That's definitely interesting to think about. My first thought is that we can't really talk about space expanding without thinking about time. Is spacetime expanding? Or is space expanding while time contracts? Does space expand into time, and vice versa? The relationship between space and time seems reciprocal, so I'd be inclined to think space is expanding into time. In a contracting universe, the opposite would be true. There's a way to think about this, and it implies the universe is finite in time. If the universe is finite in time, then as space expands, there is less time. So we can imagine space expanding into time in that sense. But in an infinite universe, well I guess time could be an infinite empty void, and space is a bubble within that is destined to expand forever. But that seems even more bizarre to think about.

I've seen an episode of PBS that makes claims along the lines of space and time switching places inside a black hole... that is, space is one dimensional and time is three dimensional. I can wrap my head around the concept of one dimensional space, all geodesics point in the same direction... towards the singularity... and it is only in this direction you can go. But I do not understand how time can be three dimensional. I mean sure, there's the past, present and future, but if you can go back in time inside a black hole then why not go back to a time when you weren't inside the black hole? It kinda implies that it's not possible to go inside a black hole because there is no part of your past when you were inside the black hole. So that's a mind bender too.