The Ontology of Matter Points in Natural Philosophy and Physics

1. The metaphysics of entanglement,Oxford, 26 January 2015The natural philosophy of classical and quantum physics Michael Esfeld Université de Lausanne Michael-Andreas.Esfeld@unil.ch

2. The methodology • natural philosophy: general and fundamental ontology of the natural world: prima philosophia • physics and philosophy coming in one • against both a priori metaphysics & neo-positivism

3. The ontology 1) matter points: spatial structure 2) change: dynamical structure book project Extended substance: The ontology of the natural world “The ontology of Bohmian mechanics”, BJPS 65 (2014), 773-796, with Dustin Lazarovici, Mario Hubert and Detlef Dürr “The physics and metaphysics of primitive stuff”, BJPS forthcoming, with Vincent Lam, Dustin Lazarovici and Mario Hubert “The dynamics of matter points” &“A particle ontology for the Dirac sea in QFT”, with Dirk-André Deckert and Andrea Oldofredi

4. Democritos (about 460-370 before J.C.) “There is an infinite number of impenetrable atoms, without qualities and indestructible, which move in the void where they are distributed.But when they come close to each other or collide, their aggregation results in water, in fire, in a plant, or in a human being.”

5. Newton, Opticks (1704) “… it seems probable to me, that God in the Beginning form'd Matter in solid, massy, hard, impenetrable, moveable Particles … the Changes of corporeal Things are to be placed only in the various Separations and new Associations and motions of these permanent Particles."

6. Atomism • proposal for a fundamental ontology that is most parsimonious & most general and that explains the familiar macroscopic world • macroscopic objects composed of fundamental, indivisible particles • all the differences between the macroscopic objects – at a time as well as in time – accounted for in terms of the spatial configuration of the particles and its change • greatest triumph in classical mechanics • but also quantum mechanics one needs ontology of matter distributed in physical space (otherwise measurement problem)

7. First approximation • discrete (particles) • inserted into absolute background space; 3d, Euclidean •  particle = what occupies a point of space •  variation: points of space occupied or empty • change in which points of space are empty and which ones are occupied as time passes • If change such that continuous lines of occupation of points of space, then worldlines = continuous sequences of events = particles (QM: Bohmian mechanics) • If not, then only single events (QM: GRW flash theory)

8. Problem • What makes up the difference between a point of space being occupied and a point of space being empty? • no intrinsic properties such as mass or charge (dynamical parameters in CM; not attributed to particles individually in QM) • no primitive thisness (haecceity) • bare substrata with primitive stuff-essence mysterious

9. Contra gunk • continuous fundamental ontology (gunk) instead of discrete objects (particles) (QM: GRW matter density theory) • Allori et al. (2014): “Moreover, the matter that we postulate in GRWm and whose density is given by the m function does not ipso facto have any such properties as mass or charge; it can only assume various levels of density.” • What does constitute the various levels of density of matter at points of space, if there are no properties such as mass or charge available? •  primitive stuff-essence that can assume various levels of density at points of space

10. Fundamental ontology • nocogent answer to the question of what distinguishes matter from space available •  abandon dualism of matter and space: no absolute space into which matter is inserted • relationalism about space (Leibniz): matter points connected by spatial relations (non-vanishing distance and direction) • only matter points and spatial relations, no points of space • background independence • Cartesianism: matter points, because connected by spatial relations (res extensa); standing in spatial relations distinguishes matter points from (hypothetical) mind points. • matter points persisting: substances (but no intrinsic physical properties) (Parmenides: no being out of nothing)

11. Ontic structural realism • all there is to the matter points are the spatial relations •  structurally individuated, spatial relations their essence • “internal relatedness of all things” (Schaffer), but not monism: plurality of substances • moderate ontic structural realism: objects and relations mutually ontologically dependent • If one removed the spatial relations, there would not remain bare substrata; there would then be nothing. •  OSR not against object-oriented metaphysics, but against property-oriented metaphysics • permutation invariant • at least weakly discernible • network of spatial relations: spatial structure

12. Matter points: summary • fundamental: matter points not composed of anything, compose everything else • primitive objects: no intrinsic physical properties, but not bare substrata; spatial relations their essence. • factual: configuration of matter points simply there •  most parsimonious and most general way to conceive fundamental ontology of the natural world that is able to account for familiar macroscopic domain: matter points connected by spatial relations

13. Introducing dynamics • no change, no motion: homogeneous configuration of matter points; no variation in, no variation out • deviation from homogeneity: variation within configuration •  change in spatial relations, trajectories • Parmenides: change / motion eternal, existing due to variation in fundamental ontology •  time from change as suitable parametrization; no absolute time, no absolute space

14. Velocity law • if change in spatial relations among the matter points such that velocity remains constant (e.g. Newtonian inertial motion), specify initial velocity  whole change in the configuration thereby fixed • if change such that velocities also change, interaction among the matter points: their velocities change in a correlated manner •  velocity has to be specified for each transition from one configuration of matter points to another one • task: fix velocity such that specifying initial conditions at an arbitrary time and plugging them into velocity law is sufficient to determine the motion of the matter points at any time • further dynamical parameters necessary: mass, charge, energy, wave-function, etc.  dynamical structure

15. Newtonian mechanics • Newton‘s gravitational constant G and masses of matter points as determining the potential V (given the spatial relations) & the initial velocities: dynamical structure of Newtonian classical mechanics

16. Bohmian quantum mechanics • Newton’s gravitational constant G and and masses of matter points as determining the potential V, Planck’s constant & the initial wave function Ψ0: dynamical structure of Bohmian quantum mechanics

17. Dynamical structure • spatial structure: permutation invariant • dynamical structure: distinguishes matter points; sorts them into various particle species •  particle species through dynamics, not intrinsic • dynamical structure defined only for particle configuration as a whole:to solve the equations, initial data for entire configuration required • dynamical relations that couple motion of particles to one another interaction = correlated change of velocities • no properties needed: structure all there is: spatial structure individuating material objects, dynamical structure fixing change of spatial relations

18. Dynamical structure • spatial structure: factual • dynamical structure: modal: fixes for any configuration of matter points given as initial condition what the world would be like if that configuration were the actual one = how the world would evolve if that configuration were the actual one • Humeanism: nothing modal in the world •  dynamical structure only structure of theory that describes change in spatial relations in most simple & informative way (best system); only spatial relations and change that happens to occur in their configuration in the world • modal realism: dynamical structure real physical relations like spatial structure •  power that literally determines change in spatial relations

19. Dynamical structure:classical & quantum • in any case non-local correlations • stronger in quantum physics than in classical physics: one wave-function Y for whole particle configuration  correlates in principle the velocity of all matter points independently of their distance • small deviations in initial conditions will lead to widely divergent trajectories •  more prominent role for probabilistic descriptions • only difference between classical and quantum •  objects the same through theory change, dynamical structure varies

20. Conclusion • spatial configuration of matter points; persisting, substances; structurally individuated by spatial relations • variation in the spatial relations  change; dynamical structure to capture change • spatial structure: permutation invariant; dynamical structure: sorts matter points into different kinds of particles • spatial structure: factual; dynamical structure: modal, power that determines correlated change in spatial relations (interaction) • dynamical structure applies in any case to the configuration of matter points as a whole; correlations between velocities of matter points stronger in quantum physics than in classical physics • objects the same through theory change; dynamical structure varies