It is argued that Minkowski space-time cannot serve as the deep structure within a ``constructive'' version of the special theory of relativity, contrary to widespread opinion in the philosophical community.

A number of recent theories of quantum gravity lack a one-dimensional structure of ordered temporal instants. Instead, according to many of these views, our world is either best represented as a single three-dimensional object, or as a configuration space composed of such three-dimensional objects, none of which bear temporal relations to one another. Such theories will be empirically self-refuting unless they can accommodate the existence of conscious beings capable of representation. For if representation itself is impossible in a timeless world, (...) then no being in such a world could entertain the thought that a timeless theory is true, let alone believe such a theory or rationally believe it. This paper investigates the options for understanding representation in a three-dimensional, timeless, world. Ultimately it concludes that the only viable option is one according to which representation is taken to be deeply non-naturalistic. Ironically then we are left with two seemingly very unattractive options. Either a very naturalistic motivation—taking seriously a live view in fundamental physics—leads us to a very non-naturalistic view of the mental, or else views in the philosophy of mind partly dictate what is an acceptable theory in physics. (shrink)

Current debate in the metaphysics of time ordinarily assumes that we should be realists about time. Recently, however, a number of physicists and philosophers of physics have proposed that time will play no role in a completed theory of quantum gravity. This paper defends fictionalism about temporal thought, on the supposition that our world is timeless. We argue that, in the face of timeless physical theories, realism about temporal thought is unsustainable: some kind of anti-realism must be adopted. We go (...) on to provide an argument against eliminativism about temporal thought. While it doesn't follow from this argument that fictionalism about temporal thought is true, we suggest that this nonetheless shows that fictionalism should be regarded as the preferred view. (shrink)

Several approaches to quantum gravity signal the loss of spacetime at some level. According to spacetime functionalism, spacetime is functionally realised by a more fundamental structure. According to one version of spacetime functionalism, the spacetime role is specified by Ramsifying general relativity. In some approaches to QG, however, there does not appear to be anything that exactly realises the functional role defined by a Ramsey sentence for GR. The spacetime role is approximately realised. It is open to the spacetime functionalist (...) to adopt a ‘near enough is good enough’ attitude to functional realisation, and maintain that spacetime is functionally realised nonetheless. In this paper I present a challenge for such an ‘approximate’ spacetime functionalism. The challenge, in brief, is to provide an account of how ‘close’ is close enough for approximate realisation to occur. I canvass a range of options for spelling out a similarity relation of the relevant kind, and argue that none are successful. In light of the challenge, I recommend giving up on the functional realisation of spacetime. I argue, however, that even if spacetime as a whole is not functionally realised, some of the functions of spacetime may still be performed. (shrink)

This paper offers a new way to evaluate counterfactual conditionals on the supposition that actually, there is no time. We then parlay this method of evaluation into a way of evaluating causal claims. Our primary aim is to preserve, at a minimum, the assertibility of certain counterfactual and causal claims once time has been excised from reality. This is an important first step in a more general reconstruction project that has two important components. First, recovering our ordinary language claims involving (...) notions such as persistence, change and agency and, second, recovering enough observational evidence so that any timeless metaphysics is not empirically self-refuting. However, the project of investigating causation in a timeless setting has a greater relevance than its application to timeless physical theory alone. For, as we show, it can be used to model the assertibility conditions of causal claims more generally. (shrink)

The implications for the substantivalist–relationalist controversy of Barbour and Bertotti's successful implementation of a Machian approach to dynamics are investigated. It is argued that in the context of Newtonian mechanics, the Machian framework provides a genuinely relational interpretation of dynamics and that it is more explanatory than the conventional, substantival interpretation. In a companion paper (Pooley [2002a]), the viability of the Machian framework as an interpretation of relativistic physics is explored. 1 Introduction 2 Newton versus Leibniz 3 Absolute space versus (...) an affine connection 4 Anti-relationalist arguments 5 Rehabilitating relationalism 6 Dynamics on the relative configuration space 7 Intrinsic particle dynamics 8 Conclusion. (shrink)

The `problem of time' is a cluster of interpretational and formal issues in the foundations of general relativity relating to both the representation of time in the classical canonical formalism, and to the quantization of the theory. The purpose of this short chapter is to provide an accessible introduction to the problem.

