You say in your book that black holes are bigger on the inside than they are on the other side.
So black holes, contrary to reputation, are small. The whole point of the black hole is that it has tremendous heft for its incredibly small size. So if I look at the sun, the sun is a million and a half kilometres across. If I were to imagine some evil genius converting the sun into a black hole, its event horizon is only six kilometres across. So you've taken all the heft of the sun and jammed it into the size of a city. And so black holes really are spatially small.
As you fall in, you would see eons passing, civilizations come and go. You would see kind of paparazzi flashes of exploding stars.
- Janna Levin
You might presume, well, if it's only the size of a city on the outside, it should only be the volume of a city on the inside. But that's not the case. Black holes can harbour an incredible volume on the inside due to the benefits of curving spacetime and the trickery that allows you to do that. And some people have even speculated that there's an entire universe inside the black hole, that when things fall in, they get blown out into a new big bang and a new ecosystem with new stars and new black holes all inside that six kilometre perimeter.