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
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Natural philosophy
Aristotle (389-323 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 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 space
four 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.”
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.”
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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
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
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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
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
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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.
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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.
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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.
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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