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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 (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.”
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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
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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
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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.
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
