http://www.nature.com/news/cosmologist-claims-universe-may-not-be-expanding-1.13379
Maybe it’s not a good analogy, but when you blow up a balloon (imagined as a miniature big-bang type universe) the expanding balloon does not create space, it occupies previously-existing space. So an expanding universe must be moving into SOMETHING when it expands. As the Unfrozen Caveman Lawyer used to say on SNL, “My primitive mind cannot grasp these concepts.”
http://www.nature.com/news/cosmologist-claims-universe-may-not-be-expanding-1.13379