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)

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)

This paper analyses the anti-reductionist argument from renormalisation group explanations of universality, and shows how it can be rebutted if one assumes that the explanation in question is captured by the counterfactual dependence account of explanation.

Dans cet article nous analysons des écrits réflexifs de fin de formation de mentors, afin d’identifier les marques de transformation de l’identité professionnelle et de l’agir professionnel. Nous proposons une analyse thématique et langagière des textes en tant que porteurs d’un rapport au monde professionnel en cours d’élaboration. Nous mettons en évidence que ces textes contiennent des traces de renormalisations issues des apprentissages conceptuels et formels autant que des apprentissages expérientiels réalisés durant la formation. Cette analyse interroge au bout du (...) compte la formation elle-même avec ses multiples attendus. (shrink)

It is commonly claimed that the universality of critical phenomena is explained through particular applications of the renormalization group. This article has three aims: to clarify the structure of the explanation of universality, to discuss the physics of such RG explanations, and to examine the extent to which universality is thus explained. The derivation of critical exponents proceeds via a real-space or a field-theoretic approach to the RG. Building on work by Mainwood, this article argues that these approaches ought to (...) be distinguished: while the field-theoretic approach explains universality, the real-space approach fails to provide an adequate explanation. (shrink)

Effective quantum field theories are effective insofar as they apply within a prescribed range of length-scales, but within that range they predict and describe with extremely high accuracy and precision. The effectiveness of EFTs is explained by identifying the features—the scaling behaviour of the parameters—that lead to effectiveness. The explanation relies on distinguishing autonomy with respect to changes in microstates, from autonomy with respect to changes in microlaws, and relating these, respectively, to renormalizability and naturalness. It is claimed that the (...) effectiveness of EFTs is a consequence of each theory’s autonomyms rather than its autonomyml.1Introduction2Renormalizability2.1Explaining renormalizability3Naturalness3.1An unnatural but renormalizable theory4Two Kinds of Autonomy5The Effectiveness of Effective Quantum Field Theories6Conclusion. (shrink)

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)

An effective theory in physics is one that is supposed to apply only at a given length scale; the framework of effective field theory describes a ‘tower’ of theories each applying at different length scales, where each ‘level’ up is a shorter-scale theory. Owing to subtlety regarding the use and necessity of EFTs, a conception of emergence defined in terms of reduction is irrelevant. I present a case for decoupling emergence and reduction in the philosophy of physics. This paper develops (...) a positive conception of emergence, based on the novelty and autonomy of the ‘levels’, by considering physical examples, involving critical phenomena, the renormalisation group, and symmetry breaking. This positive conception of emergence is related to underdetermination and universality, but, I argue, is preferable to other accounts of emergence in physics that rely on universality. (shrink)

I give an introduction to the conceptual structure of quantum field theory as it is used in mainstream theoretical physics today, aimed at non-specialists. My main focuses in the article are the common structure of quantum field theory as it is applied in solid-state physics and as it is applied in high-energy physics; the modern theory of renormalisation.

Quantum gravity is understood as a theory that, in some sense, unifies general relativity (GR) and quantum theory, and is supposed to replace GR at extremely small distances (high-energies). It may be that quantum gravity represents the breakdown of spacetime geometry described by GR. The relationship between quantum gravity and spacetime has been deemed ``emergence'', and the aim of this thesis is to investigate and explicate this relation. After finding traditional philosophical accounts of emergence to be inappropriate, I develop a (...) new conception of emergence by considering physical case studies including condensed matter physics, hydrodynamics, critical phenomena and quantum field theory understood as effective field theory. This new conception of emergence is unconcerned with the ideas of reduction and derivation (i.e. it holds that we may have emergence with reduction or without it). Instead, a low-energy theory (or model) is understood as emergent from a high-energy theory if it is novel and autonomous compared to the high-energy theory, and the low-energy physics is dependent in a particular, minimal sense on the high-energy physics (this dependence is revealed by the techniques of effective field theory and the renormalisation group). While novelty is construed in a broad sense, the autonomy comes essentially from the underdetermination of the high-energy theory by the low-energy theory, which reflects the minimal way in which the emergent, low-energy theory depends on the high-energy one. It results from the scaling behaviour of the theories and the limiting relations between them, and is demonstrated by the renormalisation group and effective field theory techniques, the idea of universality, and the phenomenon of symmetry-breaking. These ideas are important in exploring the relationship between quantum gravity and GR, where GR is understood as an effective, low-energy theory of quantum gravity. Without experimental data or a theory of quantum gravity, we rely on principles and techniques from other areas of physics to guide the way. As well as considering the idea of emergence appropriate to treating GR as an effective field theory, I investigate the emergence of spacetime (and other aspects of GR) in several concrete approaches to quantum gravity, including examples of the condensed matter approaches, the ``discrete approaches'' (causal set theory, causal dynamical triangulations, quantum causal histories and quantum graphity) and loop quantum gravity. (shrink)

