# Baby Universes and Worldline Field Theories

### APA

Rangamani, M. (2021). Baby Universes and Worldline Field Theories. Perimeter Institute. https://pirsa.org/21040015

### MLA

Rangamani, Mukund. Baby Universes and Worldline Field Theories. Perimeter Institute, Apr. 06, 2021, https://pirsa.org/21040015

### BibTex

@misc{ pirsa_21040015, doi = {10.48660/21040015}, url = {https://pirsa.org/21040015}, author = {Rangamani, Mukund}, keywords = {Quantum Fields and Strings}, language = {en}, title = {Baby Universes and Worldline Field Theories}, publisher = {Perimeter Institute}, year = {2021}, month = {apr}, note = {PIRSA:21040015 see, \url{https://pirsa.org}} }

Mukund Rangamani University of California System

## Abstract

The quantum gravity path integral involves a sum over topologies. Superficially, this feature is similar to Feynman diagrams of quantum field theory and the genus expansion of worldsheet string theory. There are however some key differences. While the standard construction leads to the non-abelian algebra of quantum fields, the quantum gravity path integral has been argued to define an abelian algebra associated with partition function type observables. We will discuss these issues and argue that one needs to make certain discrete choices to construct a Hilbert space from path integrals that sum over topologies. In particular, the natural choices for quantum gravity differ from those used to construct QFTs as we shall illustrate in the context of one-dimensional models.