Abstract
Contemporary physics can be nowadays characterized by the acknowledgment of four forces or interactions (taken as) fundamental, namely, (1) electromagnetism; (2) strong nuclear force; (3) weak nuclear force and (4) gravity. Regarding these forces, only gravity resists to a description in terms of quantum theory. (1), (2) and (3) are depictured in terms of the standard model of elementary particles; itself framed according to Field Quantum Theory (FQT), albeit (4) is presented in accordance to the principles of General Relativity (GRT), whose conceptual model (principles, parameters, world picture) is logically incompatible with FQT. Universal laws, however, understood as the basis of science's intellectual architecture, aim to be valid to all facts of nature: FQT and GRT cannot be both universal, cannot both take the whole physical universe as their application domain  similarly, cannot be the world divided into two systems, one of which governed by relativistic laws whilst the other is governed by quantum laws. In principle, FQT and GRT rule the same physical systems. As a matter of course there are situations in which both theories must interact; such reconciliation (a socalled theory of quantum gravity) consists on the greatest challenge of modern theoretical physics. The unification of microphysics and cosmology, as well as the presentation of a universal theory (a theory of everything) consists in the ambitious proposal of string theory. Although the proposal of a perspective shift from points to onedimensional strings goes back to the sixties, the mathematical complexity of string theory's axiomatical architecture implies on a great spectrum of interpretations and speculations of concepts (physical, mathematical) classified as (1) empirically unconfirmed and (2) perhaps empirically unconfirmable. Examples vary from a considerable number of extra dimensions to the prediction of unobservable parallel universes in cosmic inflation. String theory's scientific status and the amount of eminent theoretical physicists working on the field, however, suggest that the lack of empirical evidence, once argument to deny scientificity to a given hypothesis, although undeniably worrying is not enough to discard it as candidate for a theory of everything and, in a broader perspective, more complex and dynamical epistemological criteria of evaluation as the ones described by traditional empirist philosophies of science (Popper, Carnap) and to some extent neglected by less rigid, historical approaches (Lakatos, Feyerabend) make up modern microphysics methodological practices. Of direct relevance to philosophers of science, string theory offers up methodological novelties about how science works. Could we, given the impossibility of direct corroboration due to technological limitations (situated at the Planckscale, 1033 cm, the scale of the strings is eighteen orders of magnitude beyond the energy scale testable by current LHC experiments at CERN) designate nonempirical epistemological evaluation criteria? Can the underdetermination principle play the role of a boundary factor? What meaning can string theory possess, if not testable? The problematic ideal of a theory of quantum gravity suggests a deep revision of our notions of space, time and matter; similarly, being string theory a quantum theory, its foundations imply ontological difficulties similar to those which have been worried physicists and philosophers since the birth of quantum mechanics. Since there is no (physical) evidence of gravitational quantum effects and string theorists built its theory for theoretical coherence reasons, questions regarding justification, methodology and how string theory can be linked with the world, to be pursued on this research, allow us to catch a glimpse on the importance of epistemological and philosophical backgrounds in scientific progress. (AU)