The universality of critical phenomena is best explained by appeal to the Renormalisation Group (RG). Batterman and Morrison, among others, have claimed that this explanation is irreducible. I argue that the RG account is reducible, but that the higher-level explanation ought not to be eliminated. I demonstrate that the key assumption on which the explanation relies – the scale invariance of critical systems – can be explained in lower-level terms; however, we should not replace the RG explanation with a (...) bottom-up account, rather we should acknowledge that the explanation appeals to dependencies which may be traced down to lower levels. (shrink)

This contribution aims to understand the process of renormalisation operated at the level of internship tutors by the management team in a French physiotherapy training institute, faced with the implementation of a reform of the studies. The study is based on the concepts of corporate social responsibility (CSR) and leadership and on a three-year interview survey with the management. The results highlight the issues encountered in the first year and the training dynamics implemented in the third year. The discussion (...) debates the evolution of CSR and the concomitant leadership it develops. (shrink)

This paper critically contrasts Laudan’s normative naturalism with Friedman’s arguments about the importance of a priori concepts in scientific methodology. I do not take issue with Laudan’s claim that taking philosophy and science to be continuous does not preclude a normative role for the philosophy of science. The main focus of criticism instead is Laudan’s assertion that if normative philosophy employs the methods found in the sciences themselves, then this precludes any a priori or philosophical justification of methodological rules. I (...) make the case that not only are such justifications possible, they are central to any proper philosophical understanding of scientific methodology, and must figure prominently in any plausible version of normative naturalism. To make this case I sketch Laudan’s position and his reasons for the ban on a priori justification. I then contrast Laudan’s position with Friedman’s recent studies on the prominence ofrelativised constitutive a priori principles within science and show that this view can serve as the basis of a contrasting variation of naturalised philosophy of science. I elucidate Friedman’s position in order to identify some prima facie difficulties with Laudan’s ban on the a priori in our understanding of science but also to provide an example of a competing variation of philosophical naturalism. Finally, I further highlight the difficulties that attend Laudan’s position through a case study, the central methodological role of renormalisation in quantum field theory. (shrink)

This paper critically contrasts Laudan’s normative naturalism with Friedman’s arguments about the importance of a priori concepts in scientific methodology. I do not take issue with Laudan’s claim that taking philosophy and science to be continuous does not preclude a normative role for the philosophy of science. The main focus of criticism instead is Laudan’s assertion that if normative philosophy employs the methods found in the sciences themselves, then this precludes any a priori or philosophical justification of methodological rules. I (...) make the case that not only are such justifications possible, they are central to any proper philosophical understanding of scientific methodology, and must figure prominently in any plausible version of normative naturalism. To make this case I sketch Laudan’s position and his reasons for the ban on a priori justification. I then contrast Laudan’s position with Friedman’s recent studies on the prominence ofrelativised constitutive a priori principles within science and show that this view can serve as the basis of a contrasting variation of naturalised philosophy of science. I elucidate Friedman’s position in order to identify some prima facie difficulties with Laudan’s ban on the a priori in our understanding of science but also to provide an example of a competing variation of philosophical naturalism. Finally, I further highlight the difficulties that attend Laudan’s position through a case study, the central methodological role of renormalisation in quantum field theory. (shrink)

Die Arbeit schlägt eine beweistheoretische Analyse der mathematischen Physik im Gegensatz zu gegenwärtigen modelltheoretischen Ansätzen vor. Über eine oberflächliche Analogie hinaus haben beweistheoretische Techniken und Renormalisationsverfahren ein gemeinsames Ziel: die Ausschaltung von Unendlichkeiten in einer konsistenten Theorie. Die Geschichte der Renormalisation in Quantenfeldtheorien wird kurz skizziert und eine allgemeine These über die Natur und Justizfizierung von Theorien in der mathematischen Physik vorgeschlagen. Wir schließen mit den Grundlinien für ein Forschungsprogramm für eine physikalische Logik.