Theory Assessment in String Theory and Cosmic Inflation

The proposed project is a follow-up to the first project phase "Changes of the Scientific Paradigm in String Theory". The first project phase was devoted to the question as to what extent characteristics of string physics were at variance with aspects of the classic conceptions of science and could offer new perspectives on conceptual questions in philosophy of science. The present project will focus on inner-theoretical theory assessment and extend the analysis to the field of inflationary cosmology. The comparison between string theory and inflationary cosmology will analyse parallels and differences between the two cases and will contribute to a broader understanding of the question of theory assessment in contemporary fundamental physics. Contemporary high energy physics and cosmology are characterised by increasing time spans between theoretical conceptualisation and empirical testing and by strong commitments of involved physicists to the validity of theories which are as yet empirically unconfirmed (and often theoretically incomplete). The recent controversial debates between critics and exponents of string theory - which constitutes the most influential of the currently unconfirmed theories - illustrate the significant irritations the emerging new character of fundamental physics causes in parts of the physics community as well as among philosophers of science. The issues of theory confirmation and the legitimate range of theoretical reasoning raised in that context are of importance in inflationary cosmology as well. In the latter case, however, the role of empirical evidence is stronger than in the case of string physics. Of particular interest are the multiverse theories in cosmology which posit worlds empirically inaccessible to us in order to provide a coherent theory of the world we observe. A primary aim of the present project is to formulate a conception of theory assessment that is in accord with the scientific praxis in fundamental physics today.

The project develops a philosophical perspective on the ways to assess a scientific theorys viability in the absence of empirical confirmation. The question of the status of such assessments is particular interest with respect to fundamental physical theories like string theory and cosmic inflation, since empirical testing is very difficult in those contexts and often remains unattainable for very long periods of time.The following claims were developed in the project.Non-empirical theory assessment can provide a strong basis judging a theorys viability.The strength of arguments of non-empirical theory assessment does not simply rely on a theorys qualities like elegance, of simplicity but is rather based on observations regarding the scientific process. Three main arguments are based on i) the observation the no alternatives to the given theory were found, ii) the given theory explains more that it was created to explain, and iii) theories in th research field that fulfilled the first two conditions often turned out predictively successful.All three described arguments can be understood in terms of an assessment of the spectrum unconceived scientific alternatives to the given theory.Non-empirical theory assessment can, under very plausible assumptions, be formalized as theory confirmation (within the framework of so-called Bayesian confirmation theory). This justifies calling the given cases of theory assessment non-empirical confirmationAn analysis of those points was published in the book String Theory and the Scientific Method at Cambridge University Press in 2013.Another part of the project work was devoted to understanding the role on non-empirical theory assessment in the context of the search for the Higgs particle that culminated in the discovery of that particle in 2012. It is argued that a Bayesian perspective on the discovery criterion for the new particle can be instructive in some respects and reveals connections to non-empirical theory assessment.