## Video URL

http://pirsa.org/23090105# Creases, corners and caustics: properties of non-smooth structures on black hole horizons

### APA

Reall, H. (2023). Creases, corners and caustics: properties of non-smooth structures on black hole horizons. Perimeter Institute for Theoretical Physics. http://pirsa.org/23090105

### MLA

Reall, Harvey. Creases, corners and caustics: properties of non-smooth structures on black hole horizons. Perimeter Institute for Theoretical Physics, Sep. 21, 2023, http://pirsa.org/23090105

### BibTex

@misc{ scivideos_PIRSA:23090105, doi = {}, url = {http://pirsa.org/23090105}, author = {Reall, Harvey}, keywords = {Quantum Gravity}, language = {en}, title = {Creases, corners and caustics: properties of non-smooth structures on black hole horizons}, publisher = {Perimeter Institute for Theoretical Physics}, year = {2023}, month = {sep}, note = {PIRSA:23090105 see, \url{https://scivideos.org/index.php/pirsa/23090105}} }

Harvey Reall University of Cambridge

## Abstract

The event horizon of a dynamical black hole is generically a non-smooth hypersurface. I shall describe the types of non-smooth structure that can arise on a horizon that is smooth at late time. This includes creases, corners and caustic points. I shall discuss ``perestroikas'' of these structures, in which they undergo a qualitative change at an instant of time. A crease perestroika gives an exact local description of the event horizon near the ``instant of merger'' of a generic black hole merger. Other crease perestroikas describe horizon nucleation or collapse of a hole in a toroidal horizon. I shall discuss the possibility that creases contribute to black hole entropy, and the implications of non-smoothness for higher derivative terms in black hole entropy. This talk is based on joint work with Maxime Gadioux.

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Zoom link: https://pitp.zoom.us/j/98839294408?pwd=cytNYThQaDV4Y2lob1REY0NyaTJNUT09