I've been fascinated lately by two aspects of "space" in aikido.

There's the sort of movement that creates space, or in other words a vacuum, when uke finds himself drawn into this emptiness.

Then there's the sort of movement where you occupy space that uke either used to occupy (displacement) or wanted to occupy but couldn't (interrupting).

For example, the first technique in this video demonstrates to me the idea of creating a vacuum, while the second and third technique involve occupying uke's space and displacing him.