Fivebranes and Fractons

Last Friday, I had the opportunity to give a very fun talk at the MIT student journal club on our Baby Universe Hypothesis . A major theme of the talk, and the resulting discussion, was that holography isn't free! In many ways, this is the heart of the Swampland: if you just throw whatever junk you want into the Euclidean path integral, there's really no reason to expect anything but junk out the other end. This is strikingly different from quantum field theory, where (up to canceling anomalies) you are free to write down whatever you wish. In this post, I want to share some observations that make this difference between gravity and other quantum systems more obvious, as well as point the way towards the type of mathematical structure we need in order to guarantee holography. The miracle of holography, and the true heart of the issue, is not that a bulk gravitational system becomes a quantum system on the boundary, but rather that it becomes a local quantum system on the bound