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Kavli Institute for Theoretical Physics (KITP)

While it is widely acknowledged that string theory provides a framework for addressing quantum gravitational (and even quantum field theoretic) questions, the precise nature of its organizational principle remains obscure. Nearly three decades ago, when the question “What is string theory?” was asked, the perturbative string worldsheet viewpoint played the starring role. Since then, the discovery of D-branes, string dualities, and the holographic AdS/CFT correspondence has had spacetime dynamics taking center-stage. Much insight has been gleaned from these developments. We now have, for example, a much broader class of string backgrounds with better control over compactifications; strong constraints on the low energy effective field theories; a plethora of gauge-string dualities as well as applications of holographic techniques to a wide class of physical problems; and new angles on semiclassical gravitational physics from a fruitful interplay with quantum information in holography. Together with an influx of new tools and techniques, we have a very rich set of perspectives that illuminate the subject we continue to call string theory. While all these developments are interesting in and of themselves, it is an opportune moment to attempt to synthesize these, often disparate, strands and arrive at a deeper answer to the question in the title.

High Energy Physics, Particles and Fields,    Astronomy, Astrophysics and Cosmology

Institute for Pure and Applied Mathematics (IPAM), UCLA

Geometric structures associated with bipartite graphs on surfaces have recently emerged and turn out to be crucial for studying a variety of problems. On the one hand, probabilists working in statistical mechanics are interested in finding appropriate embeddings of planar graphs that lead to discrete complex analysis theories, which are well suited for observing conformally invariant objects in the scaling limit. In the course of doing so, they established deep connections between specific immersions of the underlying graphs, integrability of the models, and Harnack curves. On the other hand, several spaces of geometric objects have recently been found to be parametrized by weighted bipartite graphs on surfaces, relating them to cluster algebras and integrable systems. These include objects from discrete differential geometry (e.g. Q-nets, Darboux maps), positive Grassmannians, and higher Teichmüller spaces. Moreover, connections between knot theory and the dimer model have started to emerge and beg for a better understanding.

Part of the Long Program Geometry, Statistical Mechanics, and Integrability

Analysis,    Thermodynamics, Fluid Dynamics and Statistical Physics

The international conference Loops ‘24 is the most recent in a long tradition of biennial meetings focused on loop quantum gravity and background independent approaches to quantum gravity. The conference will be held from Monday, May 6 through Friday, May 10, 2024, at the campus of Florida Atlantic University in Fort Lauderdale, Florida (USA). The program will feature morning plenary talks complemented by contributed talks. Plenary sessions will be held in the auditorium of the Broward County Main Library one block away from the campus. The conference will highlight recent developments in canonical loop quantum gravity, covariant loop quantum gravity (spin foams), and other approaches to quantum gravity, as well as applications to symmetry-reduced models, quantum cosmology, black holes in quantum gravity, and other topics. Foundational, mathematical, numerical and phenomenological aspects will be covered.

Gravitation and Cosmology

Astronomy, Astrophysics and Cosmology,    High Energy Physics, Particles and Fields