I analyse the conceptual and mathematical foundations of Lagrangian quantum field theory (QFT) (that is, the ‘naive’ (QFT) used in mainstream physics, as opposed to algebraic quantum field theory). The objective is to see whether Lagrangian (QFT) has a sufficiently firm conceptual and mathematical basis to be a legitimate object of foundational study, or whether it is too ill-defined. The analysis covers renormalisation and infinities, inequivalent representations, and the concept of localised states; the conclusion is that Lagrangian QFT (at least (...) as described here) is a perfectly respectable physical theory, albeit somewhat different in certain respects from most of those studied in foundational work. (shrink)

The paper presents a program to construct a non-relativistic relational Bohmian theory, that is, a theory of N moving point-like particles that dispenses with space and time as fundamental background structures. The relational program proposed is based on the best-matching framework originally developed by Julian Barbour. In particular, the paper focuses on the conceptual problems that arise when trying to implement such a program. It is argued that pursuing a relational strategy in the Bohmian context leads to a more parsimonious (...) ontology than that of standard Bohmian mechanics without betraying the original motivations for adopting a primitive ontology approach to quantum physics. It is also shown how a relational Bohmian approach might clarify the issue of the timelessness of the dynamics resulting from the quantization of a classical relational system of particles. (shrink)

The paper presents an inquiry into the question regarding the compatibility of Bohmian mechanics, intended as a non-local theory of moving point-like particles, with background independence. This issue is worth being investigated because, if the Bohmian framework has to be of some help in developing new physics, it has to be compatible with the most well-established traits of modern physics, background independence being one of such traits. The paper highlights the fact that the notion of background independence in the context (...) of spacetime physics is slippery and interpretation-laden. It is then suggested that the best-matching framework developed by Julian Barbour might provide a robust enough meaning of background independence. The structure of Bohmian dynamics is evaluated against this framework, reaching some intermediate results that speak in favor of the fact that Bohmian mechanics can be made background independent. (shrink)

We present a new metaphysical framework for physics that is conceptually clear, ontologically parsimonious, and empirically adequate. This framework relies on the notion of self-subsisting structure, that is, a set of fundamental physical elements whose individuation and behavior are described in purely relational terms, without any need for a background spacetime. Although the specification of the fundamental elements of the ontology depends on the particular physical domain considered---and is thus susceptible to scientific progress---, the empirically successful structural features of the (...) framework are preserved through theory change. The kinematics and dynamics of these self-subsisting structures are technically implemented using the theoretical framework of Pure Shape Dynamics, which provides a completely relational physical description of a system in terms of the intrinsic geometry of a suitably defined space called shape space. (shrink)

We have recently developed a new understanding of probability in quantum gravity. In this paper we provide an overview of this new approach and its implications. Adopting the de Broglie–Bohm pilot-wave formulation of quantum physics, we argue that there is no Born rule at the fundamental level of quantum gravity with a non-normalisable Wheeler–DeWitt wave functional \(\Psi\). Instead the universe is in a perpetual state of quantum nonequilibrium with a probability density \(P\ne \left| \Psi \right| ^{2}\). Dynamical relaxation to the (...) Born rule can occur only after the early universe has emerged into a semiclassical or Schrödinger approximation, with a time-dependent and normalisable wave functional \(\psi\), for non-gravitational systems on a classical spacetime background. In that regime the probability density \(\rho\) can relax towards \(\left| \psi \right| ^{2}\) (on a coarse-grained level). Thus the pilot-wave theory of gravitation supports the hypothesis of primordial quantum nonequilibrium, with relaxation to the Born rule taking place soon after the big bang. We also show that quantum-gravitational corrections to the Schrödinger approximation allow quantum nonequilibrium \(\rho \ne \left| \psi \right| ^{2}\) to be created from a prior equilibrium ( \(\rho =\left| \psi \right| ^{2}\) ) state. Such effects are very tiny and difficult to observe in practice. (shrink)

