(Potentially relevant link)

People are always having such trouble thinking about space, so during a debate once I wrote this introduction (very slightly edited). It's not super!well written, but it's something. Enjoy:

Intro to the meaning of 'Universe'

There are two ways of thinking about the universe .One is that it's everything, as the good Toilet¹ said. The other is the big blob of space expanding outwards from the point of the Big Bang.

People usually don't distinguish between the two, because usually we say they are the same thing.

Getting a grasp on the concept of 'space'

Imagine two things as close together as possible. There is no room between them at all. They are touching--at the subatomic level if you need think of it that way.
Now imagine: There's a large solar system in between the two things.
That's right, a large solar system between two things that have no space in between them. So the solar system isn't in space. Does that make sense? For the moment, let's say no. After all, 'in' or 'next to' or 'between' are all in spacial terms: if something is between two other things, it is in the space between the two things.

Now think about the 'edge' of space. Beyond that is just like between the two touching things: there is no space past it, because it's the edge. Now, does it make sense to say there's another thing past the edge? No, there's nowhere for it to be. It's just like being between the two things. And we said that makes no sense. (But maybe we lied.)

Metaspace

The problem most people have is that they can't think except in terms of space. They can't imagine something (like the universe) not being somewhere. So they tacitly and unconsciously make up a 'metaspace' that contains normal space. If you do that, the normal big bang space is at some metalocation and there could be another big bang space at another metalocation. This makes it all very easy to talk about such things. Unfortunately, it makes it easy to talk about them incorrectly, because people don't notice that they've gone from normal space to metaspace.

Suppose you have a nice big metaspace*, and inside it there are two big bangs. One of these big bangs is fortunate enough to have us in it, and the other is a bizarre place filled with tree frogs (but no trees, sadly). Suppose we wanted to rescue these unfortunate tree frogs by flying our infinitely-fast spaceship to their space and supplying them with lots of trees. Where do we fly to?
This ship is just like your car. Sure, it's faster and can fly, but it's the same in that it only travels through normal space. It can't take you to the solar system between to touching objects, because that's somewhere in metaspace, not in our normal space. And it's the same with the frogspace: you can't fly off the edge of normal space, because then you're flying in metaspace, which is an entirely different thing.

Turtles

Our happy big bang space is in metaspace, riding on two strange creatures, known as metaspace turtles. We know they're turtles because they have shells on their backs and go really slowly, but don't look at all snailish.

Reality

So we can't leave our normal big bang space, and things outside our normal big bang space can't come in.
So what is it that makes the other things real?

Footnotes

* Of course, if we really truly need a metaspace, then we also need a metametaspace, and a metametametaspace, and so on. How irksome!

Credits

General Wesc: better than Hawking and twice as pompous.²

Blogspace Footnotes

¹ The user Toilet of Doom posted earlier on the topic.

² I originally posted this on eCritters using my 'Isaac Asimov' account rather than my Wescian account.