The dynamical approach to spin-2 gravity

This paper engages with the following closely related questions that have recently received some attention in the literature: (a) what is the status of the equivalence principle in general relativity (GR)?; (b) how does the metric field obtain its property of being able to act as a metric?; and (c) is the metric of GR derivative on the dynamics of the matter fields? The paper attempts to complement these debates by studying the spin-2 approach to (quantum) gravity. In particular, the paper argues that three lessons can be drawn from the spin-2 approach: (1) different from what is sometimes claimed in the literature, central aspects of the non-linear theory of GR are already derivable in classical spin-2 theory; in particular, ‘universal coupling’ can be considered a derived ‘theorem’ in both the classical and the quantum spin-2 approach; this provides new insights for the investigation of the equivalence principle; (2) the ‘second miracle’ that Read et al. argue characterises GR is explained in the classical as well as in the quantum version of the spin-2 approach; (3) the spin-2 approach allows for an ontological reduction of the metrical part of spacetime to the dynamics of matter fields

Explaining Unification in Physics Internally

In this paper I challenge two widespread convictions about unification in physics: (1) unification is an aim of physics and (2) unification is driven by metaphysical or metatheoretical presuppositions. I call these external explanations of why there is unification in physics. Against this, I claim that (a) unification is a by-product of physical research and (b) unification is driven by basic methodological strategies of physics alone (without any appeal to metaphysical or metatheoretical presuppositions). I call this an internal (or methodological) explanation of why there is unification in physics. To support my claims, I will investigate the actual practice undertaken in physics in paradigmatic examples of unification

Quantum Gravity: A Dogma of Unification?

The quest for a theory of quantum gravity is usually understood to be driven by philosophical assumptions external to physics proper. It is suspected that specifically approaches in the context of particle physics are rather based on metaphysical premises than experimental data or physical arguments. I disagree. In this paper, I argue that the quest for a theory of quantum gravity sets an important example of physics’ internal unificatory practice. It is exactly Weinberg’s and others’ particle physics stance that reveals the issue of quantum gravity as a genuine physical problem arising within the framework of quantum field theory

On Progress in Metaphysics

In a recent paper, Kerry McKenzie identifies theory change in science as a source for doubts about the value of engaging in metaphysics of science before a final theory is at hand. According to McKenzie, the basic problem is that naturalized metaphysics lacks a concept of progress. More specifically, naturalized metaphysics lacks a concept of progress as approximation that can easily be taken to correspond to the scientific sources of naturalized metaphysical inquiry. In this paper, we criticise the proposed concept of progress as approximation as too narrow a concept, notably, even in science, and propose an alternative notion of scientific progress that metaphysical investigations can and do latch on to, namely progress understood as exploring and constraining theory space. First, we motivate this notion of progress via an examination of progress in particle physics and propose that it can be applied to metaphysics as well. Second, we argue that this notion of progress leads to a convincing reply to McKenzie's argument. Third, we discuss how this notion of progress relates to the program of naturalized metaphysics and argue that it speaks in favor of a more lenient version of naturalistically-inclined metaphysics, namely inductive metaphysics

Philosophy, physics, and the problems of spacetime emergence

According to theories of quantum gravity, spacetime may be non-fundamental. The implications of this observation are now widely debated in the philosophy of quantum gravity. In this paper we argue that what is often discussed under the umbrella term of `spacetime emergence' in the philosophy of quantum gravity literature in fact consists of a plethora of distinct and even highly different problems. We therefore advocate to cast such debates more specifically in terms of emergent spatiotemporal aspects as is already done in the physics literature. We first show how ambiguous the notion of spacetime is and offer five understandings of what the problem of spacetime emergence may still amount to. We then argue, however, that there are many philosophical problems relating to spacetime emergence and that none of the five understandings picks out a problem that is exceptional among these. Next, we observe that different spatiotemporal aspects are emergent in different quantum gravity approaches whereby speaking of quantum gravity collectively is problematic. Finally, we illustrate how inquiries about spacetime emergence are actually aided by conducting the investigation at the level of specific spatiotemporal aspects

A Dynamical Perspective on the Arrow of Time

It is standardly believed that the generally time-reversal symmetric fundamental laws of physics themselves cannot explain the apparent asymmetry of time. In particular, it is believed that CP violation is of no help. In this paper, I want to push back against a quick dismissal of CP violation as a potential source for the arrow of time and argue that it should be taken more seriously for conceptualising time in physics. I first recall that CP violation is a key feature of our best physical theory which also has large-scale explanatory import regarding the matter-antimatter asymmetry of the universe. I then investigate how CP violation may help to explain the directionality of time. I argue that accounts à la Maudlin that posit an intrinsic fundamental direction of time are not convincing and instead propose to utilise recent results from work on the dynamical approach to relativity theory

The constructivist’s programme and the problem of pregeometry

Prominently, Norton (2008) argues against constructivism about spacetime theories, the doctrine that spatiotemporal structure in the dynamics only has derivative status. Among other things, he accuses Brown and Pooley's dynamical approach to special relativity of being merely half-way constructivist: setting up relativistic fields as presupposed in the dynamical approach to special relativity already requires spatiotemporal background structure (pregeometry from now on). We first assess a recent solution proposal by Menon and then provide our very own defense of constructivism along two independent lines