In the pure powers ontology (PPO), basic physical properties have wholly dispositional essences. PPO has clear advantages over categoricalist ontologies, which suffer from familiar epistemological and metaphysical problems. However, opponents argue that because it contains no qualitative properties, PPO lacks the resources to individuate powers, and generates a regress. The challenge for those who take such arguments seriously is to introduce qualitative properties without reintroducing the problems that PPO was meant to solve. In this paper, I distinguish the core claim (...) of PPO: (i) basic physical properties have dispositional essences, from a hitherto unnoticed assumption: (ii) the dispositional essences of basic physical properties exclusively involve type-causal relations to other basic physical properties. I reject (ii), making room for a structuralist ontology in which all basic physical properties are pure powers, individuated by their places in a causal structure that includes not only other powers, but also physically realized qualitative properties such as shapes, patterns and structures. Such qualities individuate pure powers in the way that non-mental input and output properties individuate realized mental properties in functionalist theories of mind, except that here it is basic physical powers that are individuated by relations to realized non-powers. I distinguish one Platonic and two Aristotelian version of this theory, and argue that the Aristotelian versions require that grounding is not always a relative fundamentality relation, because the powers ground the qualities that individuate them. By considering ontic structural realism, I argue that symmetric grounding is the best way to make sense of relational individuation in structuralist ontologies, and is therefore no additional commitment of the one proposed here. (shrink)

Les théories de la mécanique quantique et de la gravité quantique exigent-elles que l’espace-temps soit un trait fondamental de bas niveau, ou l’espace-temps peut-il être conçu comme un élément émergent de ces théories? Tandis que plusieurs commentateurs ont émis de sérieux doutes sur l’idée de se dispenser de l’arrière-plan d’un espace-temps standard, nous ferons valoir qu’une défense de ces interprétations de l’espace-temps émergeant des hypothèses de la mécanique et de la gravité quantiques peut être conduite soit par inférence à la (...) meilleure explication, soit en mobilisant une autre stratégie. De plus, on montrera que l’idée que l’espace et le temps peuvent émerger d’un niveau du réel tout à fait différent et non spatiotemporel a des précédents historiques variés, en particulier aux xviie et xviiie siècles. Cette prise de conscience peut aider à dissiper une partie du mystère associé à ces types d’hypothèses. (shrink)

In this paper, I discuss whether the results of loop quantum gravity (LQG) constitute a fatal blow to Humeanism. There is at least a prima facie reason for believing so: while Humeanism regards spatiotemporal relations as fundamental, LQG describes the fundamental layer of our reality in terms of spin networks, which are not in spacetime. However, the question should be tackled more carefully. After explaining the importance of the debate on the tenability of Humeanism in light of LQG, and having (...) presented the Humean doctrine, I review two cases which present serious threats to Humeanism, one concerning the fundamentality of vectorial quantities and the other concerning quantum entanglement. In particular, I recall the strategies that are usually employed in these two cases in order to save Humeanism: in the first case, the strategy consists in amending the characterization of the Humean mosaic; in the second case, it consists in adopting a realist or nomological interpretation of the wave function. These solutions will turn out to be helpful in my discussion of LQG where, after describing LQG, I show that Humeans might save their doctrine either by endorsing a realist interpretation of spin networks, or by giving them a nomological status and, at the same time, by revisiting the characterization of the Humean mosaic. However, I conclude that both solutions are wanting. (shrink)

This article discusses the peculiar features of quantum entanglement and quantum non-locality within the algebraic approach to relativistic quantum field theory (RQFT). The debate on the ontology of RQFT is considered in the light of these well-known but little discussed features. In particular, this article examines the ontic structural realist understanding of quantum entanglement and quantum non-locality and its contribution to this debate.

Must a theory of quantum gravity have some truth to it if it can recover general relativity in some limit of the theory? This paper answers this question in the negative by indicating that general relativity is multiply realizable in quantum gravity. The argument is inspired by spacetime functionalism—multiple realizability being a central tenet of functionalism—and proceeds via three case studies: induced gravity, thermodynamic gravity, and entanglement gravity. In these, general relativity in the form of the Einstein field equations can (...) be recovered from elements that are either manifestly multiply realizable or at least of the generic nature that is suggestive of functions. If general relativity, as argued here, can inherit this multiple realizability, then a theory of quantum gravity can recover general relativity while being completely wrong about the posited microstructure. As a consequence, the recovery of general relativity cannot serve as the ultimate arbiter that decides which theory of quantum gravity that is worthy of pursuit, even though it is of course not irrelevant either qua quantum gravity. Thus, the recovery of general relativity in string theory, for instance, does not guarantee that the stringy account of the world is on the right track; despite sentiments to the contrary among string theorists. (shrink)

While the relation between visualization and scientific understanding has been a topic of long-standing discussion, recent developments in physics have pushed the boundaries of this debate to new and still unexplored realms. For it is claimed that, in certain theories of quantum gravity, spacetime ‘disappears’: and this suggests that one may have sensible physical theories in which spacetime is completely absent. This makes the philosophical question whether such theories are intelligible, even more pressing. And if such theories are intelligible, the (...) question then is how they manage to do so. In this paper, we adapt the contextual theory of scientific understanding, developed by one of us, to fit the novel challenges posed by physical theories without spacetime. We construe understanding as a matter of skill rather than just knowledge. The appeal is thus to understanding, rather than explanation, because we will be concerned with the tools that scientists have at their disposal for understanding these theories. Our central thesis is that such physical theories can provide scientific understanding, and that such understanding does not require spacetimes of any sort. Our argument consists of four consecutive steps: We argue, from the general theory of scientific understanding, that although visualization is an oft-used tool for understanding, it is not a necessary condition for it; we criticise certain metaphysical preconceptions which can stand in the way of recognising how intelligibility without spacetime can be had; we catalogue tools for rendering theories without a spacetime intelligible; and we give examples of cases in which understanding is attained without a spacetime, and explain what kind of understanding these examples provide. (shrink)