Symplectic reduction is a formal process through which degeneracy within the mathematical representations of physical systems displaying gauge symmetry can be controlled via the construction of a reduced phase space. Typically such reduced spaces provide us with a formalism for representing both instantaneous states and evolution uniquely and for this reason can be justifiably afforded the status of fun- damental dynamical arena - the otiose structure having been eliminated from the original phase space. Essential to the application of symplectic reduction (...) is the precept that the first class constraints are the relevant gauge generators. This prescription becomes highly problematic for reparameterization invariant theories within which the Hamiltonian itself is a constraint; not least because it would seem to render prima facie distinct stages of a history physically identical and observable functions changeless. Here we will consider this problem of time within non-relativistic me- chanical theory with a view to both more fully understanding the temporal struc- ture of these timeless theories and better appreciating the corresponding issues in relativistic mechanics. For the case of nonrelativistic reparameterization invariant theory application of symplectic reduction will be demonstrated to be both unnec- essary; since the degeneracy involved is benign; and inappropriate; since it leads to a trivial theory. With this anti-reductive position established we will then examine two rival methodologies for consistently representing change and observable func- tions within the original phase space before evaluating the relevant philosophical implications. We will conclude with a preview of the case against symplectic re- duction being applied to canonical general relativity. (shrink)

The canonical formalism of general relativity affords a particularly interesting characterisation of the infamous hole argument. It also provides a natural formalism in which to relate the hole argument to the problem of time in classical and quantum gravity. In this paper we examine the connection between these two much discussed problems in the foundations of spacetime theory along two interrelated lines. First, from a formal perspective, we consider the extent to which the two problems can and cannot be precisely (...) and distinctly characterised. Second, from a philosophical perspective, we consider the implications of various responses to the problems, with a particular focus upon the viability of a `deflationary' attitude to the relationalist/substantivalist debate regarding the ontology of spacetime. Conceptual and formal inadequacies within the representative language of canonical gravity will be shown to be at the heart of both the canonical hole argument and the problem of time. Interesting and fruitful work at the interface of physics and philosophy relates to the challenge of resolving such inadequacies. (shrink)

Hamiltonian constraints feature in the canonical formulation of general relativity. Unlike typical constraints they cannot be associated with a reduction procedure leading to a non-trivial reduced phase space and this means the physical interpretation of their quantum analogues is ambiguous. In particular, can we assume that “quantisation commutes with reduction” and treat the promotion of these constraints to operators annihilating the wave function, according to a Dirac type procedure, as leading to a Hilbert space equivalent to that reached by quantisation (...) of the problematic reduced space? If not, how should we interpret Hamiltonian constraints quantum mechanically? And on what basis do we assert that quantisation and reduction commute anyway? These questions will be refined and explored in the context of modern approaches to the quantisation of canonical general relativity. (shrink)

This paper is an attempt to answer the question, ‘could there be causation in a timeless world?’ My conclusion: tentatively, yes. The paper and argument have three parts. Part one introduces salient issues and spells out the importance of this line of investigation. Section two of the paper reviews recent arguments due to Baron and Miller, who argue in favour of the possibility of causation in a timeless world, and looks to reject their arguments developed there. Section three is a (...) response to a response. In their, Baron and Miller also argue that an argument in favour of the possibility of causation at timeless worlds, that I put forward, is an argument that fails. In section three, my response to Baron and Miller is that their argument against me succeeds, but that there is a nearby argument that we can appeal to in order to demonstrate the possibility of causation at timeless worlds. (shrink)

Within the philosophy of time there has been a growing interest in positions that deny the reality of time. Those positions, whether motivated by arguments from physics or metaphysics, have a shared conclusion: time is not real. What has not been made wholly clear, however, is exactly what it entails to deny the reality of time. Time is unreal, sure. But what does that mean? There has been only one sustained attempt to spell out exactly what it would mean to (...) endorse a temporal error theory; a theory that denies the reality of time—Baron & Miller’s ‘What is temporal error theory?’. Despite the fact that their paper makes significant strides in spelling out what would be required of a temporal error theory, my claim in this paper is that their position must be rejected and replaced. As well as looking to reject Baron and Miller’s position, I also look to provide that replacement. (shrink)

