Dijkgraaf, RobbertGopakumar, RajeshOoguri, HirosiVafa, Cumrun2019-09-222006Dijkgraaf, Robbert, Rajesh Gopakumar, Hirosi Ooguri, and Cumrun Vafa. 2006. “Baby Universes in String Theory.” Physical Review D 73 (6). https://doi.org/10.1103/physrevd.73.066002.1550-23681550-7998http://nrs.harvard.edu/urn-3:HUL.InstRepos:41385098The description of 4D BPS black holes in terms of branes wrapped on various cycles in a Calabi-Yau space gives us the opportunity to study various issues in quantum gravity in a definite way by means of the worldvolume theory of the branes. In the particular example discussed here, there is a simple worldvolume description in terms of 2D Yang-Mills theory. The latter is an exactly solvable system of free fermions in one dimension. The exact answer for the free energy of this system can be written in a way that suggests an interpretation in terms of contributions from multiple (baby) universes.en-USJournal Article2019-09-2210.1103/PhysRevD.73.066002