1 LMU The ontology of physics 15 October 14 The beginning of natural philosophy: from the Presocratics to Newton Michael Esfeld LMU-MCMP & Université de Lausanne

Natural philosophy Aristotle ( before J.C.):  physis: the realm of what exists in itself; physics: the science of that realm  metaphysics: the general principles of being  Newton: Philosophiae naturalis principia mathematica (1687)  physics and philosophy in one: physics on the basis of the definition of general concepts about nature  contra positivism: mathematical formalism does not speak for itself  contra armchair metaphysics: no knowledge about nature without empirical knowledge  Aristotle, Descartes, Leibniz, Newton, Einstein

Knowledge about nature: physical theory  ontology: what there is (to on, ousia, hyle)  law: what describes the behaviour of what there is (nomos, kosmos)  1) What is matter?  2) What are the properties of matter so that certain laws describe its behaviour?  3) How do matter and its properties / laws explain the observable phenomena?  justification by coherence: universal theory of nature that makes it possible to predict and explain the phenomena

First Presocratic philosophers Thales (about 640 before J.C.) Anaximander (about before J.C.) Anaximenos (about before J.C.)  natural philosophers: bold hypotheses about the constitution of the universe as a whole  search for primary matter: matter as stuff (“gunk”) stretching out throughout space four elements: water, fire, earth, air

Democritos (about 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.”

6 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.”

Particles 1)What is matter? = What are the physical objects?  matter = particles distributed in three-dimensional space (background)  particle = material object that is so small that it is localized at a point in space  indivisible  particle = point of space occupied instead of empty  impenetrable  particles = primitive matter  definite number of particles, defined by number of points of space that are occupied

8 Discernibility  stipulation in atomism: each matter point is distinct from all the other ones by some metrical relations  absolutely discernible individuals  Leibniz: principle of the identity of indiscernibles  particles distinct in time through trajectory

Why particles?  Democritos, Newton: atomism: matter = distribution of particles in space = primitive fact that some points of space are occupied while others are empty  matter: atoms  plurality of substances  only initial variation: point of space occupied or empty more matter in some regions of space than in others: in some regions, more points are occupied than in others  Presocratics: matter = a single substance distributed all over space (“gunk”)  initial variation: more matter at certains points of space than at others

10 Contra gunk  contemporary gunk: 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

11 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  no primitive thisness (haecceity)  primitive stuff-essence mysterious  If there are essences, they better be constituted by properties (or relations), but never be primitive.

12 Descartes, Leibniz vs. Newton  ontology: discrete objects (particles)  matter points being connected by metrical relations (non-vanishing 3-dim distance between any two matter points that distinguishes them)  Leibniz: no commitment to absolute space: only matter points and metrical relations, no points of space  Cartesianism: matter points, because connected by metrical relations (res extensa); standing in spatial relations distinguishes primitive matter stuff from (hypothetical) primitive mind stuff.

13 Ontic structural realism  all there is to the matter points are the metrical relations in which they stand  matter points structurally individuated by metrical relations  metrical relations their essence  ontic structural realism  matter points primitive stuff in the sense that (a) fundamental (= not being composed of anything else, but compose everything else), (b) primitive objects (= no essence constituted by intrinsic properties); but no primitive stuff-essence.

Change  distribution of matter in space changes in time  variation in time: as time passes, change in which points of space are occupied and which ones are empty  = change in the metrical relations that connect the matter points as time passes  change such that there are continuous trajectories of particles  motion  each particle has an identity in time that distinguishes it from all the other particles  other possibility: events; but it is simpler to suppose that the fundamental objects continue to exist as time passes (= continue to exist in changing their position) than to suppose that the fundamental objects are created and annihilated all the time

Matter: three conceptions  particles  stuff, gunk  events

Change  2)What are the properties of matter so that certain laws describe its behaviour?  properties: what determines the way in which the objects change / develop in time