What does quantum chemistry tell us about the relationship between theories and models??

JUAN CAMILO MARTÍNEZ GONZÁLEZ; HERNÁN ACCORINTI

Atlanta

Congreso; Twenty-Fifth Biennial Meeting of the Philosophy of Science Association; 2016

PHILOSOPHY OF SCIENCE ASSOCIATION

p { margin-bottom: 0.25cm; direction: ltr; color: rgb(0, 0, 0); line-height: 120%; }p.western { font-family: "Times New Roman",serif; font-size: 11pt; }p.cjk { font-family: "Times New Roman",serif; font-size: 11pt; }p.ctl { font-family: "Times New Roman",serif; font-size: 10pt; }a:link { color: rgb(0, 0, 255); }Duringthe last decades, the notion of scientific model has attracted agreat attention in the philosophy of science. Disputing the leadingrole played by theories in the philosophical reflection of thetwentieth century, many authors have begun to acknowledge that modelsare an essential and indispensable resource of modern science. Inthis conceptual context, the following question acquires a specialrelevance: what is the relationship between theories and models inscience? Accordingto the semantic view of scientific theories, models depend ontheories and are their truth-makers. Therefore, any model is always amodel ofa theoryand cannot contradict it. The corrections or de-idealizationsintroduced in a model should either derive from or be legitimated bythe theory. From this theory-drivenconception, theories are endowed with epistemic priority; models areonly tools designed to apply the theory to specific situations. Onthe basis of the analysis of certain historical cases, some authorshave challenged the theory-driven view: many scientific models arepurely phenomenological, in the sense that they are proposed as aresponse of a phenomenon and without support on the theories of thetime. Since phenomenological models cannot be formulated withoutspecific empirical data, they cannot be conceived as the mere resultof a process of de-idealization. This position leads to aninstrumentalist view of scientific theories, sometimes called?toolbox? view.Thediscussions between the two views (specifically da Costa and Frenchfor the syntactic view, Suárez and Cartright for the tool-box vie)mainly rely on certain paradigmatic historical examples, such as thebrothers London?s model of the Meissner effect. On this basis, theyseem to arrive to a dead end since those examples, althoughphenomenological, admit the possibility that the model be subsumedunder a theory in the future. It is in this point that certain modelscoming from quantum chemistry may provide a breath of fresh air to abogged-down discussion.Inthis case, we will consider the Born-Oppenheimerapproximation (BOA), which stands at the heart to quantum chemistry,since almost all molecular models are based on this approximation.The BOA begins by formulating and solving the ?clamped nuclei?Hamiltonian, which describes the movement of electrons in a molecularstructure of nuclei fixed in space; only when this first stage isaccomplished, the motion of nuclei is reintroduced. But, as someanti-reductionist authors point out (Lombardi, Chang), this strategyimplies a contradiction with Heisenberg principle, one of the basicprinciples of quantum mechanics. But even some reductionist authors(e.g. Hettema) acknowledge that the methods of quantum chemistry maydraw concepts out of context and re-use certain concepts in a mannernot admissible to the theory in which they were first introduced. Onthis basis, we will argue that the models of quantum chemistrysupport an instrumentalist and non-representationalist view ofscientific models.