The Enigma of Black Hole Horizons

by Prof. Abhay Ashtekar (PSU)

Friday 21 Oct 2022, 16:00 → 18:00 Europe/Berlin

Max-Wien-Platz 1/2-HS 1 - Hörsaal 1 (PAF, FSU Jena)

Gravitational wave observations have established that black holes are ubiquitous in our universe. But what exactly is a black hole? What exactly is it that forms as a result of a gravitational collapse and evaporates due to quantum radiation? The common answer is of course „event horizons“. But they are teleological and have unphysical properties. An event horizon may be contained in the room you are sitting in – and growing – in anticipation of a gravitational collapse that may take place a billion years from now. Similarly, much of the confusion about the „information loss issue“ stems from over-reliance on event horizons. Is there a better notion of black hole horizons? We will see that the answer is in the affirmative and leads to new and interesting insights. For example, they have opened up the possibility of gravitational wave tomography: although horizons are invisible to outside observers, one can reconstruct an image of their dynamics using gravitational waveforms at infinity.