Alexander Franklin

Many would regard rigour as self-evidently a virtue in philosophical theorising. By considering two vignettes from recent debates over reduction in philosophy of physics I'll argue that the pursuit of rigour has distracted philosophers from the questions that motivated their research: in both contexts I'll suggest that less rigorous analysis would better enable such questions to be satisfactorily answered. I'll claim that these case studies exemplify aspects of the broadside against rigour developed in Wilson (2021).

Effective quantum field theories (EFTs) 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 (autonomy ms ), from autonomy with respect to changes in microlaws (autonomy ml ), and relating these, respectively, to renormalizability and naturalness. It is claimed that the effectiveness of EFTs is a consequence of each theory’s autonomy ms rather than its autonomy ml. 1Introduction 2Renormalizability 2.1Explaining renormalizability 3Naturalness 3.1An unnatural but renormalizable theory 4Two Kinds of Autonomy 5The Effectiveness of Effective Quantum Field Theories 6Conclusion.

Recent literature has raised what I'll call the 'multiscale argument' against reduction (see e.g. Batterman (2013), Wilson (2017), Bursten (2018)). These authors observe that numerous successful scientific models appeal to features and properties from a wide range of spatial/temporal scales. This is taken to undermine views that the world is sharply divided into distinct levels, roughly corresponding to different scales, and that each higher level is reducible to the next lowest level. While the multiscale argument does undermine a naive conception of levels and reduction, in this paper I argue that alternative views of reduction and levels can withstand this argument. After articulating the multiscale argument in more detail, I show that this does not undermine a version of reduction that accepts methodological pluralism in science, yet maintains that the adequacy of any model can be explained by appeal to details at smaller scales. I go on to discuss a case study – dislocations in steel –e used by Batterman and Wilson in defence of the multiscale argument. I argue that the version of reduction advocated above is available in this context. I conclude by arguing that, in the face of the multiscale argument, levels are either everywhere or nowhere.

The modern Everett interpretation of quantum mechanics describes an emergent multiverse. The goal of this paper is to provide a perspicuous characterisation of how the multiverse emerges making use of a recent account of (weak) ontological emergence. This will be cashed out with a case study that identifies decoherence as the mechanism for emergence. The greater metaphysical clarity enables the rebuttal of critiques due to Baker (2007) and Dawid and Th\'ebault (2015) that cast the emergent multiverse ontology as incoherent; responses are also offered to challenges to the Everettian approach from Maudlin (2010) and Monton (2013).

Scientific realists don’t standardly discriminate between, say, biology and fundamental physics when deciding whether the evidence and explanatory power warrant the inclusion of new entities in our ontology. As such, scientific realists are committed to a lush rainforest of special science kinds (Ross, 2000). Viruses certainly inhabit this rainforest – their explanatory power is overwhelming – but viruses’ properties can be explained from the bottom up: reductive explanations involving amino acids are generally available. However, reduction has often been taken to lead to a metaphysical downgrading, so how can viruses keep their place in the rainforest? In this paper, we show how the inhabitants of the rainforest can be inoculated against the eliminative threat of reduction: by demonstrating that they are emergent. According to our account, emergence involves a screening off condition as well as novelty. We go on to demonstrate that this account of emergence, which is compatible with theoretical reducibility, satisfies common intuitions concerning what should and shouldn’t count as real: viruses are emergent, as are trout and turkeys, but philosophically gerrymandered objects like trout-turkeys do not qualify.

Whether or not quantum physics can account for molecular structure is a matter of considerable controversy. Three of the problems raised in this regard are the problems of molecular structure. We argue that these problems are just special cases of the measurement problem of quantum mechanics: insofar as the measurement problem is solved, the problems of molecular structure are resolved as well. In addition, we explore one consequence of our argument: that claims about the reduction or emergence of molecular structure cannot be settled independently of the choice of a particular resolution to the measurement problem. Specifically, we consider how three standard putative solutions to the measurement problem inform our under- standing of a molecule in isolation, as well as of chemistry’s relation to quantum physics.

Multiple realisation prompts the question: how is it that multiple systems all exhibit the same phenomena despite their different underlying properties? In this paper I develop a framework for addressing that question and argue that multiple realisation can be reductively explained. I illustrate this position by applying the framework to a simple example – the multiple realisation of electrical conductivity. I defend my account by addressing potential objections:contra Polger and Shapiro, Batterman, and Sober, I claim that multiple realisation is commonplace, that it can be reductively explained, but that it requires asui generisreductive explanatory strategy.

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.

Recent discussions of emergence in physics have focussed on the use of limiting relations, and often particularly on singular or asymptotic limits. We discuss a putative example of emergence that does not fit into this narrative: the case of phonons. These quasi-particles have some claim to be emergent, not least because the way in which they relate to the underlying crystal is almost precisely analogous to the way in which quantum particles relate to the underlying quantum field theory. But there is no need to take a limit when moving from a crystal lattice based description to the phonon description. Not only does this demonstrate that we can have emergence without limits, but also provides a way of understanding cases that do involve limits.

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.