1 LMU The ontology of physics 22 October 14 Properties and laws Michael Esfeld LMU-MCMP & Université de Lausanne

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

3 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

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

Change / Laws I  change of position of the particles  property of velocity (= first temporal derivative of position dq / dt = v)  initial velocity  certain motion of the particles  initial velocity explains motion of particles  initial velocity conserved if it is the only property to be taken into account  inertial motion  Newton’s first law: “Every body perseveres in its state either of rest or of uniform motion in a straight line, except insofar as it is compelled to change its state by impressed forces.”

Change / Laws II  change not only in the points that the particles occupy, but also in their state of motion = change of velocity  more properties necessary than velocity  properties that determine the temporal development of velocity (acceleration, second temporal derivative of position)  forces  Newton’s second law: “The change in motion is proportional to the impressed motive force and is made along the straight line on which the force is impressed.”

Properties II  particles: mass  in virtue of possessing mass, the particles attract each other  no ontological commitment to forces necessary; forces units for mathematical calculation of the change of velocity of the particles, but don’t exist in nature (no animism)  distribution of the particles in space at t = distribution of mass in space at t  change of velocity (acceleration) of the particles at t determined  law of gravitation

Laws: general scheme  general scheme:  dx/dt : explanandum, what the theory seeks to explain  D 1 … D n : explanans, what does the explanatory work  D 1 … D n : properties that determine the temporal development of x  dispositions  dx/dt : manifestation of properties / dispositions  D 1 … D n : causes ; dx/dt : effect (  physical causation without passing of time between cause and effect)  universal, deterministic

Newton: particular choice  initial velocity  change in position (first order)  mass  forces  change in velocity (second order)  second order theory pursued throughout classical mechanics  initial position, initial velocity & mass, charge  forces  simpler choice: first order theory: initial position & property / properties that determine the change in position

The aim 3)How do matter and its properties / laws explain the observable phenomena?  (a) macrophysical objects composed of microphysical particles; (b) the differences between the macrophysical objects can be traced back to the position (configuration) and the change of position (motion) of the microphysical particles