Project

quantum gravity; mereology; duality; metaphysics; emergence

Lead
Le projet vise à participer à la construction d’un nouveau champ de recherche, la métaphysique de la gravité quantique, en comblant le fossé qui sépare le travail des physiciens de celui des philosophes.
Lay summary
Le projet vise à participer à la construction d’un nouveau champ de recherche : la métaphysique de la gravité quantique. L’expression « gravité quantique » désigne une collection de programmes de recherche qui aspirent à unifier l’ensemble des connaissances obtenues à l’aide de nos deux théories physiques les plus fondamentales : la relativité générale et la théorie quantique des champs. La théorie quantique des champs offre une caractérisation exceptionnellement précise de l’univers et de ses aspects quantiques ; cependant, elle ne décrit pas la gravitation. D’un autre côté, la relativité générale décrit brillamment la gravitation, en l’appréhendant comme un aspect géométrique de l’espace-temps. Toutefois, cette dernière ne permet pas de décrire les effets quantiques. Ceci est problématique dans la mesure où nous avons besoin d’une théorie de la gravité quantique si nous voulons décrire les phénomènes faisant intervenir à la fois des effets quantiques et des effets relativistes, des phénomènes tels que les trous noirs et les premiers instants de l’univers. Or, d’après ces programmes de recherche, l’espace-temps n’existe pas fondamentalement et des descriptions de la réalité qui semblent au premier abord décrire des mondes très différents sont en fait équivalentes, une bizarrerie nommée « dualité ». L’objectif de ce projet est de construire une interprétation métaphysique de l'émergence de l’espace-temps et des dualités. L’hypothèse principale de ce projet est qu’il est possible de réaliser cet objectif en soutenant que l’émergence de l’espace-temps et la dualité peuvent s’analyser comme une composition d’entités spatio-temporelles à partir d’entités non-spatio-temporelles.

Direct link to Lay Summary

Last update: 21.05.2019

Active participation

Communication	Title	Media	Place	Year

Title	Year

The project aims at participating to the building of a new field: the metaphysics of quantum gravity. Quantum gravity is a constellation of research programs aimed at finding a new framework to weave together all we know from General Relativity (GR) and Quantum Field Theory (QFT). QFT does a very good job at describing the universe with its quantum effects, but it does not describe gravitation. On the other hand, GR offers an excellent characterization of gravitation, describing it as a geometrical aspect of spacetime; however, it does not take into account quantum effects. But we do need a theory of quantum gravity in order to describe the phenomena that include both relativistic and quantum effects, such as black holes or the earlier stages of the universe. In order to build such a theory, various research programs have been developed in many directions. Two points of particular interest for metaphysics are, first, that many of these approaches, such as Loop Quantum Gravity (LQG) and String Theory (ST), deny the fundamental reality of spacetime (or at least of some of its main features) and claim that spacetime, and space and time as we ordinarily conceive of them, do emerge from “something else”. Second, some physical theories, in particular in ST, are mysteriously related by relations of correspondence which have come to be known as dualities, suggesting that our theories merely describes particular aspects of something more fundamental. This project will propose to build an ontological interpretation of spacetime emergence and dualities by using mereological notions such as proper parts and mereological sums (cf. Paul 2002, 2006, 2012, forthcoming).Philosophy of physics has addressed these issues, but not much has been written on the metaphysical assumptions consistent with emergence and duality, and it becomes urgent to get a better understanding of the ontological implications of spacetime emergence and duality. At the present time, the philosophy of quantum gravity is almost exclusively occupied by physicists and philosophers of physics. The project will participate in the recent appeal to correct this situation (cf. for instance Muntean 2015) by offering clear ontological interpretations of spacetime emergence and duality, using the toolbox of analytic metaphysics. The project will look at this problem with a focus on the notion of composition and propose several metaphysical interpretations of spacetime emergence and duality.In the sub-project 1 entitled “Emergence as Composition”, I will focus on the problem of extended simples, namely that some views about quantum gravity, such as loop quantum gravity, entail that building blocks of the physical world are both extended and lacking proper parts, a puzzling idea. I will argue that the problem follows from the use of notions based on the emergent spacetime, rather than on the fundamental ontologies suggested by quantum gravity, and propose to identify spacetime emergence with logical composition (in L.A. Paul’s sense, 2002, 2006, 2012, forthcoming). I will then defend that extended simples look mysterious only because these entities are looked at from two different perspectives: the fundamental non-spatio-temporal perspective, and the derivative spatio-temporal perspective. Second, I will argue that the composition of spacetime from non-spatio-temporal building blocks leads to a form of scepticism about the fundamental ontology of the actual world, since the very same emergent spacetime is consistent with alternative fundamental ontologies.In the second sub-project entitled “Emergence and Duality as Composition”, I will use mereology in order to understand the metaphysics of emergence and duality in a particular research program: string theory. I will focus on the metaphysical lessons to be drawn from S-duality and, in particular, from the fact that particles construed as being elementary in one particular dual may be mapped onto the particles taken to be composite in its dual description. Second, I will use mereology to propose a novel ontological explanation of T-duality, S-duality and the AdS/CFT correspondence, arguing that although the dual descriptions are empirically equivalent, they are nonetheless numerically distinct, arguing that the phenomenal space is identical to the mereological sum of the dual structures.