You do not know black holes are infinitely dense. You can presume it with some math jiggling but knowing ? You need to go there and come back to be sure.
Besides the universe is not a vacuum.
Edit: if someone utters the word "quantum" I'll go bursar on him.
You're right of course, it's not a vacuum because it's filled with charged particles and stuff
Everything we see in our universe makes up for a tiny amount of the total energy density in our universe. maybe 4 or 5 % That's why they invented dark matter, to explain the rest away. Yet another made up thing to make their calculations work lol
You don't actually think dark matter or dark energy is real do you?
2 scientist chat over the discovery of atoms...
"Oh look, stuff is made up of smaller stuff, let's call the smaller stuff, hmmmm, atoms.
Oh look, atoms have positively charged protons in the middle, all squished together, wait, hang on, 2 positives should push away from each other. So what keeps all these these positives squished together? I'm not sure, i guess there must be some kind of strong force squishing them together, hmmm, let's call it the strong force.
Oh hang on though, look, there's even smaller, quirky, stuff inside, hmmm, let's call those quarks, they must be all be glued together in there with something, hmm, let's say they're glued together with, hmmm, gluons... Hey man, we're doing science..." And it goes on and on... lol
It's all made up gibberish to hide the true nature of the universe... lol