environment. While this process is a consequence of unitary dynamics, and hence significant to many if not all approaches to quantum theory, it plays a central role in many recent articulations of the Everett or `many worlds' interpretation. A highly idealized model of a locally interacting system and environment is described, and investigated in several situations in whi…Read more
  •  173
    We conduct a case study analysis of a proposal for the emergence of time based upon the approximate derivation of three grades of temporal structure within an explicit quantum cosmological model which obeys a Wheeler-DeWitt type equation without an extrinsic time parameter. Our main focus will be issues regarding the consistency of the approximations and derivations in question. Our conclusion is that the model provides a self-consistent account of the emergence of chronordinal, chronometric and…Read more
  •  6
    Time in Quantum Gravity
    In Heather Dyke & Adrian Bardon (eds.), A Companion to the Philosophy of Time, Wiley. 2013.
    Physical time plays a different role in general relativity than in quantum mechanics and the particle physics based on it. The first section of this chapter provides a brief survey of the main approaches to quantum gravity and then proceeds to consider the lessons that can be drawn from two distinct strategies for discovering a theory of quantum gravity. In the next section, the chapter first explicates the fate of time in approaches to quantum gravity that start with general relativity (GR) and…Read more
  •  245
    It has long been thought that observing distinctive traces of quantum gravity in a laboratory setting is effectively impossible, since gravity is so much weaker than all the other familiar forces in particle physics. But the quantum gravity phenomenology community today seeks to do the (effectively) impossible, using a challenging novel class of `tabletop' Gravitationally Induced Entanglement (GIE) experiments, surveyed here. The hypothesized outcomes of the GIE experiments are claimed by some (…Read more
  •  623
    Philosophy Beyond Spacetime: Introduction
    In Christian Wüthrich, Baptiste Le Bihan & Nick Huggett (eds.), Philosophy Beyond Spacetime: Implications From Quantum Gravity, Oxford University Press. pp. 1-15. 2021.
    The present volume collects essays on the philosophical foundations of quantum theories of gravity, such as loop quantum gravity and string theory. Central for philosophical concerns is quantum gravity's suggestion that space and time, or spacetime, may not exist fundamentally, but instead be a derivative entity emerging from non-spatiotemporal degrees of freedom. In the spirit of naturalised metaphysics, contributions to this volume consider the philosophical implications of this suggestion. In…Read more
  •  12
    A popular-level discussion of the mutual significance of physics and philosophy over the ages.
  • This is a chapter of the planned monograph "Out of Nowhere: The Emergence of Spacetime in Quantum Theories of Gravity", co-authored by Nick Huggett and Christian Wüthrich and under contract with Oxford University Press. (More information at www<dot>beyondspacetime<dot>net.) This chapter sketches how spacetime emerges in causal set theory and demonstrates how this question is deeply entangled with genuinely philosophical concerns.
  •  461
    This is a chapter of the planned monograph "Out of Nowhere: The Emergence of Spacetime in Quantum Theories of Gravity", co-authored by Nick Huggett and Christian Wüthrich and under contract with Oxford University Press. (More information at www<dot>beyondspacetime<dot>net.) This chapter introduces the problem of emergence of spacetime in quantum gravity. It introduces the main philosophical challenge to spacetime emergence and sketches our preferred solution to it.
  •  41
    Missing the point in noncommutative geometry
    with Tushar Menon and Fedele Lizzi
    Synthese 199 (1-2): 4695-4728
    Noncommutative geometries generalize standard smooth geometries, parametrizing the noncommutativity of dimensions with a fundamental quantity with the dimensions of area. The question arises then of whether the concept of a region smaller than the scale—and ultimately the concept of a point—makes sense in such a theory. We argue that it does not, in two interrelated ways. In the context of Connes’ spectral triple approach, we show that arbitrarily small regions are not definable in the formal se…Read more
  •  62
    Lost horizon? – modeling black holes in string theory
    with Keizo Matsubara
    European Journal for Philosophy of Science 11 (3): 1-19. 2021.
    The modeling of black holes is an important desideratum for any quantum theory of gravity. Not only is a classical black hole metric sought, but also agreement with the laws of black hole thermodynamics. In this paper, we describe how these goals are achieved in string theory. We review black hole thermodynamics, and then explicate the general stringy derivation of classical spacetimes, the construction of a simple black hole solution, and the derivation of its entropy. With that in hand, we add…Read more
  •  1711
    This is a chapter of the planned monograph "Out of Nowhere: The Emergence of Spacetime in Quantum Theories of Gravity", co-authored by Nick Huggett and Christian Wüthrich and under contract with Oxford University Press. (More information at www<dot>beyondspacetime<dot>net.) This chapter introduces causal set theory and identifies and articulates a 'problem of space' in this theory.
  •  293
    This is a chapter of the planned monograph "Out of Nowhere: The Emergence of Spacetime in Quantum Theories of Gravity", co-authored by Nick Huggett and Christian Wüthrich and under contract with Oxford University Press. (More information at www<dot>beyondspacetime<dot>net.) This chapter investigates the meaning and significance of string theoretic dualities, arguing they reveal a surprising physical indeterminateness to spacetime.
  •  399
    This is a chapter of the planned monograph "Out of Nowhere: The Emergence of Spacetime in Quantum Theories of Gravity", co-authored by Nick Huggett and Christian Wüthrich and under contract with Oxford University Press. This chapter analyses the nature and derivation of spacetime topology and geometry according to string theory.
  • Philosophical Foundations of Quantum Field Theory
    In Peter Clark & Katherine Hawley (eds.), Philosophy of Science Today, Oxford University Press Uk. 2003.
  •  126
    Spacetime "Emergence"
    In Eleanor Knox & Alastair Wilson (eds.), The Routledge Companion to Philosophy of Physics, Routledge. 2022.
