Individuality and the account of non-locality: the case for the particle ontology in quantum physics

The paper explains why an ontology of permanent point particles that are individuated by their relative positions and that move on continuous trajectories as given by a deterministic law of motion constitutes the best solution to the measurement problem in both quantum mechanics and quantum field theory. This case is made by comparing the Bohmian theory to collapse theories such as the GRW matter density and the GRW flash theory. It is argued that the Bohmian theory makes the minimal changes, concerning only the dynamics and neither the ontology nor the account of probabilities, that are necessary to get from classical mechanics to quantum physics. There is no cogent reason to go beyond these minimal changes

A law-constitutive explanation of fundamental material objects and “bodies that surround us”

What becomes of our clearest theories of explanation, when faced with the unpalatable quantum phenomena that seem to undermine the direct conceptual connection between the fundamental material entities and the self-standing material objects of everyday parlance? The general explanatory theory advocates unification of explanatory concepts with everyday discourse, identification of essentially similar characteristics between direct experience and the hypothesised explanatory ontology, and a conceptualisation of phenomena in terms of objects enduring causally regulated change. On the other hand quantum theory feeds anti-realist suspicions about the worth of (metaphysical) realist explanatory endeavour with examples of phenomena in which the structure of material separation and individuation based on spatial extension is insufficient for construction of deeper explanatory narratives. An example from history of science, that of Newton’s law-constitutive definition of objects in response to Descartes problem of bodies is used to suggest a possible strategy for explanations unifying the quantum and common-sense conceptual domains, provided the anti-realist challenge to such enterprise is read as questioning the epistemological justification of interpretation of experience in both cases. (IN CROATIAN: Što se događa s najjasnijim dostupnim teorijama objašnjenja kada se suoče s problematičnim kvantnim pojavama koje naizgled potkopavaju neposrednu konceptualnu poveznicu između fundamentalnih materijalnih entiteta i samoopstojnih materijalnih predmeta iz svakodnevnog govora? Opća teorija objašnjenja preporuča objedinjenje teoretskih eksplanatornih pojmova sa svakodnevnim govorom, određenje esencijalno sličnih karakteristika između neposrednog iskustva i hipotetske eksplanatorne ontologije te konceptualizaciju pojava kroz predmete koji istraju kroz uzročno regulirane promjene. S druge strane, kvantna teorija potkrjepljuje antirealistične sumnje o valjanosti eksplanatornog nastojanja (metafizičkog) realizma primjerima pojava u kojima je struktura materijalne razdvojenosti i individuacije temeljene na prostornoj protežnosti nedovoljna za izgradnju dubljih eksplanatornih narativa. Primjerom iz povijesti znanosti, Newtonovom definicijom predmeta temeljenom na zakonima kao odgovorom na Descartesov problem materijalnih tijela, daje se moguća strategija izgradnje objašnjenja koja objedinjuju kvantne i “zdravorazumske” konceptualne domene, ukoliko se antirealistična kritika te izgradnje u oba slučaja shvati kao propitivanje epistemološkog opravdanja tumačenja iskustva.

Does gravity have to be quantized? Lessons from non-relativistic toy models

It is often argued that gravity has to be a quantum theory simply because a fundamentally semiclassical approach would necessarily be inconsistent. Here I review recent Newtonian toy models of (stochastic) semiclassical gravity. They provide one option to implement a force semiclassically without getting into the known problems associated with mean-field. These models are not complete theories and should not be considered too seriously, but their consistency shows that semiclassical gravity is hard to dismiss on purely theoretical grounds.Comment: 16 pages -- written for the proceedings of the DICE 2018 workshop in Castiglioncello -- provides a more detailed account of the technical arguments in arXiv:1802.0329