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 historical claims concerning (...) Newton, and argue that the dynamical account does not undercut ontological issues as the books claim. *Received January 2009; revised March 2009. †To contact the author, please write to: Department of Philosophy, 1423 University Hall MC 267, University of Illinois at Chicago, 601 S. Morgan Street, Chicago, IL 60607; e‐mail: huggett@uic.edu. (shrink)

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.

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. But now we are looking at a problem (...) that is physically and formally well-defined, proving that the problems of renormalization, by themselves, cannot refute QFT. (shrink)

We explicate recent results that shed light on the obscure and troubling problem of renormalization in Quantum Field Theory (QFT). 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. But now we are looking at a (...) problem that is physically and formally well-defined, proving that the problems of renormalization, by themselves, cannot refute QFT. (shrink)

Book Review of: "Everywhere and Everywhen: Adventures in Physics and Philosophy" by Nick Huggett.

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.

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.

Numerous approaches to a quantum theory of gravity posit fundamental ontologies that exclude spacetime, either partially or wholly. This situation raises deep questions about how such theories could relate to the empirical realm, since arguably only entities localized in spacetime can ever be observed. Are such entities even possible in a theory without fundamental spacetime? How might they be derived, formally speaking? Moreover, since by assumption the fundamental entities cannot be smaller than the derived and so cannot ‘compose’ them in (...) any ordinary sense, would a formal derivation actually show the physical reality of localized entities? We address these questions via a survey of a range of theories of quantum gravity, and generally sketch how they may be answered positively. (shrink)

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 historical claims concerning (...) Newton, and argue that the dynamical account does not undercut ontological issues as the books claim. (shrink)

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.

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 oscillator, there are no measurements ‘outside’ string theory (...) that could distinguish the duals. Second, whether duals agree or disagree on the radius of ‘target space’, the space in which strings evolve according to string theory. I argue for the latter position, because the alternative leaves it unknown what the radius is. Since duals are physically equivalent yet disagree on the radius of target space, it follows that the radius is indeterminate between them. Using an analysis of Brandenberger and Vafa (1989), I explain why – even so – space is observed to have a determinate, large radius. The conclusion is that observed, ‘phenomenal’ space is not target space, since a space cannot have both a determinate and indeterminate radius: instead phenomenal space must be a higher-level phenomenon, not fundamental. (shrink)

This paper investigates the mathematical representation of time in physics. In existing theories time is represented by the real numbers, hence their formal proper- ties represent properties of time: these are surveyed. The central question of the paper is whether the existing representation of time is adequate, or whether it can or should be supplemented: especially, do we need a physics incorporating some kind of ‘dynamical passage’ of time? The paper argues that the existing mathematical framework is resistant to such (...) changes, and might have to be rejected by anyone seeking a physics of passage. Then it rebuts two common arguments for incorporating passage into physics, especially the claim that it is an element of experience. Finally the paper investigates whether, as has been claimed, ‘causal set theory’ provides a physics of passage. (shrink)

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.

Weyl symmetry of the classical bosonic string Lagrangian is broken by quantization, with profound consequences described here. Reimposing symmetry requires that the background space-time satisfy the equations of general relativity: general relativity, hence classical space-time as we know it, arises from string theory. We investigate the logical role of Weyl symmetry in this explanation of general relativity: it is not an independent physical postulate but required in quantum string theory, so from a certain point of view it plays only a (...) formal role in the explanation. (shrink)

This paper develops and defends three related forms of relationism about spacetime against attacks by contemporary substantivalists. It clarifies Newton's globes argument to show that it does not bear on relations that fail to determine geodesic motions, since the inertial effects on which Newton relies are not simply correlated with affine structure, but must be understood in dynamical terms. It develops remarks by Sklar and van Fraassen into relational versions of Newtonian mechanics, and argues that Earman does not show them (...) to trivialize the debate. (shrink)

