I like the idea: 我们的这个宇宙也可说是一个黑洞

I guess "外面" doesn't really mean the outside, because time and space only make sence within the universe and after the big bang. This "外面" may still exist, through a way we couldn't imagine from our 3D or 4D system.

It reminds me the movie "The chronicles of Riddick", in which the bad guy claimed he's seen the "UnderVerse", whatever that means.