Humean Supervenience is the view that (a) there are a plurality of fundamental beings, (b) there are no inexplicable constraints on modal space, and hence the fundamental nature of each such being is independent of those of all the rest and of the fundamental relations in which it stands to the rest, (c) the fundamental beings stand in no fundamental causal or nomic relations, and hence (d) the distribution of any causal or nomic relations in which they do stand globally (...) supervenes on their fundamental natures and the non‐nomic, non‐causal fundamental relations in which they stand. If Humean Supervenience is true, then as A.J. Ayer put it, it's just one damn thing after another. Radical Pluralism is the view that Humean Supervenience is true, and, moreover, that none of the fundamental beings stands in any fundamental relations at all. If Radical Pluralism is true, then, as William James puts it, the world's pieces are held together by nothing more than conjunction: it's just one damn thing and another. I argue that Radical Pluralism is very likely true, conditional upon Humean Supervenience. Any philosopher pluralist enough to be Humean ought to be radically pluralistic. (shrink)

In General Relativity in Hamiltonian form, change has seemed to be missing, defined only asymptotically, or otherwise obscured at best, because the Hamiltonian is a sum of first-class constraints and a boundary term and thus supposedly generates gauge transformations. By construing change as essential time dependence, one can find change locally in vacuum GR in the Hamiltonian formulation just where it should be. But what if spinors are present? This paper is motivated by the tendency in space-time philosophy tends to (...) slight fermionic/spinorial matter, the tendency in Hamiltonian GR to misplace changes of time coordinate, and the tendency in treatments of the Einstein-Dirac equation to include a gratuitous local Lorentz gauge symmetry along with the physically significant coordinate freedom. Spatial dependence is dropped in most of the paper, both restricting the physical situation and largely fixing the spatial coordinates. In the interest of including all and only the coordinate freedom, the Einstein-Dirac equation is investigated using the Schwinger time gauge and Kibble-Deser symmetric triad condition are employed as a \ version of the DeWitt-Ogievetsky-Polubarinov nonlinear group realization formalism that dispenses with a tetrad and local Lorentz gauge freedom. Change is the lack of a time-like stronger-than-Killing field for which the Lie derivative of the metric-spinor complex vanishes. An appropriate \-friendly form of the Rosenfeld-Anderson-Bergmann-Castellani gauge generator G, a tuned sum of first class-constraints, is shown to change the canonical Lagrangian by a total derivative, implying the preservation of Hamilton’s equations. Given the essential presence of second-class constraints with spinors and their lack of resemblance to a gauge theory, it is useful to have an explicit physically interesting example. This gauge generator implements changes of time coordinate for solutions of the equations of motion, showing that the gauge generator makes sense even with spinors. (shrink)

Science depends on judgments of the bearing of evidence on theory. Scientists must judge whether an observation or the result of an experiment supports, disconfirms, or is simply irrelevant to a given hypothesis. Similarly, scientists may judge that, given all the available evidence, a hypothesis ought to be accepted as correct or nearly so, rejected as false, or neither. Occasionally, these evidential judgments can be made on deductive grounds. If an experimental result strictly contradicts a hypothesis, then the truth of (...) the data deductively entails the falsity of the hypothesis. In the great majority of cases, however, the connection between evidence and hypothesis is non-demonstrative, or inductive. In particular, this is so whenever a general hypothesis is inferred to be correct on the basis of the available data, since the truth of the data will not deductively entail the truth of the hypothesis. It always remains possible that the hypothesis is false even though the data are correct. (shrink)

What it would take to vindicate folk temporal error theory? This question is significant against a backdrop of new views in quantum gravity—so-called timeless physical theories—that claim to eliminate time by eliminating a one-dimensional substructure of ordered temporal instants. Ought we to conclude that if these views are correct, nothing satisfies the folk concept of time and hence that folk temporal error theory is true? In light of evidence we gathered, we argue that physical theories that entirely eliminate an ordered (...) substructure vindicate folk temporal error theory. (shrink)