Learning through original texts can be a powerful heuristic tool. This book collects a dozen classic readings that are generally accepted as the most significant contributions to the philosophy of space. The readings have been selected both on the basis of their relevance to recent debates on the nature of space and on the extent to which they carry premonitions of contemporary physics. In his detailed commentaries, Nick Huggett weaves together the readings and links them to our modern (...) understanding of the subject. Together the readings indicate the general historical development of the concept of space, and in his commentaries Huggett explains their logical relations. He also uses our contemporary understanding of space to help clarify the key ideas of the texts. One goal is to prepare the reader (both scientist and nonscientist) to learn and understand relativity theory, the basis of our current understanding of space. The readings are by Zeno, Plato, Aristotle, Euclid, Descartes, Newton, Leibniz, Clarke, Berkeley, Kant, Mach, Poincaré, and Einstein. (shrink)

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.

Much apprehension has been expressed by philosophers about the method of renormalisation in quantum field theory, as it apparently requires illegitimate procedure of infinite cancellation. This has lead to various speculations, in particular in Teller (1989). We examine Teller's discussion of perturbative renormalisation of quantum fields, and show why it is inadequate. To really approach the matter one needs to understand the ideas and results of the renormalisation group, so we give a simple but comprehensive account of this topic. With (...) this in hand, we explain how renormalisation can and should be understood. One thing that is revealed is that apparently very successful theories such as quantum electro-dynamics cannot be universally true; resolving the tension between success and falsity leads to a picture in which any theory may be viewed as irreducibly phenomenological. We explain how, and argue that the support for this view is tenuous at best. (shrink)

I want to review some ways in which Quantum Mechanics seems to affront our “common-sense” notions of identity. Let’s start with a list.

This paper considers the implications for the relational-substantival debate of observations of parity nonconservation in weak interactions, a much neglected topic. It is argued that 'geometric proofs' of absolute space, first proposed by Kant (1768), fail, but that parity violating laws allow 'mechanical proofs', like Newton's laws. Parity violating laws are explained and arguments analogous to those of Newton's Scholium are constructed to show that they require absolute spacetime structure--namely, an orientation--as Newtonian mechanics requires affine structure. Finally, it is considered (...) how standard relationist responses to Newton's argument might respond to the new challenge of parity nonconservation. (shrink)

There has been considerable recent philosophical debate over the implications of many particle quantum mechanics for the metaphysics of individuality (cf. Huggett [1997]). In this paper I look at things from a rather different perspective: by investigating the significance of permutation symmetry. I consider how various philosophical positions link up to the physical postulate of the indistinguishability of permuted states-permutation invariance-and how this postulate is used to explain quantum statistics. I offer an explanation of the statistics that relies on (...) the neglected parallel between permutations and covariant spatial transformation. And I explore the parallel, showing that a further kind of symmetry explains why permutations are invariant when spatial symmetries are not. (shrink)

Review of Dominic Gregory's "Showing, Sensing, and Seeming".

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 (but disputed by others) to provide a `witness' of (...) the underlying quantum nature of gravity in the non-relativistic limit, using superpositions of Planck-mass bodies. We inspect what sort of achievement it would possibly be to perform GIE experiments, as proposed, ultimately arguing that the positive claim of witness is equivocal. Despite various sweeping arguments to the contrary in the vicinity of quantum information theory or given low-energy quantum gravity, whether or not one can claim to witness the quantum nature of the gravitational field in these experiments decisively depends on which out of two legitimate modelling paradigms one finds oneself in. However, by situating GIE experiments in a tradition of existing experiments aimed at making gravity interestingly quantum in the laboratory, we argue that, independently of witnessing or paradigms, there are powerful reasons to perform the experiments, and that their successful undertaking would indeed be a major advance in physics. (shrink)

A number of commentators (especially French and Redhead, 1988, and Butterfield, 1993) have investigated the status of the principle of the identity of indiscernibles (PII) for bosons and fermions. In this paper I extend that investigation to the full range of quantum particles of any allowed kind of statistics -- `quarticles', that is. I show that for any kind (except bosons and fermions) there are states in which PII is violated by every pair of particles, some pairs and not others, (...) and by no pairs. (shrink)

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.

