[__MatrixMan__]

These are the properties of our universe, and of course we'll only ever have one to study. But words change, right? Atoms are no longer indivisible. Black holes are no longer fully black. So I'm really going for the properties that a thing must have in order to be considered a universe, so we don't end up with a change that's obnoxious. I'd hate it if "universe" eventually just meant "any old really big astronomical structure".

Perhaps the laws of physics would allow for different kinds, they just aren't ours (Lee Smolin's "Life of the Cosmos" is a fun exploration of this, recommended).

Overall I like your descriptions, but I'm going to have to do some thinking about the direction of a gravitational depression being one that points towards the past. I'm under the impression that many cosmologists reject the idea that something warped must be warped into some other dimension. The warping, I've read, can be intrinsic: Imagine a colored lens which is unevenly saturated with dye.

(I am also not a real physicist)