The universe is finite in size because it was originally taking up no space, and 13.7 billion years later it takes up all the space and continues to expand (as space expands). If it is expanding at a measurable rate, it isn't expanding infinitely, and therefore cannot be infinitely sized (and is therefore finite).
As far as I am aware, current multiverse theory does not suggest some plane of space in which all universes sit, expanding and contracting. It suggests that there are multiple "spaces" that expand and contract, and that these are contained within some kind of dimension (or even multiple dimensions). If you are thinking about the multiverse in terms of a room full of balloons, constantly expanding and contracting, then you are thinking about it wrong. There isn't any space between the universes in multiverse theory, but they are separated rather by dimensions. As I've stated before, all space is constrained within a universe. There isn't any space outside of the universe. This is simple physics...
Quote:the expansion of the universe, and the space that comprises itThe space doesn't comprise the expansion of the universe...the expansion of the universe is the expansion of space.
As far as I am aware, current multiverse theory does not suggest some plane of space in which all universes sit, expanding and contracting. It suggests that there are multiple "spaces" that expand and contract, and that these are contained within some kind of dimension (or even multiple dimensions). If you are thinking about the multiverse in terms of a room full of balloons, constantly expanding and contracting, then you are thinking about it wrong. There isn't any space between the universes in multiverse theory, but they are separated rather by dimensions. As I've stated before, all space is constrained within a universe. There isn't any space outside of the universe. This is simple physics...
