Einstein’s Unified Field Theory Program

Einstein explicitly used the term ‘unified field theory’ in the title of a publication for the first time in 1925. Ten more papers appeared in which the term is used in the title, but Einstein had dealt with the topic already in half a dozen publications before 1925. In total he wrote more than forty technical papers on the subject. This work represents roughly a fourth of his overall oeuvre of original research articles, and about half of his scientific production published after 1920. This contribution is an attempt to characterize Einstein’s work on a unified field theory from four perspectives, by looking at its conceptual, representational, biographical, and philosophical dimensions. The space spanned by these four dimensions constitutes Einstein’s unified field theory program. It is characterized by a conceptual understanding of physics that provides the foundational physical knowledge, the general problems, and the heuristic expectations. The mathematical representation both opens up and constrains the possibilities of elaborating the framework and exploring its inherent consequences. The biographical pathway, historically contingent to some extent, takes Einstein from the elaboration of one approach to the next. Finally, Einstein’s most vivid philosophical concern was at the heart of this enterprise, and his insistence on the possibility and desirability of a unified field theory cannot be understood without fully acknowledging his philosophical outlook.