Download Metaphysical Konowledge, Paris, 31 March 2012 Kausale

The metaphysics of entanglement,
Oxford, 26 January 2015
The natural philosophy of
classical and quantum
physics
Michael Esfeld
Université de Lausanne
[email protected]
1
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
The ontology
1)
2)
matter points: spatial structure
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
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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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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)
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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)
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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 (dynamical parameters in CM; not attributed
to particles individually in QM)
no primitive thisness (haecceity)
bare substrata with primitive stuff-essence
mysterious
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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
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Fundamental ontology
no cogent 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)
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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
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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
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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
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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, wavefunction, etc.  dynamical structure
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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
15
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
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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
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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
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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
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Conclusion
1) spatial configuration of matter points; persisting, substances;
structurally individuated by spatial relations
2) variation in the spatial relations  change; dynamical
structure to capture change
3) spatial structure: permutation invariant; dynamical structure:
sorts matter points into different kinds of particles
4) spatial structure: factual; dynamical structure: modal, power
that determines correlated change in spatial relations
(interaction)
5) 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
6) objects the same through theory change; dynamical structure
varies
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