In this Special Issue of Foundations of Physics, string theory experts will reflect on the current status of the theory what has been achieved, what are the key unresolved issues, the strengths of the theory and its weaknesses what directions for the future. Discussions of the foundations of theories are however just as important, for they clarify the meaning of those theories they identify hidden assumptions or weaknesses and suggest new directions.
Science progresses through new models and ideas string theory has been prolific in this respect in the last forty years. Scientific journals are the proper place for this discussion. It is therefore time for the scientists involved in string theory and quantum gravity, as well as philosophers of science, to discuss the foundational issues relevant to string theory. Discussions of the foundations of string theory have however been virtually absent from the scientific literature. These concerns are addressed in one of our contributions.Ĭriticism of string theory has recently impacted the popular science media. The landscape is also discussed, a topic that-as several others-is regarded by some as a virtue and by others as a vice.įinally, some critics have pointed out that sociological issues are also at stake in the way string theorists are doing science: in this view, string theory monopolizes the best jobs in the academic career market, so that young talented researchers have no choice but following the trends if they want to have a chance of an academic career. Non-string theorists and string theorists alike discuss this issue.
Such qualification is provided by our authors, who not only review current progress in this direction, but also reflect on what the meaning of ‘fundamental variables’ for a final theory might be.Īnother topic widely discussed in this issue is the sense in which string theory is a theory of quantum gravity, and in particular the extent of its background dependence. Therefore, calling string theory a ‘theory’ deserves qualification. Another, and in some respects more disturbing problem, is that a fundamental formulation of string theory is not yet known-not only in the mathematical way or rigor, but even in the physical sense of finding the ‘fundamental variables’ of the theory. Among the shortcomings mentioned by our authors, there are the lack of directly testable experimental predictions that would signal ‘string physics’.
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Yet string theory is neither a complete theory nor free from criticisms, as the present special issue reflects. Today, string theory is a mature field that has produced an unprecedented amount of work and new ideas in theoretical physics. For these reasons, string theory is described by many as a ‘framework’ rather than a theory. It has established new connections between field theories and gravity and far-away disciplines such as mathematics, condensed matter, and fluid dynamics especially in mathematics, string theory has produced astonishing results such as the mirror symmetry conjecture. String theory has also shown its ability to shelter under its umbrella entire fields which at first were seemingly disconnected from it, such as supergravity and black holes. Among its results are microscopic computations of black hole entropy and the suggested implication, acknowledged by Hawking, that black holes do not violate quantum theory spectacular success in describing perturbative and non-perturbative aspects of gauge theories the holographic description of gravity realized in string theory, which has led to key conceptual insights in understanding gravity and geometry it has also provided new ideas and tools in cosmology, such as the existence of a finite number of false vacua (the so-called ‘string theory landscape’). Since then, string theory has undergone several metamorphoses and is regarded by the majority of the community as the most promising quantum theory of gravity. For these reasons, many lost interest in the theory, while for some it made an interesting candidate as a unifying theory of gravity and quantum field theory. A few years later, QCD appeared as a superior model for the strong interactions furthermore, in 1974 it was realized that strings contain gravitons in their spectrum. The history of string theory started around 1970 when Nambu, Nielsen, and Susskind realized that Veneziano’s 1968 dual model, devised to explain the particle spectrum of the strong interactions, actually describes the properties of quantum mechanical strings.
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