1

LMU The ontology of physics15 October 14

The beginning of natural philosophy: from the Presocratics to Newton

Michael EsfeldLMU-MCMP &Université de Lausanne

Natural philosophy

Aristotle (389-323 before J.C.):physis: the realm of what exists in itself; physics: the science of that realmmetaphysics: the general principles of beingNewton: Philosophiae naturalis principia mathematica (1687) physics and philosophy in one: physics on the basis of the definition of general concepts about naturecontra positivism: mathematical formalism does not speak for itself contra armchair metaphysics: no knowledge about nature without empirical knowledgeAristotle, 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 611-549 before J.C.)Anaximenos (about 600-550 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 spacefour elements: water, fire, earth, air

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.”

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

indiscerniblesparticles 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

emptymore 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

particlesstuff, gunkevents

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