Pragmatic Ontology Identifying Propensity as Substance

1. Pragmatic OntologyIdentifying Propensity as Substance Ian Thompson Physics Department, University of Surrey, Guildford.

2. Aristotle matter in some form Descartes (essentially) extension Newton, Boyle: corpuscles Leibniz whose nature requires its separate existence Locke real essence unknown Boscovich point centre of forces Whitehead, Russell only events Views of Substance: synopsis

3. Substance and Form • Return to basic Aristotelian (physical) view: • Particular objects: • Exist, separately or in relation • All composed of some substance in some form • Form may be mathematical or qualitative. • Substance (generic) to be determined • called ‘matter’ (hyle) by Aristotle.

4. Form • Examples • shape, number, symmetry, function, field, wave, point, length, area, volume and amplitude • also: manner of aggregation of parts • Pure forms without substance cannot exist, • whether they be information, mathematics or functions • the world may have triangular objects, but is not made of triangles (or ‘wave functions’)

5. Dispositions • Examples • cause, propensity, power, capability, potentiality, energy (kinetic and potential), mass, charge, field coupling, force, pressure, momentum, impetus, elasticity or rigidity • Propensities = dispositions which manifest as probabilities • Investigated in detail by the sciences • Find explanations in terms of a few underlying dispositions + structure of aggregation

6. Dispositional Essentialism • Necessary for Causation: • to answer ‘what would happen, if ..’ • Never explainable by non-dispositional • So Dispositions are Essential to Nature • See recently eg Molnar “Powers” (OUP) • justification would require another talk • Question now: • “How are dispositions related to substance?”

7. ‘Pragmatic Ontology’ • Find what is sufficient for the dispositional causation of events • interpret this realistically, • postulate it to exist • Try to find just what is necessary for a cause to give the effect. • pragmatic, as existence inferred from effects. We find an effective ontology.

8. Places where actions can occur • Every thing is (at least) at the places (in space & time) where it has a disposition to immediately act or interact • pragmatic in the sense that there is no need for it to be anywhere else, since it can never have an effect there! • ‘Where’ and ‘when’: both necessary to describe actions • do not assume that everything is acting all the time (important for quantum physics)

9. Substance • “The substance of a thing is defined as the set of propensities for how it can act.” • pragmatic, because there is nothing else needed to be given to specify an object, apart from when and where it is, and how it can act. • “The substance of an object is constituted by the set of underlying propensities for how it can act or interact” (more specifically)

10. Common Expressions • Physicists often say: • ‘electromagnetic force fields’ • ‘potential energy fields’, • ‘matter is a form of energy’. • In each case, • a dynamical property (force or energy) is being pragmatically identified as some kind of substance • Is it possible to make philosophical sense of this?

11. Fields • The distribution of propensities over a region of space time is a field. • this is the distribution’s form. • Interactions from overlapping fields • as both objects then act together • Composite objects: structure of many overlapping fields of its parts.

12. Substance & Form • Propensity is the substance • (Aristotle: this is the matter, hyle) • Field is the form • Objects are ‘substance in a form’, •  ‘fields of propensity’. • May be many kinds of propensity • many specifications of how actions occur. • e.g. mass, charge, mass+charge, etc.

13. Successive events • We might well assume: • “Between any pair of succeeding events in time of an object, other interactions are possible.” • We might also assume: • “Such intermediate-in-time events are not necessary” • This distinguishes classical & quantum

14. Movable Substances • Definition so far: • Substances endure over the time between successive events • Generalise: • The same form (shifted in spacetime), & the same propensities, before and after an event  successive stages of the `same substance’ (now movable)

15. Quantum Substances? • See whether these ideas help understand quantum physics (QM) • Newton’s corpuscles are inadequate • those with definite ‘extension, hardness, impenetrability, mobility, and inertia of parts’ • Need to have some ideas about: • wave-particle duality, nonlocality, measurements, etc

16. Fields of Propensities • Not necessarily located in small fixed volumes of space • no centre as the ‘true substance’ • only ‘source’ is the previous event • only localised very briefly at times just after this event • most of the time they may have significant spatial extensions • Like the ‘wave packet’ of QM.

17. Measurements are ‘Actual Selections’ • Actual measurements are selections of alternate histories • Unphysical alternatives actually removed by some (undiscovered) dynamical process. • This sets to zero any residual coherence between nearly-decoherent histories, if a branch disappears. • Different alternatives in QM often summarised by an operator of which they are distinct eigenfunctions.

18. Wave Equation? • I suspect that the field distributions may be described by wave equations. • but that is another talk • If it were so: • obtain wave behaviour • (diffraction, interference, etc).

19. No hidden particles! • There are no such things as small particles like corpuscles with definite properties. • Nor are there such things as small particles with uncertain or indeterminate properties. • Measurements are not the process of assigning values to properties of particles, even if we allow that they are ‘peculiar particles’ in not having definite properties at all past times. • Nor are measurements the momentary production of particles with definite properties for that moment.

20. Particle Behaviour? • Yes: • Propensity fields (wave packets) are unitary objects • Definite shape at any time • Interact by overlaps (eg field quanta)

21. Wholeness & Non-locality • The propensity fields: • extend over finite space regions and time intervals, so are non-local, • act to select just one actual alternative, • subsequent propensity fields develop from the actual alternative selected, • ‘whole’ substances, but: • usually contain many ‘virtual substances’ in whole ‘unitary compound’ • So express using configuration space, not in 3D. • We need further analysis of ‘quantum composition’.