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.

In this paper we critically review the various attempts that have been made to understand quantum field theory. We focus on Teller's (1990) harmonic oscillator interpretation, and Bohm et al.'s (1987) causal interpretation. The former unabashedly aims to be a purely heuristic account, but we show that it is only interestingly applicable to the free bosonic field. Along the way we suggest alternative models. Bohm's interpretation provides an ontology for the theory--a classical field, with a quantum equation of motion. This (...) too has problems; it is not Lorentz invariant. (shrink)

I criticize a certain view of the 'quanta' of quantum mechanics that sees them as fundamentally non-atomistic and fundamentally significant for our understanding of quantum fields. In particular, I have in mind work by Redhead and Teller (1991, 1992 and Teller 1990). I prove that classical particles do not have the rather strong flavour of identity often associated with them; permuting positions and momenta does not produce distinct states. I show that even the label free excitation formalism is compatible with (...) a mild form of atomism. Finally, I summarise some of the principle objections to an 'oscillator' interpretation of quantum fields. (shrink)

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 (...) address some important philosophical and conceptual questions: the confirmatory value of the derivation, the bearing of the model on recent discussions of the so-called ‘information paradox’, and the implications of the model for the nature of space. (shrink)

This work first explicates the philosophy of classical and quantum fields and particles. I am interested in determining how science can have a metaphysical dimension, and then with the claim that the quantum revolution has an important metaphysical component. I argue that the metaphysical implications of a theory are properties of its models, as classical mechanics determines properties of atomic diversity and temporal continuity with its representations of distinct, continuous trajectories. ;It is often suggested that classical statistical physics requires that (...) many particle states be represented so that permuting properties leads to distinct states; this implies that individuals can be reidentified across possible worlds in a non-qualitative way. I show there is no evidence for this conclusion, an important result, for it is claimed that quantum particles are not individuals. This claim is based on the misconception about classical statistics, but also on a conflation of notions of identity; I show that, while transworld identity is incompatible with quantum mechanics, other classical notions may be consistently ascribed. I also give a field-particle distinction that applies usefully in both quantum and classical domains. In the former the distinction helps defeat claims of underdetermined by data, in the latter it helps provide a minimal field metaphysics. ;Next I tackle renormalisation: I show how divergences occur in approximate, perturbative calculations, and demonstrate how finite, empirically verified, answers are obtained. These techniques seem to show that the predictions are not logical consequences of the exact theory. I use the techniques of the renormalisation group to establish that perturbative renormalised quantum field theory does indeed approximate the consequences of field theory. ;Finally, I discuss the idea that renormalisation proves that there can be no quantum theory of everything, only a patchwork of effective theories. The preceding chapter shows that renormalisation demonstrates only that the picture is consistent, and this is insufficient to show that physics must be phenomenological. (shrink)

Since the collapse of the 'received view' consensus in the late 1960s, the question of scientific realism has been a major preoccupation of philosophers of science. This paper sketches the history of this debate, which grew from developments in the philosophy of language, but eventually took on an autonomous existence. More recently, the debate has tended towards more 'local' considerations of particular scientific episodes as a way of getting purchase on the issues. The paper reviews two such approaches, Fine's and (...) Hacking's, describing their positions, their prospects, and how they are related. Finally, the paper suggests that local philosophies of science offer a way for our discipline to engage more fruitfully with the public and the scientific community. (shrink)

Was the first book to examine the exciting area of overlap between philosophy and quantum mechanics with chapters by leading experts from around the world.