We investigated, experimentally, the contention that the folk view, or naïve theory, of time, amongst the population we investigated is dynamical. We found that amongst that population, ~ 70% have an extant theory of time that is more similar to a dynamical than a non-dynamical theory, and ~ 70% of those who deploy a naïve theory of time deploy a naïve theory that is more similar to a dynamical than a non-dynamical theory. Interestingly, while we found stable results across our (...) two experiments regarding the percentage of participants that have a dynamical or non-dynamical extant theory of time, we did not find such stability regarding which particular dynamical or non-dynamical theory of time they take to be most similar to our world. This suggests that there might be two extant theories in the population—a broadly dynamical one and a broadly non-dynamical one—but that those theories are sufficiently incomplete that participants do not stably choose the same dynamical theory as being most similar to our world. This suggests that while appeals to the ordinary view of time may do some work in the context of adjudicating disputes between dynamists and non-dynamists, they likely cannot do any such work adjudicating disputes between particular brands of dynamism. (shrink)

The conditional probability interpretation of quantum gravity has been criticized for violating the constraints of the theory and also not giving the correct expression for the propagator. We have shown that following Page’s proposal of constructing an appropriate projector for the stationary state of a closed system, we can arrive at the correct expression for the propagator by using conditional probability rule. Also, it is shown that a unitary evolution of states of a subsystem at local level may be a (...) consequence of non-unitary projection of appropriate states at global level. (shrink)

Classical mechanics is presented so as to render the new formulation valid for an arbitrary temporal variable, as opposed to Newton’s Absolute Time only. Newton’s theory then becomes formally identical (in a precise sense) to relativity, albeit in a three-dimensional manifold. (The ultimate difference between the two dynamics is traced to the existence of the relativistic ‘mass-shell’ condition.) A classical Lagrangian is provided for our formulation of the equations of motion and it is related to one of the known forms (...) of the corresponding relativistic Lagrangian, which is the analogue of the Polyakov Lagrangian of string theory. (shrink)

The conceptual and technical difficulties involved in creating a quantum theory of gravity have led some physicists to question, and even in some cases to deny, the reality of time. More surprisingly, this denial has found a sympathetic audience among certain philosophers of physics. What should we make of these wild ideas? Does it even make sense to deny the reality of time? In fact physical science has been chipping away at common sense aspects of time ever since its inception. (...) Section 1 offers a brief survey of the demolition process. Section 2 distinguishes a tempered from an extremely radical form that a denial of time might take, and argues that extreme radicalism is empirically self-refuting. Section 3 begins an investigation of the prospects for tempered radicalism in a timeless theory of quantum gravity. (shrink)

Ajan luonnetta koskevissa käsityksissä on tyypillistä erottaa kaksi eriävää kantaa: A-teoreettinen presentismi ja B-teoreettinen eternalismi. Edeltävän väitetään tyypillisesti sopivan yhteen inhimillisen ajallisen kokemuksen kanssa ja jälkimmäisen ontologisesti perustavanlaatuisen luonnontieteen kanssa. Ilmikuvamme ajasta sisältää ehdottoman nykyisyyden ja yksisuuntaisen ajan kulun menneestä tulevaan. Tieteellinen kuva ajasta ei sisällä erityistä nykyisyyttä eikä ajan kulun edellyttämää dynaamista aikamuotojen muutosta. Monet ovat pitäneet kokemustamme ajan kulusta illuusiona. Tässä artikkelissa keskitytään A-sarjan mukaisen ajankulun virheteoreettiseen tulkintaan. Tarkastellaan mahdollisuutta, jonka mukaan meillä ei ole kyseistä kokemusta vaan kuvailemme (...) kokemustamme virheellisesti ajan virtaukseen liittyvillä vertauskuvilla. Tätä tukee fysikalistinen argumentti: Jos ajan kulun kokemuksellamme ei ole fysikaalista perustaa, meillä ei voi olla sen mukaista kokemustakaan ajasta. (shrink)

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, variational-problem description of classical mechanics, from which the link between gauge symmetry and the apparent violation of determinism is easy to understand; only towards the end will the Hamiltonian description be considered. -/- The other purpose is to warn against adopting too unified a perspective on gauge theories. It will be argued that the meaning of the gauge freedom in a theory like general relativity is (at least from the Lagrangian viewpoint) significantly different from its meaning in theories like electromagnetism. The Hamiltonian framework blurs this distinction, and orthodox methods of quantization obliterate it; this may, in fact, be genuine progress, but it is dangerous to be guided by mathematics into conflating two conceptually distinct notions without appreciating the physical consequences. (shrink)

