Vincent Lam

Maître-assistant
Epistemology and Philosophy of Science
University of Lausanne
Department of Philosophy
CH-1015 Lausanne
e-mail : vincent.lam@unil.ch
Phone +41 (0)21 692 29 23

Specialisation: space-time philosophy, philosophy of physics.

Competence: philosophy of science, epistemology, theoretical physics, metaphysics, philosophy of mind.

This dissertation investigates the nature of space-time as described by the theory of general relativity. It mainly argues that space-time can be naturally interpreted as a physical structure in the precise sense of a network of concrete space-time relations among concrete space-time points that do not possess any intrinsic properties and any intrinsic identity. Such an interpretation is fundamentally based on two related key features of general relativity, namely substantive general covariance and background independence, where substantive general covariance is understood as a gauge-theoretic invariance under active diffeomorphisms and background independence is understood in the sense that the metric (or gravitational) field is dynamical and that, strictly speaking, it cannot be uniquely split into a purely gravitational part and a fixed purely inertial part or background.
More broadly, a precise notion of (physical) structure is developed within the framework of a moderate version of structural realism understood as a metaphysical claim about what there is in the world. So, the developement of this moderate structrual realism pursues two main aims. The first is purely metaphysical, the aim being to develop a coherent metaphysics of structures and of objects (particular attention is paid to the questions of identity and individuality of these latter within this structural realist framework). The second is to argue that moderate structural realism provides a convincing interpretation of the world as described by fundamental physics and in particular of space-time as described by general relativity. This structuralist interpretation of space-time is discussed within the traditional substantivalist-relationalist debate, which is best understood within the broader framework of the question about the relationship between space-time on the one hand and matter on the other. In particular, it is claimed that space-time structuralism does not constitute a `tertium quid' in the traditional debate.
Some new light on the question of the nature of space-time may be shed from the fundamental foundational issue of space-time singularities. Their possible `non-local' (or global) feature is discussed in some detail and it is argued that a broad structuralist conception of space-time may provide a physically meaningful understanding of space-time singularities, which is not plagued by the conceptual diffculties of the usual atomsitic framework. Indeed, part of these difficulties may come from the standard differential geometric description of space-time, which encodes to some extent this atomistic framework; it raises the question of the importance of the mathematical formalism for the intrepretation of space-time.

Keywords: Substantivalism, relationalism, general covariance, background independence, structural realism, space-time points, identity, fibre bundles, space-time singularities, locality, Einstein algebras.

• Foundational issues in contemporary space-time physics : space-time singularities and gravitational energy. The aim of this project is to investigate the questions of space-time singularities and of gravitational energy within general relativity. Indeed there are many aspects of these fundamental questions that remain badly understood, not only at the technical level but also at the conceptual level. Despite their importance, they have attracted the attention of surprisingly few philosophers of physics (notable exceptions are Earman (1995), Curiel (1999) and Mattingly (2001) about space-time singualrities and Hoefer (2000) and Curiel (2000) about gravitational energy). So, the first step is to clarify as precisely as possible the various philosophically interesting aspects involved in these questions. About space-time singularities, these (interrelated) aspects include among others the question of the relevance of space-time singularities for the investigation of the nature of space-time, the meaning and the implications of the theorems about space-time singualrities, the very definition of space-time singualrities, their non-local or global features, their fate in the quantum gravity regim and in particular their possible dissolution in loop quantum cosmology (Bojowald 2001). Moreover, space-time singualrities may constitute an interesting case study within the framework of the investigation of the link between classical and (possible) quantum aspects of space-time. Concerning the gravitational energy, the main aspect that needs to be further investigated is its well-known but badly understood non-locality. In particular, the possible implications for the debate about the nature of space-time need to be clarified. In this persepctive, the theoretical developments invovling quasi-local and global quantities (ADM mass for instance) should be carefully discussed.
  
  
• The physical basis and the metaphysics of structural realism. It is widely accepted that contemporary fundamental physics, in particular the quantum (field) theory and the (general) relativistic theory, has deeply changed our conception of the world. Many aspects of these two fundamental physical theories have been discussed in some details, such as for instance the possible violation of locality in quantum theory or the absence of absolute simultaneity in the theory of relativity. However, no global worldview, no general metaphysical conception of nature that encompasses the fundamental features of contemporary fundamental physics has been developed in a systematic way. This is the aim of this research project. And the main claim of this project is that structural realism, conceived as a metaphysical thesis, does provide such a global worldview. Structural realism finds its contemporary origin in the epistemological insight that the intrinsic nature of objects cannot be known in principle and that only the relations among objects are accessible; consequently, structural realism has been set out as an epistemic thesis in the first place. However, in recent years, structural realism has been put forward as a metaphysical thesis about what there is in the world as well, namely only structures. We gain knowledge about the world through science, and more particularly through fundamental physics as far as fundamental aspects of nature are concerned. Consequently, any metaphysical thesis about the world has to be supported by what fundamental physics says about the world. Indeed, the structuralism move is grounded in the difficulties created by contemporary fundamental physics for the traditional metaphysical framework: the standard worldview, which can be traced back to Aristotle at least and according to which the world is made of a plurality of independently existing entities that enter into relation to one another, is deeply challenged by fundamental physics, in particular by quantum theory and general relativity theory. This research project aims first to present in a detailed way the main features of fundamental physics that challenge this traditional atomistic conception of nature. Then, starting from these empirical facts, it aims to develop a metaphysics of structure, called moderate structural realism, that accounts for these fundamental features. The core idea of moderate structural realism is that fundamental objects do not possess any intrinsic identity, the relations (structures) are the ways in which the objects exist. Clearly, this move constitutes a radical metaphysics of nature that raises many questions. A fundamental one is about the link of such a metaphysics with our experience of acting beings in the world. This research project aims to show that such a metaphysics of nature, even if exclusively motivated by fundamental physics, is able to account for causation as a fundamental feature of the world and therefore can ground our experience of acting beings. Thus, the research project globally aims at developing a coherent and experimentally well-founded metaphysics of nature.
  
  

• V. Lam, 'Causation and Space-time', Hist. Phil. Life Sci., 27, 483-499, 2005 (refereed).
• V. Lam, 'Is a world only made up of relations possible ? A structural realist point of view', in M.Esfeld (ed.), John Heil. Symposium on his ontological point of view, Frankfurt : Ontos, 2006.
• M. Esfeld and V. Lam, 'Moderate structural realism about space-time', Synthese, 160, 27-46, 2008 (refereed).
• M. Esfeld and V. Lam, 'Holism and structural realism' with M.Esfeld, forthcoming in R.Vanderbeeken & E.Weber (eds.): Worldviews, science and us: Studies of analytical metaphysics. A selection of topics from a methodological perspective.
• V. Lam, 'The singular nature of space-time', Philosophy of Science (Proceedings PSA 2006), 74, 2007 (refereed)..
• V. Lam, 'Structural aspects of the singular feature of space-time', in D. Dieks (ed.), Ontology of Spacetime. Philosophy and Foundations of Physics Series. Vol.2, 111-131. Amsterdam : Elsevier, 2008 (refereed).
• M. Esfeld and V. Lam, 'Structures as the objects of fundamental physics', with M. Esfeld, Proceedings of the Max Planck Institute research colloquium 'Epistemic objects' (forthcoming).
• M. Dorato, M. Esfeld, V. Lam, "GRW as a fundamental physical theory : an ontology of structures and dispositions" (submitted).