2 ms·
> I thought a pretty big defining factor of black holes was that nothing (not even light!) ever escaped it? Nothing ever escapes from inside the hole's horizon
by pdonis 5y ago
> I thought a pretty big defining factor of black holes was that nothing (not even light!) ever escaped it?
Nothing ever escapes from inside the hole's horizon. But there can still be a lot of interesting things happening outside the hole's horizon as matter either falls in, or orbits the hole, or some combination of the two; and we can certainly observe things happening outside the hole. That has been known for decades.
- alex_young 5y ago> Nothing ever escapes from inside the hole's horizon. Well, kind of. Hawking radiation [0] causes black holes to eventually evaporate, although no actual information from inside the horizon escapes. [0] https://en.m.wikipedia.org/wiki/Hawking_radiation https://en.m.wikipedia.org/wiki/Hawking_radiation
- pdonis 5y agoI wasn't including Hawking radiation because, however likely it is considered, it's still not a confirmed prediction, and the theoretical basis for it is not rigorous (since we don't have a consistent theory of quantum gravity to back it up, just various heuristic arguments). (Also, even if it does exist, it is negligible by many, many orders of magnitude in the scenarios under discussion here.) Also, if Hawking radiation does turn out to be confirmed, it might end up that the radiation does carry information from inside the hole. The quantum effects that are involved in Hawking radiation, at least as we currently understand them, violate the conditions that ground the "no information can escape from a black hole" theorems in classical GR.