On the ontological status of molecular structure: is it possible to reconcile molecular chemistry with quantum mechanics?

SEBASTIAN FORTIN; MARTÍN LABARCA; OLIMPIA LOMBARDI

Paris

Congreso; 2017 ISPC International Society for Philosophy of Science Annual Symposium; 2017

University Paris Diderot

It is well-known that the classicalconcept of molecular structure (namely, a set of atoms with a definedarrangement in space held together by chemical bonds) is central to modernchemical thought given its predictive power. It is also a very useful conceptin chemistry education to rationalize and visualize microscopic phenomena. However,such a concept seems to find no place in the ontology described by quantummechanics, since it appeals to classical notions such as the position of theatomic nuclei or the individuality of electrons, both ideas strongly challengedin the quantum context. Although this problem has attracted the attention ofseveral authors, the discussion is far from settled: the opinions about thelink between quantum concepts and the notion of molecular structure divergemarkedly. Many authors have stressed the conceptualdiscontinuity between quantum mechanics and molecular chemistry. In fact, aquantum system is a contextual entity, described by its non-separable statevector, and maintaining non-local correlations with other quantum systems. Inmolecular chemistry, on the contrary, a molecule is an individual entity, withdefinite properties ?as its shape? and without non-local correlations with other molecular entities (cfr. e.g. Amman 1992, Primas 1994). Inthis context, while some authors adopt an explicitly reductionist position andadvocate to reconstruct the concept of molecular structure within the frameworkof the quantum theory of atoms in molecules (Hettema 2012), others appeal tothe concept of emergency to understand this notion (Hendry 2010). The aim of this work is to propose a new line ofargumentation to address this problem. Indeed, the ontological pluralism (Lombardiand Pérez Ransanz 2012) is a particularly fruitful philosophical framework whenthe problem is to interpret the relations between ontologies described by equallysuccessful scientific theories from an empirical point of view. Thisperspective allows admitting the equally ?real? existence of differentontologies, with no reduction or priority relationships among them. In thisKantian-rooted philosophical framework, since any ontology results from thesynthesis between the ?noumenal? independent reality and the conceptual schemeof a theory, the quantum ontology is not a conceptually independent domain buta realm as constituted as the realm of molecular chemistry. Therefore, thequantum world has no priority over the world of molecular chemistry: chemicalentities do not need the support of quantum entities to legitimate their objectiveexistence. From this perspective, it is then possible to state that molecularstructure does exist in the ontology of molecular chemistry, in spite of thefact that it does not exist in the quantum world. This ontological pluralismhas been applied in a fruitful way to different problems in the field of thephilosophy of the special sciences. In the field of philosophy of chemistry hasbeen applied to address the general problem of the relationship betweenchemistry and physics, traditionally interpreted in reductive terms (Lombardiand Labarca 2005), as well as to account for the problem of the ontologicalstatus of  the atomic orbitals (Labarcaand Lombardi 2010).