The objective of this thesis is to present a naturalised metaphysics of information, or to naturalise information, by way of deploying a scientific metaphysics according to which contingency is privileged and a-priori conceptual analysis is excluded (or at least greatly diminished) in favour of contingent and defeasible metaphysics. The ontology of information is established according to the premises and mandate of the scientific metaphysics by inference to the best explanation, and in accordance with the idea that the primacy of physics (...) constraint accommodates defeasibility of theorising in physics. This metametaphysical approach is used to establish a field ontology as a basis for an informational structural realism. This is in turn, in combination with information theory and specifically mathematical and algorithmic theories of information, becomes the foundation of what will be called a source ontology, according to which the world is the totality of information sources. Information sources are to be understood as causally induced configurations of structure that are, or else reduce to and/or supervene upon, bounded (including distributed and non-contiguous) regions of the heterogeneous quantum field (all quantum fields combined) and fluctuating vacuum, all in accordance with the above-mentioned quantum field-ontic informational structural realism (FOSIR.) Arguments are presented for realism, physicalism, and reductionism about information on the basis of the stated contingent scientific metaphysics. In terms of philosophical argumentation, realism about information is argued for primarily by way of an indispensability argument that defers to the practice of scientists and regards concepts of information as just as indispensable in their theories as contingent representations of structure. Physicalism and reductionism about information are adduced by way of the identity thesis that identifies the substance of the structure of ontic structural realism as identical to selections of structure existing in re to combined heterogeneous quantum fields, and to the total heterogeneous quantum field comprised of all such fields. Adjunctly, an informational statement of physicalism is arrived at, and a theory of semantic information is proposed, according to which information is intrinsically semantic and alethically neutral. (shrink)

The conceptual incompatibility between General Relativity and Quantum Mechanics is generally seen as a sufficient motivation for the development of a theory of Quantum Gravity. If - so a typical argumentation - Quantum Mechanics gives a universally valid basis for the description of the dynamical behavior of all natural systems, then the gravitational field should have quantum properties, like all other fundamental interaction fields. And, if General Relativity can be seen as an adequate description of the classical aspects of gravity (...) and spacetime - and their mutual relation -, this leads, together with the rather convincing arguments against semi-classical theories of gravity, to a strategy which takes a quantization of General Relativity as the natural avenue to a theory of Quantum Gravity. And, because in General Relativity the gravitational field is represented by the spacetime metric, a quantization of the gravitational field would in some sense correspond to a quantization of geometry. Spacetime would have quantum properties. But, this direct quantization strategy to Quantum Gravity will only be successful, if gravity is indeed a fundamental interaction. Only if it is a fundamental interaction, the given argumentation is valid, and the gravitational field, as well as spacetime, should have quantum properties. - What, if gravity is instead an intrinsically classical phenomenon? Then, if Quantum Mechanics is nevertheless fundamentally valid, gravity can not be a fundamental interaction; a classical and at the same time fundamental gravity is excluded by the arguments against semi-classical theories of gravity. An intrinsically classical gravity in a quantum world would have to be an emergent, induced or residual, macroscopic effect, caused by a quantum substrate dominated by other interactions, not by gravity. Then, the gravitational field (as well as spacetime) would not have any quantum properties. And then, a quantization of gravity (i.e. of General Relativity) would lead to artifacts without any relation to nature. The serious problems of all approaches to Quantum Gravity that start from a direct quantization of General Relativity (e.g. non-perturbative canonical quantization approaches like Loop Quantum Gravity) or try to capture the quantum properties of gravity in form of a 'graviton' dynamics (e.g. Covariant Quantization, String Theory) - together with the, meanwhile, rich spectrum of (more or less advanced) theoretical approaches to an emergent gravity and/or spacetime - make this latter option more and more interesting for the development of a theory of Quantum Gravity. The most advanced emergent gravity (and spacetime) scenarios are of an information-theoretical, quantum-computational type. A paradigmatic model for the emergence of gravity and spacetime comes from the Pregeometric Quantum Causal Histories approach. (shrink)

