LMU The ontology of physics 22 October 14

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

Knowledge about nature: physical theory z z 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? z 3) How do matter and its properties / laws explain the observable phenomena? z justification by coherence: universal theory of nature that makes it possible to predict and explain the phenomena

Ontic structural realism z z z all there is to the matter points are the metrical relations in which they stand matter points structurally individuated by 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. 3

Change z 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 z 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 z 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 annihilated all the time

Change z 2) What are the properties of matter so that certain laws describe its behaviour? z properties: what determines the way in which the objects change / develop in time

Change / Laws I z change of position of the particles ® property of velocity (= first temporal derivative of position dq / dt = v) z initial velocity certain motion of the particles z initial velocity explains motion of particles z 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 z 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 z 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 z particles: mass z 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) z 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 z law of gravitation

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

Newton: particular choice z initial velocity change in position (first order) z mass forces change in velocity (second order) z second order theory pursued throughout classical mechanics ® initial position, initial velocity & mass, charge forces z 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? z (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