Black hole cosmology suggests that the Milky Way and every other observable galaxy in our universe is contained within a black hole that formed in another, much larger, universe.
The theory challenges many fundamental models of the cosmos, including the idea that the Big Bang was the beginning of the universe.
It also provides the possibility that black holes within our own universe may be the boundaries to other universes, opening up a potential scenario for a multiverse.
Mine blown 🤯
The black hole idea is actually weirdly solid, its a case of the maths says we definetaly should be but observation and just intuition says its crazy. If you consider the event horizon to be the surface of a volume, black holes get less dense as their radius increases, you can have a black hole with the same density as rock, water, air, even the miniscule density of the gas in a vacuum, so long as teh black hole is large enough. The average density of the observable universe is higher than the density of a black hole the size of the observable universe so technically we should be in one.
Technically this doesn’t have to affect anything, larger black holes can have gentler gravity gradients and nothing in physics actually demands all the mass inside be concentrated at a miniscule central point, it just works out that way for black holes of the size we’ve seen so far. So the entire universe could be a black hole (assuming its finite) with the event horizon just being functionally inacessable and the black hole so large that internal conditions aren’t really influenced in any way.
Surely at some point it stops being useful to apply the same terminology to such vastly different concepts. If the universe is a black hole and Sagittarius A* is a black hole then “black hole” doesn’t communicate anything effectively outside of extremely niche astrophysics conversations.
The mass of the visible universe is apparently enough to make a black hole with an event horizon ten times larger than the visible universe’s. I don’t understand how that hasn’t happened already, but apparently it just doesn’t look like it’s happened (“unless…”).
It could totally have happened already and we just don’t notice, though there’s kind of a critical size where a black hole just gets infinitely big as adsorbing a stray hydrogen atom in the vacuum of space increases its radius enough to encompass multiple new hydrogen atoms and the whole thing just expands to encompass the entire universe. Kind of when everything is a black hole then nothing is a black hole sorta situation.