One of Julian Barbour’s main aims is to solve the problem of time that appears in quantum geometrodynamics (QG). QG involves the application of canonical quantization procedure to the Hamiltonian formulation of General Relativity. The problem of time arises because the quantization of the Hamiltonian constraint results in an equation that has no explicit time parameter. Thus, it appears that the resulting equation, as apparently timeless, cannot describe evolution of quantum states. Barbour attempts to resolve the problem by allegedly eliminating (...) time from his interpretation of QG. In order to evaluate the efficacy of his solution, it is necessary to ascertain in what sense time has been eliminated from his theory. I proceed to do so by developing a form of conceptual analysis that is applicable to the concept of time in physical theories and applying this analysis to Barbour’s account. (shrink)

The purpose of this paper is to evaluate the `Lorentzian Pedagogy' defended by J.S. Bell in his essay ``How to teach special relativity'', and to explore its consistency with Einstein's thinking from 1905 to 1952. Some remarks are also made in this context on Weyl's philosophy of relativity and his 1918 gauge theory. Finally, it is argued that the Lorentzian pedagogy---which stresses the important connection between kinematics and dynamics---clarifies the role of rods and clocks in general relativity.

In a companion paper (Pooley & Brown 2001) it is argued that Julian Barbour's Machian approach to dynamics provides a genuinely relational interpretation of Newtonian dynamics and that it is more explanatory than the conventional, substantival interpretation. In this paper the extension of the approach to relativistic physics is considered. General relativity, it turns out, can be reinterpreted as a perfectly Machian theory. However, there are difficulties with viewing the Machian interpretation as more fundamental than the conventional, spacetime interpretation. Moreover, (...) this state of affairs provides little solace for the relationist for, even when interpreted along Machian lines, general relativity is a substantival theory although the basic entity is space, not spacetime. (shrink)

Quantum gravity is supposed to be the most fundamental theory, including a quantum theory of the metrical field (spacetime). However, it is not clear how a quantum theory of gravity could account for classical phenomena, including notably measurement outcomes. But all the evidence that we have for a physical theory is based on measurement outcomes. We consider this problem in the framework of canonical quantum gravity, pointing out a dilemma: all the available accounts that admit classical phenomena presuppose entities with (...) a well-defined spatio-temporal localization (“local beables” in John Bell's terms) as primitive. But there seems to be no possibility to include such primitives in canonical quantum gravity. However, if one does not do so, it is not clear how entities that are supposed to be ontologically prior to spacetime could give rise to entities that then are spatio-temporally localized. (shrink)

In this paper I wish to make some headway on understanding what \emph{kind} of problem the ``problem of time'' is, and offer a possible resolution---or, rather, a new way of understanding an old resolution. The response I give is a variation on a theme of Rovelli's \emph{evolving constants of motion} strategy. I argue that by giving correlation strategies a \emph{structuralist} basis, a number of objections to the standard account can be blunted. Moreover, I show that the account I offer provides (...) a suitable ontology for time in both classical and quantum canonical general relativity. (shrink)

This paper addresses the extent to which both Julian Barbour‘s Machian formulation of general relativity and his interpretation of canonical quantum gravity can be called timeless. We differentiate two types of timelessness in Barbour‘s (1994a, 1994b and 1999c). We argue that Barbour‘s metaphysical contention that ours is a timeless world is crucially lacking an account of the essential features of time—an account of what features our world would need to have if it were to count as being one in which (...) there is time. We attempt to provide such an account through considerations of both the representation of time in physical theory and in orthodox metaphysical analyses. We subsequently argue that Barbour‘s claim of timelessness is dubious with respect to his Machian formulation of general relativity but warranted with respect to his interpretation of canonical quantum gravity. We conclude by discussing the extent to which we should be concerned by the implications of Barbour‘s view. (shrink)

Julian Barbour's approach to dynamics is reviewed. With a particular focus on questions of explanation and confirmation, the approach is contrasted with standard formulations of dynamics. This paper expands upon my commentary on Lawrence Sklar's paper at the Philosophy of Time Society meeting at the APA's Central Division meeting in Chicago, April 2004. Although a commentary, the current paper is comprehensible without reference to Sklar's paper.