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 historical claims concerning (...) Newton, and argue that the dynamical account does not undercut ontological issues as the books claim. (shrink)

Why is our knowledge of the past so much more ‘expansive’ (to pick a suitably vague term) than our knowledge of the future, and what is the best way to capture the difference(s) (i.e., in what sense is knowledge of the past more ‘expansive’)? One could reasonably approach these questions by giving necessary conditions for different kinds of knowledge, and showing how some were satisfied by certain propositions about the past, and not by corresponding propositions about the future. I take (...) it that such is the approach of Chapter 6 of Time and Chance (T&C). Here’s another such a proposal, similar to that of, but significantly different from T&C; my purpose in this section is to highlight the differences, by showing how this account fails. (shrink)

In this paper we contrast the idea of a field as a system with an infinite number of degrees of freedom with a recent alternative proposed by Paul Teller in Teller (1990). We show that, although our characterisation lacks the immediate appeal of Teller's, it has more success producing agreement with intuitive categorisations than his does. We go on to extend the distinction to Quantum Mechanics, explaining the important role that it plays there. Finally, we take some time to investigate (...) the way in which strings are to be considered fields, and the important differences with scalar fields. Overall, we aim to show that many types of systems may be viewed as fields, and to point out significant distinctions amongst them, thereby expanding our understanding of what it is to fall in this category. (shrink)

Numerous approaches to a quantum theory of gravity posit fundamental ontologies that exclude spacetime, either partially or wholly. This situation raises deep questions about how such theories could relate to the empirical realm, since arguably only entities localized in spacetime can ever be observed. Are such entities even possible in a theory without fundamental spacetime? How might they be derived, formally speaking? Moreover, since the fundamental entities can't be smaller than the derived by assumption and so can't 'compose' them in (...) any ordinary sense, would a formal derivation actually show the physical reality of localized entities? We address these questions via a survey of a range of theories of quantum gravity, and generally sketch how they may be answered positively. (shrink)

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 turn, philosophical methods and insights are brought to bear on the (...) foundations of quantum gravity itself. For instance, the idea of functionalism, borrowed from the philosophy of mind and discussed by several essays, exemplifies this mutual interaction the collection seeks to foster. (shrink)

This is the table of contents and first chapter of Physics Meets Philosophy at the Planck Scale (Cambridge University Press, 2001), edited by Craig Callender and Nick Huggett. The chapter discusses the question of why there should be a theory of quantum gravity. We tackle arguments that purport to show that the gravitational field *must* be quantized. We then introduce various programs in quantum gravity and discuss areas where quantum gravity and philosophy seem to have something to say (...) to each other. (shrink)

Prior research found correlations between reflection test performance and philosophical tendencies among laypeople. In two large studies (total N = 1299)—one pre-registered—many of these correlations were replicated in a sample that included both laypeople and philosophers. For example, reflection test performance predicted preferring atheism over theism and instrumental harm over harm avoidance on the trolley problem. However, most reflection-philosophy correlations were undetected when controlling for other factors such as numeracy, preferences for open-minded thinking, personality, philosophical training, age, and gender. Nonetheless, (...) some correlations between reflection and philosophical views survived this multivariate analysis and were only partially confounded with either education or self-reported reasoning preferences. Unreflective thinking still predicted believing in God whereas reflective thinking still predicted believing that (a) proper names like ‘Santa’ do not necessarily refer to entities that actually exist and (b) science does reveal the fundamental nature of the world. So some robust relationships between reflection and philosophical tendencies were detected even among philosophers, and yet there was clearly more to the link between reflection and philosophy. To this end, demographic and metaphilosophical hypotheses are considered. (shrink)

We review the various factors that limit adaptation by natural selection. Recent discussion of constraints on selection and, conversely, of the factors that enhance “evolvability”, have concentrated on the kinds of variation that can be produced. Here, we emphasise that adaptation depends on how the various evolutionary processes shape variation in populations. We survey the limits that population genetics places on adaptive evolution, and discuss the relationship between disparate literatures. BioEssays 22:1075–1084, 2000. © 2000 John Wiley & Sons, Inc.