    Could spacetime be derived rather than fundamental? The question is pressing because attempts to quantize gravity have led to theories in which (arguably) there are either no, or only extremely thin, spacetime structures. Moreover, recent proposals for the interpretation of quantum mechanics have suggested that 3-dimensional space may be an ‘appearance’ derived from the 3N-dimensional space in which an N-particle wavefunction lives (cross- reference). In fact, I will largely assume a positive an…Read more
  •  90
    This paper introduces some basic ideas and formalism of physics in non-commutative geometry. My goals are three-fold: first to introduce the basic formal and conceptual ideas of non-commutative geometry, and second to raise and address some philosophical questions about it. Third, more generally to illuminate the point that deriving spacetime from a more fundamental theory requires discovering new modes of `physically salient' derivation.
  •  78
    This paper aims to address conceptual issues concerning black holes in the context of string theory, with the aim of illuminating the ontological unification of gravity and matter, and the interpretation of cosmological models. §1 describes the central concepts of the theory: the fungibility of matter and geometry, and the reduction of gravity and supergravity. The ‘standard’ interpretation presented draws on that implicit in the thinking of many (but not all) string theorists, though made more …Read more
  •  107
    Philosophy Beyond Spacetime assesses the state of play in the philosophy of quantum gravity. Research in this field aims at a unified theory in which quantum matter is related dynamically to relativistic spacetime. This volume highlights the conceptual questions involved, showing how physics and metaphysics can illuminate each other.
  •  148
    The (A)temporal Emergence of Spacetime
    Philosophy of Science 85 (December): 1190-1203. 2018.
    This paper examines two cosmological models of quantum gravity to investigate the foundational and conceptual issues arising from quantum treatments of the big bang. While the classical singularity is erased, the quantum evolution that replaces it may not correspond to classical spacetime: it may instead be a non-spatiotemporal region, which somehow transitions to a spatiotemporal state. The different kinds of transition involved are partially characterized, the concept of a physical transition …Read more
  •  62
    Interpretive Introduction to Quantum Field Theory. Paul Teller
    with Robert Weingard
    Philosophy of Science 63 (2): 302-314. 1996.
    Paul Teller's new book, “An Interpretive Introduction to Quantum Field Theory”, is a pioneering work. To the best of our knowledge it is the first book by a philosopher devoted not only to explaining what quantum field theory is, but to clarifying the conceptual issues and puzzles to which the theory gives rise. As such it is an important book, which we hope will greatly stimulate work in the area as other philosophers and physicists react to it.
  •  24
    Beyond Spacetime: The Foundations of Quantum Gravity (edited book)
    with Keizo Matsubara and Christian Wüthrich
    Cambridge University Press.. 2020.
    A collection of essays discussing the philosophy and foundations of quantum gravity. Written by leading philosophers and physicists in the field, chapters cover the important conceptual questions in the search for a quantum theory of gravity, and the current state of understanding among philosophers and physicists.
  •  7
    Recently, Simon Saunders has applied Quine's account of discernibility to the theory of identical particles, ultimately to argue that quanta can be weakly discernible. I want to expand on this work along two axes. First, to explain how the results apply to higher kinds of statistics -- 'quarticles'. Second, to dispute the claim that quanta are weakly discernible: I question whether the operators used to discern the particles do not represent the properties that they are claimed to.
  •  1
    Space from Zeno to Einstein. Classic Readings with a Contemporary Commentary
    Tijdschrift Voor Filosofie 62 (4): 781-782. 2000.
  •  85
    Essay Review: Physical Relativity and Understanding Space-Time (review)
    Philosophy of Science 76 (3): 404-422. 2009.
    The two books discussed here make important contributions to our understanding of the role of spacetime concepts in physical theories and how that understanding has changed during the evolution of physics. Both emphasize what can be called a ‘dynamical’ account, according to which geometric structures should be understood in terms of their roles in the laws governing matter and force. I explore how the books contribute to such a project; while generally sympathetic, I offer criticisms of some hi…Read more
  •  10
    Exposing the Machinery of Infinite Renormalization
    with Robert Weingard
    Philosophy of Science 63 (5). 1996.
    We explicate recent results that shed light on the obscure and troubling problem of renormalization in Quantum Field Theory. We review how divergent predictions arise in perturbative QFT, and how they are renormalized into finite quantities. Commentators have worried that there is no foundation for renormalization, and hence that QFTs are not logically coherent. We dispute this by describing the physics behind liquid diffusion, in which exactly analogous divergences are found and renormalized. B…Read more
  •  79
    The emergence of spacetime in quantum theories of gravity
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 44 (3): 273-275. 2013.
    This is the introduction to the special issue of Studies in the History and Philosophy of Modern Physics on the emergence of spacetime in quantum theories of spacetime.
  •  33
    Atomic Metaphysics
    Journal of Philosophy 96 (1): 5. 1999.
  •  120
    Target space ≠ space
    Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 59 81-88. 2017.
    This paper investigates the significance of T-duality in string theory: the indistinguisha- bility with respect to all observables, of models attributing radically different radii to space – larger than the observable universe, or far smaller than the Planck length, say. Two interpretational branch points are identified and discussed. First, whether duals are physically equivalent or not: by considering a duality of the familiar simple harmonic oscillator, I argue that they are. Unlike the oscil…Read more
  •  32
    The quantum gravity program seeks a theory that handles quantum matter fields and gravity consistently. But is such a theory really required and must it involve quantizing the gravitational field? We give reasons for a positive answer to the first question, but dispute a widespread contention that it is inconsistent for the gravitational field to be classical while matter is quantum. In particular, we show how a popular argument falls short of a no-go theorem, and discuss possible counterexample…Read more