3 ms·

In my opinion, it’s the relative (hah) gentleness of the tidal forces at the Schwarzschild radius of supermassive black holes that astounds me. Assuming for a m

In my opinion, it’s the relative (hah) gentleness of the tidal forces at the Schwarzschild radius of supermassive black holes that astounds me. Assuming for a moment that the black hole firewall doesn’t exist, the notion that one can pass through the event horizon, alive, into space that is functionally entirely separate from the rest of the universe is incredible.

raattgift 3y ago
> functionally entirely separate from the rest of the universe It's not really separate, because more things can fall in. It's also not really separate if black holes may evaporate, in part because it is the outside conditions that determine when (and even if) evaporation begins. There are unsettled questions about whether black holes, even given suitable exterior conditions, fully evaporate; and exactly how to connect what fell into the black hole with what's left after complete evaporation. However, it is the mass inside that gives rise to Hawking radiation outside, so there is some connection. Otherwise I think you're quite right, particularly about the gentleness of the Weyl curvature (the tidal part of the Riemann curvature tensor) around the event horizon of a large black hole. "Pass through the event horizon, alive" is the "no-drama conjecture" that is part of the firewalls debate. Indeed, extremely massive black holes should have the least drama in the classical theory which describes black holes in the first place, so what feature of some quantum theory generates extremely high energy particles that we don't find anywhere between the Earth and Moon, or in the Jovian system, etc? "The firewall radiation can only be seen upon crossing an event horizon and there isn't one in those parts of our solar system" is not very satisfying, and it turns out that the arguably best-developed answer to that (by Afshordi/Dykaar/Abedi) is not significantly supported by gravitational wave data (so called repeating damped "echoes" cannot reliably be extracted from the noise) from LIGO, Virgo, and Kagra so far.
ck2 3y ago
Penrose white-holes would like a word. Though they might just be mathematical abstracts and not "real". https://en.m.wikipedia.org/wiki/White_hole https://en.m.wikipedia.org/wiki/White_hole https://physics.stackexchange.com/questions/740527/penrose-diagram-of-hypothetical-astrophysical-white-hole https://physics.stackexchange.com/questions/740527/penrose-d...

raattgift 3y ago

> functionally entirely separate from the rest of the universe It's not really separate, because more things can fall in. It's also not really separate if black holes may evaporate, in part because it is the outside conditions that determine when (and even if) evaporation begins. There are unsettled questions about whether black holes, even given suitable exterior conditions, fully evaporate; and exactly how to connect what fell into the black hole with what's left after complete evaporation. However, it is the mass inside that gives rise to Hawking radiation outside, so there is some connection. Otherwise I think you're quite right, particularly about the gentleness of the Weyl curvature (the tidal part of the Riemann curvature tensor) around the event horizon of a large black hole. "Pass through the event horizon, alive" is the "no-drama conjecture" that is part of the firewalls debate. Indeed, extremely massive black holes should have the least drama in the classical theory which describes black holes in the first place, so what feature of some quantum theory generates extremely high energy particles that we don't find anywhere between the Earth and Moon, or in the Jovian system, etc? "The firewall radiation can only be seen upon crossing an event horizon and there isn't one in those parts of our solar system" is not very satisfying, and it turns out that the arguably best-developed answer to that (by Afshordi/Dykaar/Abedi) is not significantly supported by gravitational wave data (so called repeating damped "echoes" cannot reliably be extracted from the noise) from LIGO, Virgo, and Kagra so far.

ck2 3y ago

Penrose white-holes would like a word. Though they might just be mathematical abstracts and not "real". https://en.m.wikipedia.org/wiki/White_hole https://en.m.wikipedia.org/wiki/White_hole https://physics.stackexchange.com/questions/740527/penrose-diagram-of-hypothetical-astrophysical-white-hole https://physics.stackexchange.com/questions/740527/penrose-d...