22. Conclusions • Pragmatic approach to Ontology • what is necessary and sufficient for the dispositional causation of events is interpreted realistically, and postulated to exist. • Substance identified by dispositions • not just the ‘bare subject’ for dispositions. • Forms of objects are spacetime fields, • Substances are ‘fields of propensity’

23. References • Website • www.generativescience.org • Dispositional Essentialism: • Alexander Bird, Toby Handfield, Steven Mumford, George Molnar, • Ian Thompson: BJPS, 39 (1988) 67-79 • and others from Aristotle on. • Propensity Fields • Nicholas Maxwell (UCL)

24. Revisit: Hamiltonian QM ‘Active Energy’ Propensity Wave Actual Outcome (Hamiltonian Operator) (Wave function) (Measurement) Born’s Probability Rule Schrödinger Equation • Energy operator generates the wave function, • according to Schrödinger’s time-dependent equation • Propensity wave generates the actual measurement • according to Born’s Probability Rule for ||2 • Actual measurements = selections of alternate histories • ‘Energy’, ‘propensity waves’ are 2 kinds of propensity.

25. Measurements are ‘Actual Selections’ • Actual measurements are selections of alternate histories • Unphysical alternatives actually removed by some (undiscovered) dynamical process. • This sets to zero any residual coherence between nearly-decoherent histories, if a branch disappears. • Different alternatives uioften summarised by an operator A of which they are distinct eigenfunctions: Aui=i ui, labeled by eigenvalues i .

26. ‘Nonlocal Hidden Variables’ in ordinary QM: • ‘Energy’, ‘propensity’ and ‘actual events’ are all present, though hidden, in a ‘generative’ sequence. • Energy and propensity exist simultaneously, continuously and non-locally. • Actual events are intermittent. • Does this describe QM as we know it? • General connection: • Continuous existence  determinism • Intermittent existence  indeterminism (why?)

27. Wholeness & Non-locality • The propensity fields: • extend over finite space regions and time intervals, so are non-local, • act to select just one actual alternative, • subsequent propensity fields develop from the actual alternative selected, • ‘whole’ substances, but: • usually contain many ‘virtual substances’ (see later) in whole ‘unitary compound’ • So express using configuration space, not in 3D. • We need further analysis of ‘quantum composition’.

28. Multiple Generative Levels • Description of ordinary quantum mechanics requires the idea of ‘multiple generative levels’ • General idea: • ‘Multiple generative levels’ are a sequence ABC  .. in which A‘generates’ or ‘produces’ new forms of B using the present form of B as a precondition. • Then B generates C in the same way, • and so on until end when nothing is active.

29. Multiple Generative Levels II: Reality • In the general case, Multilevel Propensities are ‘parallel processes’ all equally real. • Level B, for example, is not just an approximate description of successive forms of other levels A or C. • Neither is B a microscopic constituent of either of levels A or C. • Rather, levels A, B, C,... are real processes ‘in parallel’ that interact with other by relations of ‘generation’ and ‘pre-condition’.

30. Principles, Causes and Effects • The sequence ‘energy  propensity  actual event’, does not have the three levels playing homogeneous roles as in the general case ABC • If we look in more detail, we see: • energy  ‘principle’ • Conservation of energy via H governs the process • propensity  ‘cause’ • Time evolution and propagation of influence • actual event  ‘effect’ • The final result • Pattern appears : Principle  Cause  Effect

31. Potentials from Virtual Particle Exchange • Where does the Hamiltonian come from? We cannot just invent it! • We know that the potential energy part of the Hamiltonian really comes from field-theoretic virtual processes. What are these events? • Kinetic energy, also, has a mass which is ‘dressed’ by virtual processes. • Propose: the Energy Operator is itself ‘generated’ by (further) previous levels.

32. Propensities for Virtual Processes • Propose: 2 linked sets each of three generative levels • both with (broadly) corresponding processes, • i.e. still in pattern ‘PrincipleCause Effect’. • Virtual processes (in some way) ‘generate’ the terms of the Energy Operator (the Hamiltonian). Field Lagrangian Virtual Quantum Fields Virtual Events Energy Operator Propensity Wave Actual Events ‘Principle’ ‘Effect’ ‘Cause’

33. Virtual ‘PrincipleCause Effect’ • The field-theoretic Lagrangian + Variational Principle starts the generative sequence. • Propagating field quanta (virtual quantum field substances), • e.g. photons, gluons, quarks, leptons, ... • derived from the Lagrangian by a Variational Principle. • generate virtual events when interacting. • Virtual events (of quantum field theory) are point events which generate the potential energy part of the Hamiltonian operator. • They do not all actually occur because, for example, they may generate potentials that are never active in the selected sequence of actual outcomes.

34. VIRTUAL EVENTS Point events (not=point measurements) Interactions Microscopic interactions Continuous Deterministic (apparently) Contribute to alternate futures Have intrinsic group structure (e.g. gauge invariance, renormalisation) ACTUAL EVENTS Visible events in history (e.g. measurement) Selections Macroscopic decoherence Discrete Probabilistic Definitely occur (or not) Have branching tree structure Virtual and Actual Events

35. Complications: are all the stages needed? • Some physicists try to derive probabilities of actual outcomes directly from field theory, without a Hamiltonian or potential. Is the idea of a potential only an approximation suitable for some energy scales? • I would ask: Are there not still some roles for mass, kinetic and potential energy, & energy conservation? • I agree that a Hamiltonian (etc) is a ‘composite object’, whose detail reflects its genesis: ‘Natural things are more complicated, and more beautiful, the more you look into them’

36. A BIGGER Picture? Spacetime formation? Some speculative ideas!

37. Conclusions • I hope that this is an accurate classification of the several ‘stages’ in nature, as seen in QM. • Should help to understand quantum physics and what really goes on. • We can find ‘what the wave function describes’, if we think carefully and with imagination. • More work needed to understand the mathematical substructures at each level, • We should look for new physics (new theories and new experiments).