quote:I suppose a black hole could exist within the event horizon of another, but I can't imagin a universe like ours being a really big black whole because, well, to be blunt: because they're really fucking dense... Isn't our universe less dense than a black hole?
The universe is no less dense than a universe-sized black hole would be. It uses the Schwarzchild equation here. "Common Sense" from small blackholes - that they are massively dense, doesn't hold for black holes of truly massive size.
"The Schwarzschild radius is proportional to the mass " (see e.g. wikipedia or any other site about the equation). You can infer all you need to from that one mathematical observation.
Doubling the mass, doubles the radius of the event horizon. When the radius of a sphere doubles, the volume is 8 times as great. This means each time you double the mass of a black hole, density drops by 3/4.
There is an inter-relationship between mass, radius and density. Given any one of these you can calculate the other 2 black hole values.
you can plug the observed density of the known universe in, and get an estimate of the size of event horizon which is not far off the observed distance to the earliest galaxies.
Oh, and btw, a "closed" space would wrap-around, so there's no "point" for the singularity to be, just as we do not observe a "middle" from which the universe expands. A totally curved space doesn't need a "middle".
"though I wouldn't be surprised if every "center of gravity" was determined to actually be a miniature black hole."
Echetos, Here you really reveal that you're no physicist. What's the net gravitational force at an objects centre of gravity? ZERO. It's defined as the point where all forces balance out. So there is NO high-gravity region inside the Earth, it's pressure that crushes you from stuff in the high-gravity region - which is greatest at the surface. If they Earth was hollow, you'd float in free-fall at the centre, it's purely mathematical and has no special physical properties.
Same, a "singularity" doesn't exist as a magical force or object or place, drawing everything in. Everything is gravitationally affected by everything else.